Sunday, November 27, 2011

SDR Meets DJ Gear

Hi there! Some of you may know that I am quite busy with music, dance and the stuff concerned.
Some rare occasions have it, and hamradio mixes with music mixing, aka DJing. And here is one of those occasions:
The DJ Mouse
http://www.dj-mouse.com/
Basically, there is nothing special about this mouse, other than the regular scroll wheel is somewhat wider and parallel with a jog wheel. It is just this jog wheel that makes all the difference.
All SDR software solutions I am aware of, are using the scroll wheel for sweeping the frequency. I always felt that this was somewhat awkward. Now we got a mouse with a rotary encoder, just like a VFO knob.
Still I scratch my head what can be done with the "scratch" button...

Thursday, November 24, 2011

Central Heating Aerial

Dear readers, there was not much going on here lately, sorry about that!
Today, some weird incident triggered another thought in me.... and here it comes:

Returning home, I felt an unfamiliar chill in my house... That's no good, I thought, and checked the central heating system, which indeed was dead. Quick check and the culprit was found. The expansion vessel (expansievat, Ausdehnungsgefäss, vase d'expansion, whatever you wanna call it) leaked. The local hardware store was still open, hence I hurried up to get a replacement of similar size.
Just €22.- will get you one with a 17l capacity.
Speaking of capacity, that came to my mind on my way back home. What about using the defective one as top-capacity for a short vertical? The roundish things got a nice thread which would easily fit Cu pipes and respective fittings.
The vessel itself is made from steal (Fe) most likely. OK, that's somewhat on the heavy end, electrically however, not that inferior to Al, which is used most.
The plan is to build a short tapered vertical from Cu-pipes with an expansion vessel on top.
I figure, one may also consider a short loaded dipole.
Possibly, just 2 of such vessels could make a broadband dipole for VHF.... one could also think of a broadband vertical for VHF, using just one vessel on a ground-plane.

There may just be one down-side, your neighbors will think you're completely mental, putting the expansion vessel of your heating system 5m above your roof ;-)

Happy experimenting.

Tuesday, November 8, 2011

Most Interesting

What is going on here? A local station, a dx station and the radar, which seems to dislike the condx...


Broad-Band Aerial Update

Short update on the 11m half-wave aerial conversion.

The 4:1 UnUn is placed, that was one of the two options. Actually, this was the easy option, since the UnUn came wound up and ready to use from a surplus dealer.

11m half wafe aerial base portion
The arial, about 5.5m long, w/o any further modification could be matched easily with the IC-703 builtin tuner on the band from 80m to 10m, with the exeption of 30m. I figure, some additional Al-tube extension could solve that problem.

Saturday, October 29, 2011

SDR for the 600m band

Some short not on an idea for the 600m band.
The typical SDR, as we all know, uses 4x the center frequency so that the 90 phase-shifts can easily be created by flip-flops.

In 2012, the Netherlands will most likely open the range 501-505kHz for ham radio operators. I figure a simple RX (maybe also TX) solution could be a 2.000MHz canned oscillator. This will get us spot on 500kHz center frequency, just as you may want. Comfortable 1 to 5kHz audio, which any sound card can handle easily, with a sample rate of only 24kHz. A further experiment should show if side-band suppression is required at all. I figure, a decent pre-selector should be enough already.
Should however, following a decision at the WRC-12, the range open to hams change to the range proposed by CEPT (472 to 480kHz), a 2.000MHz SDR-LO would be somewhat too high. In this case, the oscillator could easily be swapped with a 1.8432MHz one. Resulting in a center frequency of 460.8kHz. Audio up to 20kHz would still be somewhat a challenge for cheap sound hardware, never the less, a sample rate of 48kHz would cover it all.

No to the TX-part of it. One could either use a sound card generated signal, as provided by some software solution. One could also thing of generating an I/Q modulation signal at 4x the audio signal, divide and phase shift similarly to the LO chain. Unfortunately, we would now have a rich audio square wave. I figure some severe filtering will be required here, in order to end up with a sine wave.
I would not consider an AF phase-shifting network. I believe the frequency range is to great as provide accurate phase-shifting.
However, as in the RX part, it may be conceivable to filter the side-band at the RF range. A series of tank and trap circuits could possibly be enough. Mind you, the aerial matching itself is very selective too.

Friday, September 23, 2011

New Item in the Marine Radio Collection

Could not stop myself from buying an "Emergency Radio Type 610". I believe it is made by Clifford & Snell, but I am not sure about that.
The radio services the frequencies 500kHz (RX/TX), 2182kHz (RX/TX) and 8364kHz (TX). As in this sort of package, cranks are provided as a power source.

The transmitter seem to be built around two electron tubes (have not checked the types yet), while the receiver seem to employ OC transistors, Germanium that is.
Whilst test TXing into the built-in dummy load, on 2182kHz (A3E), the antenna current meter nicely peaks when the matching variometer (coil with dive-in ferrite rod) is agitated. The two other frequencies would require the operator to have a third arm!?? My radio was supplied with the emergency instructions, which showed one operator only, even the text referred to a single operator doing the cranks and the communications all at once. Who ever wrote this may have never operated a radio himself. While in A3E, a carrier in generated anyway. One hand operating the crank, the other to tune the variometer, no problems here.
It is a different story with 500kHz and 8364kHz. Those are A2A frequencies. No, there is not typoe, A2A it is, AF modulated code. And yes, that makes sense. The signal is received in both, an AM receiver as well as a receiver employing a BFO. However, when tuning the emergency transmitter, one would need one arm/hand operating the crank for energy, a second arm/hand for operating the manual key and a third arm/hand for operating the tuning knob.
The makers of the radio seemed to have spent some thought on this issue, although, maybe not enough. The radio is equipped with a mechanical auto-keyer. Keying the transmitter for tuning can therefore be done, sort of, without three arms. However, the designers seemed to never had the code operator in mind. The built-in manual key is so close to the position of the cranks, that operating both at the same time seems to be a challenge per se. However, if that was your option to survive at sea, that what you would be going for.

Enough about the transmitter, lets have a word on the aerial system provided. A system which managed to impress me. As in all of those sets, the aerial is contained in the box itself. Motto: if your vessel is sinking, throw the emergency radio overboard, get in the life raft and hope for the best. Hence, the floating waterproof box of the emergency radio has to contain everything required to perform emergency communication, including the aerial.
The 610 comes with an antenna base, about 1m long, having a rubber foot (for not damaging the life raft's soft bottom). On this foot, a stainless steel telescopic whip is to be mounted, the whip having an impressive length of estimated 4m (maybe more).

To the downside, and the reason why this radio is not widely available.
In order to keep it smaller, I presume, the designers choose to have a low profile for the cranks. Fair enough... however, they put the cranks so low that they can't be used when the radio laying perfectly flat on the ground. A problem that the very similar TRP1 does not have. Is the TRP1 really as similar? Maybe not... think of it, the TRP1 uses TTL circuits, whilst the 610 employs electron valves and Germanium transistors...

Do I regret having bought on of the 610s? No! Would I buy another one? No!
What is the best thing about the type 610? The aerial provided. I believe, there is no other (convenient) way to get your hands on stuff alike... Think of it!

73!

Friday, September 16, 2011

Cheap Android Tablet Going Strong

Some time ago, I reported about a very cheap Android Tablet (from kijkshop), which I used regularly for this and that.
The table came with some port accessory, which holds two regular USB ports and an Ethernet connection. Writing this, I am presently using the tablet via Ethernet (thus no WLAN) with a wireless keyboard attached via USB for convenient typing. The port accessory actually seem not to have functioned when I got the device first. However, in the course of time, I really could not believe that a design fault was the cause. Well, the was a design fault, not in the electronics though. The plastics chassis appeared to be too large and had to be sanded down in order to allow all pins to make contact. Seen that the tablet costed € 100.-, I should have bought a second one, since said shop stopped selling those devices.
Still, I have not mentioned any details about the product...
it is an iLC 7" tablet PC using an ARM 800MHz processor with 256MB RAM
the OS being Android 2.2 (Android Market installed) on 4GB flash storage, allowing for a microSD card
the device is further equipped with WiFi, stereo speakers, a headphone connector and a built-in microphone
finally, there is the port accessory, providing 10baseT and 2x USB
All in all, the gadget look comparably cheap, matching up with the proce somehow. At times the device's response is somewhat sluggish. Would I buy the gadget once again? YES!

Monday, September 12, 2011

4:1, 6:1 or 9:1?

Thinking back and forth a bit, again on aerials, I came to the conclusion that using 75Ohms feedline some 4:1 would be appropriate.
But why?!

The developers at Diamond thought that for the BB6W, or the BB7V for good measures, a 6:1 transformation would be the way to go. This aerial design assumes a 50Ohms feedline. The aerial's feedpoint is therefore considered having an impedance of 300Ohms. Remember, in this design, there is 600Ohms of termination resistor to ensure a maximum SWR of 2:1.

Assuming that the average auto-ATU will match a transmitter's 50Ohms antenna connector to a 75Ohms feedline easily, a 4:1 transformation will do in order to match a feedpoint impedance of 300Ohms when using 75Ohms feedline.
This actually brings together good news from two worlds:
  1. 75Ohms coax cable has got less losses than 50Ohms coax (it is cheaper too)
  2. a 4:1 transformer is easier to make than a 6:1 transformer (QRP: old TV-xformers)
So, now what about the 9:1 UnUn that so many use with endfed aerials? Personally, I used a 9:1 transformer with 50Ohms feedline. The 450Ohms feedpoint impedance works with endfed wires, about as good as 450Ohms window line (using a suitable ATU).

