My 3.4GHz system is built around a
DEMI transverter which I swapped for a Toshiba PA, and one of the
very same PA's. The PA needs 1mW in for around 55Watts output on 3.4GHz. The
actual transverter seemed a little odd when run on its own, with a nice set of
harmonics on the output when driving a 50ohm load. This was cured by gluing a
strip of lossy rubber to the inside of the enclosure above the TX driver /
filter sections. The inside of the enclosure is just a little bigger than C-band
waveguide!
Picture - Transverter mounted on base plate.
The above picture shows the entire transverter mounted in its waterproof box on test. In the lower right of the picture, you can see the LNA - this was salvaged from a C-band LNB as the entire LNA section was separate. I have a DEMI 3.4GHz LNA to build up and install in place of this one. The current system has an overall gain of 40dB and a noise figure of 1.9dB. It is hoped that this will improve with the addition of the DEMI LNA.
Above the LNA is an oscillator and multiplier. The crystal is in an oven inside the box, and is insulated with 10mm polystyrene - The only addition to the oscillator chain will be a G4JNT PSU to provide a separate stabilised supply. This is needed because on TX the supply drops 100mV or so, and changes the LO frequency by a couple of hundred Hz at 3.4GHz. The oscillator and sequencer came from VK5EME at a very reasonable price. In the transverter, the PA is mounted on a large heat sink which is fan cooled. The fan is controlled by the PTT line out of the sequencer and is fed by a simple FET delay timer such that when the PTT is released, the fan continues for around one minute. The back of the transverter has a 5 inch hole in with a cover, air is drawn in from outside, over the heat sink fins and out through a hole which can be seen in the bottom of the above picture. The air is routed such that is doesn't cool the oscillator too much. This transverter needs 18Amps at 13.8V to operate, and is usually supplied with a compact switched mode power supply that is mast mounted.
The antenna change over relay is a Dynatech non-latching variety that is driven by a G3PHO 12v to 24v converter. The entire transverter is sequenced and the DEMI transverter unit has been modified to require separate 12v feeds for TX and RX. The sequencer is configured as follows;
| 1) +12v to the RX stage and Gasfet preamp |
| 2) +12v to TR relay and fan driver |
| 3) PTT feed to 55W power amplifier |
| 4) +12v to transmit side of transverter |
In the above picture, you can see the completed transverter mounted behind the dish for the May 2004 UHF and up contest. The dish diameter is 2.4M and its using a G3PHO 3.4GHz feed with chaparral type scalar ring. The transverter is connected to the feed with a short length of FSJ-450.
Here is the dish mounted on the pole and up in the air. In the background you can see the 2.3GHz and 1.3GHz antennas.