[Elecraft] Re: Elecraft Digest, Vol 16, Issue 11

[John J. McDonough]

- Original Message - 

Date: Wed, 10 Aug 2005 08:03:59 -0400
From: tom.w3qs [EMAIL PROTECTED]
Subject: [Elecraft] Interference from Computers
To: 'Elecraft Reflector' elecraft@mailman.qth.net


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 WB8RCRhttp://www.qsl.net/wb8rcr
didileydadidah QRP-L #1446 Code Warriors #35

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Re: [Elecraft] Re: Elecraft Digest, Vol 16, Issue 11

[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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