G3PHO/P 24GHz

This is a photo of my 24GHz portable equipment as at October 1996.

This is a wideband FM transceiver based around  Philips GDHM32 doppler module. This module consists of a Gunn diode oscillator and an in-line diode mixer for receive. The output power is a few milliwatts (nominally 5) while the receive noise figure, not measured (!), is possibly 12 to 15dB....not very good by modern narrowband standards but this little rig has worked many paths over 100km in length (best being 136km).

The unit works on the duplex system as the receive/transmit intermediate frequency is 10.7MHz. In operation it is just like using a telephone...no send/receive switching is needed.

During 1996 I also used a separate 50mW Gunn transmitter, mounted on an identical dish to the one shown here (35cm diameter offset-fed type). The low power transceiver in this photo then became a receiver only. Both the units and their dishes are now mounted on a common horizontal boom on the tripod. With the increased transmit output power, I have extended my best 24GHz DX to 141km.

During the winter of 1996-7 I plan to build a narrowband cw/ssb system based on pcbs and kits by G4DDK, G3WDG and DB6NT together with useful  power amplifier and receive preamplifier modules taken from a Digital Microwave Corporation 22/23GHz unit. If all goes well, the power output should be around 50 to 80 milliwatts but  this represents, say,  a 30dB system gain improvement over the wideband system!

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