WISPY TX gets better (and even cheaper!)

Today I did a rebuild of the TX only version of the WISPY 10m WSPR beacon to improve it in several ways.  Switching to germanium diodes helps produce a much better looking DSB signal out of the mixer. With silicon diodes there was not quite enough drive. The second change was to remove the 2N3866 PA and replace it with a couple of paralleled up 2N3904s (each with a small emitter resistor so they share current properly). A 2N3866 is around £1.50 whereas a couple of 2N3904s are about 6 pence.  Output is now a clean DSB signal, even without the low pass filter, with a conservative 200mW DSB out (100mW equivalent SSB signal in the WSPR band). This is now a very pleasing little design that can be built for even less.  Within 5 minutes of turning it on it got a remarkable -3dB S/N report from EA8FF over 3000kms away.

WISPY (Polyakov RX) - 1st spot

I rebuilt my 10m WSPR RX today (the rig has to be called Wispy) onto a tidier, smaller board using MeSquares and took a few steps to reduce the 50Hz common mode hum pickup, although there is still too much there and more work is needed. Someone suggested it was radiation of the 28MHz 2nd harmonic of the oscillator mixing with 50Hz in nearby PSUs being re-radiated and detected. Still unsure of the mechanism but there are lots of things to overcome this.

EA8FF on the Polyakov RX (note the 50Hz and harmonics lines locally generated)

However, the good news. The RX, even without a preamp, can detect down to an amazing -127dBm MDS, possibly lower but this is as low as my signal generator will allow and I did not try with an attenuator. My first reception of a WSPR signal was EA8FF at -18dB S/N. Remember this is a DSB RX so the noise figure is actually 3dB worse as it is picking up noise from both sidebands.

Next stage is to add a small preamp to see if this helps reduce the common mode 50Hz pick-up and increase the sensitivity another few dB.