HFU HF Underground
Technical Topics => Equipment => Topic started by: joczo on December 09, 2022, 1508 UTC
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Hi guys,I have a Pi 4 laying around,and I'm thinking about putting out a beacon with it.
Anyone did it before?
I've read it can do a couple 10mWs,with a nice antenna it should be an interesting thing to hunt in openings,maybe in the ISM bands,or somewhere on HF.
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The Pi can generate a square wave, and AFAIK, plenty of harmonics to go with that square wave.
You are likely going to want (and need IMO) a bandpass filter between the output and antenna.
I have no real idea of the output impedance at the Pi connection, but given the low power, I would not be too concerned about closely matching it. Given the few mWs of power contrasted against feedline and matching losses, I would look at placing the Pi and filter as close to or even right at the transmitting antenna feedpoint if possible.
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I've digged through a couple sites and youtube videos,and things did not get much clearer ;D
Some states the 10mW range is correct,while others say it's way over in the 50mW range,and with no antenna the signal went 200m far.
As far as I know the output is between a sinewave and a squarewave,it is done with messing with the original squarewave's harmonics to get as close to sin.
An lpf would be ethical at least for on air plans,maybe my first try will be wspr,as there's 2 youtube videos showing it got pretty far on hf with only the Pi and a resonant antenna.