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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