As a side remark, the feedpoint impedance at the voltage maximum is considered to be 5kOhms. Neither window line nor a 9:1 transformer gets us there. This can only be matched using ladder line (or open wire line) with a symmetric coupler.

Friday, September 9, 2011

Kizomba, the Name of the Game

Hi folks,
this is completely off topic.You may have wondered why I am sooooo slooooow writing technical articles, well, there are some reasons. One of them reasons being, I am much more into dancing once again... and kizomba is the name of that game. Some may already know that I am severely into mambo dancing, this remains. For those of you readers that are into dancing, check out kizomba, aka. African tango. The dance is from Angola, the music is a mix of French creole "zouk" and Angolan "semba".
Dear fellow ham radio operators, there is more to life than a microphone or a Morse key. Get out, get social enjoy life, also on the dance floor!
BTW, WCS (West Coast Swing) is cool too! Go for it, grab a girl and off you go!

Saturday, August 27, 2011

Surplus RF-Transformers for Random Wire Antennas

In some of my last posts I was sharing thoughts about broadband aerials using transformers to match the high impedance of the non-resonant "random" wire. Well, the leghth of those wires is not that random at the end. Some typical lengths that come to my mind 6m, 7m, 7.5m, 11.5m, etc. you may know some more...

Now, let's have a look at some options provided by surplus (the junk box respectively).

CFL bulb transformer  vs.  surplus iron powder toroid
On the left side we have a transformer that was in a (defective) CFL bulb, aka as energy-saving light. The thing on the right side is one of the is a surplus transformer based on a T68-2, which came in bags of 5pc for just 0.80 €-cents.

So, what do we have, the CFL transformer countd 3:3:12 windings. Using the black and the white in series, that would be 6:12. This would be, in other words, be a fine 9:1 UnUn.

The T68-2 is provided with 12 bifilar windings. This would therefore make you average 4:1 UnUn. Obviously, those can also be 1:1 isolation transformer.

Both junk-box items are proven in ham-radio designs. I figure, I will experiment with both out of the box options. Additionally, I may possibly try a 6:1 UnUn, as in the BB6W/BB7V design. Staying at QRPP levels would even offer the change of trying the termination resistor used in the BB6W/BB7Vs.
Oh, I forgot, to get closer to the BB7V, I will add some additional Al-pipe to top of the 5.5m  long 27MHz vertical.

Thursday, August 25, 2011

Half-wave 27MHz Antenna as Broadband Vertical

Years and years ago, a friend of mine gave me a (brand new) half-wave CB antenna. Well, I have never used it, for the reason of not being QRV on 11m. For 10m I had my double bazooka, so there was no need for it. Now that it has been sitting in a corner for a while, I thought, maybe it could be useful for something else. Some else as in broadband vertical...

Now, let's have a look how those things are built:

aerial schematics
This drawing is not made by me, however, it nicely sketches what the following photographs of my very own version of that antenna show.

all still in one part


taken apart
What we have is the cavity and the transformer that was sitting in it. The air core transformer has got a winding ratio of 7.5:2. I figure, using a ferrite or iron powder toroid would improve performance on lower frequencies.
The cavity measures 35mm in diameter, having a depth of 24mm. This clearly offers enough space to house a smaller toroid transformer.

At this place, I would like to remind you of the BB7V (Diamond) having an UnUn transformer with (resistive) termination shunt. This vertical would be 6.7m tall. The regular 11m half-wave vertical could possibly be stretched to a tallness somewhat beyond 5.5m. Close enough to me.

Now let's think... for QRP work a T80-2 would make an ok UnUn. With some luck, transformers with a T130-2 core could possibly be squeezed in the cavity, if made carefully.
Reconsidering the BB7V's terminator, would I put one in there? Only if I would be using this aerial for QRPp only. The base of the CB-aerial is made from plastics material, which is not able to conduct any heat. Hence, heat created inside the cavity would never be dissipated. For QRSs/QRPp, the resistive terminator is a very appealing option, in particular since for such power levels, a T50-2 transformer would offer sufficient empty space for the terminator.
A T130-2 would possibly be good for a regular 100W rig. However, in a worst case, 50W of heat have to be dissipated, hence, some cooling of the termination would be required, therefore, this is a no-go. Some adjustments and selective use of bands would still be an option for such an arrangement.
Personally, I am very tempted to try a version of a T68-2 transformer (not sure about termination yet), in combination with my IC-703. This is somewhat of a compromise...
Should I ever again get into QRPp/QRSs/WSPR/WSJT/ROS actively, my preference would be the small transformer&terminator option.

Additionally, I figure, it could be of use to add an additional Al-pipe of about one meter to the top of the vertical. This will result in a total length of about 6.4m and a further distance to a quarter-wave on 20m, without getting too close to a quarter-wave on 30m.

There you have it, a new life for a cheap half-wave 11m vertical.

Saturday, August 6, 2011

455kHz SDR - a second thought

My previous blog was all about the idea of adding a softrock, or any other simple SDR-DC-RX, to a cheap (synthesized) AM radio. Well, honestly said, when thinking of it, this may be a totally unnecessary overkill.
Why? Well, very simple. The main purpose of all the quadrature stuff is to make the two sidebands that a DC-RX receives different. But, what if there is not other sideband? The following may not apply to the absolute cheapest of AM-receivers.
Concerning the ATS-404, I have ambiguous information. While some technical data mention the AM i.f. being 450kHz, the schematics diagram mentions a LT455H, which is a 455kHz ceramic filter having +/-3kHz 6dB bandwidth (+/-9kHz for attenuated bandwidth). If we tap before that filter, we definitely need quadrature, should we however tap the i.f. behind that filter, a non-quadrature SDR would be OK too.
Most of the better world-band receivers use a first i.f. somewhere high with a relatively wide crystal filter. Most of the narrow filtering is done at 455kHz. In this case, we probably wont need quadrature at all. All we have to do is to ensure that our SDR center frequency (or SDR-l.o.) falls close to but outside the range of the intermediate frequency range. In such a scenario, there would not be a second sideband to care about and also a simple mono-audio interface would already do the job.
The Target HF3 would be an example for such a receiver. The first i.f. is at 45MHz having a bandwidth of +/-3.75kHz. The second i.f. band would consequently be 455-3.75=451.25 to 455+3.75=458.75 kHz. In yesterday's example, using a 1.8432Mhz local oscillator, we ended up at an SDR center frequency of 460.8kHz, which is close but outside the HF3's second i.f. band. A regular direct conversion receiver with a local oscillator at 460.8kHz would therefore receive only a lower side-band, since there is no signal in its upper side-band.
My idea would be to try that out using a canned oscillator and two flip-flops for frequency division. With some isolation amplification a singled ended diode mixer and a cheap USB audio adapter should round up that experiment.

ATS-404 idea

Using the second intermediate frequency, often at 455kHz, is widely known. A suitable I/Q-SDR would be based on a 1.8432MHz (canned) oscillator, resulting in a 460.8kHz center frequency. Assuming a 24k sample rate, would be adequate to cover the range from 450 to 460kHz perfectly.

Many I/Q-SDR kist are available, due to the size and the low price, the softrock lite could be suitable best.

So, why the ATS-404. I was looking for a relatively cheap wide coverage receiver having direct frequency entry. The 5kHz tuning steps on shortwave suit the 10kHz wide SDR just fine.
The ATS-404 uses the TA8132AN AM/FM-receiver IC. This IC has go the advantage of providing an IF-out at pin 9 (see data-sheet). Slight downside: the TA8132 employs a 450kHz intermediate frequency...
A service manual for the ATS-404 can be found here:
 http://www.thiecom.de/ftp/sangean/ats404/

The remaining question... where to put the I/Q-SDR? Using a softrock lite, one may consider using the battery compartment. Speaking of battery, the radio runs of 4 AA cells. It can also be operated from 6V external power. I wonder if 5V from a USB-port would be sufficient, finally, the idea is to use a computer for the SDR anyway.
Which brings me to the last idea... a cheap (stereo!) USB-sound-interface could also be accomodated in the battery compartment, so that only connection would be a USB cable to the computer.

Sunday, July 17, 2011

BB6W / BB7V clones for QRSS

If you browse the wide of the internet on the hunt of information about Diamond's BB6W or BB7V, you will most likely come across some images and blogs. One of the most helpful blogs, in my view, is Martin's ECLECTIC AETHER. The link points to the actual article....
As to images, for me, the image found here: http://www.cqcqde.com/shop/88_108.html is most informative.


Referring to Martin's blog, it seems that the "matching" device actually is a 6:1 UnUn ferrit toroid transformer with a 600Ohm (120W) termination resistor. The aerial being rated 250W, this means that up to 50% or 3dB of power is burnt in said resistor. The bandwidth of the aerials is mentioned to be 2Mhz to 30MHz.
Martin mentions the inferior performance of the 6:1 UnUn the why it was wound in the original BB6W. To my believe there is actually some thought in this. Japan, that where the aerial comes from, is a very noisy, QRM that is, country. Hence, Diamond seems to have decided to compromise power coupling versus common mode noise by reducing the capacitive coupling between the windings.

