BITX20 Update #29

It works!

Finally, after over 12 months off and on, I can now say that I have achieved something. I made my first QSO on my BITX20 to a local ham, Graeme VK3GL.
I finally got the Huff & Puff problem resolved. It turned out the the problem was not with the DC power supply but actually within the Huff & Puff circuit. One of the relays on the linear amplifier board was causing the oscillator on the Huff & Puff to shift each time the relay was energised. Because the oscillator changed the resolved frequency changed and the Huff & Puff would try to correct it.
The VFO had not actually moved but the correction voltage forced the VFO to shift beyond the range of the Huff & Puff circuit and therefore the Huff & Puff would unlock. All this happened in less than a second.
So I moved the Huff & Puff circuit board about 20 mm and the problem was solved. Prior to moving the board I had done the following:
  • Added a relay to remove the audio feedback at PTT
  • Change the VFO regulator from Zener to 78L05 + resistors regulator
  • Added a DC choke to the +12 Volt supply
  • Changed the DC supply electrolytic capacitors to tantalum capacitors
  • Moved the DC power for the Huff & Puff from the amplifier board to the BITX20 Board
  • Changed the PTT ground return path for the relays from the BITX20 board to the linear amplifier board.
All of which did nothing to help the unlocking problem.
After getting the Huff & Puff to work properly I tuned up 14.185 MHz and started calling CQ. After 3 calls Graeme, VK3GL, answered my call.
Graeme and I chatted for about 15 minutes and the BITX20 stayed on frequency and showed no problems at all. Graeme tells me that there has been some good DX on 20m in recent nights so I will have to have a tune around tonight and see who else I can work.
My next challenge is to add the AGC/S meter modification and perhaps the SWR/Power meter as well.
I also need to finalise a case for the radio as the current case is just slightly too small and upside down.
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