Sunday, August 30, 2009


Not sure what's going on here... This would be a spectrum image (30m) from essentially dc to just beyond 5kHz.

We see RTTY, PSK31 and WSPR (at about 2.7kHz). And, we see two strange noisy snakes, about 500Hz apart. Any idea what that could be?

Half of the image was taken with the aerial (rockloop) pointing North-South, during second half of that spectrum scan, the aerial was pointing East-West.

QRN, nature transmits on 30m

Here's some stuff one can observe when no AGC interferes and the risk of a lightning hitting the (indoors) aerial is minimal. Actual I am reminded now that I had intentions to build some meteorological receivers...

This spectrum-image nicely shows the storm passing with a maximum intensity. Traces of QRSS signals in this spectrum.

Black clouds passing
These structures were seen in my spectrum receiver earlier. Honestly, they remained a mystery to me. That changed with today's observation however.
Sitting at my study's desk doing paperwork, the sky got extremely dark all of a sudden. Usually I have half an eye on the spectrum receivers, also today, with not much going on. Besides this:

In order to be able to compare the atmospheric stuff with man made signals, I temporarily changed SpectrumLab's settings to cover the 30m WSPR band. To me this result clearly shows that I am not looking at an ionospheric phenomenon.

The plan for the next front transient is to capture even wider spectra.

Grabber on USB finally

Having had enough complaints about my grabber grabbing DSB, I finally decided to include the crucial crystal. Oh, btw, people complaining were of the kind who never actually run or built a grabber by themselves.
However, the suburban subharmonic direct conversion receiver is now equipped with a 10.140MHz crystal, used as a band-pass. Schematics are to be found on my webpage....
I wonder if the crystal makes a big difference, some (theoretical) improvement is expected anyway.

Friday, August 28, 2009

Green Radio

A long time ago, I spent a little money and got myself a GRC9. Yep, green radio. That was to a time where you got whole sets and not just the main event. It came with all aerials, spare parts, headphones, microphone, morse key, speaker, power amplifier (LV80), inverters, two rucksacks full of stuff, all cables, service manuals, etc... It still sits in Freiburg and is waiting for me to pick it up.

Meanwhile, I decided it was time to obtain a SEM 35. In contrast to the GRC9 it came naked. Yep, it really did. Just the transceiver and the clipon power supply - no handset, no aerial, no power cable and worst of all, no circuit diagram.
Took me about four full evenings on the internet to finally locate eight image files on the circuit diagram. Ohhh boy!!! Now, I ordered a handset, speakers seem to be unavailable. Let's hope for the best!

It was claimed the SEM 35 was comparably stable, even with the PLL disabled (there is a mod on the internet that allows for continues tuning of the rig telling so).
Here come in options for modifications, i.e. expanded usability...
The rig has got a first i.f. of 11.5MHz and a second i.f. of 470kHz. One could considered doing something with that. Something like adding an SDR to the intermediate frequencies. This would give a range of about +/- 48kHz (96k-sampling rate) about the center of a channel. With a channel spacing of 50kHz, the whole range is covered with nice overlap.
For the first i.f. options are a 46.0MHz oscillator for the normal approach and 15.333MHz for the "softrock lite 30" approach. Honestly, since there are no crystals, one need to think of a more advanced solution.
The second i.f. could be dealt with using a 1.880MHz oscillator, which to me again looks like a more advanced thing to do. But there is an offset solution: 1.8432MHz, resulting in a center SDR frequency of 460.8kHz. Actually, I do prefer this, for various reasons.
The plan is, as soon as I got my act together, to add an SDR receiver, maybe a softrock, in front of the 470kHz i.f.-filter.
I am curious if the stability of this green radio from the seventies is good enough to capture 10m WSPR and QRSs.

If the above project is successfull, one could consider of doing something similar to the transmit train, allowing for CW. The PA of the SEM 35 looks linear to me, which, in a pure FM rig, does not make much sense however. Before running sideband through it, some more thinking and testing is required.

