WISPY progress (TX side)

Despite promising to finish off the 472kHz transverter properly first, I decided to have a go at the TX side of the 10m DSB WSPR and PSK transceiver (WISPY). Starting with the PA and working back to the drivers I breadboarded a simple linear amp based on a couple of 2N3904s and a 2N3866. Power out is around 1.2W pep. I also added the osc/doubler and single balanced mixer later but have not optimised the overall strip. This phone image shows the breadboard I was working on - not a pretty sight. If time allows tomorrow I'll continue this and maybe get to hook it up to an antenna and a PC on TX.

On with the projects.....

Back home now, so it is on with the autumn projects list.

Several people have been contacting me about the latest 472/500kHz 10W transverter. Someone in OK-land is designing a PCB and I hear a "dead bug" version has been successfully built in the USA - not sure whether an exact copy or "based on" - but it has already been used on MF WSPR with a report from over 2000km up the USA east coast. So, I will continue with refining this design first and then get on with the "WIPSY" 28MHz simple WSPR transceiver next.

The non line-of-sight optical beaconing tests will resume a little later when the evenings start to draw in. I want to set up a more powerful, semi-fixed 481THz optical beacon so that I can do a series of DX tests under various degrees of cloud cover. Tests last winter suggest much further will be possible than the 9km NLOS ranges achieved with clear air scatter when signals were audible by ear. By using much lower sub-carrier frequencies the optical detector sensitivity will be very much greater allowing even weaker signals to be detected on QRSS3 and QRSS30.

Progress on the WISPY transmitter

This afternoon I managed to do a little more work on the WSPR transceiver for 10m, building the oscillator/x2 multiplier stage and the balanced mixer for the TX part using a couple of 1N4148 diodes and a T50-6 tuned circuit. Carrier suppression is around 30dB without much effort. Next stages will be to add a linear amplifier to bring the DSB output to around 1W (500mW pep SSB carrier). Although I could combine the same mixer on RX and TX, I may stick with the Polyakov RX mixer as this is working so well. 

I should have added that with a linear PA, the WISPY transceiver should also be perfect for PSK31 as the 14.060MHz crystal (when doubled) will certainly pull to the PSK31 10m sub-band.

A bit further with the WISPY RX

Although not in the best of shape today, I spotted CX1BP (11131km) and EA8FF on 10m WSPR today.  Not bad for a handful of cheap parts.

I had a bit of trouble today with the SE602 I was using for the TX part of WISPY (it may have been faulty but I was unable to get a clean DSB signal out of mine), so when I get back on the project after a week of interruptions coming up I'm going to go for the simple 2 diode single balanced mixer instead on TX. I know this works well and is less expensive.  The TX part can be simpler than the RX I believe.

Spots with WISPY RX

FR1GZ and others coming through just fine

This is the PC screen capture using WISPY as the 10m receiver for WSPR in the last hour or so. It is working just fine.

WISPY Schematic (more clearly)

For some reason when I put multiple images on a post it is not easily possible to see them clearly when clicked (at least with Firefox). So here is the schematic again. Clicking this image should bring up the full sized image clearly.

Hum fixed on the 28MHz WISPY WSPR RX

Rev B 28MHz WSPR receiver

Adding more audio decoupling around the oscillator and adding a common base FET RF preamp has totally fixed the common mode hum issues with my Polyakov mixer based DC receiver (WISPY) for 28MHz WSPR. Even running from a mains PSU I am getting good sensitivity and no hum. The board is working on the bench with no attempt at screening and appears totally fine. The oscillator buffer appears redundant, so has been removed.

Wispy Rev B (built using MeSquares)

One possible further mod is to make the input to the RF amp a series tuned circuit. This would be needed when the full transceiver version is made (back-to-back diodes would short the cap to ground on TX).  For now, I will leave the little RX running to see what I spot.

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.