(modified) PA0RDT-Mini-Whip

The "Target HF3/W", which is supposed to service me on the boat, offers switchable 12V supply via the antenna socket. Very nice, now for some active antenna to actually make use of the possibility.

Some research on the internet brought up a design by PA0RDT (pls search for it yourself). He call's the thing "mini whip". Some would call it an EH-antenne (haha, got you there), some others would call it an amplified E-probe. The latter it actually is. It is a capacitor probing the E-component of an RF-field.

However the design may be called, is it any good?

First to mention, there are many positive reports on this device. I had my doubts, but never the less, on a yacht, aerials are a compromise whatever one does. Thus, in particular inspired by the positive feedback found, I decided to give it a chance.

The key to the amplifier-circuit seems to be the 1MOhm resistor input network. I figure, 10MOhms would propably do a better job. However, not having 10MOhms-resistor in my stock, I went for 1MOhms. Which reduced my stock that much, that the next thing I'll do will be visiting my electronica-boer in order to buy said resistors.

Here comes the modification, unvoluntary, sort of... even though a 2N5109 seems widely available, it was not in my stock... I decided to replace it with a 2N918; this required to change the emitter-resistor to something higher-ohmic, in order to reduce Ic. I went for a conservative 470 Ohms. As for the DC-separating inductor, I went for what I found (whatever it was).

And this is, what I ended up with:

The result was pretty nice, although I tested indoors only. I am curious what this probe could do, when "flying" meters above my house's roof...

Should I ever build another one, that's what I would change:

• use a 2N5109 (will propably give better results... or not)
• increase the "ground-plane" part of the probe by reducing the "12V-part"

Conclusion: The probe will have to prove itself, when hoist to the top of my ship's mast. Presently it appears to be a nice alternative to something more vulnerable, since, rugged it is!

Dutch pirates too...

Some minutes later, some Dutch pirates QSOed on 3490kHz, on top of a QSO in Arabic(?)... much stronger, no wonder, I am living in the Netherlands...

A few minutes later, this was received on 3490kHz....

To me that reads like: KKB QSY 666 HI

Hmmm, interesting, them pirates know some code... hmmmm

French pirate-stations

Caught this with the SDR:

LSB signals in French language on 3460kHz and 3490kHz. Personally, I was not interested enough to follow the conversation... It's however nice to see, that voice is readable...

CW-skimmer

Works nicely with the FA-SDR. Choose the settigs for the Soft-Rock.

more on SDR

Weekend, contest time, and so they do on 80m. Ideal to have the new setup hooked on the GPA50.

There are still faint traces of the soundcard's birdies... a prominant role they do not play anymore...

Screenshots of the action... in Rocky, the CW-click filter is activated, thus, we get nice traces of even normal speed CW.

SDR update

Some playing with programs and parameters reveiled the first results. Test were perfomed on my EeeTop (Atom N270, builtin soundcard). The soundcard creates birdies however. The image below show's a screen-catpure of Winradio with the receiver connected to the soundcard, but not the any mains supply.

1) Winradio by I2PHD works well. best results were obtained by setting the sample-rate to 96000. With an antenna connected, but by far to early in May (15:xx UTC) for the band to be open.

2) Rocky offers less features, seems however a nice choice for just listening into the band. Rocky offers two different screen setups. It's a very intuitive...

First capture shows Rocky in spectrum mode.

The second capture shows Rocky in waterfall mode.

3) SpectrumLab is very complex again. It's propably usefull to setup a grabber, for use as a receiver, it's a bit too complicated.

No other software was under scrutiny yet. As soon as there are signals on the band, I will continue testing, also publish some of my experiences in this very place.

SDR

Cool thing, sort of.... I am just about to explore the possibilities. Stands and falls with (the available) software. Personally, I will be to lazy to write anything myself. Thus, let check out what has been done before, and if it's any good to use.

First glance was promising however!

(SDR-Kit provided by "Funkamateur", box73.de, coming with a CD containing some free SDR-software).

