I didn't notice that you said you get it with no antenna. That does make
it more complicated.
The fact that you get it on the main but not the sub points to the T/R
switch, since the sub receiver does not go through the T/R switch if the
sub is set to AUX to use either the non-transmit antenna or the BNC
input. If you don't know, turn on the sub and hold BSET -- you will see
either MAIN or AUX.
73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/
On 10 Feb 2016 19:10, Jon Zaimes wrote:
Thanks for the tips.
Any filter likely would have to be inserted internally, since I am getting
this RFI without any antennas connected to the radios.Unless it is coming in
on the 12v power cord, which is still a possibility. I only tried a couple
ferrites and they may not have been the right one for choking out the FM
signal.
I did observe that I am only hearing it on the main receiver in my K3 that
has a sub RX, but not on the sub RX. Also, while checking for this, and then
going back to the main RX, the RFI signal on the main RX was greatly
reduced. Perhaps a relay contact issue. It is still just as strong as
previous on my other K3 (which has no sub RX). Toggling through PRE and ATT
did not eliminate it (though changed signal level as it would for any
signal).
73/Jon AA1K
-----Original Message-----
From: Elecraft [mailto:[email protected]] On Behalf Of Vic
Rosenthal 4X6GP/K2VCO
Sent: Wednesday, February 10, 2016 10:20 AM
To: [email protected]
Subject: Re: [Elecraft] 12 meter K3 RFI from nearby FM station
Jon,
I had a similar problem with a 50 kW AM BC station a few miles away. It
turned out to be strong enough to override the bias in the K3's T/R switch.
I built a high-pass filter which solved the problem.
You would need a low-pass filter in your case. Make sure it can handle 100w,
because you must connect it in the main antenna path -- the RX in/out path
is before the T/R switch.
73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/
On 10 Feb 2016 16:58, Jon Zaimes wrote:
I had been noticing some RFI on 12 meters for some time that I
initially had thought was power line noise. My use of 12 meters is
seldom so it wasn't very high up on the list of things to track.
When I was reminded of it while listening for VP8STI recently, I did a
little more snooping and realized it was actually splatter from a BC
signal at the low edge or slightly below the 12 meter band, centered
about 24.89 mHz but audible from 24.87-24.91 mHz.
The distorted splatter is audible as a BC station, all talk, no music,
but not clear enough to decipher any ID.
A few days ago I decided to try to pinpoint the source, so listened to
the RFI on one ear while scanning the AM and SW bands with the sub RX
on the other ear. But I could find no matches, though did find the
splatter popped up centered on these additional frequencies:
813 kHz
996 kHz
2.820 mHz
3.626 mHz
19.4 mHz
Figuring it must be an FM BC station, I started going through a list
of Delaware FM stations and on the third one, 91.1 mHz, matched the
audio peaks to my splatter. Further research determined this was a
public radio station with a transmitter on a commercial tower just a half
mile west of my QTH!
While I of course was aware of the tower, which I knew to carry a
couple of cell sites and trunking radio, I hadn't been aware of the FM
station, which has apparently been there about 2 years. FCC data shows
it has 2.1 KW ERP. I had not had any previous issues with the site over
the past 17 years.
Thinking that mixing or rectification might be produced either at the
TX site or on my own QTH, I decided to track with my mobile rig, an
IC-706 MK2G. But there was NO evidence of the splatter on the 706.
Further debugging found that I was hearing the same splatter on BOTH
of my
K3 radios (no. 3021 and 3057). Even when ALL cables are removed (only
the power lead connected). Grounding or ungrounding made no change. I
tried the radios on a battery but still had the RFI. Tried some
ferrites on the power lead but no change.
So I'm thinking now there's some internal mixing in the K3 going on,
and wondering if any others have had similar issues and found any
solution.
73/Jon AA1K
Felton, Delaware
www.aa1k.us
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