Wednesday, May 13, 2009

subharmonic dc-rx in operation


Not only has it been a nice weekend project, the subharmonic receiver issue was actually meant to replace my FT-817 in the grabbing setup. And... it did by today. There are still some issues to be solved, however, the thing starts to catch flying W by now. Features amoungst: no AGC (see me releasing RF a few meters off the rx-aerial, the very red signal @ 22:39), stable canned oscillator, no carrier DC in the AF, no BFO sideband noise. The flying W actually fades in about 22:47.

Traces of WSPR-signals to be observed. Since WSPR-software is bound to a effective BFO-frequency of 10.1387MHz on 30m, my 10.1376MHz LO/BFO will not enable for decoding the WSPR-signals. My hope is, that in future versions of the WSPR-software, receivers other than appliances will be supported.

Update, since in the above image, not so much can be seen, here's another one. The spectrum lab bandwith covers the WSPR band too. This spectrum shows the time span of 06:07 to 06:27 UTC (May 13th 2009). It covers the range of about 10139.800kHz to 10140.310kHz.

The above images also shows a 50Hz signal, all over. The source is located, it is the sound-card internal to my computer. The problem's source is the following. A single transistor in the af-stage seems just about enough to satisfy the microphone input of that respective sound-card, however, sensitivity is maxed. At the chosen settings, the 50Hz lines even remain when the receiver is disconnected. I will work on that and hopefully improve S/N-R in this respect.

Cheers, Joachim