If you guys think the computer noise is bad on 160, you should hear what it
does to VHF bands. It's realy hard to deal with both ends of the spectrum at
the same time because what works for 160 will probably not work for VHF and
vice versa. This topic is timely for me because I've been trying to re-build
the old 2 meter EME station and have been having difficulty dealing with the
show stopping computer noise.
Some things I've discovered the relate to both ends of the spectrum:
CRT monitors are generally worse noise producers than CPU's. It's easy, but
expensive, to fix. LCD monitors are extremely quiet. I recently purchased a new
HP LCD and I cannot find any detectable noise from it in any part of the
spectrum I've listened to.
ADSL modems and routers are also bad as has been reported here before. I have
2.4 GHz wireless service here and a Lynksys cable router. That combination is
quiet on topband but does make some noise on VHF. Worse is the ADSL sounding
noise coming from a produce packing plant about 1/2 mile away. When they start
up in the morning, the entire 75 meter band just disappears!
Much has been said about ferrite solutions, but they have been a big
disapointment for me. I have NEVER had a snap on type of core make any
difference on any frequency. One piece cores sometimes help, but it takes a
dozen or more to raise the impedance enough to be effective on 160, so that's
usually not practical.
Desktop CPU's vary widely but in general the older "commercial grade" boxes are
quieter than the newer consumer cheapies. I have a Compaq Deskpro XL575 that is
virtually perfect. Unfortunately it's not fast enough to run todays software!
Some folks have told me the answer is a loptop. Others have said they can't
find one that is as quiet as their desktop. It's too expensive for me to
experiment with that option. I think they are better on the low bands primarily
because of the LCD display.
Integrated line filters / ac connectors have been mentioned but that doesn't
always work either. The replacement CPU for the retired Compaq had a cheap
common mode filter installed in the ATX power supply. I replaced the AC
connector with a good integrated common mode filter and saw no improvement at
all on VHF. Even with all the external cables disconnected, except for AC
power, the noise kills the 2 meter band. I even cleaned the paint off the
cabinet so the pieces would make better contact and shielding with no effect!
Since I failed to check the "before" noise on 160, I can't say if it made any
improvement there.
Moving the RX antennas away from the house/shack seems to be the best way to
deal with the problem. Assuming you have acres to work with, coax is cheaper
than other fixes on the low bands. Not so on VHF.
Results of my efforts are mixed. On 160 my locally generated spurious noise is
low enough not to be a problem. Noise from sources off the property which I
have no control over seem to come and go and are sometimes bothersome depending
on which RX antenna I'm using. Nothing has been a show stopper yet. On VHF I
have made no progress at all and if I can't figure out some eccomomical fix,
the EME effort will have to be shelved. I'm waiting for someone to come up with
a magic bullet!
Too bad there is no way to go back in time to the period when you didn't need
computers to operate! Progress is a bitch!
73,
Larry - W7IUV
http://w7iuv.com
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