My interpretation of this aerial comes close to a short end-fed random wire, which is broadened by a sort of termination known from aerials like the T2FD, with a twist however.
Here is what I believe is interesting about the concept. Usually end-fed random wires are used in combination with 9:1 UnUn transformers, which result in a feed point impedances of 450Ohms. The BB6W matching unit however transforms to 300Ohms only, where the termination is twice that. Obviously, one does not want 300Ohms of termination, that would just form a dummy load...

So, what we got here is a short broadband aerial, horizontal or vertical in which half the power is absorbed.
In QRO, the tricky bit is the non-inductive resistor. It is doable, and certainly to a lower price than Diamond sells the aerials.
In QRSS, which essentially is QRPP, we are not troubled by the problem mentioned above. In fact, we could use a regular 1/4W carbon resistor and still we would be fine.

Two things came to my mind
  1. use a 9:1 UnUn with a 900Ohms resistor
  2. use an air-core (auto-) transformer
Further, I would use a longer radiator to improve performance on 80m and allow for 160m. A low horizontal broadband aerial for 80m and 40m could be an interesting solution for NVIS operations on modes other than QRSS.
It would also not be too difficult to build a termination resistor being good for 10W or so....

Last thing, what way of winding the UnUn would be most appropriate? You decide... Diamond's way would provide you with less RX-QRM, Martin's method would pass more TX-power to the wire.

Saturday, June 11, 2011

XPware was made freeware!

XPware is freeware now! It runs under WinXP (have not tested any other win-flavor).
http://www.glaswerks.com/xpware/

It can talk to the following controllers (test myself):
  • Kantronics KAM(+)
  • AEA PK900
  • SCS PCT+
  • SCS PTCIIe
The handling of the software depends on the respective controller.

I did those tests on the grabber pc, which in parallel was running one instance of winamp, two instances of spectrum and argoupload. Since modern PCs are not equipped with serial ports anymore, USB2Serial cables were used. All in all I believe being fine to going on with NBDP acitivities.

NBDP what's that? You may ask... This is the modern name for the mode family FEC, SelFEC and TOR. The acronym stand for Narrow Band Direct Printing.

PS: if you are on facebook, feel free to join the recently created group "Teleprinting Over Radio"

Tuesday, June 7, 2011

Teleprinting Over Radio Revival?

Guys, I was wondering if it would be possible to revive a mode that seems to be lost, TOR (AmTOR or if you want - or NBDP as it is called today). To it's time, AmTOR was kinda expensive/hard to get qrv on easily. Transceivers needed a certain RX-TX switch over timing, modems were not cheap, software hard to get hold of. I remember, to the time I had some AmTOR software running on my trusted Apple II.... but that is a long time ago.
In that time, multi-mode controllers came on the market, worth more than a short-wave transceiver... so, I could not afford any of those. Even worse, the transceiver I could afford was a second hand Drake TR4, which would never have had a single chance to meet the timing demands of AmTOR. Hence, I was stuck to my trusty combination of the TR4 and a Siemens T100 doing Radio TeleTYping (aka RTTY).
Oh... and those ARQ signals where present everywhere!
Today, TOR (AmTOR for good measures) is relatively dead. Although, hardware is cheaply available today, and there is also some software downloadable, emulating the hardware solutions. Today's transceivers don't need to be modified anymore, to achieve the timing required for ARQ. AmTOR is a robust mode, good for some straight keyboard communication.... I wonder if we could revive this mode for amateur radio.
Mind you, this mode TOR (Teleprinting Over Radio) is still in use in GMDSS. Actually, it still is the preferred mode in today's maritime communication. Actually, for my GMDSS GOC, I lately had to learn how to connect to a Telex land-line.
Folks, would it not be cool to give this AmTOR a second life? In particular since second hand hardware is available as cheaply as presently....

PS: if you are on facebook, feel free to join the recently created group "Teleprinting Over Radio

Friday, May 27, 2011

SWL PSK-20 for JT65 & WSPR

PSK31 is fun, agreed, however, would there be an additional option for using the PSK-20 transceiver for other weak signal modes? The question is, would it be possible to modify the PSK-20 such that instead of operating in LSB on 14.071MHz, it would also be operating USB on 14.0775MHz (corresponding to a "dial frequency" of 14.076MHz)?

Lets have a look at the PSK-20's design. We are dealing with a 9.000MHz i.f., with a 9.002MHz b.f.o. obviously. The l.o. operates at 5.070MHz. Both oscillators use crystals, a pulled up 9MHz one and a pulled up 5.0688MHz one.

Looking what could be done for the LSB to USB modification, I figure the 9MHz xtal could either pulled down by means of inductors, "penned" down or it can be replaced with another one.
Replacement would be provided by two different options. Since 9MHz is a very popular i.f., side-band crystals are available for not too much money. The second option possibly already sits waiting in the junk-box somewhere. The CB channel 3 transmit (overtone) crystal has got a nominal frequency of 26.985MHz. On the fundamental that would result in a 8.995MHz beat frequency. Still somewhat too low.... but.... in the original design, the 9MHz crystal is pulled up, remember? The CB crystal would therefore fit perfectly! Lets just assume the b.f.o. would be at 8.9985MHz.
Penning the crystal in place down, I would do "in situ". That way, everything will be set when the desired frequency is reached and only the crystal's housing would have to be soldered in place again.

Now lets have a look at the local oscillator. The JT65 centre frequency is 14.0775MHz. With an i.f. of 9.000MHz, this would be reached by a l.o. at 5.0775MHz obviously. Equally you could add up the b.f.o. and l.o. frequencies to end up at the "dial frequency". 5.0775MHz looks a an ambitious 8.7kHz up-wards pull for a 5.0688MHz crystal, and most likely it will be in the existing discrete oscillator.
 However, all is not lost. Seen that 2x5.0775 results in 10.155, there would be a couple of great options for (pulled!) digital gate oscillators and Flip-Flop dividers, namely CB synthesizer crystals.
  • 10.160 / 2 = 5.080 for JT65a: 5kHz downwards pull on 10MHz
  • 10.140 / 2 = 5.070 for PSK31: 2kHz upwards pull on 10MHz
Such digital stuff is very rich on harmonics. This is something rather annoying. However, there is a crystal ("Y4") built in the rig already. It is serving as an oscillator... ok... but... with removing the jumper "L4", and bridging (removing) the oscillator circuitry, the attenuated and Flip-Flopped digital oscillator signal can be fed into the crystal, which then will serve as a harmonics filter.

Alternatively, the 10.160MHz xtal could be "penned" down to 10.155MHz; equally, a 10.150MHz xtal could be penned down to 10.142MHz to allow for the 20m PSK31 frequency.

In this way, I hope I can create a decent dual frequency narrow-band data transceiver.

Tuesday, May 24, 2011

Look What I Found!

A local hardware store offered those:

F2BNC

F Type Connector to Bayonet Nay Connector adaptor. Those essentially conclude my usage of overpriced 50Ohms stuff for QRP applications.
Well, the adaptors did not came cheap, they are €2.40/pc, but I feel they are totally worth it.

Monday, May 23, 2011

QRSS Studies - the Results

Seen that there is no more for me to investigate in QRSS, other radio topics will soon become more relevant to me, and also to this blog.


The results I can report on QRSS
  • You can operate a decent visual grabber in very densely populated regions. One will see the neighbours' TV sets, which in many cases is not more than just annoying.
  • The reception of WSPR is not affected by urban noise, low profile and even indoor antennas give good results.
  • There is no need to occupy your expensive main rig or a professional receiver, a cheap and cheerful home fixed frequency RX does the jobs.
  • Setting up an online grabber is something that anyone with internet access can do, no excuses here. The demands on the respective computer are minimal. An Intel ATOM can easily operate two grabbers and WSPR (rx in my case), have a third instance of speclab running, be a print and file server and operate winamp for internet radio... all at once.

Conclusion I learned from my experiments, on-air and off-air
  • There are many more transmitting stations than receiving ones.
  • Despite my efforts to motivate the installation of additional grabbers, there are still only a few.
  • Operating a grabber blocks other activities, at least on the bands the grabbers are active on.

What I miss in QRSS is interaction, consequently, I will for the time being cease QRSS activity until further notice.

My focus for the time to come will be on data modes such as PSK500, ALE, etc.
Another thing that crossed my mind occasionally, going QRO with some homebrew kit. Saying QRO, I mean QRO, i.e. legal limit. It is not so much the urge of being heard, it's more the design challenge here.

Thursday, May 19, 2011

Froyo & Market on the A7ht

Someone hacked it, the Archos 7 home tablet. What a pleasure to see froyo and google market running on the gadget. At times it seems to struggle during bootup, this could be due to the lack of cell-network hardware.
With expanded options of market, the cheap tablet is really useful to me now. Let ne give you an example, there are apps out there for watching webcams... perfect to keep an eye on one or more grabbers...
Froyo is not slowing down the device, this was the first thing I feared. What  like about froyo in particular, the orientation of the plain desktop changes with rotation of the device. Occasionally is comes really handy.
Now looking for some interesting ham-radio apps...

