It is unusual for AM BCB signals on a 10 khz raster to produce signals
every 5 khz.
It is relatively simple to insert a MW rejection filter in a RX ant loop
which should alleviate or cure the problem without having it affect 160m
signals. For example:
http://www.cliftonlaboratories.com/z10020_am_medium_wave_band_reject_filter.htm
or https://arraysolutions.com/Products/bcb_filters_top1.htm
Filters that you can transmit thru are also available such as:
https://arraysolutions.com/Products/BCB%20RF%20Filters.htm
73 Don
VE6JY
On Tue, Mar 4, 2014 at 2:21 AM, Gary Smith <Gary@ka1j.com> wrote:
> I've been plagued by a problem I have finally identified but now need
> help in resolving. I thought it was birdies but realized it had an
> external component when I removed my antennas and they went away.
>
> I'm in a location where I can't put up a tower but have made
> extensive use of wires in trees and use my 160M Inv-L for 160, 20,
> 15, 12 & 10 meters. the 80M mostly vertical wire also serves for 80,
> 17, and 12 meters.
>
> I have been hearing birdies on 18 meters for a long time but recently
> I bought a P3 to fit the K3 and now can see much more than my alone
> ears noticed before. I only used CW and never listened to the signals
> and only bypassed them. When I had the 160M ant in line & switched to
> 18M, I saw lines 5KHz apart on the P3. Usually I only have the 80M
> antenna in-line on 17M so this was a real discovery for me. Seeing
> that the interference was audio I listenbed on AM & could hear audio
> which using the 80M ant & narrow CW filters, I never had before. With
> the 160M antenna what used to be an irritation was now overwhelming
> interference to reception. And what I thought were birdies were the
> centers of the carrier on regularly spaced narrow AM signals
> generated in the circuitry.
>
> One station was an AM station from Puerto Rico and the other I never
> did listen long enough to, to hear the call but was stateside.
> Switching in the 80M antenna makes the lines on the P3 far less
> aggressive and switching to a 30M vertical, I see no lines
> whatsoever.
>
> I took two waterfall screenshots from the P3 and birdie1.jpg is
> showing 11KHz on each side of center and birdie2.jpg shows 100KHz on
> each side of center. Each line is 5 KHz.
>
> http://doctorgary.net/birdie1.jpg
> http://doctorgary.net/birdie2.jpg
>
> These are the worst on the transmit antenna but also am hearing them
> to a lesser extent on the HI-Z Triangular antennas as well.
>
> It seems like I should have a filter in line to block the BCB signals
> but then that would block 160 signals as well. I use the HI-Z for
> lowband work and certainly don't want to block those signals & the
> same goes if I put a filter in the coax for my transmit antenna.
>
> Any suggestions of some kind of filter so I can get rid of these?
>
> Gary
> KA1J
>
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