A bit of gain for 10GHz - for free....

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radiogareth
Posts: 1215
Joined: Wed Jan 06, 2016 9:46 am

A bit of gain for 10GHz - for free....

Post by radiogareth » Tue Jun 29, 2021 6:34 pm

The old adage 'never throw anything away, it might come in useful one day' has just visited my personal stock again. Back when BDB mini-dishes were all over the surplus market I picked up a total of 4 (not sure how, probably £1 each or 2 for a £5). I've recently used the lovely little dishes for /P work on 3.4, 5.6 and 10GHz. Out of curiosity I took an LNB apart and found a lovely neat 3 stage front end, a mixer and DRO oscillator along with the required bias system. On Noel G8GTZ and Collins G4EML suggestion, (that 'gain is gain') why not try using it as per the popular Franco boards.
A bit of eyeballing showed that a SMA two-hole flange socket could be soldered to the ground plane at suitable in and out points and that coupling capacitors could be salvaged from the board to link the RF without upsetting the device bias. The pictures show the result, not quite like BSB imagined but it has plenty of gain, enough in fact to require the Pluto output turning DOWN to -10dB (even though I'm using the 5th harmonic).
My problem now is how best to measure what will only be I guess a few milliwatts of power at this frequency so that I can compare solutions and choose next steps.
I've plenty of old Gunn diode TX/RX pairs and there is a simple RF power meter in the Microwave HB Vol 3 using such a thing. Be nice to have a bench instrument that does a really big range of RF frequency and power, might start saving up for something. I have a R&S CRTU that goes up to 2.7GHz, but nothing for the region above.
Pictures show the received waveform across the shack via my LNB, the output arrangement taken after the filter and the input arrangement which picks up the RF probe line that was inside the waveguide of the LNB. A bit of sawing, filing and drilling to clear these two sockets and the screening all fitted back on which rendered the device stable.
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2021-06-29 17.06.35.jpg
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2021-06-29 17.06.44.jpg
2021-06-29 17.06.44.jpg (118.74 KiB) Viewed 1279 times

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