Thursday, 26 September 2013

DSB finally

Working today on the 10m Wispy transceiver, which is the design here

After a lot of headscratching, discussion with others etc, it looks like im finally getting somewhere with it. The odd phenomenon of the 42MHz AM output started me investigating the doubler stage further. I then noticed that C16, 35pF in this design, was marked as 60pF in the original Tx only version. 42MHz is the 3rd harmonic of 14MHz, was the stage working as a tripler instead? Patching 15pF across C16 brought the 2nd harmonic peak up more than the 3rd, whereas before they were equal. Hmmm, lets try 33pF in parallel then, lo and behold, an even bigger 2nd harmonic peak! Switching back then to probe the  output of the mixer, I see this
a 28Mhz double sideband signal! At last! OK, so the carrier suppression isnt very good yet, but its DSB, and at this stage thats whats important. I can now tidy this signal up, and start getting the amplifiers up and running properly.

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