Hi,
sometimes I think it can be interesting to see in practice what a
transmitted product is like and whether it is troublesome... Some time ago I
measured the spectral output of a Mk1 FT690 (a 6m all mode portable). The
second harmonic was at quite a high level, I believe it was only
about -40dBc...
Certainly the level was unusually bad, where I worked at the time we had a
log periodic so I ran the radio into that and tuned around another receiver
to a broadcast station coincident with the second harmonic of the FT 690...
the aerial was less than 100ft away from the other. Surprisingly with the
field strength of the broadcasters in the London area the second harmonic of
the FT 690 was lost under their signals. So although we may strive for
perfection a technically poor transmitter is not automatically a problem, it
depends to a great extent on what those products are competing with!
With transmitted IM products it looks like a "spectrum occupancy" plot
integrated over a reasonable sample period using a realistic modulation
source makes a lot of sense, so that the power supply and alc get to see
some dynamics. I believe though cannot prove that a lot of the third order
products we generate are within our nominally "occuppied" bandwidth.
Regards David G0FVT
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