Pierce Crystal Oscillator

Stupid me! I should have known.... After some RTFL (literature) the mystery about my 74HC86 oscillator seems to be solved. The high frequency is not due to the inner values of the XOR-gates, it is actually caused by the chosen oscillator type "Pierce". In the literature it reads that a Pierce crystal oscillator does oscillate above the crystals series resonant frequency. There we go... I should/could have known that one....

The LO for the PSKmail-TRX

First steps first... investigate if I can reach 10148kHz using standard crystals.

The idea, as shown in an earlier post, is, to use a 6144kHz LO and and I.F. of 4000kHz. This short of 4kHz. A lot, one may think.

However, when building my 30m-MEPT, I experienced that oscillators based on 74HC86 generate a frequency much higher than the crystal's nominal. Using a 5068.8kHz XTAL, I thought I was way to low, but then, I had hours of experimentation, before I got the frequency down into the qrss-band.

Thus, today, the idea was, if I can repeat this with 6144kHz crystals to close the 4kHz gap.

Well, the gap is closed, by far exceeding my expectations. The 6144kHz crystal produced a 6154kHz signal. Yes, 10kHz above the nominal frequency. Further experiments revealed, an inductor of 15µH and a capacitor with 47pF both in series with the crystal, brought the frequency down to 6146kHz. Close, but still more room for improvement appeared. The photograph shows the LO with the experimental capacitor (the long legged blue thing).

Two more gates of the 74HC86 will be used to generate an in-phase and an out-off-phase LO signal for use in a 74HC4066-mixer.

The remaining fourth XOR-gate will become the 4000kHz BFO.

Rainscatter

Just had my first rainscatter-QSO on 3cm in years. Actually, I was more prepared of testing only, in preparation of tomorrows electric storms over Germany.

Quick and dirty setup, transverter/dish behind my topfloor window (double pane, insulation and stuff). PI7EHG came in loud and strong, 55s, I figure.

Just for the fun of it, also testing the transmit-train, I called CQ; it caught me by surprise as after the first "pse k", Uffe (PA5DD) called me. QSO-time, kneeling on the floor in the most awkward position to key... no pen, no paper, no clock... as indicated, I was totally unprepared (sorry Uffe).

It also has been a surprise, that in fact the transverter still works after last use about six years ago, and even more or less on frequency.

Rainscatter saison 2009, here we come!

dc-rx and/or super-het (for the qrss-trx?)

Did some research today. And again, I stumbled accross Tasić's superb weg-page full of information on all fronts of qrp and sdr: http://yu1lm.qrpradio.com/index.htm

The present idea is, to use one 74HC86 for both oscillators, the synthesizer-mixer and the phase-shifting. The resulting signals will be fed in a 74HC4066. Frequencie? Standard crystals, what else?!

4000kHz + 6144kHz = (tataaaa) 10144kHz.

First, very simple option: pull either one or crystals down a bit, as to reach, lets say, 10142kHz or so. Now the qrss-range will fall into the lower side-band. Not nice, at least not for a grabber, a start however.

Second, more sophisticated approach: have one crystal w/o pull, lets say the 4000kHz one. Now, the other has to cope with all the pull. Thus, why not just add a second crystal and have a super-VXO? I've never tried a super-VXO using digital ICs before. Anyone out there having experience in said field?

You may wonder why I do not consider a 10140kHz crystal in the first place. Very simple... the crystal-synthesizer approach opens the option of modifying the design into a super-het, without need for changing a lot. In fact, just the 4000kHz signal needs to be taken off the synthesizer-mixer and re-routed to a product-detector behind a side-band filter (e.g. ladder made from 4000kHz crystals).

The advantage of a super-het, to me at least, seems obvious. Depending on the super-VXO, substantial portions of the 30m-band are in reach, e.g. the Hell-band, whilst a dc-rx with a single crystal filter, binds to the frequency of the (qrss-) crystal used.

more crystals

More crystals on the way to my "brievenbus" (Dutch for letter-box), thanks to the great service of Rich N4ESS and his company.

http://www.expandedspectrumsystems.com/

30m QRSS-RX/MEPT part 2

The control of the whole beast in planned to be done by a PICAXE-08M. In the present MEPT, this controller generates DC voltage for the modulation of the 5068.8kHz oscillator by means of PWM and a low pass filter. Further the controller delivers a keying signal to the 74HC240 final.

