Hello,
Kevin Ravenhill wrote:
I have found out the hard way that the rectifier diodes in some power
supplies can generate truly enormous amounts of harmonic hash at these
frequencies.
Not only on LF! Sometimes it is a problem on HF too. Many direct conversion
receivers suffer from hum problems when powered from a mains supply, no
matter how well regulated the supply is. There is more hum when using
unbalanced antennas. The reason seems to be that local oscillator energy
is leaking out on the antenna and some of this signal finds its way back to
ground through the PSU rectifier. The signal is "chopped" by the rectifier
diodes at the mains frequency (much like a sub-harmonic mixer) and the
result is hum sidebands.
The problem can often be solved by putting 0.1 uF capacitors across each
rectifier diode.
73 de Johan, SM6LKM
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