I have also found that some keyboards are more susceptible to RF than
others. I don't know why, but there are definitely differences.
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
Above is a link to a great article about common mode filter chokes, and
although most of it is aimed at balun chokes used for received noise
reduction, there is a lot of general knowledge about ferrite chokes in
general, including how to buy FT-240-43's for $5 in lots of 50. A common
mode filter right where the keyboard gets connected to the computer, as well
as one on the power cable, may be what's needed here.
Ron N6AHA
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
To: <tentec@contesting.com>
Sent: Thursday, October 26, 2006 8:02 AM
Subject: Re: [TenTec] RF gets into computer
On Thu, 2006-10-26 at 09:56 -0400, John K Gotwals wrote:
When I operate on 75 meter SSB with my Orion, my computer beeps and
disconnects/reconnects my USB connected keyboard. Note that I do not have
this problem on 40 meter SSB. My computer is located on the second floor
of
a brick house, and one end of my dipole is about 15 feet from my shack.
>From comments made by others on this list, I may have to put RF filters
>on
the cables and wires connected to my computer. I am contemplating the use
of
Amidon FT-240-77 ferrite toroids, which have an I.D. of 1.4 inches and
cost
$9 each. If I buy in quantities of 10, is there a cheaper source for this
toroid?
Any comments or suggestions on this problem would be appreciated.
Look at Mouser (www.mouser.com) for Fair-Rite EMI suppression Ferrite
Cores. Perhaps something like a split core in Material 31,
623-0431164181. It will fit over a half inch diameter cable for $4.
Where the cable is smaller and since you don't have to thread the cable
and connector through the hole in these split core parts you can go to
something like the 623-0431134951 that has a .200 hole for $1.47. If one
isn't a full cure, you can apply several at that price.
Pick something with high permeability and some rated impedance at 75
meters if possible. Those rated only at VHF won't do much at 75 meters.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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