Thread: AM radio noise
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Old July 24th 03, 12:56 AM
V W Wall
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rcm wrote:

That won't work. I try to run a battery one near the computer and getting
within 5 ft generates interference. It is frequency dependent so it is much
stronger in the lower AM band.

Use Internet radio to listen I guess.


There are two kinds of RF interference, conducted (usually through the
power lines), and radiated, directly through the air. PC cases are
supposed to shield against radiated interference, but openings in the case,
poor contact between side panels, etc. can negate this. As w_tom says,
the PS should have line filtering for conducted noise. (The FCC requires
units sold in the US to pass tests for this.)

All switching power supplies generate RF interference over a
fairly wide band. Even when "off", the ATX PS has a stand-by supply
that is constantly on when line power is supplied to the unit.

Since a battery receiver still has problems, it is a radiated RF
signal that is the culprit. You might try a better ground on the
computer case than that supplied by the line cord. Check for any
openings other than those required for air flow, and make sure these
have metal grills.

Wrapping the receiver in aluminum foil grounded to a water pipe,
might be a brute force way of stopping it's reception of the PS
radiated energy. You would then need an external antenna connected
by a shielded co-ax, as someone has suggested.The PS generated noise
is usually at about 40Khz, but it has strong harmonics well into
higher bands.

Virg Wall
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