In the future, said controller will also provide a PTT signal, which will switch on the active double and also switch off the grabber's rf-front-end and audio-stage. For regular QRSS or DFCW it would be conceivable to sequence the PTT signal just about the keying, thus having some sort of QSK.

30m QRSS-RX/MEPT

The plans to join the 30m-MEPT and the 30m-subharmonic receiver are on hold for today, since I believe that some of the ideas or not quite there yet.

You may have seen, that I used a 5068.8kHz crystal as modulated mother oscillator for the MEPT. An active doubler gets the signal into the 30m band, followed by a 10140kHz crystal as filter.

As I mentioned earlier on the KnightsQRSS mailing list, having a mother-oscillator running all the time could be done by switching on an active frequency doubler to TX and deactivate it for RX, thus, not prominent carrier will be present in the 30m band. One requirement to me seems, to build an oscillator that creates as few as possible harmonics. That seems to rule out all HCT/HCTTL-approaches completely. The only way of using the product of a digital oscillator that I can think of, having a second 5068.8kHz-crystal as filter in the output of the oscillator and reaaaallly carefully wrap the thing up into something RF-tight. I guess, it will still be easier and less cumbersome to build a clean oscillator from discret components.

Elektronika boer

I've been to my favorite, sort of local, electronics shop. Got rid of some €100+. However, they got stuff, others don't, such as varactors. Yes, in some design, one would not really like to use LEDs or rectifier-diodes as varicaps, sometimes, the real deal is required (even with a price-tag of €6/pc for BB112 and €2,60 for BB204).

Thus, tunable i.f. crystal filter, here we come. Well, the intention is, to have a tunable i.f.-filter in the dedicated maritime-mobile rig.

Projects in the queue, a dedicated PSK transceiver for 80m, probably something very similar to the PSK-80 Warbler. Still to come: dedicated PSKmail-TRX for 30m, we had that in other entries before. And for the fun of it, rock-mites. For the latter, more crystals are required.

Combination found....

Please ignore the question I posed on my previous blog entry, I found my combination. Again SMD, again DigiKey... 6612.813 kHz

Adding a carrier from a 3535kHz QRP crystal gets me to 10147.813kHz.

PSKmail, here we come. Another maritime mobile project in the planning.

http://pskmail.wikispaces.com/

WSPR trx using DigiKey-crystals

The idea here is: using a superhet design to create a full-blown SSB transceiver, with proper USB generation. The transceiver should be able to cover the WSPR and the QRSS band of the 30m band. That's what I found, and propably will build.

Thinking crystals and searching the DigiKey page at the same time, that's what I found:

- standard crystals for 7680 kHz

- SMD crystals for 5223.438 kHz

Doing the maths reveals:

2 x 7680 kHz = 15360 kHz

15360 kHz - 5223.438 kHz = 10136.562 kHz

BUT: 10138.7 kHz - 10136.562 kHz = 2.138 kHz

=> we are off by about 2 kHz.

Remember, this is subharmonic, thus the 2 kHz offset would need a 1 kHz correction at the LO.

The concept would be the following:

1. The SSB-filter will be built from the SMD crystals, this allows for a small filter, that even could have it's one casing.
2. Regular XO on 7680kHz, pulled up by 1.069 kHz (which should be manageable) as local oscillator.
3. A standard J310, or similar front-end, no AGC but some switchable attenuation (RX train).
4. Here comes the trick, a subharmonic mixer á la RA3AAE, i.e. two antiparallel diodes (RX train).
5. The subharmonic mixer propably also works for TX... If not, a regular doubler is required, in combination with a regular mixer (TX train).
6. Some sort of final (TX train).

So many idea, and so little time...

BTW: I am looking for a combination of standard crystals that would get me to 10148kHz. Any idea? Please let me know!

Maritime Mobile USB-TRX

Some thinking occurred in my good old walnut. Being a sailor, designing a designated MM TRX is just that tempting.