Monday, May 16, 2011

The Ultimate Icom IC-M700D+

OK, this may sound a little unfair and overdone... today I managed to secure an Icom IC-M700 purchase. That means, I will create the ultimate IC-M700(whatever)+++.
Here is the idea: All of the IC-M700xx brought their individual pros and cons. The aim is to create the ultimate transceiver based on whatever Icom had to offer in the M700 series.
I believe, I have found it!

Basis: 
  • IC-M700D: three power regimes, USB only (limited TX-QRGs, see mod)
  • IC-M700: USB/LSB, TCXO, one power regime only
Plan:
  • the modified IC-M700D will be equiped with the RF-unit of the IC-M700 and hence providing USB and LSB voice operations at three different power levels, which to me sounds like a nice rag chew transceiver.
  • the IC-M700 seems to be crippled by the use of the USB-only RF unit of the IC-M700D. However, the base band stability of the TCXO makes the USB-only unit a perfect transceiver for digital modes.
Still there is this perfect all in one box sitting in my shack, the IC-M700TY.
However, since it is very hard to get your hands on one of those, merging the IC-M700D(or F) with  an IC-M700, will get you at least half the way to an IC-700TY.

73!

Thursday, April 28, 2011

Super Radio SS-301

Yesterday I got a notification to pick up a parcel at the local supermarket. Yes, supermarket, the post office was closed and "out sourced" to my local grocery. Actually, this even has an advantage to me, opening hours are much more convenient.

So, today it was pickup time for a parcel from Thailand. In the parcel, a "Super Radio SS-301" handheld transceiver. You may not have heard about this brand nor the model... it is a clone of the Albrecht AE2990AFS, aka Magnum 1012, aka Dragon SS301. Imagine, the radio incl. shipping set me back not even €170.- (check ebay for the present conditions).

A guide for frequency coverage modification was provided inside the box. However, other than this single sheet of paper, the radio, a battery case, and wrist strap and a rubber duck aerial, the box did not contain anything in addition. I guess, I will have to hunt down a manual on the internet (probably not the most difficult task ever).

The actual modification itself, from whatever mode to 12m/10m operation, was done in not time at all. Contrary to the guide, two solder bridges had to be removed (Soder Wick) first. Temporary shorten terminals 1 and 2 whilst switching on the radio is a bit tricky, not difficult however. Having selected the correct code, for hams "0" would be ideal, the two solder bridges 2-3 and 4-5, have to be put in place again.

The radio is a bit annoying what beeping is concerned. Julian G4ILO describes how to solve is issue.

Listening to my 10m MEPT (A1A), which happen to run today, I noticed a slight jitter in the PLL. I am not yet sure what this means and what causes it, I hope that this could be solved in the same way the PLL-jitter in the Target HF-3 was removed, by retuning individual sections of the frequency synthesis.

The radio employs the following modes of operation: FM, AM, USB and LSB. There is no CW. I noticed that between USB and LSB pure noise sounds very differently. Another indication that factory tuning may not be ideal.
The transceiver is provided with microphone and external speaker jacks. Digital modes, provided the jitter is gone, should therefore not be a problem.
The lack of CW, although kinda natural to a HT, kinda sucks. As soon as the bands are open again, I will use a keyed sine generator for transmitting CW using the side-band modes via the microphone jack. Due to the low locking speed of the PLL, QSK is no option... so what! Audio keying a transceiver has got an added bonus: power regulation can be done by audio level control.

Can't wait until CONDX provide us with open high bands, so I can have DX-QSOs whilst walking to work.

Thursday, April 21, 2011

Day to Night Transition

Just a spectrum I would like to share. It nicely shows the transition from day time propagation to night time propagation.


Tuesday, April 19, 2011

Skanti Marinetta TRP 1

I got lucky! Ever since I made my GMDSS-GOC, I wanted one of those:

Skanti Marinetta TRP 1 portable survival radio
In the Scheepvaart en Transport College Rotterdam, where I studied for the GMDSS-GOC, those units are on display. You can only guess how happy I am to finally got one into my collection of marine radios. The best thing on this purchase, the set is complete with all standard accessories.
I would like to thank Willy PA0WMR for keeping this rig in near original state. Willy also stated that the transmitter delivers about 5W on 600m.

What is all the fuss about a yellow box anyways you may ask. And the question is well justified. First of all, the box, with the lid closed, swims ;-) It is yellow! (That would be a reference to Douglas Adam's Hitchhiker's Guide to the Galaxy).

OK, lets be serious, why am I so happy to finally posses one?
Having a look at the manual/schematics we see that the rig
  • has a modern (digital) design
  • operates on 500kHz, 2182kHz and 8364kHz
  • is crystal controlled
  • allows for CW and AM
  • has a built in dummy load
  • employs an antenna current meter
  • contains an ATU
  • can create its own energy (by means of cranks)
  • can be energized by an external source

500kHz, 2182kHz and 8364kHz are (former) distress frequencies and must not be use by ham- radio operators! 

Where is the hamradio use of these units? Well, we all hope for the 600m band. The 500kHz signal is created by a  2.000MHz gate-XO and digital dividers. Depending on what band we will finally get, this crystal can simply be replaced by a fitting one. However, since it is a digital XO, on simply could remove the crystal and feed a DDS generated signal into the digital gates.

According to the schematics, the transmitter's 8364kHz crystal can easily be replaced by a 40m crystal. However, the receiver employs some resonant LC-stuff with varactor tuning, which should not pose a major problem to modify to 40m, e.g. 7030kHz.

The receiver uses a 2682kHz crystal oscillator to the 2182kHz emergency frequency. The transmitter employs a 2182kHz digital gate oscillator. We got two options for ham-bands here, 160m or 80m. Both have pros and cons. 2182kHz originally is an A3 frequency. The wiring inside the TRP 1 is providing AM modulation accordingly.
On the 80m band, AM is used in places, hence, that would be a nice possibility to join the action. However, filters will have to be modified.
On the 160m band one may want to aim for A1 operation. A 1.843MHz crystal would do the trick here... However, the wiring will have to be changed to engage the BFO in the "2182kHz" labeled switch position.

What is the prospect for the future use of the rig?
I believe it would provide endless fun during field day operations. In particular when operated from cranks, independently from any power supplies.
The (yellow) box contains everything needed for QRP-ops, including a telescopic vertical antenna and a "long(er) wire" aerial.

I figure it could be reasonable to replace the TBA570 receiver with a NE612 superhet design for side-band use.
The XOs could be replaced by either a DDS or some synthesizers for enhanced flexibility.
Some PIC controls seem obvious, the automatic SOS-TXing is inadequate, obviously.

It all comes down to how much modification is actually wanted. Maybe the greatest fun can be obtained when staying as close as possible to the original functionality, i.e. AM on 80m, CW on 40m and 600m.

Other than that, it is an extremely nice addition to my marine radio collection.

Thursday, April 14, 2011

Magnetic Loop Antenna Idea

Had an idea... again, I have not tried this yet.
A magnetic loop antenna, as we all know, are relatively narrowband. For mono-band QRSS, WSPR or WSJT activity this is not a problem at all. But what if one would like to receive (well, let's start looking at RX only at this point) on an additional frequency at the same band or maybe even in another band, such a simple magnetic loop antenna would not be so ideal.

Now that the problem is defined, let's have a look at possible solutions. The basic idea is to build two loops sharing one coupling loop by using heavy gauge speaker twin lead.

RF-principle: Two parameters determine the resonance of a magnetic loop antenna, the diameter of the loop and the capacitor.

For a second frequency in one band one may consider to shorten one cable of the twin lead by just the right amount. This will certainly result in a second resonance close to the first resonance. Since the two leads are somewhat close, there will certainly be some capacitive coupling, what influence this will have, if at all, will be subject to experimentation. The second consequence of the proximity of the leads would be that the lengths cannot be drastically different, hence, using the same capacitor, the frequency offset would be small.

For dual-band use, the two loops should be resonated by individual capacitors. Here, the capacity between the loops will certainly have a dramatic impact on the resonance frequencies.

There is yet another possibility, probably the most messy one... Connecting the second loop to the resonating capacitor of the first loop symmetrically using identical high(er) value capacitors. This will (slightly) increase the resonance frequency of the second loop. I figure, this third possibility is somewhat impractical.

Whatever option is chosen, the (single) coupling loop will couple both loops equally well, since the size of the coupling loop is defined relative to the size of the main loop(s), i.e. 1/6 to 1/4 depending on the loop's environment.

Wednesday, April 6, 2011

17m XTAL Controlled QRSS / WSPR / QRP / SDR

Sorry for having been silent for a while. Some new thought, although not entirely mine, I believe sharing it this way would be more than appropriate.
The idea about the frequency generation is borrowed from DJ1ZB. Ha-Jo uses CB crystals on their fundamental and doubles the result.

Doubling sounds very much like two things I previously disclosed on this blot, namely, the subharmonic direct conversion receiver (e.g. this) and the subharmonic I/Q-SDR (see earlier posts on the SDR and possible frequencies).
Both designs rely on a local oscillator on half the operating frequency.

