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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>
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