Monday, August 24, 2009

SW PSK-20 upgrade ideas

Lets face it, I cannot help it and have to think of alternative uses regularly.
QSOing on 20m in PSK31 is fun. However, I think there are more options for the PSK-20.

The first thing that came to my mind, adding some switchable local oscillators. The design of the PSK-20 is a 9.0MHz i.f. with a 5.07 l.o. (5.0688MHz crystal). Here comes the idea, one could add some voice channels using cheap crystals:
  • 14.120 = 9.0 + 5.120
  • 14.185 = 9.0 + 5.185
  • 14.200 = 9.0 + 5.200
Or, with oscillators divided by two:
  • 14.120 = 9.0 + (10.240 / 2)
  • 14.350 = 9.0 + (10.700 / 2)
Using (external) oscillators, one may consider using superVXOs for increased coverage.
This however would require to run a microphone preamp with an active low pass filter. The crystal filter of the PSK-20, for obvious reasons, is wider than a sideband filter.

The second idea is focused on the fact that the intermediate frequency is 9.0MHz.
As you may have seen, I was experimenting with a softrock lite on 30m. Those experiments where mainly aimed at the usablility of the softrock lite for 30m QRSS reception.
The softrock uses super-Nyquist, in short, the center frequency is 0.75 times the l.o.-frequency. This makes it comparably easy to use the softrock lite to "look" at a 9.0MHz i.f. with a l.o. crystal of 12.0MHz. This would add SDR and panoramic display to the PSK-20.
But, not only, since there also is a crystal 5.0MHz (or 10.0MHz divided by two):
  • 14.000 = 9.0 + 5.0
Reception of the better part of the CW band and the QRSS region at the lower band edge would be possible. For QRSS reception it would be advisble to pull the 12.0 MHz softrock l.o. down.

And finally, one could think of penning down a 5,0688MHz crystal, in order to reach the QRP frequency. All one would need for a CW qso would be a 800Hz sine generator.

Sunday, August 23, 2009

SW PSK-20 done

Built a nice piece of equipment from a superb kit: the Small Wonder Labs PSK-20.

The kit was perfect, no missing parts, quality p.c.b., well packed and sorted bits and pieces, clear instructions...
Compared to what I built earlier, kits, homemade, homebrew etc. this is one of the easier ones. The layout is not as busy as in many other designs, this is reflected in the total build time of something like 6 hours.

The building instructions are good. Not too long, but still enough detail. The advice on the installation order seems logic most of the time. Sometimes I just wondered but did not further care. At rare instances I severely deviated from this advice however.
The author is aware of essentially all difficulties one can face and gives good instructions how to overcome said difficulties.

I missed the progess tests/checks à la Ten Tec Kits. Not that I would do all of them, however, I do some. And so I did in the PSK-20 project. I think this would be a nice addition which would prevent the less experienced builder to continue the installation of parts when a section of the built went wrong.
In the middle of the solder session, when the receiver was completed, I wired the project up to 12V and an antenna to "hear" if everything works sofar. Yep, it did.
Additional tests in earlier stages could be, for instance, checking if the L.O. and the B.F.O. are functional by listen to the carriers with a general coverage receiver.

One erratum is corrected (indicated on a sticker on the instructions CD's cover), another one slipped through, I will mail it to Dave.

After a quick alignment, searching for cables to wire up a computer, finding a computer, realising that it had no PSK31-software on it, installing said software, firing up everything, I managed to have a qso with SV-land. :-))

Saturday, August 15, 2009


Whilst I was looking at crystal frequencies for the new qrss-ranges, I came along a very nice combi for a 3 band qrp trx for the bands 80m, 20m and 15m. (Frequencies in MHz)
  • 3,560 = 11,0592 - (15,000/2)
  • 14,060 = 11,0592 + (6,000/2)
  • 21,060 = 11,0592 + (20,000/2)
The division will be done by a flip-flop.