For ease of construction, low cost and frequency stability, a superhet using a VXO (super VXO) with a ladder or lattice XTAL-filter.

The arising questions here:

1) Which QRGs are used by the most popular (useful) nets?

2) Which (standard) crystal are available?

3) Is there a chance for regular ham-radio-operations?

4) Any design tricks?

Answers:

1) QRGs

There are a couple of networks, some frequencies are most popular:

1. 14300kHz - Maritime Mobile Service Net, Seafarer's Net, PAC Maritime Net, Intercon Net
2. 14313kHz - Maritime Mobile Service Net, Seafarer's Net, International MM Net, Med. Sea MM et, German MM Net, Intercon Net

2) XTALs

Here, the thinking starts, and that would be y solution. Standars crystals are available for 4194,812kHz and 4194,304kHz. The first idea that pops up would be an intermediate frequency of 4194,812kHz, using a pulled down BFO using a 4194,304kHz-crystal.

Filtering could be done by ladder (the easy choice) or lattice. The latter option would use crystals of both frequencies, this option needs further investigation, i.e. bandwidth.

VXO-frequencies that would mix to the above NET-QRGs (a tiny bit of pulling required):

1. 10106kHz - 30m QRP-crystal
2. 10120kHz - 30m crystal

Pulling a bit further (up) other networks could be reached:

• 14303kHz - UK Maritime Net, Swedish Maritime Net
• 14305kHz - Confusion Net
• 14315kHz - Tony's Net
• 14316kHz - Indian Ocean MM Net, South African MM Net

Other networks will be available with other standard crystals, such as 10115kHz, 10125kHz and 10145kHz.

3) HamRadio

Yes, there are options for regular, non maritime that is, ham-radio-operations. A 9830,4kHz-crystal would result in 14024kHz, thus A1A-operations. For J3E, there are 10000kHz rocks available, well ... add 4194kHz, that's were one ends for USB. For operations at those frequencies, and some better ranges, I will go for a super-VXO for the A1A-part. For the voice, there is choice: super-VXO using crystals or even a greater range using a ceramic resonator.

4) Tricks

Not a trick yet, more a design idea at the present stage.

My 30m MEPT is using the PWM-output of a PICAXE to apply an analogue signal to a varactor (well, the MEPT actually uses a rectifier diode as varactor).

Advantages a suitable (PICAXE-)µ-controller offers:

• channel selection/switching by digital i/o-ports
• RIT/XIT and/or VXO pulling voltages provided by PWM
• VFO/RIT/XIT controls by using on-chip ADCs
• memories by selection of crystals and pulling voltages
• sweeping VXO pulling frequencies
• squelch by use of an on-chip ADC
• channel/memory scanning with halt/stop by squelch

Besides µ-controllers, there's some more to think of, such as power amplifiers, data traffic, maritime aerials.... Not to mention position reporting and distress alerting. For the latter I probably would rather rely on GMDSS-gear/procedures....

Open questions here, with an I.F. of 4194kHz, would there be any obvious choice of standard-xtal to use for PACTOR? Please let me know....

73

One noise source down...

... so many others to go ...
Experimentation revealed, one of the noise sources, I actually have power over. It is the light dimmer in my living room. Now, that's an easy one, just not use it during grabbing. In the image, one can see the effect of that source, interrupted by a WSPR transmission.

Grabber on the Rock(s)

Nice QRM seen on the grabber today. Ideal to test the difference between the G5RV-jr and the rockloop. At 16:55 I connected the rockloopto the receiver with the loop being in the shack for tuning, afterwards it was back to the G5RV-jr. 17:03, the rockloop reconnected, but now located on the topfloor of my house, directed NE/SW; 17:05, directivity chance to NW/SE. 17:09, short reconnect of the G5RV-jr.

Signal strengths went down, S/N-R went up however. As for the next hours, I will leave the grabber connected to the rockloop.

subharmonic dc-rx in operation

Howdy!

