dinsdag 25 december 2018

SAQ Transmission

Yesterday morning early I listened to the Christmas Eve morning transmission of SAQ. This Swedish station was built in 1924 to transmit messages in Morse code to North America. SAQ transmits a few times a year at a frequency of 17.2 kHz.

Antenna set up
About twenty years ago I made a large loop to listen to VLF stations. The loop consist of a cable of 5.6 meters with 12 wires, that are connected is series, to get a strong signal. A loop amplifier of a FET and a bipolar transistor pick up the signal of the loop.
The signal is fed back into the loop to  increase the Q-factor. With a 10-turn potentiometer I can adjust the Q-factor. I can even run the loop smoothly into oscillation. Which is really great to determine the resonance frequency.
The signal of the loop amplifier is fed into a frequency converter, built with a SO42p. I listen to the signal on my FT-817.

VLF Loop antenna in the shack - PA1B
My main objective of the morning was to first tune the loop.
After that I would write down the message, that was to be transmitted in CW (morse code).

The tuning was an immediate success. When I heard SAQ transmitting   vvvv SAQ  I started tuning by placing and removing capacitors with different values.  I ended up with 3 capacitors in parallel. 47 nF, 43nF and 8.2 nF. Yes, I don't know were it came from, but it is really 43 nF. Hi.

The signal was strong, I give a 579 by ear. I did not look on the S-meter.

Paper --> Dead circuit
After tuning, it was time to make room for a paper, to write down the message, that would be transmitted.
When I moved the breadboard with the loop amplifier about an inch, the circuit went dead. When I moved the circuit back,I heard the signal again. Then I let go of the circuit, it went dead again and whatever I did, it would not come alive again. OOPS. I still don't know what it is. I found one loose wire, the white wire in the picture below, but that was not the only problem. So I missed the message.

Terrible for a while
At first I felt terrible, but later that day I realized that, I did what I wanted to do. I had easily tuned the loop and I heard how loud the signal was. So I could give a report.
If it would happen to someone else, I would say: "Well, you have a great story to tell."

Loop amplifier on a breadboard - PA1B

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