Concentrating what could be interesting for QRP, QRSS and WSPR, lets have a closer look to the available crystals.
  • 27.105MHz (12T) => 9.035MHz x 2 = 18.070MHz
  • 27.135MHz (15T) => 9.045MHz x 2 = 18.090MHz
  • 27.155MHz (16T) => 9.051667MHz x 2 = 18.103333MHz
  • 27.165MHz (17T) => 9.055MHz x 2 = 18.110MHz
The frequency generated with a 15T-XTAL appears to be ideal for I/Q-SDR since the whole CW & Data & beacons range will be covered by 48kHz sampling rate. Have a look: difference 18.090-0.024=18.066 and sum 18.090+0.024=18.114.
Additionally, 18.090MHz is the quite close to the QRP frequency, a subharmonic direct conversion receiver would be an obvious choice, so would be a transmitter with a doubler...

Very obviously, the other frequencies are directed more to QRSS and WSPR. I am not going into the QRSS feature here, it is kinda trivial (see above).

Remaining topic: WSPR. The frequency produced by the 16T-XTAL is very very close to the WSPR "dial frequency" 18.1046MHz. With a Pierce oscillator the tiny amount of 633Hz upwards pull should not be a big deal; remember, on half the frequency, one only needs to pull half the distance.
RX: subharmonic direct conversion.
TX: subharmonic mixing of the local oscillator with an audio signal should create a DSB signal... that's the theory... I have not yet tried it yet, however, I fail to see any reason why this should not work.

Saturday, March 19, 2011

75Ohms Coax update

Low loss & cheap, that was just one part of the story about RG-6 sat-coax. The other side would be the (cheap) accessories one can get for the 75Ohms F-system. My secondary grabber system (Target HF3 & Yaesu FRT-7700) is hooked up to 75Ohms for a couple of days. Additionally I am using one of those ("Sat-Flex"-adapter):

For the readers who have never seen those before, such devices are use to lead a TV-sat signal from the LNC to the indoors sat-receiver. Those adapters are squeezed between a window and a window frame.

There are other accessories available at very very low prices. Splitters, barrels, splitters, etc.

And even better news. I not buying the cheapest available, one may be lucky and obtain this:
Well, it was slightly more expensive (€8.- for 10m @ HEMA) than the previous example, and it did not come with F-connectors. However, see the air-cells? Next to the Al-foil shield, there is a Cu-braid, the soul is made from Cu too. This cable can be soldered just fine.
Somehow the stuff reminds me of aircom-plus (€3.35 for 1m)... many times cheaper though...

Monday, March 14, 2011

75Ohms, why not?!

I have been experimenting a bit with more or less cheap (inexpensive that is) materials lately. Came across something called RG-6, or, in other words, very inexpensive 75Ohms coax-cable for TV-satellite reception.
TV-sat-RX means, that losses at frequencies between 1GHz and 2GHz are acceptable. The cable itself proofs on that point, foam dielectric....
We amateurs are using stuff called RG-58, RG-213 etc. for ages.... This relatively expensive stuff is rated 50 (or 52) Ohms, as most of our transceiver's aerial connectors. Most of the modern times transceivers however still employ so called UHF-connectors... something sooo outdated, you would not believe it! And further, look at the inside of 'm transceivers, there is not 50Ohms match found anywhere.... So, what is that hype about 50Ohms anyway?! I don't know!
And hence, I don't care!
However, nowadays UHF-connector have a thread for the the shield. The soul of the sat-coax is copper and hence can be soldered easily. There is hence an easy way to adapt 50Ohms PL-connectors to 75Ohms F-connectors.


F-connector 75Ohms coax and a 50Ohms UHF-connector


My local hardware store provides me with satellite-grade 75Ohms cable for a price of about €5.- per 10m including two of the so called F-connectors... a price, RG-58 cannot match, not to speak about the (two) UHF-connectors aka PL259.
Let's further search for justification of using more expensive 50Ohms-stuff rather than 75Ohms-mass-ware. A dipole is mentioned to have an impedance of 60Ohms.... OK 50Ohms is marginally closer to that than 75Ohms would be.... but... does that matter? I don't think so!
Let's turn to the connectors for a change. I mentioned UHF-connector (aka PL-connectors) before. To the time these connectors have been invented, names like UHF were justified, I believe. However, in modern times, this merely reflects a relict from the glorious past... UHF connectors are considered good for shortwave and lower frequencies. Connectors considered suitable for UHF as of today would be BNC and N-connectors (both 50Ohms nevertheless).
Still 50Ohms, but why? I believe, we stick to 50Ohms (or 52Ohms) for reasons of tradition. Industry seems to like that, since there still is a reason to produce (and sell) 50Ohms coax like RG-58 and RG-213.
As radio-amateur, or HAM for good measures, you always want to watch your options.
I watched mine, and I came to the conclusion that, where ever I would need coax-cable the cheapest commercial (i.e. mass market) solution available was the best for the purpose. Hence I will use RG-6 or whatever (low loss) will be available for cheap at my local hardware store. Who needs specialized retailers, if a tiny change in the setup will do?
Up to now I was writing about low power and low-noise reception. Let's face the other option for a change... QRO! When facing high power, I would anyway not consider using coax-cables. Those just get hot on losses. For QRO, I personally would/will/do go for open wire feed-lines. If that appears too difficult to do, I still would propose using high ohmic window-line for the purpose.
Conclusion: use cheap satellite-TV-coax and forget about expensive 50Ohms stuff!
73!

Friday, March 4, 2011

6m QRSS

This is an extremely easy one. Most QRSS operators once built a 30m MEPT. There is an easy way to recycle those transmitters for 6m. With a converter circuit running a 40MHz oscillator, a 10.140MHz MEPT would be right away transmitting on 50.140MHz. Not too bad, I figure. A NE612 would probably be the easiest and cheapest way to get there this way.
Alternatively, a subharmonic mixer (two anti-parallel diodes) on a 20MHz oscillator would be even easier to build.
There are canned oscillators for 40MHz and 20MHz available, not to mention those cheap crystals.

Wednesday, March 2, 2011

2m QRSS

Something I was thinking of occasionally, QRSS on VHF, UHF, SHF and EHF bands.

Lets first start with a band that is accessible to all of us, the 2m band.

A short chat with Dave (G7UVW) brought up two frequencies of interest.
  • 144.070 MHz
  • 144.4905 MHz (WSPR)

Both QRGs can be reached with CB-TX-crystals on their fundamental frequency and doubling the signals a couple of times. 9.x MHz will have to be multiplied by a factor of 16. With a little pull and the right oscillator circuit, this all should be fairely easy.

144.070 MHz
Channel 5T (27.015MHz) will be, very obviously, be 9.005MHz on the fundamental frequency. The resulting frequency on the 2m would be 144.080MHz. A little harmless down pull to 9.004375MHz on the fundamental will get us to 144.070MHz.

144.4905 MHz (WSPR-QRG)
We got two options here,  channels 11T (27.085MHz) and 12T (27.105MHz).
11T would require a Pierce oscillator which oscillates above the series frequency of the crystal. The fundamental of 11T is 9.028333MHz, while the required frequency for the target-frequency would be 9.03065625MHz. The difference of 2.323kHz is not problem to a Pierce oscillator at all.
12T will provide a 9.035MHz signal. The pull of 4.344kHz to 9.03065625MHz is doable, could however result in a less stable oscillator.

Put the design into practice seem not to be a great deal, however, frequency stability is a great deal here. So, I figure, good temperature stabilization is in order. The rest is in fact pretty straight forward. I do have to admit that the first ever ham-radio transmitter I built (age 15, just licensed) was a 144MHz A1A TX, based on a CB crystal and BF199 transistors.

Monday, February 28, 2011

The T2SFM Antenna

The T2FD (aka TTFD, Terminated Tilted Folded Dipole) may be know to many of us. No, I am not going to discuss the T2FD here. It is just mentioned since it forms the basis for the following design considerations.
The only thing we should keep in mind, the span of a T2FD is 30% of the lowest wavelength, not 50% as a regular folded dipole would be. The distance of the fold is 1% of the wavelength.

In a country as densely populated as Holland, one needs to think of room saving antenna solutions regularly. The goal of the game is hence to reduce the span of antenna setups.

The aerial I am thinking of needs to the at least the popular QRSS bands 80m - 30m, possibly 160m and 20m.

First design step, the a quarter-wave radiator for 30m and tilt it. The length of such radiator would be 7.6m.

Second step, a trap terminating the 30m radiator. This trap also acts as loading inductor for the lower frequencies. As a fist assumption, I was randomly picking 10µH, the resulting capacitance is 25pF.

Third, the folding distance is chosen to be 50cm, reflecting an operation wavelength of 50m, which is somewhere between 40m and 80m obviously.

The last and remaining bit would be the second "T" of the name, i.e. the termination. I figured 600Ohms could be a good value to start from. When putting this into reality, one needs to remember that the termination resistor should not be induction and should be rated at least 30% of the power applied to the aerial.

There the MMANA script a hacked in:


80m - 20m T2SFM
*
10.12
***Wires***
4
0.0,    0.0,    0.0,    -7.0,   0.0,    3.0,    8.000e-04,    -1
-7.0,   0.0,    3.0,    -7.0,   0.0,    3.5,    8.000e-04,    -1
-7.0,   0.0,    3.5,    0.0,    0.0,    0.5,    8.000e-04,    -1
0.0,    0.0,    0.0,    0.0,    0.0,    0.5,    8.000e-04,    -1
***Source***
1,    1
w1b,    0.0,    1.0
***Load***
2,    1
w2c,    0,    2.17,    114.0,    0.0
w4c,    1,    600.0,    0.0
***Segmentation***
800,    80,    2.0,    1
***G/H/M/R/AzEl/X***
2,    0.0,    1,    600.0,    120,    60,    0.0
###Comment###
Mod by Joachim, PA1GSJ 2/28/2011 9:55:09 PM
Created by Joachim, PA1GSJ 2/28/2011 9:08:01 PM


The first simulations look promising, still a lot room for optimizations. Would be time to also start putting stuff together and try out if this contraption is any good.

