[Elecraft] Interesting K3 QRM problem

[Charlie T, K3ICH]

I'd go for a series tuned trap to ground.  That would seem to the least 
disruptive, if that's the right word, to your system.

I remember working at Vectrol in Rockville MD fairly close to an AM transmit 
antenna site.  We designed & built big three phase SCR controllers and of 
necessity, had to isolate any oscilloscope's chassis ground.    You could 
always see the low level AM signal on the scope.  A similar trap worked, but 
it would have required dozens of them to cover all the scopes etc.. 
Luckily, when you're looking a 60Hz waveforms, we just ignored the BCI.

73, Charlie k3ICH


----- Original Message ----- 
From: "Vic Rosenthal 4X6GP/K2VCO" <k2vco.vic at gmail.com>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Thursday, October 23, 2014 6:58 AM
Subject: [Elecraft] Interesting K3 QRM problem


>I live about 3.3 miles from a 50 kW BC station on 1080 kHz. It is on 24 
>hours a day, transmitting in Arabic, not that that matters.
>
> I have two antennas: an R8 vertical and a Pixel Loop receiving loop.
>
> With either antenna, I hear a wideband noise on my K3 that is synchronized 
> with the program material of the BC station on the 14, 10 and 7 MHz bands.
>
> I first determined that it was not affected at all by the attenuator in 
> the K3. So I assume that it is not caused by front-end overload in the K3.
>
> I noticed that if I listen on the Pixel Loop via the K3's RX ANT input the 
> noise completely goes away when I unplug the R8 from the K3's ANT 1 
> connector!
>
> I also noticed that the noise is reduced when I bypass my amplifier or my 
> SWR/wattmeter, which are connected between the ANT 1 connector and the R8. 
> Reduced, but not eliminated.
>
> I conclude that what is happening is that the BC RF is being picked up by 
> the R8, and the diodes in the wattmeter and the amplifier and the K3 
> finals are creating IMD products which I am hearing. The K3 seems to be 
> the major contributor.
>
> I am thinking that maybe the IMD products are being re-radiated by the R8 
> and picked up by the Pixel Loop.
>
> I tried one more experiment: I have a BC band filter which is used with 
> the MFJ antenna analyzer when there are nearby BC signals. Sure enough, 
> putting this in series with the K3 ANT 1 connector kills the noise. Of 
> course I can't transmit through it.
>
> Has anyone had a similar problem? I am thinking that the solution is a 
> highpass filter or trap at this spot. I don't operate on 160, so it 
> shouldn't be too hard to make.
>
> -- 
> 73,
> Vic, 4X6GP/K2VCO
> Rehovot, Israel
> http://www.qsl.net/k2vco/
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to pincon at erols.com