The combination offers the option for a ladder filter at 11,0592. In this case, one could consider, as an experiment at least, a subharmonic b.f.o. using a 5,5MHz ceramic oscillator in combination with a RA3AAE-mixer.

Writing of ceramic resonators, there is one for 6,0MHz. This would enable a nice v.f.o.-range for the 20m band.

When crystals are to be used, one could consider using a super-vxo.

UPDATE: Jan came up with an idea of adding 40m by using the combination
  • 7,037 = 18,096 - 11,059
OK, 7kHz is quite a stretch to pull, possible however, TNX Jan!

Friday, August 14, 2009

New QRSS xtal combinations

Following the idea having the QRSS region about 100Hz below the WSPR region on every band, new considerations had to be made in order to allow for MEPTs controlled by cheap crystals.

For the bands 40m and 30m the situation is very simple:
  1. 10,140MHz crystal available from N4ESS (no change anyway)
  2. 7,040MHz QRP crystal available
  3. 7,038MHz QRP crystal, which could serve as a basis for a d.c.-receiver
Design ideas... well... I will leave that up to you!

80m slightly more tricky, but no big deal at all!
  1. 3,595 = 7,190 / 2
Design ideas: The crystal is available at the same source as the 30m-crystal (N4ESS). The division by two can easily be done with a Flip-Flop. In order to get the signal into the QRSS range, one has to pull down the oscillator by 2kHz, which should not pose any further problem.

For the bands 160m, 20m, 17m, 12m and 10m, a combination of two crystals will do the trick to generate a frequency in the QRSS range.
The following frequencies (in MHz) are reached by mixing of two fundamental crystal frequencies:
  1. 1,8372 = 8,8672 - 7,030
  2. 14,096 = 10,000 + 4,096
  3. 14,096 = 18,096 - 4,000
  4. 14,097 = 12,000 + 2,09715
  5. 18,106 = 8,000 + 10,106
  6. 24,926 = 14,7456 + 10,180
  7. 28,125 = 18,000 + 10,125
Design ideas: the easiest way of generating the wanted signal appears to be using a 74HC86 as demonstrated here:
It seems appropriate to note that the 12m combination under point 6 uses a 10,180MHz crystal which can be found in older crystal-synthesized CB radios.

The 15m band can be reached by means of multplication and division:
  1. 21,096 = 4,096 + 2 * 8,500
  2. 21,097 = 2,09715 + 38,000 / 2
Design ideas: Solution #1 involves a 8,5MHz crystal (available from DigiKey) which is doubled obviously. In terms of filtering, this combination is advantageous since the primary mixing products will be nicely separated. However, if doubling is not done perfectly, contributions of the crystal's fundamental will spoil the fun! E.g. second harmonic 3 * 8,5 = 25,5 --> 25,5 - 4,096 = 21,404.
Solution #2 looks more promising to me for the following reasons. 38,0 divided by two gets us to 19,0. Mixing products will be 21,097 and 16,903. We certainly would need a band trap for 16,9MHz, which should be doable. As divider I would propose the usual Flip-Flop. The best part is, there are canned oscillators available for 38MHz.

Monday, August 10, 2009

HF-3W improved - long time drift

Had the receiver WSPRing all night. The result is pretty conclusive.
There is no drift as such. The receiver however shows significant thermal dependence.
  • Window closed, everything stable, room temperature stable resulted in no drift.
  • Window open, room temperature sinking, drift kicks in between 0340 and 0610 a 20Hz drift is observed (IQ4DJ MEPT).
The problem could probably be solved by adding an oven. For me this thermal behaviour is understood well enough to just don't care about. My HF-3 will remain as is.

BTW, the jumps did not reoccur.