REVISION
Had another thought about the 30m trap. The easiest way to make a trap would be a coax trap. With a diameter of 4cm, a length of 4cm a coax trap would have a self-inductance of 2.17µH and a capacitance of 114pF. Purely mechanical, 117cm of RG58 are required in order to form 8 turns on a 4cm diameter.

Thursday, February 24, 2011

Inexpensive Small Computer

Remember when I was writing about a "grabber viewer gadget" some weeks ago?
Well, the thing can be used for more, apparently, since it most likely was not build for grabber-viewing anyway ;-)
First, lets have a look what a minimal setup can look like...

ARCHOS 7 HT
The cost of the total setup is about €150.- for the ARCHOS 7 HT (8GB SSD, microSDHC, WiFi), €20,- for the wireless mini keyboard and €5.- for the USB gender-changer. The USB cable and the power supply are provided with the ARCHOS.

The only thing one has to do is to enable the USB HOST MODE in the ARCHOS' configuration menu. As soon as a pointing device is recognized, a mouse pointer is shown on the screen.

Amongst USB accessories I tested were a Micro Hub, a card-reader, thumb drives, a keyboard with built-in Hub, mice.

There seem to be ways to toggle to an alternative window manager. Android is perfect for touch-screens, operation, however when used with keyboard and mouse, the advantages of Android don't really help.

Monday, February 21, 2011

Propagation JO29 --> JO22

Most interesting! Two Norwegian stations, LA5GOA and LA9BEA (neighbors), running MEPTs from JO29.

The locations of the two stations, as googled, are:
LA5GOA in JO29OI
LA9BEA in JO29OG
Steen Erik wrote on the KnightsQRSS list "LA5GOA and LA9BEA live about 15km apart on the island Karmøy on the west coast of Norway". Seen from my QTH, both stations share the same heading and hence, LA9BEA is by 15km closer to my location than LA5GOA.

And here comes the interesting part, not surprising however. Both transmitters create comparable field strengths in my humble grabber (located in JO22DA).
The following spectra were received by my 30m grabber setup: 30m-DCTL & subharmonic direct-conversion receiver. Note, the receiver does not employ AGC circuitry.
Please observe the different field strengths caused by the two friends and enjoy our ionosphere in action!






Thursday, February 17, 2011

Just an Idea

From VHF and UHF operations we know to use preamps at the antenna feedpoint as to improve SNR. SHF and EHF amateur radio operation is usually done by having the transverter at the antenna's feedpoint, since losses in the transmission line would eat up the signals completely...

So, what's the idea? Well, in QRSS, we also hunt for the best possible SNR. So, why not moving half or more of a QRSS station's circuitry to the antenna?
Half? Yes, I would prefer/advice to have frequency determining blocks, i.e. oscillators, in a controlled environment, e.g. the shack.

DC-Feed
The basic trick on all of the following would be feeding DC from the shack to the device at the antenna, whatever the device will be. Feeding is done in the well known way for active aerial or mast-head preamps.

TX
Easy things first, lets have a look at transmitters. The only bit that needs to be at the antenna feedpoint would be the final amplifier. The only thing to watch out for would be the Ohmic loss of the transmission line, since the final stage will require some current. If one cares about the voltage which the final is driven from, one should take this transmission line DC resistance into consideration.

RX
Reception is somewhat more challenging. Why do it in the first place? A preamp could do that. Yes, it could. However, some designs (e.g. w/ the NE612) do not really need pre-amplification...
Here's a look at the different cases:

Direct Conversion
In this case, the LO would be in the shack, and the whole rest of the receiver remote at the antenna location. It should not pose any problem to combine/split LO-RF, RX-AF and DC. However, the supply DC can carry mains hum residuals. A decent high-pass will be necessary before the AF can be fed into any sound-card.


Supersonic-Heterodyne (Superhet)
In such a scenario, front-end, mixer and IF filter (xtal-ladder) would be distal. LO, BFO, product detector and AF-amp would proximal. It is conceivable/advisable to add a second xtal-ladder to split IF and BFO frequencies. The downside would be the more complex frequency splitting at the distal part. A crystal filter would come handy here, and therefore, a "cheap crystal combination" would be recommendable for such a design, however tempting a DDS design would be.


RX&TX
Now to the tricky stuff... RX/TX-toggle could possibly done by polarity reversal, e.g. by diodes and relays.
I would like to leave it to your imagination what would be possible...

Conclusions
This may not be necessary to think about at all...
However, in case of reception, having all the low-noise stuff at the distal location, one may consider using cheap twin lead cable to connect the remote head with the shack.
For transmission, the obvious advantage would be that the final could be matched to TX-aerial, whatever it may be in balance and/or impedance.

Thursday, February 10, 2011

JUMA-RX1 kit arrived

Unboxing of a kit... I would usually not make any noises about. However, this time it seems appropriate to share this experience with you.

SRAT sent the kit in a solid cardboard box with more than sufficient padding. I received an email the day the kit was shipped, with tracking info! The shipment was tagged "1st class - PRIORITY" and "RECOMMANDÉ". I am impressed!

The 1st class treatment continues inside the box, carrying a bag containing a TEKO casing. The kit itself is contained inside the TEKO casing:

JUMA-RX1 receiver kit
Note, the kit supplies you with everything you could possibly require... even rubber pads.

Wednesday, February 9, 2011

JUMA-RX1 possible mod

To the time of writing this post., my JUMA-RX1 kit is still waiting with postal services. Will be pick the kit up tomorrow....

Time to look into some possible modifications. Why, you may ask, why the hack modify a well thought through design? Vy vy simple, the receiver, due to the simplicity of the design, is limited to bands 40m and lower, i.e. 100kHz to 7.5MHz.

So, what is that constraint all about? The design uses a 16F819 as controller. This PIC is limited to a 20MHz clock frequency. The clever bit of OH2NLT's design is to use the 16F819's clock for the AD9833 DDS too. This however limits the DDS output frequency. One possibility would be to have the DDS running at another clock frequency. Such a modification would however require reprogramming of the firmware, in order to adapt to the new DDS clock. Possible, ok, but somewhat intensive.

OH7SV designed a direct conversion receiver with an active switching mixer. Absolutely nothing wrong with this design. If we sacrifice the 136kHz band, we could gain the 30m and 20m bands by doubling the LO. The frequency coverage will move from 100kHz-7.5MHz to 200kHz-15MHz.
There is one downside to this game, the LO frequency steps are also doubled. The 10Hz minimal steps would result in 20Hz QRG change... also frequency readout will have to be doubled to determine the QRG.

Here would be my preferred solution: introduce a second front-end having a low-pass filter, a subharmonic mixer and a low noise op-amp AF preamp. A dual switch toggles the antenna input and the preamp output between the original and the additional circuits. Extracting signal to the subharmonic mixer may require an additional adjustable driver.
Such a mod will preserve 136kHz operation and better fine tuning in direct conversion mode and offer improved performance and wider coverage in subharmonic mode.

Should there be no need for 136kHz and/or 10Hz steps, the whole front-end could be modified easily by changing low-pass filter components and adding a frequency doubler between the DDS and the RX boards.
In case subharmonic advantages are on the wish-list, the MUX-mixer could be replaced by a RA3AAE-mixer (don't forget the low-pass!). In this case the differential preamp should be modified too.

I am sure that even more possibilities would be obvious to the skilled artisan.

Stay tune for practical experience, as soon as I picked up and built the kit.

Monday, February 7, 2011

Grabber Viewer Gadget

This is actually a little bit off topic. For various reasons, I decided to buy a tablet gadget. Several options were thought through:

iPad: too big, too expensive, no USB, no memory card
Galaxy Tab: GPS, too expensive
Archos 5: 160GB HDD, 3G, GPS, screen too small
Archos 70: 250GB HDD, no memory card, sold out :-(
Archos 7: cheap, just 8GB storage, nevertheless: bought

Yes, initially, I opted for the Archos 70, in particular for its 250GB HDD. However, the Archos 70 was sold out... Moreover, the Archos 70 carries ballast I don't need, such as a webcam and BlueTooth.

So, there we go, the Archos 7 home tablet it is (for the time being). Why am I posting this on my RF blog anyway? Very simply said. This gadget allows me to observe grabbers conveniently when being in reach of an accessible WLAN. The Android 2.1 GUI allows for putting URLs on a virtual desktop for easy access. Hold the device vertically, i2NDT's compendium fits perfectly on the 7in screen, hold it horizontally, an individual grabber spectrum will fill the screen for comfortable observation.

The Archos 7 home tablet is big enough as to not being fiddly to operate (virtual keyboard size), yet small enough to carry about.

Thursday, February 3, 2011

You don't always get what you want, but you do get what you need!

That at least was the motto of my ex. Very respectfully I would like to point out that we are not together anymore for a reason, we are still friends however!

