Dr. Gerald N. Johnson wrote:
> On Sun, 2007-04-22 at 16:22 +0000, John B. Egger wrote:
>> 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.
>>>
>
>>>
>>>
>> 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
>>
> Seeing the problem cured with the dummy load points to the antenna. You
> need to either reduce power or move the antenna. You are getting plenty
> of RF exposure that close to the antenna as the computer is detecting.
> USB bandwidth includes 40 meters so a choke on the outside of the cable
> may not have effect.
>
> Look to Mouser, www.mouser.com for more toroids.
>
> 73, Jerry, K0CQ
>
Not so much the antenna, though that could be the source if it is close
by, but more likely the feed line. Is your antenna properly balanced
so that there is no current flowing on the outside of the coax --
assuming you are using coax? If not, you may need a balun at the feed
point or possibly a "1:1 current balun" ("unun") in the shack.
Ferrites on the computer wiring may help -- I generally use 6-8 turns on
type 43 cores. This helps to suppress computer to receiver interference
also.
I haven't had a problem with interference to the computer, even running
QRO. But you've got minimize RF in the shack.
73 Martin AA6E
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