[TenTec] RF gets into computer

[John K Gotwals]

RF wise, my situation is not very desirable: My shack is on the second 
floor, one end of a 110 feet dipole fed with open-wire line is 15 feet from 
my computer, the feedline droops some but does parallel the dipole on its 
run to the shack, and I sometimes operate at the kW level on 160 thru 10 
meters.

When I would operate high-power, my computer would beep and the keyboard 
would be disconnected. In addition, I would also hear a hum in the computer 
connected Bose speaker system. The computer keyboard, optical mouse, and the 
Navigator digital mode interface are all USB connected to my computer. My 
system is now clean, and it took very little in the way of filtering to 
clean it up, but it took a fair amount of time to experiment with various 
configurations until I found one that works.

I recommend a four page article titled "RFI Page" at
http://www.aa5au.com/gettingstarted/rtty_rfi
In this article, the author states that he has not had good results with the 
clip-on types of inductors, and that has been my experience also. Ferrite 
toroids and rods seem to work better, and the rods are easier to use with 
cables which already have attached connectors. I purchased 4 inch long 
ferrite rods (part # R-050400-33) from CWS ByteMark
http://www.cwsbytemark.com/ and they did the job for me. Although the 
optical mouse, Navigator interface, and the keyboard all had small circular 
inductors around the cable, the keyboard was being disconnected. I wrapped a 
portion of the keyboard cord, next to the computer, around a ferrite rod, 
and taped the wire in place. I did the same thing for the stereo cord 
running from my soundcard output to my Bose speaker system, but at the Bose 
end of the cord. Now my computer no longer beeps when I operate at the kW 
level, and the hum is absent from the Bose speakers.

One final comment - Although type 33 material is not normally used at HF, 
other more suitable ferrite material does not appear to be available in the 
form of rods.

John, N9JG

= = = = = = Original Message = = = = = =
Date: Sun, 22 Apr 2007 16:22:28 +0000
From: "John B. Egger" <john_egger at comcast.net>
Subject: Re: [TenTec] RF gets into computer
To: Discussion of Ten-Tec Equipment <tentec at contesting.com>
Message-ID: <462B8BC4.7070703 at comcast.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
[snip]
Old thread, but something is exacerbating my problem recently. On 40m CW
the Orion II at full power is now QRM'ing my computer; I had to copy
some traffic by pen and paper this morning because of it.

Two experiments, after wrapping the keyboard cord in three Radio Shack
snap-on ferrite filters: (1) Moving the keyboard about 3' from the
Orion, instead of its usual 1', allows full power keying without
interference, and (2) using a dummy load on the Orion, and then on the
output of the MFJ 993B autotuner, allowed full power without
interference, with the keyboard in its normal place. (Reattaching the
antenna produced the QRM again.)

Any thoughts? I thought perhaps the RFI was from the Orion front panel,
which might explain the moved-keyboard success, and I was surprised to
see the problem disappear with the dummy load.

--John K3GHH
Registered Linux User #291592