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Old 20th Jan 2023, 4:15 pm   #172
Ian - G4JQT
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Join Date: Jun 2004
Location: Reading/Fakenham, UK.
Posts: 1,320
Default Re: Questions on 160/80 metre AM transmitters.

I don't think anyone has come to grief over the harmonic output of an AT5. It's unlikely to interfere with significant services, although it probably won't meet modern harmonic suppression requirements, but for amateur radio those seem fairly vague anyway.

From Ofcom - UK AMATEUR RADIO LICENCE
Section 2
Terms, conditions and limitations:

The Licensee shall ensure that:
(a) the emitted frequency of the apparatus comprised in the Radio Equipment is as
stable and as free from Unwanted Emissions as the state of technical development
for amateur radio apparatus reasonably permits; and
(b) whatever class of emission is in use, the bandwidth occupied by the emission is
such that not more than 1% of the mean power of the transmission falls outside the
nominal modulated carrier bandwidth.

Unless I'm mistaken, that means the surprisingly low harmonic attenuation of only 20dB for amateur equipment is sufficient, although I'd want anything I built to have harmonic and spurious suppression to be at least 30 dB!

See here: https://www.ofcom.org.uk/__data/asse...teur-terms.pdf
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