630m (472kHz) Transverter

This page details the build of a transverter for the 630m amateur band, released in the UK Jan 1st 2013.

Results on 630m (472kHz) have been very encouraging with WSPR reports from many stations in Western Europe as far as Finland with an ERP of about 10mW. OH1LSQ (1736km) has copied my 472kHz WSPR signal with the transverter.

The latest version of the transverter saw me go back to a design using a double balanced mixer. I had issues with a transistor mixer (stability problems that were hard to fix, although these may have been simply decoupling weaknesses) and with the double balanced mixer the circuit is working very well. I have built a couple of samples with almost identical performance. The whole unit is currently housed in a small plastic box but I think a larger metal box is advisable so that the PA heatsink heat does not cause the LO crystal to drift. I am seeing about 1Hz movement during a WSPR 2 minute transmission cycle because of this. This is OK but could be eliminated with more thermal isolation between the PA and LO. There would be no problem with CW.

The Schematic

This is the latest version - Rev L - of the circuit schematic. It is always open to further modifications and improvements, but I will post the latest version here

Please note that WIMO FKP 600V capacitors were used in the PA output circuits.

Earlier Versions

The transverter described here is based on an earlier design for the 500kHz band (now withdrawn in the UK). On 500kHz, using an 80-100m square loop the best DX was Finland with over 100 unique stations spotting my 5W (ERP low mWs) WSPR signal. There is a video of this earlier design on my YouTube channel.

472kHz needs more people!

The band could definitely do with a few more stations, especially on TX. For WSPR it is NOT necessary to use big antennas or high ERPs. Please, if you can, get on the band. You will not be disappointed.

Preamp on RX?

Some years ago I was sent a 472kHz preamp by an anonymous person It was very kind. To this day I have no idea who this kind person was.

The preamp brings the FT817ND up to full sensitivity, but I find I am copying the same stations with or without the preamp. The preamp allows me to give better S/N reports. In theory, the preamp should allow very weak stations to be copied but I am copying no more stations! I guess this says my sensitivity is limited by EXTERNAL noise, not the noise figure of my rig.

Versions by others

Several people have built versions of this design both in Europe and in North America. G4BAO made an SMA version. There are many others too.

There is a clearer circuit in "LF Today" from the RSGB. If I can get this image clearer I shall.