Subject: Re: [44net] Raspberry Pi - FM transmitter From: David Ranch amprgw@trinnet.net Date: 12/11/2013 04:49 AM
To: AMPRNet working group 44net@hamradio.ucsd.edu
Hello Tom,
One of my elmers tried setting something similar up for WSPR but even with adding the various filters, the harmonics on the higher frequencies were very significant and went well out of the HAM bands!
Well, the article says that the harmonics must be 43dB down to meet FCC regulations, or maybe 40dB when reading the complicated if-then-else-if sentences in those paragraphs (why not use a table?).
That is quite harsh, for a 10mW transmitter. 1uW is not a lot of power. A homeplug device probably transmits a lot more than that.
Rob
Hello Rob,
That is quite harsh, for a 10mW transmitter. 1uW is not a lot of power. A homeplug device probably transmits a lot more than that.
Yeah.. I hear what you're saying but I was really surprised when he even disconnected the antenna, I could still hear his HF signal through I think it was the 7th odd harmonic 360 ft away! He's recently been thinking that part of the problem was that ribbon cable connecting the Rpi to the filter board but he hasn't tested out that theory yet.
None the less, a Rpi makes a pretty amazing WSPR beacon for cheap!
--David KI6ZHD
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David Ranch -
Rob Janssen