South Coast Repeater and Beacon Group

GB3SCS - 2.3GHz beacon

Overview - by Andy G4JNT

Click to enlarge This is how it started life....

The original version started off with a 96.7MHz crystal in a Butler oscillator followed by a X4 multiplier to 387MHz in a single module. A clip on crystal heater reducing oscillator drift over variations in external temperatures. The output went to a second module, a modified DDK004, which further multiplied the signal by X6 for the final output at 2320.905MHz.

The output from the DDK004 was fed to a cascaded pair of RF2126 devices to generate 1 Watt of RF, then via a two stage comb filter to the output. At the end of 15 metres of LDF-450 feeder it gave about 0.8W at the antenna.

The antenna is a two electrical-wavelength-long Alford slot with an estimated gain of 6dBi, giving an EIRP in the region of 3 Watts.

On-off keying of the beacon was generated by switching the power to the final multiplier stage in the DDK004 with a PNP transistor. After some experimentation with keying earlier multiplier stages, it was found that if these were switched, the change in loading tended to get fed back to the oscillator and cause the keying to chirp. The message data is generated with a G0IAY/G4JNT PIC based keyer module which allows CW messages of different speeds as well as programmable pause lengths to be embedded within the single transmission.

Then, eventually, after all the other beacons had been locked to a master reference, GB3SCS followed suit...
This time a DDS followed by a PLL multiplier did the job.....

And Now... Completely Rebuilt with JT4G and increased power

Latest update
The GB3SCS driver based on DDS plus multiplier had spurious levels that caused problems with some local stations. So after a session needed to cure a controller failure, the opportunity was taken to rebuild teh GB3SCS driver using an improved solution with fewwer spurii. This uses Direct Upconversion allowing a cleaner fixed frequency RF source to be used, modulated via quadrature upconverter chip with the WSJT modes generated separately, at baseband. Q65-60D modulation, one of the latest from the WSJT suite, was adopted this time.