The same applies to the PFR-3 paddles... initially I wanted those, since they were fitting the PFR-3. A week after I ordered, I learned about Jerry's (W5JH) paddles, which equally attach to the PFR-3. However, having ordered the original paddles, I postponed any additional order.
Until I learned (two months after ordering) that I wont get any PFR-3 paddles...

Jerry's kit comes with two beautiful black anodized aluminum plates and three brass bars. Those five parts are machined and finished to the highest quality standard! Believe me, the manufacture of those parts is really really good!
The kit practically built itself!

So, I didn't get what I initially wanted... however, regarding the rock solid quality of Jerry's paddles, I got what I needed!

Monday, January 31, 2011

NVIS QRSS

This could be a fun one to do: dual band NVIS QRSS.

Not sure what NVIS is? Please have a "google" to find out. There is a lot of excellent documentation available.
The only bit of info about NVIS I would like to point out in the post would be the fact that the 40m band is good during the average day and the 80m band is good for the average night. Running both in parallel could show some interesting daytime nighttime transitions.

Due to the harmonic nature of the 80m and 40m bands the easiest approach for a transmitter design would be to build an oscillator for either band and generate the other frequency by division or doubling. The downside here: shifts and offsets would also be divided or doubled.

A receiver also could make use of a single local oscillator. Here the most simple design would be a regular direct conversion mixer for 80m and a subharmonic direct conversion mixer for 40m. The respective audio frequencies could be fed into one single stereo sound card using left and right channels.

Frequency-wise, there are two obvious possibilities.  Both have pros and cons:
  1. 3500400Hz & 7000800Hz
  2. 3579545Hz & 7159090Hz
The first option will make this sort of QRSS activity visible in grabbers as presently operated, it is however, due to the price of the crsytals more expensive than the second option.
The second option uses frequencies for which very inexpensive crystals are available, the big pro on the second option would be that is will enable many more hams to operate a transmitter legally (the ole novice story).

By now, you may have asked yourself why crystals still play a role here. Well, not so much for the transmitter, although they make nice filters for oscillators using digital gates. For a possible receiver those crystals would make ideal narrow front-end side-band filters, which are in particular important when operating in the middle of a busy band.

Want something more complicated?
What about a "superhet" design? With center (intermediate) frequency of 5.250800MHz and a 1.750MHz local oscillator the mixing products would be 3500800Hz and 7000800Hz. When shifting the intermediate frequency, both the 80m and the 40m frequencies will shift by the equal amount in the same direction, that's kinda cool!
Now to the tricky business how frequencies could be generated. Lets start with the easy one. 1.75MHz is subharmonic to 3.5, 7.0 and 14.0MHz. The first two call for trouble since those are too close to the final operating frequencies (*). But what about 14.0MHz? Crystals and even oscillators are available for this one! A division by 8 (ripple counter) will result in a very stable 1.75MHz local oscillator.
And here is the challenge: 5.250800MHz. There is a crystal for 5200kHz, but a 50kHz pull is too much and grinding is a tricky business. There may be a 10.5MHz crystal available, somewhere... As a last resort, a DDS would possibly do a superb job. This however would also be the most expensive solution.
(*) Problem for the TX, solution for the RX, subharmonic to 80 and 40 and the same time!

Want something even more complicated? No problem! That one is so overcomplicated, that is should rather be seen as experiment in thought. What about SDR? Take a 10m QRP crystal (28.060MHz). This frequency is perfect for a 40m SDR, center frequency: 7.015MHz. A quadrature local oscillator can be derive by a division by 2, resulting in a 14.030MHz local frequency and a 3.5075MHz SDR center frequency. For reception, 2 stereo channels are needed and to provide I and Q for both bands. TX in such a case could be done by either individual audio frequency generators w/ 90 phase shift networks or in a way similar to the LO, with a 56.9kHz generator.
As I said, the SDR is somewhat hypothetical, not practical in any way....

The superhet TX design presently appears to be favorable, together with a subharmonic direct conversion receiver for 80 (1.75x2) and 40 (1.75x4).

Friday, January 28, 2011

4MHz - the Magic QRSS I.F.

Although the QRSS-community seems not to be as technical as it used to be, some thoughts about the matter from my side.

Some OM, again I am writing about novice/foundation/newcomer-lis, may not be allowed the lower band edge. But still, most activity takes place at those spots.

I asked myself, if I could find crystals to suite both needs. You will find some combis for one or the other option on this blog.

Meanwhile, I believe that 4.000MHz is the ideal I.F. for QRSS. Here's what can be done (more or less easily):

600m 4.5025MHz-4.000MHz=(27.015/6)MHz-4.000MHz=502.5kHz
The trick here, use a CB transmit (overtone) crystal for 27.015MHz (5T) and operate it a its fundamental, i.e. 9.005MHz. A division by 2 (flip flop) will end up at 4.5025MHz. A VXO at 9MHz may be pullable by a few kHz, hence, we may be able to cover a substantial portion of the present 600m hamradio band.
Should a future allocation be somewhat higher, there are many other CB-TX-XTALS available.
Should a future allocation be somewhat lower, there are many CB-RX-XTALS available.

NAVTEX 4.5175MHz-4.000MHz=(27.105/6)MHz-4.000MHz=517.5kHz
Essentially the same as above... the crystal being a 12T. For those who are not aware, there is maritime navigational (and weather) information transmitted on 600m, to be precise, 518kHz (international frequency) in FEC.
NAVTEX also knows a local frequency, which is 490kHz. This frequency is reached with a 39R (26.940MHz) xtal.

80m 4.000MHz-500kHz=3.500Mhz
500kHz can easily be generated from a 4MHz signal by dividing the latter by 8 (ripple counter). Running a 4MHz Pierce oscillator, the generated frequency will be above the 4MHz series frequency. Assume we generated a frequency of 4001kHz, 1/8 would be 500.125kHz, resulting in a mixed QRG of 3500.875kHz (TX).
For RX, a tweaked (fine tuned) L.O. can be used as B.F.O. to provide a reasonable beat for reception.

40m 4.000MHz+3.000MHz=7.000MHz
That would be the lower band edge solution... further comments here... however, there are better options!

40m 11.000MHz-4.000MHz=7.000MHz
Again the lower band edge, however, this is subtractive, therefore, temperature drifts will not add up but rather cancel (or at least reduce another).

40m 11.059MHz-4.000MHz=7.059MHz
This QRG is open to novice/foundation/newcomer-license holders! Temperature drifts will not add up but rather cancel (or at least reduce another). The frequency is at the upper edge of the 40m data segment, I believe, it is an ideal playground for testing all sorts of modes.

30m 4.000MHz+6.144MHz=10.144MHz
The classical 30m QRSS frequency is in close range. A local oscillator will have to generate a frequency of 6.139Mhz, which is reachable by either pulling of penning of a 6.144MHz standard crystal.

20m 4.000MHz+10.000MHz=14.000MHz
This is a no-brain-er! Just run a 10.0MHz LO.

20m 18.000MHz-4.000MHz=14.000MHz
This is a no-brain-er having improved temperature behavior... subtractive...

17m 4.000MHz+14.080MHz=4.000MHz+2x7.040MHz=18.080MHz
Here, the local oscillator would be sub-harmonic. 7.040MHz is just one example of many possibilities opened by crystals available for the 40m ham-radio band.

15m 25.000MHz-4.000MHz=21.000MHz
This again is a no-brain-er having improved temperature behavior... subtractive...

10m 4.000MHz+24.000MHz=28.000MHz
This is a no-brain-er...


10m 4.000MHz+24.000MHz=4.000MHz+2x12.000MHz=28.000MHz
Subharmonic.


Please feel free to add some ideas as a comment!

Saturday, January 22, 2011

The JUMA-RX1 a DDS Controlled Grabber Receiver

Yep, this time it's Finnish, guys. JUMA, I guess that is short for JUha (OH2NLT) and MAtti (OH7SV), sells some nice DDS kits. I found them when looking for 136kHz and 500kHz transmitters.

JUMA also offers shortwave kits. I figure, the RX1 kit makes a very nice grabber receiver, covering the 2.2km, 600m, 160m, 80m and 40m bands by means of a DDS VFO.
The rest of the receiver is old skool direct conversion, so using there is no side-band rejection. Not a great deal for 3500800Hz or 7000800Hz, since, not much signal is to be expected below our bands.
The QRSS range in the 2.2km, 600m or 160m bands are at frequencies where the other, i.e. lower, side-band can be occupied. Filtering for those bands will be a necessity. For the 160m band one may consider building a crystal front-end filter for the QRSS frequency. For 2.2km and 600m, this would certainly not do. Not all is lost for LF and MF, since preferred aerials (magnetic loops and frames) are ideally very narrow-band and will, if tuned right, help to at least reduce the lower side-band.
Additionally, filters can be build for the 80m color burst frequency, 40m WSPR and for any other frequency for which crystals are available.

The RX1 kit is all SMD, this could be seen as a hinder by some builders. Personally, I slowly get used to the tiny parts. With a proper PCB holder, a special SMT soldering iron and respective 0.5mm solder SMT is not much harder than regular through hole electronics. SMT has even got advantages, e.g. no excess leads need to be trimmed.

