I found I was getting slight 60 Hz and 120 Hz modulation of signals
received with the Pegasus. This was not noticeable by ear, but
using the Waterfall display of a PSK31 program it was very
obvious on strong signals, with spurious images of the main signal
at +/-60 Hz and +/-120 Hz, each about 20 dB down on the main signal.
This only appeared as MODULATION of incoming signals; there was
no obvious 60 Hz or 120 Hz component in the absence of signal.
This occurred with an Astron RS-20A on the floor next to
the Pegasus, with the RS-20A on the right side of the Pegasus,
separated from it by about an inch.
By placing the RS-20A on the LEFT side of the Pegasus, even
touching it, the modulation disappeared. Using a search coil
to probe the magnetic field around the RS-20A, I found that
at the left side of this power supply, presumably closer to the
transformer, the 60 Hz and 120 Hz magnetic field was at least
10 dB stronger than at the right side of the power supply.
Maybe this potential magnetic cross-modulation within the Pegasus
(and probably most other receivers) is well known, but I'm
posting this in case the information is useful to anyone else.
73
Darrel Emerson, aa7fv.
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