Thursday, July 30, 2009

portable sat-comm station VHF PA

Well, not a great deal of technical skill involved here... I was able to locate an Yaesu FL-2025 linear amplifier which attaches to the back-side of my FT-290RII.

The FT-x90RII series appears not to be the most practical for satellite work, however, I now the series, I am one of only a few who actually like the handling and they have those neat clip-on linears. In a /p or /m setup, what counts in my view is having a box, as small as possible, in which all equipment fits uncluttered.
The series however has got a major down-side, tuning steps for European units are 12.5, 25 and 50kHz. Not exactly usable for the FM-sats as AO-51. However, there is help, with a simple mod one can change the FM-tuning steps to 5, 10 and 20kHz. More info on this: here (sorry, the important bit is written in German).

Now that Next step would be to build a crate for the two transceivers (290 and 790) and the linears, ensure sufficient cooling of the linears, provide a common power supply, feed preamp-supply to the antenna connectors, and some additional stuff for operating convenience.

Still a lot to be done, but now that all required gear is present, this work could be started any time.

Wednesday, July 29, 2009

short update on the WSPR/QRSS trx

This project has been resting for a a while. Yesterday, some progress was made. The local oscillator now has got a buffer/amplifier producing much more power than the mixing stage would ever need. This stage uses a 2N2222A in an emitter follower like configuration.

Even though the signal is pretty clean, in order to sure, I added a crystal as filter. Output level is adjustable to the needs of the mixer by a trimmer.

Here's a photograph of what there is sofar.

Presently I assume that I would need something like 2V peak to peak to properly drive the Polyakov-mixer, thus the buffer will be run with stabilized 5V.
Oscilloscope shows 1V/div, no further surprise here...

Let's see how far I come today....

Saturday, July 25, 2009


Well, I did the test, and actually started a revision of the design, check out the 2nd schematics on my webpage.

As I am running all my test with a regulated laboratory power supply, I not only can control the voltage, but also the current of the power source. Having done that, I realized that more power shows up at the output of the lowpass-filter at a particular reduced current. I measured the input current of the 74HCT00 and found out that it best performs at about 15-16mA (??, but OK). A little math in my head, and I added a 220Ohms resistor between the regulator and pin 14 of the quad-nand.

But now, running the NANDs in parallel, with optimum waveform and output, made the frequency shift much larger (???), something like 20Hz, in place of 5Hz before (!). Additionally, the frequency slightely dropped (well, ok, that I do understand).

No math helps here, pure experimentation. Remember, the shift is predominantly determined by the resistor connecting the HCT00 and the 12F629...
For sentimental reasons, I left in the 47kOhms resistor which started it all. It has now got a partner on its' side, they are even allowed to hold hands, a 470kOhms resistor in series. Seems that in the new arrangement, 0.5MOhm makes the trick, shift is now back to 5Hz. Ouuffff!!!

Seems there is a delicate balance between the few critical elements. And now limiting the current seems a factor too.... Am I using the HCT-gates in some sort of analogue mode?

And what about the results? Well, here we are. @ 50Ohms, I measured 0.8Vpp, resulting in about 1.6mW. Actually, the waveform looks even better now! Presently running a stability test (RX=FT817 w/TCXO).


As announced earlier today, some information about last nights project will be released as soon as possible. You can have a first glance at the schematics on my webpage
under "20m MEPT".

More detailed explanations and keyer source code will follow soon.

Some first impressions of the MEPT in question.
Initially I wanted to squeeze the filter between the 12F629 (8 pin controller in a 16 pin socket) and the 74HCT00, however, I was running out of space... well, ok, in a very first version of this transmitter, the filter actually was there. With the appearance of the 47k resistor in that particular spot, the filter could not be fit in again :-(

Further one can identify the "high quality, high power" dummy load. Well, actually this dummy load really is high power for the setup shown... two quarter Watt 100Ohms resistors in parallel seem good for about half a Watt, right? And well, look at the display of my lab-TV blow...

First of all, it looks like a nice sine signal. The vertical division was set to 0.1V/div, making the signal a whopping 550mV @ 50Ohms or 740µW.

As one further test I will run the two "shaping NANDs" in parallel, just to see what this does.

Midnight Oil

Well, what a night! I severly was burning midnight oil, with results however.

Found a way to modulate a crystal oscillator, FSK that is, w/o any additional efforts. Not sure if it has been done in that way ever before. By now, I am too tired to create some schematics, I will offer something on the webpage (not here thus) soon.

To give an appetizer, I think, building a MEPT for QRSS on 20m is done in less than five minutes... with me having spent night on that, that is....

