16 July 2011

Q: How Many Secrets Does a Man Need to SOLF?

We are talking about communication. Nothing is as easy as sitting together and talking.

But things get difficult when people are living several hundred kilometers apart. Ok, you can use the phone, but that is really to easy. You know what is coming? Right! You can use morse code. But for that you need equipment. And you have to decide which transceiver to buy, better to build.

After the decision had been taken it was time to dig deeper. Yesterday I was reading the preliminary manual of the SOLF. It was a lot to read and I missed the overview. But it was there - in 4 parts.

1. Block diagram with TX Outgoing filterbanks, RX/TX Preselectors, ...

2. Block diagram with 9MHz SSB-Exciter, IF Emplifyer, Filters, ...

3. Block diagram with Controller, Audio-Section, CW Tonedecoder,  ...

1. Block diagram with RX/TX Switching Module, ...

 That looked pretty scary. I had no chance. I had to dig deeper to get an overview about all these different parts which had to be pressed into that little cabin. So here is the list of secrets which lay before me:

VFO with controller and DDS Referenz
  1. LO-Signal -Module
    with 9 VCOs (Colpitts-Oscillator) for each Band, PLL
  2. TX/RX Mixer 
  3. RX crystal filter 1 (can be defined to your pleasure CW and/or SSB)
  4. RX - IF Board
  5. Audio Filter with active Low pass filter and band pass filter, CW-sidetone
  6. CW Tuning aid
  7. Decoupling amplifier for digital processing
  8. Low Frequency amplifier (LM386-4)
  9. SSB-Exciter
  10. Controller for BFO and CW-carrier oscillators 
  11. CW carrier generator
  12. HF RX/TX Switch electronically controlled for QSK
  13. TX Pre-Amplifier
  14. Main Amplifier
  15. 9 MHz IF Decoupling
  16. TX/RX Switching board
  17. RX/TX Preselector
  18. TX Outgoing filters (7 groups)
  19. S-meter 
And have a look at one of the VCOs out of 9 (see above)

But as you may have noticed, I am a man who likes to hear what is going on. So I started to climb up the signal path from behind: the audio section. Of course you are right: The most important thing is: You can only hear what the receiver is capable to catch from the antenna signal. And there is a lot of noise in the air so you have to filter the input in the best way possible, so that there are no mixing products from outside the band in my signal. So what can the SOLF hear? The answer is: He can resolve signals down to  < -135dBm . He can hear more than most receivers can hear. My K2 was measured by the ARRL: -130dBm and with preAmp on 136 dBm. (You will find comparison sheets here (Look for Main Receiver Test Data Comparison Table.)

I am sorry to say: I can not hear the storms on Jupiter.

Wrong, I could hear them if I had a better antenna system.

So if the guys of the SOLF did their math and (I am sure they did it) designed the best possible filtering system for a band, I get the best possible signal. 

On this point things might get easy if there is only one station on the frequency calling CQ. I could just start to talk to the other ham. But normally things are not so easy. If you have a frequency bandwidth of about 2,4 kHz there could be 5 or 10 signals (people) making a hell of a noise. So how do you select that one QRP station whose signal is just a bit over the noise level. First thing you have to narrow the bandwidth. In the manual of the SOLF they described a crystal filter board with 500 Hz and 2,4 kHz. That would not help very much in my situation. But the developers are men who know how to work in a pile up. So you can build a second crystal board and you can build filters as YOU like them: 2400 Hz, 1000 Hz,  500 Hz and 300 Hz. So this is what I will do: I can switch from 2400 down to 300 Hz and have only 3 stations left. 

Now comes the hard part: You have to synchronize the signals with your side tone, so that you are really transceive. And you can pull an additional filter of about 150 Hz. So the morse code from the other station is filtered to the least possible bandwidth. And I hope that the signal is not ringing - I hate this. So the rest is depending on my ears.

So far the design of the SOLF should satisfy my ears.

A: It depends on how you want to count:
  • 19 logical secrets with many tricks and magic bags
  • 29 if you just count the boards
The SOLF is not a mystery to be solved in one afternoon.

Stay Tuned!