[Elecraft] 12 meter K3 RFI from nearby FM station

[Chris Hallinan]

I have a similar problem.  I have a 1KW AM station about 1/2 mile away
(1100W by day, 110W by night).  With nothing connected to the radio, and
even with a 50-ohm terminator on RX Ant in, I can clearly hear the signal
at several places, most prominently at 14.220 MHz. Nothing I've tried,
including expensive filters, shielded cables, etc. has helped.  I get some
relief using a RX Loop antenna basically nulled (broadside) to the tower,
but that antenna is not always the best one for band and/or conditions. :(
 Some frequencies are simply unusable, and it overloads a front end
protector I purchased to try to kill the COR relay clicking when I
transmit, making it unusable.

Chris
K1AY

On Wed, Feb 10, 2016 at 5:53 PM, Fred Jensen <k6dgw at foothill.net> wrote:

> I easily could have misread the original emailed problem, but he included
> the note that this RFI occurred with all antennas [and I guess other
> cables] disconnected which is very strange indeed.  If that is so, then I
> doubt stubs/filters on the antenna circuits would cure the problem.
>
> His list of frequencies might suggest some sort of intermod between
> constant signals, one being the FM carrier, and possibly their harmonics.
> Very strange problem at any rate.  FWIW, and Phil can correct me, but US
> FM/TV stations are usually authorized in EIRP, I think ... we referred to
> KSBY-TV, where I worked while in college, as "Full-power television for the
> Central coast, one hundred thousand watts on Channel 6 in San Luis Obispo"
> on ID's.  That was EIRP, 10 KW to a 10 dB turnstile.  If that's still true,
> it would seem a 2 KW EIRP FM station 2 miles away shouldn't be a big deal.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the Cal QSO Party 1-2 Oct 2016
> - www.cqp.org
>
>
> On 2/10/2016 2:04 PM, Ron D'Eau Claire wrote:
>
>> I agree. Even better.
>>
>> 73, Ron AC7AC
>>
>> -----Original Message-----
>> From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Bob
>> McGraw K4TAX
>> Sent: Wednesday, February 10, 2016 9:18 AM
>> To: elecraft at mailman.qth.net
>> Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
>>
>> An electrical 1/4 wavelength of coax as an open stub at the FM frequency,
>> connected using a T at the receiver input, will notch the FM TX signal.
>> It
>> won't attenuate other frequencies across the ham bands including 6M.  Plus
>> one can transmit with the stub arrangement in place.
>>
>> 73
>> Bob, K4TAX
>>
>
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