Friday, July 24, 2009

RX Loop Experiments

Remember, some months ago I experimented with stuff called "YMVK-as 2x2.5mm²", which is doubly shielded underground mains cable - pretty sturdy stuff (expensive too)!
To that time, I cut a length of about 1.7m, connected one blue and one brown insulated lead to form a shielded double loop. Reception results were pretty amazing (see earlier post - tagged "aerial").

Today, I gave it some more testing, replaced the capacitor with a polystyrene varicap in butterfly configuration, in order to make the spindle neutral; that makes it easier to experiment with the thing.

As mentioned in the earlier posting, seems that the natural resonance of the shielded double loop is somewhere just above 7.4MHz. The capacitor, when resonating the loop to 7.0MHz, measures (MFJ-269Pro) 28pF. Bringing the resonance all the way down to the bottom results in about 5.8MHz at 62pF. Now I've got my numbers.

So, with the numbers all collected, it's hands on a piece of paper, pencil included, and maybe, by the end of the day, there is something to report about a self-resonant shielded RX-loop for 30m band.

The actual plan for the particular, above mentioned, loop is not to cut it down, but leave it just the way it is. This RX-loop, with such a capacitor seems ideal for a 40m QRSS grabber, whenever said band will be activated (volunteers?). Next to that application, the loop also covers the 49m and 41m BC bands, a hand full of underground beacons, the 45m pirate band and the RFID "medium frequency" at 6.78MHz.

RX Experiments

As a regular observer of my grabber, you may have seen two drastically different levels of noise with some very sharp crackle inbetween. Well, apart from the recent electric storms we had, that was some testing/comparing different aerials on the subharmonic receiver. Since this receiver is actually a DC-RX with no AGC, comparison between the different aerials is pretty streight forward.

The aerial producing more noise is hidden the G5RV-jr. Signal levels are slightly stronger, depending on the direction to the signal source.

The second aerial, the one that abviously produced less noise, is an indoors "rockloop". Here, additional experiments were performed to see the influence of directivity of the aerial on the signalstrength and on the level of the noise floor.

Results and Conclusions:
I found the direction of the very strong and annoying pattern often visible in my grabber. Seems to be an appliance of one of my neighbors. The G5RV-jr, as an electric dipole, picked up that noise brilliantly, often completely drawning everything else. The rockloop, as magnetic loop, also sees it, but by far less prominent. Since a portion of the magntic component is present, it seems that the source of that noise is just something like 30-60m off my house (edge of the nearfield). In Holland, that's far enough to exclude my immediate neighbors. Anyway, the difference is dramatic, thus, I decided to further investigate in the design of a shielded magnetic loop, preferably water proof.

See my next post for the plan....

Thursday, July 23, 2009

Eggbeater II (2)

Wow, that was easy. Nailed it all together. Actually, even though I found some RG62, without the delay line (some call that thing phasing), thus, linearly it will be polarized for now.The whole is mounted to a 40mm PVC pipe. No surprise here.
The surprise came when hooking it up the the MFJ analyzer. The SWR shows a minimum of 1.1:1, and, that actually takes place at 435MHz! K5OE did not promise too much. BTW, with AOL services closed, I hope Jerry's original page will show up again somewhere else.

Now that the standby RX-aerial is done, part two of the exercise will probably be to build TPMs (Texas Potato Masher) to be placed on a cheapoe rotator for TX.

The first setup is now more or less completed. Shopping for more PVC plumbing done.

Finally, I decided to leave in aerial linearly polarized. When remembering correctly, the difference would be 3dB. OK, this could make or break the link-budget, but than, this is supposed to be the first setup of its' kind that I made... collecting experience is a part of the game, I figure.

Now, lets wait for the first signals to appear!

Tuesday, July 21, 2009

UHF Eggbeater II

Having had the FT-736R inactive for sooooo looooong, it's time to think about putting together some aerials for space communications.

In the past I looked into the subject-matter before, but never actually found time and space to set things up. Thus faintly, my walnut recalled something called "The Eggbeater" and "The Eggbeater II", both, to me, are variants of the famous Turnstile. Some zick-zack thinking resulted in the decision to build an Eggbeater II for 70cm. Actually, I bought the material for the VHF version too.

If you are now puzzled what I am talking about, click here.

Here in Europe, we usually talk metric. The closest equivalent to #10 (AWG I assumed) copper wire I could find in my local hardware store was 6mm² copper wire.

The result, so far, can be seen in the image below. Bits and pieces still have to be assembled on a PVC pole. Before doing this, however, I first intend to test the aerial with both linear and RHC polarization.

Friday, July 17, 2009


Now we are getting somewhere. Frequency for the subharmonic L.O. reached. I actually got two parameters to play with for frequency adjustment, the capacitor in series with the crystal and the supply voltage of the ocillator. This is actually adjusted and measured at 5V. Oscillation stops at about 4V. The circuit itself however, is designed for stabilized 8V. Thus, here are some degrees of freedom for the final tuneup.

