Wednesday, 9 July 2014

96Mhz LO

I've been meaning to upgrade the 96MHz LO in my homebrew 23cm transverter. My own design OXCO has proven to be less than ideal. Having rescued a 106.5MHz G8ACE from an old 3cm transverter I thought I would convert it to 96Mhz in order to drive the multiplier chain in my 'Kirton' 23cm transverter ( see RSGB Microwave Handbook Vol 2).
I spent much of today calibrating the crystal turn-over temperature and then refitting the OCXO in place of the original OCXO.

With the 96MHz oscillator running on frequency I was able to hear the GB3MHZ 23cm beacon using just a three element WA5VJB PCB yagi in the shack. It sounded much cleaner that with the old OCXO,  but some of that may be down to the new beacon hardware, commissioned since I last used the transverter.

Driving the 'Kirton' transverter from the 50-100mW 144MHz output of the 'Anglian' transverter, driven in turn by the ICOM IC756Pro3, I was able to see 15W out of the PA module connected to the Kirton.

Just right to drive the 200W SSPA!!!!

The picture above shows the inside of the HB transverter with the OCXO lower right and the Mitsubishi PA module inside the huge heat sink on the back of the transverter. The 'Kirton' module is inside the tinplate box in the centre of the photo with a nice connectorised multiple band pass filters over it. This is used on receive only and effectively removes all potential out of band interferers!

At 15W out the spectrum analyser shows the output spectrum from 10MHz to 2.9GHz. The second harmonic is a credible 50dBc, but even so a 1.3GHz LPF will be needed at the output if this is connected to an antenna.

Here, the spectrum is centred on 1296.2MHz, with a span of 100kHz. The output looks pretty clean, so I think I am going to be able to use the transverter again. Looks like the TS2000X may be finding itself redundant. At least for a while!


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