24Ghz Equipment
The equipment comprises a 30cms ex-link Cassegrain dish, plus a transverter with a 145Mhz IF based on the DB6NT, design but incorporating an ex- link equipment amplifier to bring the Tx power up to 400mW. The receive amplifiers use cheap readily available GaAs fets type NE325 by NEC for use in SATV LNB equipment. (The lossy flexible waveguide is no longer part of the system!)
The internals of the 24Ghz transverter. On the extreme left is the 400mW PA with black heatsink attached and below that the relay drive circuit on Veroboard. The PA is attached to the manual waveguide switch which also has the two receive amplifiers (on copper WG20) on the opposite port. The third and fourth ports terminate the antenna and a WG 20 load. A coaxial 3 port switch, near the middle of the picture, is used to select the input to the PA or output of the receive amps for the input/output of the DB6NT transverter and waveguide filter shown near the center This switch is electrically ganged by a microswitch on the waveguide input / output switch. Adjacent to the switch driver is the WDG009 11Ghz multiplier. Lastly there is the G4DDK009 multiplier driven by an excellent G8ACE temperature controlled oven kit (OCXO); on the far right with heat insulating foam to keep everything warm. This in turn is locked to an external 10Mz standard locked to GPS.
The photo above shows in detail the mounting of the 24GHz "PA", with the all important 10BA tuning screws at the input and output of the PA plus, also on the output wavguide (extreme left) prior to the antenna and after the WG switch. These screws were worth another 80-100mW after their addition. This view also shows the tapered WG20 transitions at both input and output plus the heatsink which is clamped to the "non labeled" face of the PA module, to conduct heat away from the internal substrates.
High stability and good phase noise are a must at 24Ghz and upwards. Thus the crystal used in the LO must be of high quality and age predictably. Several suppliers have been tried for crystals and those supplied by Eisch-Kafka in Germany from a company called QT seem to be currently the prefered type. These are usually specified for operation with an oven temperature of 60degC. If stabilty is poor then even the best PLL will not hold the crystal in lock, and if the crystal has poor phase noise then a "burble" will be evident on the signal, rendering SSB unintelligible in the worst case.
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Alcatel equipment
Just recently some surplus commercial equipment has come on to the market from Alcatel. Some types of this equipment will go directly on to 24Ghz while other types of the same equipment are made for the 22-23Ghz and need modification.
Visit the South Coast Repeater and Beacon Group site at www.scrbg.org to read all about my beacon:-