User's Manual

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Appendix C - Dealing with Interference
Electromagnetic Interference
(EMI) is what prevents us from receiving a
clear signal, even when the receiver should be sensitive enough to receive
it. There are many types of interference you can experience with radio
receivers, emanating from both natural and man-made sources.
Natural interference is produced by atmospheric phenomena such as storms
and sun activity.
Not so surprisingly, man-made interference is often worse. Sources include
electric motors, power lines, passing cars, welders, fluorescent lights, fax
machines, computer networks, etc. Receiving antennas should always be as
far away from sources of electromagnetic interference as possible.
One significant source of man-made electromagnetic interference is the
personal computer, and the video monitor in particular. Since the
WiNRADiO G3 SERIES receiver requires a personal computer to operate,
this creates a potential paradox. The WiNRADiO receiver itself is designed
to be substantially immune to PC interference. However, any receiver needs
to be connected to an antenna, and antennas can’t discriminate between
useful signals and interference. The interference from your PC can either
radiate directly to the antenna, or it can be conducted to it along the outer
conductor of the lead-in cable. Even in professional radio receiving stations,
a lot of care and effort is always needed, if this type of self-interference is to
be avoided.
Some computers are worse than others in terms of generated
electromagnetic interference. The worst culprits are usually video monitors,
which radiate radio frequencies at multiples of horizontal deflection
frequencies. These frequencies range from about 30 to 100 kHz, and you
can sometimes hear their harmonics right across the entire shortwave band.
If you find strong signals sounding somewhat like a tractor engine, spaced
between approximately 30 and 100 kHz apart (on modern hi-resolution
monitors, the typical frequency is around 94 kHz), your monitor is most likely
the cause.
To check this, tune to one of the interfering signals, then switch off the
monitor and see if the signal disappears. You could continue using the
WiNRADiO receiver, and live with the fact that some useful frequencies will
be obscured by your monitor’s interference, or you can replace your monitor
with a ‘quieter’ one (modern LCD displays are far quieter than old CRT