Not only has it been a nice weekend project, the subharmonic receiver issue was actually meant to replace my FT-817 in the grabbing setup. And... it did by today. There are still some issues to be solved, however, the thing starts to catch flying W by now. Features amoungst: no AGC (see me releasing RF a few meters off the rx-aerial, the very red signal @ 22:39), stable canned oscillator, no carrier DC in the AF, no BFO sideband noise. The flying W actually fades in about 22:47.

Traces of WSPR-signals to be observed. Since WSPR-software is bound to a effective BFO-frequency of 10.1387MHz on 30m, my 10.1376MHz LO/BFO will not enable for decoding the WSPR-signals. My hope is, that in future versions of the WSPR-software, receivers other than appliances will be supported.

Update, since in the above image, not so much can be seen, here's another one. The spectrum lab bandwith covers the WSPR band too. This spectrum shows the time span of 06:07 to 06:27 UTC (May 13th 2009). It covers the range of about 10139.800kHz to 10140.310kHz.


The above images also shows a 50Hz signal, all over. The source is located, it is the sound-card internal to my computer. The problem's source is the following. A single transistor in the af-stage seems just about enough to satisfy the microphone input of that respective sound-card, however, sensitivity is maxed. At the chosen settings, the 50Hz lines even remain when the receiver is disconnected. I will work on that and hopefully improve S/N-R in this respect.

Cheers, Joachim

Subharmonic mixers in superhet designs

The subharmonic mixer being such a success in direct conversion receivers, the question is, would those mixers do a good job in as product detectors, with the BFO running on half the intermediate frequency? What about using subharmonic mixers in a bi-directional stage being modulator and product detector?
Standard frequencies [MHz] that would allow for such a configuration:

• 1.0000, 2.0000
  
• 1.8432, 3.6864
• 2.0000, 4.0000
• 2.0480, 4,0960
  
• 2.097152, 4.194304
• 2.4576, 4.9152
• 2.5000, 5.0000
• 3.0000, 6.0000
• 3.0720, 6.1440
• 3.2768, 6.5536
• 3.579545, 14.31818 (*)
  
• 3.6864, 7.3728
  
• 4.0000, 8.0000
• 4.4336, 8.8672
• 5.0000, 10.0000
• 5.1200, 10.2400
• 6.0000, 12.0000
• 6.1440, 12.2880
• 7.3728, 14.7456
• 8.0000, 16.0000
• 9.2160, 18.4320
• 10.0000, 20.0000
• 11.0592, 22.1184
• 12.0000, 24.0000
• 12.2880, 24.5760
• 16.0000, 32.0000
• 18.0000, 36.0000
• 24.0000, 48.0000

The pair marked with (*) uses four times the oscillator frequency, technically possible, however, I got doubts about the usefulness of that respective pair.

For some of the (lower) frequencies, CMOS oscillators are available, making some of the design particularly simple.

magnetic "balun"

Some weeks ago, I stumbled across the broadband aerials BB-6W and BB-7V made by Diamond. Further research resulted in so called "magnetic baluns". Well, the balun actually is a "6:1-UnUn" shunted by a heavy duty resistor.

My approach: Iron-powder toroid T200-2, 12 trifilar windings using power cord for a 9:1 UnUn, no shunt. In combination with about 7m of wire, this actually works. Well, it works, not really a pile-up breaker... For a five minutes project however, not a bad result.

10m MEPT / beacon

That's rather an old one... by now...

• 28322kHz canned osci
• 74HCT240
• PICAXE 08M

This runs in two modes: QRSS (1, 3, 10 and 30) & CWID or VHF-like locator beacon.

30m receiver

Running a grabber is somewhat fun, more for others, I guess. Firstly, it prevents me from transmitting on the band my grabber is operating on. Secondly, it blocks a receiver/transceiver that could be used for other purposes, in my case that would be my FT-817.

For the first problem, there is no obvious solution.

The second problem finds it's solution in a dedicated receiver.

Here it comes. We are talking 30m QRSS here. Signals will be seen at about 10140kHz. For grabbing this band, there is a very obvious and simple, even low element count, solution.

