Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!husc6!bunny!js07
From: js07@GTE.COM (Jack Shaio)
Newsgroups: comp.sys.ibm.pc
Subject: FCC Class A and Calss B PCs.
Summary: all is not lost
Message-ID: <7491@bunny.GTE.COM>
Date: 1 Sep 89 13:53:57 GMT
Organization: GTE Laboratories, Waltham, MA
Lines: 24

A while ago I posted an article asking about whether it was possible to use
a Class A PC at home (an ALR 25Mhz). Class A's produce higher levels of
radio frequency interference (RFI) than Class B's and are only licensed for
use in commercial environments. Most people answered to go ahead, it doesn't
matter. Well...

I tried an ALR at home, and it interfered heavily with TV channels 9-13.
A 25 Mhz machine has a 50 Mhz circuit, which also emits RFI at multiples
of 50 Mhz. Channel 9 is around 100 Mhz.

There turned out to be a simple way of solving this. Most RFI comes from
the PC to monitor cable. You can get ferrite chokes from an electronics
supply store. Wrap the pc to monitor cable 3 times around the cores, and
done. High quality cores will absorb only a selected range of frequencies;
hence you should get low quality ones. They can also be gotten from a
burned out TV. After this, it was possible to use a portable TV within
a few feet of the pc with no interference.

thought someone would like to know.


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