As a last resort, I blamed it on the crystal, as suspected before. The crystal I used in the first attempt was not good, as shown by the replacement which more of less on the spot produced the correct frequency. Ouf! I need to build myself a crystal tester, I guess. Could possibly spare me some sleepless nights ;-)

The signal itself is not that perfect yet. I will have to install some resonating filter, I guess, to smooth out those humps and bumps to something that comes closer to a sine-wave than that...
Finally, the Poliakov-type mixer works best with a well balanced sine-wave.

Oh, and if you are interested in what I actually used for transistor, it's a 2N2222A. The rest of the bits and pieces are somewhat obvious and not worth to be mentioned individually...


No matter what xtal-oscillator I build, it allways oscillates by far too high.
Now, with a huge amount of inductivity I got my 5068.8kc crystal pulled "down" to just below 5070kc.... I don't get it! I remember times, when I did not manage to pull a crystal above it's nominal frequency. OK, yes, I know the game about series and parallel resonance, and, when it unknown which one of printed on the device...
Back to experimentation, and maybe I will sort things about before going nuts!!

Thursday, July 16, 2009

Photos of the E-probe

This aerial, or better electric-field probe, is now in successful use for quite a while (see earlier posts). The design is similar to the one by PA0RDT. To me, this is a very short Hertzian dipole with high Z front-end and a high gain pre-amplifier.

The whip is encased as the two photographs show. Yes, it's plumbing parts that for the enclosure... advantage: waterproof!

The active aerial is use in combination with a Target HF3/W receiver, which supplies 12V for active antennae on the flip of a switch, very handy! The receiver itself is certainly not the best ever made, however, the combination is unbeatable in ease of use for naval weather reports, FAX reception, NAVTEX , Volmet or broadcast reception.

Tuesday, July 14, 2009

plans for this evening....

Not having done anything other than QSOing, fun too, I admit, it's again time to wrestle solder. As starter, I will tackle the 30m-WSPR-TRX.
Since this will be a subharmonic design, I wanted to ensure a nice sine-signal for the diode pair. First plan, here, a slightly pulled up 5068.8kHz crystal in a Colpitts oscillator. Somewhat standard, isn't it? The aim is a super clean sine carrier with a frequency of 5069.35kHz. The pull would thus be a whopping 550Hz, that should be doable without any further issues.
Let's see how far I get, how stable it will be and if an oven should be added...
73 for now!

Monday, July 13, 2009

no progress

Sorry to write, but there has not been any progress on any of my projects lately. This must have something to do with all the parts that had been delivered lately ;-)
Honestly, this weekend was reserved for other activities... We will see about the upcoming weeks.

Open projects:
  • the AXEmite
  • 30m PSK-TRX
  • long-wave generally
  • TRX for maritime nets (20m)
Further in the planning (amongst others):
  • combined QRSS RX for 80, 40 and 20
  • dedicated QRSS RX for 22m
  • NAVTEX RX (518kHz)
  • propagation alert RX for 6m and 10m
  • APRS TRX (old Taxi-radio)
If there only were more hours in one day...

Wednesday, July 8, 2009

today: xmas!

All my stuff came, all in one day, crystals, trimmers and the /p-antenna.

Sunday, July 5, 2009


Just bought 100 crystals having a frequency of 20,250.0kHz. Presently, I have a job for two of those only. Lets see what ideas pop up later...
BTW, the idea is to build a super VXO and divide it by two... NO, not the VXO, the frequency it generates ;-)

Friday, July 3, 2009

WSPR/QRSS transceivers

WSPR is fun, and not only, it make some sense, propagation phenomena can be looked at decently.
However, having the band of own WSPR activity blocked is bad enough, even worse, having a transceiver blocked...

For 30m-WSPR, Gene (W3PM,GM4YRE) made a nice design, check this out. Nice ideas, however, I would/will do one or the other thing in a different way. Nevertheless, the basic idea is to create a DSB-signal, with some sideband separation by a simple single crystal filter. My present design ideas will not fall short of digital ICs and probably something subharmonic...

For 20m however, another nice option is available with a combination of standard computer crystals for a superhet design.
With a carrier frequency of 14,095.6kHz, the obvious choice would be a 4,096kHz and a 10,000kHz crystal. Either one could serve as I.F. in a ladder-filter. However, I found some 4,068.5kHz crystals, thus, for my attempt, 10,000kHz will be the I.F., allowing for a second frequency suiting the 20m PSK31 range.
Additional option: add yet another crystal and be ready for the 20m QRSS band, yep, that would then be a 4,000kHz crystal.
The next building project is in the queue.

QRT for now, "back to the drawing board" if you want ;-)