Sunday, August 9, 2009

HF-3W improved - first results

The receiver is now hooked up to a short-wave antenna (G5RV-jr). Presently receiving the 30m QRSS/QSPR band. WSPR decodes with no drift on most stations. I therefore believe that the drift problem is purely cosmetic, maybe it has something to do with warming up, I would not be surprised. No jumps occured up to present.

During my test, for a short periode, the MEPT of I0/N2CQR was visible.

WSPR decodes look like this:
2114 -23 1.4 10.140241 0 F6BIA JN18 33
2116 -13 -0.4 10.140189 0 DH8SA JO53 37
2118 -26 0.8 10.140207 0 PY2GN GG56 37
2120 -15 0.6 10.140106 0 DL0TFK JN48 30
2120 -14 1.2 10.140198 0 DH5RAE JN68 37
2122 -1 2.7 10.140226 1 DL2ZQ JO42 37

Not too bad for a €299.- receiver.

Conclusions would be the following:
I now really like the HF-3W. 1kHz steps are not ideal for ham-radio. The clarifier helps, but is hard to adjust. Using a reference broadcast-station, the carrier can be set to create a 1.3kHz beat tone, that's the offset required for WSPR operations.
The receiver primarily is targeted to yachtsmen. In naval frequency lists, the center frequency between mark and space is listed. The receiver is actually built to help sailors to easily find RTTY stations transmitting weather reports and thus, the frequency display in SSB is off by about 2kHz. Meaning, that the dial for WSPR needs to be set to 14.141MHz with some odd clarifier setting.

HF-3W improved

Just gave it a shot. The Target HF-3 VLF to HF receiver is certainly not the world's best receiver, however, it is not bad either. Actually, I like it!

Tests on DCF77 reveiled, that frequency stability is not one of the big pros of the receiver. OK, no QRSS, which was shown by Des (M0AYF).

Anyway, there was one feature I never understood, and I also disliked a lot. The clarifier position. Thus, I opened the (plastic) box to see what could be done. Next to the position where the clarifier poti is wired up to, a crystal and a varicap-trimmer are to be seen. The part is the local oscillator. Ideal, lets play with the varicap first. I got what I wanted.

Since the receiver was open anyway, I took the chance and carefully played with the inductors starting from the first IF, further to the second IF and the one in the LO. The factory settings were close, but on every single trial, a bit of improvement was possible.

At the very end of the exercise, I also tweeked the reference oscillator's crystal pull. That resulted in a short back and forth between this reference oscillator and the LO.
All in all I am somewhat satisfied with the result.

As an extra bonus, the erratic jumps of several 10 to 100Hz seem to have disappeared. Seems that the reference oscillator was slightly off, causing the PLL to fail locking from time to time.
Over the time scale of about half an hour, there still seems to be a 1-2Hz drift. I can live with that. I will try the radio as QRSS receiver, but hopes are not that high. Finally, the receiver was supposed to provide me with Navtex infos, nothing more.

Thursday, August 6, 2009

Shielded 30m RX-loop

Did some cutting and soldering. With measures like "Pi mal Daumen" and a look at the previous shielded loop (resonanting between 49m and 40m, remember?), I managed to arrive at a shielded magnetic loop resonating at 30m. Diameter is about 30cm, I will however publish more precice values soon. Same materials used, some polystyrol vari-cap. Coupling done with a T37-6.
The loop receives, levels, however, are very low, as expected.

Next step, a preamp. Not sure what design to choose.

Saturday, August 1, 2009

Altoids & Co

For unknown reasons, Altoids are not sold in shops around me. Hmmm, how than to encase QRP stuff?

In search for replacement, I was visiting about ten shops. Only one got some reasonable, Barkleys. Same size as Altoids tins, I like them even better, since they have got a flat bottom that does not bulge in.

Apart from that, anyone interested in a year's supply of peppermints?

30m Grabber Receiver Infos

Schematics and (short) explanations about the simple RX can be found on my webpage.