The DDS and the housing alone would justify the expenses of the kit, the DC-RX is essentially for free. Moreover, all mechanical bits and pieces are supplied.
With JUMA even offering the source-code of the firmware for download, which is even written in C, I figure one could easily modify the hardware to a superhet (e.g. 455kHz IF) and program an offset into the firmware.
A possible mod, in my view, could be to have the receiver PCB operated at 455kHz, with a decent IF-filter in place of the 40m low-pass. The DDS-VFO will, in such a scenario, serve an additional front-end, whatever it will be...

Monday, January 17, 2011

28322 Beacon Net Receiver

With the prospect of the upcoming activity in the present solar cycle, it is about time to think of a receiver for the (Italian) 28322(kHz) beacon network.
Due to the nature of those transmitters, the frequency range we want to be looking at is something like 3kHz, maybe 4kHz, i.e. 28320 to 28324kHz.


Now that the task is defined, let's move on and look at the obvious design involving inexpensive parts.

The xx322kHz frequency immediately makes me think of 14.318MHz crystals to form a filter for the intermediate frequency.

With an intermediate frequency of 14.318MHz, a local oscillator should create a frequency of 14.00xMHz. A local oscillator that close to the intermediate frequency will however put unnecessary strain on the IF-xtal-filter and even could end up clogging up a/the IF amplifier. I further believe that LO and BFO being so close is not such a good idea.
Solution to said problems: a local oscillator at 7.00xMHz (crystal easily available) hooked up to a subharmonic first mixer (pair of anti-parallel diodes). The intermediate frequency stage would be blind to 7.0MHz LO stray.

With the mixing all sorted, the next thoughts need to be spent on filter design. A bandwidth of 3, maybe 4kHz, makes a ladder filter a hard task, in particular since such a ladder filter would require quite some amount of poles. Even being harder to make, I figure a lattice filter would be the best option here. Lattice filters however require pairs of matched crystals being a some kHz apart. That is where the work sits in. One pair of 14.318MHz xtals can be selected by measuring/matching the series frequency of stock xtals. The other pair will have be to created by penning down two xtals to the exact same frequency.

For the BFO and the product detector the most obvious choice would be the NE612, just the way one would use it anyway.


Bored of QRSS?
There could be another use for the setup: an SSB phone RX, TX or even TRX. The important bit here, the bandwidth of the crystal filter should be around 2.4kHz. Such a bandwidth is easily available with a ladder filter, however, a lattice filter would give a better response.
Very obviously having a single channel SSB radio at a frequency where beacons beep around the clock is not the best of ideas. So, the LO will have to employ a different frequency. Luckily, many crystals are available for frequencies in the 40m band, e.g. 7030kHz, 7040kHz etc., hence, channelized or VXOed rig is no problem at all. Taking things further, a VFO could be on the wish list. And there is just a perfect option. The famous NE612 (SA612,NE602,SA602) can be configured to operate as a frequency doubling ceramic resonator oscillator. With a pulled down 3.58MHz ceramic resonator (avoid 3.58MHz!), a good portion of the 10m SSB range will be available.

At this place, I would like to thank Jan (PA9QV/OZ9QV) for triggering my thoughts about a 10m upper side-band design with the simple question "do you know a combination for 28322?" :-))

Thursday, January 13, 2011

NE612 Transverter

Something I found on the internet and would like to share:
http://www.geocities.jp/ja6hic/rig/6/trans.gif
I have seen NE612 transverters before, those were using two NE612s. JA6HIC uses one chip for both RX and TX conversion. The rest of the design involves an external LO.

The circuit is fed by RX and TX control voltages, this may be handy in places, although I believe that this is merely a remainder of JA6HIC's earlier designs involving diode mixers.
However, I believe a running the transverter from the general supply could be advantageous in particular since there could be a delay between powering down the RX and powering up the TX trains, which could cause the circuit not being supplied and therefore shut down. Using an external LO, it would not matter to shut down the transverter for a moment. However, the NE612 has got an internal oscillator, when using this, we certainly would not like to power down the chip just to power it up again... this would result in terrible chirp.

So, this is my plan: make use of this very simple but elegant design for transverters for 136kHz, 501kHz and 70MHz.  I will be using the internal oscillator of the NE612 as a crystal oscillator. The following obvious options will be available cheaply (the mark (-) indicated subtractive mixing which inverts the band, (*) indicates my preference):
  • 136kHz: 2.000MHz - 160m band (-)
  • 136kHz: 2.048MHz - 160m band (-)
  • 136kHz: 3.500MHz - 80m band
  • 136kHz: 3.579MHz - 80m band
  • 136kHz: 3.686MHz - 80m band (-)
  • 136kHz: 7.000MHz - 40m band
  • 136kHz: 7.159MHz - 40m band (-)
  • 136kHz: 10.000MHz - 30m band (*)
  • 136kHz: 14.000MHz - 20m band
  • 136kHz: 14.318MHz - 20m band (-)
  • 136kHz: 27.000MHz - 11m band 
  • 501kHz: 2.458MHz - 160m band (-)
  • 501kHz: 3.000MHz - 80m band (*)
  • 501kHz: 3.072MHz - 80m band
  • 501kHz: 3.276MHz - 80m band
  • 501kHz: 4.096MHz - 80m band (-)
  • 501kHz: 4.194MHz - 80m band (-)
  • 501kHz: 6.5536MHz - 40m band 
  • 501kHz: 13.560MHz - 20m band 
  • 501kHz: 14.745MHz - 20m band (-)
  • 70.0MHz: 20.000MHz - 6m band (*)
All there is to do is to build an RF-vox circuit and an attenuator (for the TX).

Monday, January 10, 2011

Building a PFR-3A - First Impressions

Building a PFR-3A is not difficult, in fact it is quite easy, although the kit takes a lot of patience.
The first bit of patience I needed for the period between ordering and actually receiving the kit. I ordered November 10th, the shipping documents show that the kit was taken to the post-office December 21st.
I ordered paddles to go with the transceiver, however, there were none in the box, which dropped in January 7th. Although Doug refunded immediately, I would have appreciated some communication in an earlier stage.

The build manual reads that "some of the yellow, monolithic caps may be supplied with the leads being formed for 0.2" lead spacing, while the holes on the PCB are designed for 0.1" lead spacing...". WELL, this is where I needed a lot of patience. The manual should better read that most of the capacitors, be it monolithic or disk type capacitors, are supplied with a 0.2" lead spacing... and the builder therefore should be prepared to bending many many leads to fit the 0.1" spacing used on the PCB.
Ceramic disk capacitors with "narrowed" lead spacing will stick out somewhat higher above the PCB.

Speaking of the manual, there are some errata available on Doug's web-page. However, care must be taken if those are still valid.
Some supplied components may have values other than mentioned in the manual. My kit came with "green capacitors" having a 22nF capacitance, contrary to the listed 10nF. The receiver however, and this is where those capacitors are in, is working excellently.
The manual is short, which I like, but in places it is maybe a little too short. With reference to the schematics, everything can be figured out however.

Another thing that I felt was unnecessary, some of the vias were too narrow, namely the ones of the volume pot and the phones and key connectors. I solved the problem by reducing the width of individual leads.
All of that mechanical work is not difficult, however, it is also not something you would expect building an electronics kit.

The PFR3 employs a DDS. Such systems require calibration. In the PFR3 this is provided by zero-beating vs WWV. Neat, when being able to receive WWV. It would have been nice if one could set a frequency to zero beat against, e.g. RWM, which is much more accessible to Europe.

There is another calibration step, specifically calibrating the BFO. This is done in an ingenious way! Works pretty well.

One thing was striking my eye whilst building the transmitter: L7, which feeds the final, is made from 8 turns #28 magnet wire on a FT37-43 core. To my understanding, in a switch mode PA, ohmic losses should be kept minimal. Consequently, I wound the inductor from 1mm diameter magnet wire (corresponding to #18 AWG).

Enough words, here's some imagery:
some ceramic disk capacitors are bent down to fit the space available

note, the two wires from under the fat red toroid are "binding post wires"

Some additional remark to a comment I found on the internet. I do like the bright yellow color. It makes the transceiver visible, just as intended by Doug.

In an interview on youtube, Doug states, the display was chosen to be LED, rather than LCD, for better visibility in bright sunlight. This only can be a misunderstanding. Clearly LCD would perform superior to LED in bright sunlight. However, I do prefer LED over LCD. In particular red LED is perfect during night-time. Reason: rods do not see red! Therefore, night-vision, which is performed by the rods in our retina, will not be affected by red light, cf. scotopic vision and rhodopsin.

The kit contained magnet wire of several colors, nice touch, I did not need those, since no complicated multi-wire transformers are part of the design. Further I had some electronics elements left overs, namely, 1 transistor, 13 capacitors and 4 resistors, even though the PCB is fully populated. I am not sure what this means, at least I was not missing any parts ;-)

As seen from the photographs, I was ignoring the hook up wire provided in the kit and replaced it by heavier gauge speaker wire.
I also intend to act against the teachings of the build manual by using actual coax cable (RG58 or RG174) to connect the BNC connector to the PCB.

Prospect: This radio will serve me in three functions: it will be a grabber-receiver, it will accompany me on trips and travels and it will be a companion on board of my boat.
And... if time allows (I kinda doubt that), I may write my own firmware for the rig, allowing to receive maritime TTY.