Re: Elecraft Digest, Vol 16, Issue 11

[John J. McDonough-2]

----- Original Message -----
> Date: Wed, 10 Aug 2005 08:03:59 -0400
> From: "tom.w3qs" <[hidden email]>
> Subject: [Elecraft] Interference from Computers
> To: "'Elecraft Reflector'" <[hidden email]>

Tom

A few points

More recent computers seem to have less of a problem than older ones.  I
think this is partly because the very high frequencies have their spurs well
above the HF bands, but newer machines are also usually boxed up more
tightly.  There does seem to be quite a bit of difference between different
computer cases, but many cases are very carefully RF shielded. Obviously, if
you leave the side off or you don't replace those little cutouts in the
back, the RF is going to leak.  Cases are fairly cheap anymore, so if yours
doesn't have the little fingers on all the joints to be sure the sheilding
is good, you might consider a new case.

As other have pointed out, the monitor cable or the monitor itself is often
the big culprit.  Going to an LCD can help.  Most cables already have
ferrites so that doesn't help.  Frequently, though, simply changing the
resolution can move the spurs to somewhere they don't bother you.

Another big offender is often the Ethernet cable.  Here ferrites can help,
but for many people the only reason for the Ethernet is to connect to the
Internet.  Often you can simply unplug the Internet while you're operating.
The fancy Cat6 cables can help here, too.

If you have reason to suspect the power supply (and I've never seen this to
be the problem), ferrites on the power cable are likely to go a long way.

Hope this helps.

72/73 de WB8RCR    http://www.qsl.net/wb8rcr
didileydadidah     QRP-L #1446 Code Warriors #35

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[Stuart Rohre]

Another thing about modern computers and lower noise therein, is they use a
10 MHz master clock then dither it, and multiply it to the Gigahertz max
speeds.   Thus instead of a single spur at a frequency, they have the clock
energy spread over a band with each frequency having less power.

And, modern logic families are going to lower voltages, no more 3.5 to 5
volt TTL.  2 volts and less will be used to lessen the swing of voltages.

The dithered clocks may be the biggest improvement to computer noise, since
cabinets are still all plastic.
However, they incorporate tin shields over some critical areas like the
switching power supply and use ferrites and line filters there.

Stuart
K5KVH




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