The basic idea here is, 5068.8kHz doubled results in 10137.6kHz. That is 2.4kHz lower than the visual-QRSS band. What would be the easiest way to double the LO-frequency?

Jan (PA9QV) made me aware of the so called "subharmonic mixer" as proposed by RA3AAE. The subharmonic mixer appears to be widely spread, however, not really well documented in the ham-radio world. For DC-receivers, the subharmonic mixer seems to have severe advantages.

Thus, a DC-RX using a 5068.8kHz canned oscillator in combination with a subharmonic mixer would do a fine job for a grabber, where the audio-frequency, as long as it can be decoded by a sound-card, does not play a major role.

Here is my first functional version of the concept:

The setup is the following (left to right):

• common gate J310 front end, no filters yet
• anti-parallel 1N4148 diodes
• 5068.8kHz canned oscillator
• BC238C af-stage

Preliminary result: PSK31 stations were heared instantaneously in crystal ear phones when the reveiver was hooked up to my rock-loop (indoors).

In the future this receiver will probably be provided with a 10140kHz filter either in front or behind the J310 front-end, this would reject the unwanted lower side band.

72!

Hifer transmitter

You may have heard about "Hifers" before. The term relates to "HIgh Frequency Experimental Radio". Mostly this is concerned operating beacon-like transmitters in the legal licence-free realm of ISM. However, using QRPp transmitters, and that's what hifers are according to my understanding, is also done by licenced radio-amateurs. Here is my attempt to create a hifer-transmitter.

What you see:

• a (smd)-crystal oscillator using a 74HCT00
• 78L05 voltage regulator
• ID-keyer (12F629)
• low pass filter

Presently this transmitter is keyed by unused gates of the 74HCT00. This, however, causes a severe chirp.... diuuuuuuuu... diuuuu... Not really wanted. Thus, this experimental device will be keyed by a reed-relais, i.e. aerial vs. dummy load.

In order to be compliant with hifer-requirements, an attenuator (a.k.a. antennuator) will be required in order not to exceed the 42dBµA/m @ 10m. Alternatively one could consider to use an accordingly lossy aerial. It's all about magnetic field-strength, in a distance of 10m.

As licenced ham-radio operator I would be allowed to operate up to 400W at my present location and up to 750W at my home QTH, in band that is. Maybe both would be a tough call to be pulled out of a single 74HCT00 ;-)

42!

30m MEPT

As promised, here is a first impression of the 30m MEPT (Manned Experimental Propagation Transmitter).

The device is designed as follows:

• 5.0688 MHz crystal oscillator (74HC86)
• frequency modulation by a brutish rectifier diode (on the PCB's lower side)
• active frequency doubler (74HC86)
• 10.140MHz crystal filter to the final
• 74HCT240 final, run at 5V
• low pass
• keyer: PICAXE 08M

The keyer is programmed to key the final by a PTT signal and modulate the oscillator using pseudo-analogue generated by PWM. In this way a variety of signals can produced. This TX was up to now used with QRSS, DFCW and S/MT-Hell, see earlier post showing PA9QV's snapshot.

Future plan: go QRO-ish by replacing the second 7805 (next to the 74HCT240) with a 7808 and adding a PA (IRF510).

homepage back

On demand, I brought my old homepage back to life. I hope that is generally appreciated. Information on said page will successively be updated, however, switching to modern time, blogging seems to be more appropriate anyway.
Assume infos on my 10m and 30m MEPTs soon. Further, there is a receiver for 30m qrss in the making, using a subharmonic mixer.
More on shielded magnetic loops will follow...
73, Joachim

Hifer

I decided to remove information about Hifer-stuff from this page. Drop me a note/question, when you would like to know details about the topic Hifer/Midfer/Lowfer.

captured

Jan (PA9QV) captured my signals...

Technical info on the transmitter:

• 5.0688MHz crystal oscillator (74HC86) pulled by a rectifier diode
• active doubler (same 74HC86)
• 10.140MHz crystal as purity filter
• 74HCT240 as keyed PA
• smt-Hell and QRSS-CW generated by a PICAXE-08M using PWM