Sunday, 17 July 2016

70cm low noise preamp for Contesting and Satellite mode J

I have had a 432MHz version of my PGA144 preamp on the stocks for some time. I never bothered toadvertise  it because I knew it needed more development. I took the time over the last few days to look at the filters again and then put one together. As always some tweaking of values was required compared to what the design software said, die to stray capacity of pads etc.
The results are quire pleasing.
I've not yet measured the input two tone third order (IIP3), but it ought to be pretty good.
Of particular interest is the deep notch I have been able to place on 144-146MHz to suppress signals in this range. Similarly the frequency response is well down in the Upper digital TV band, GSM band and at 23cm.
The noise figure measures under 1dB ( 0.8 to 0.85dB on the prototype) on an open board, which is not the ideal way to measure noise figure due to 433MHz SRD interference.
As the accompanying plots show, the input match is exceptionally good, so that a filter could be placed at the input if required and its frequency response would not be badly affected. try that with many common 432MHz designs!
Noise figure and gain (can be varied if required) at 435MHz

Yes, I know that attenuators is spelt wrong......

Input match (in yellow) marker 1 at 435MHz and 145MHz with frequency response in blue withe same markers

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