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!

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!

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.

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!

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.

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.

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.

PFR-3 with W5JH paddles

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.