10m WSPR: the WISPY TX beacon

New Version 24.9.12

The latest version has 4 2N3904 transistors (rather than 2) in class A in the PA and produces over 500mW pep DSB (250mW SSB equivalent in the WSPR band). I have also added a small RF indicator to light up a front panel LED when the TX sequence occurs. I'll add the schematic later.

Since increasing the power, results have been very good with spots from the west coast USA earlier this evening. It now means I can free up the FT817 for other purposes and still send WSPR on 10m whenever I am at home and have the PC turned on.

WISPY beacon TX now boxed and installed with
the other kit (mostly home built) in the shack

(click image for a clearer view)

Older version

This is a derivative of my first circuit, but with improvements and cost reductions. Biggest change is switching to germanium diodes in the balanced mixer. There was not quite enough drive with silicon diodes and now the output from the mixer is a much nicer DSB signal.

The second change (from the original WSPR transceiver) is to swap out the expensive 2N3866 PA for a couple of 3 pence 2N3904 transistors in parallel, with emitter resistors to ensure current sharing. No heatsink is needed.  Overall output is a conservative 200mW DSB (equivalent to 100mW SSB in the WSPR band). I am now very pleased with this design.

Within 5 minutes of firing this up I got a -3dB S/N report from EA8FF over 3000km away when using my wire halo antenna.

Click on schematic for a larger version