15.370AM interfering with 20M in MN

Mike Webb KC0YHM

Is this possible or does it indicate an issue with my radio?
I have been plagued by a mystery noise on 20m.
After much patient 'hunting' I'm pretty sure it's associated with 15.370AM...Havanna Cuba. Their signal in MN in the morning is between 20 and 40 over.
I've noticed changes in the interference that aligned with changes on 15.370.
I'm a technology user not an engineer so I'll appreciate expert insights.
All the best.
Mike Webb
KC0YHM MN & FL

Ken - NM9P

I have posted about this station in the past.  At one point they were 20 KHz wide with audio that appeared to be a badly implemented digital audio, or perhaps poorly balanced digital amplifiers.

Their signal had very sharp transitions in the audio and was activating my WNB and NB and making my noise floor bounce and dance.  I couldn't run those settings very high at all before it wrecked them.

Be sure that your preamp is off when they are on the air, it will help a bit.  But when they are really strong, they make a mess of noise blankers.

Ken - NM9P

Mike Webb KC0YHM

Hello Ken.
I'm starting to put some pieces together today.
It seems like strong AM signals in the 15mhz area are showing up...as 'modulated noise' on 20m USB for me.  When i tune to 14.3 mhz.... switch to AM... I can hear the AM stations operating in the 15mhz area... It is really annoying.
The first pic is how wide radio havanna was...the second shows how strong it was.
RR on the Preamp...no...its off naturally.

Ken - NM9P

What settings are you using for preamp, WNB, NB, etc?

Mike Webb KC0YHM

Preamp off....WNB at 100%...NB off / NR off...RF gain at about 53%
The NR feature helps some but not much.

Ken - NM9P

You are guaranteed to get WNB pumping and all manner of other trash with strong in band and out of band signals with WNB at 100% on any band. I never run it above 97 on any band, and when there are strong sharp signals on 40 or 20 Meters I must drop it down below that, as far as down to 80. The last few steps between 97 and 100 make a BIG difference in the interaction between strong signals and WNB. Whenever I start getting noise floor and am signals superimposed on other signals in the band, the first thing I do is reduce WNB level. There is often a point you will find where almost one click either way will make the difference between trash and no trash on the signal. Good luck.

Mike Webb KC0YHM

Thanks Ken...appreciate the advice...I will give it a try

ctate243

If it becomes really problematic moving to a 6400 that has a 3rd order preselector on 20m may help keep the gremlins out of your ham bands.  or if its just a problem on 20m you can get a 20M bpf from dunestar/dxe/etc.  that you can switch in line. they are usually around $100 or less for single band.

Ken - NM9P

I think the beast may be tamed by reducing WNB a bit, though if reduced too much the "real" noise reduction may be sacrificed.  It is a bit of an art to fine tune if you want to ride the controls right "on the edge."  but it is possible.  I only have a problem a few times a week when the path to Cuba is extremely good, and Radio Havana is beaming my direction and is about 40-50 over S9.  In those cases, I sometimes need to turn WNB off entirely.  But usually I can reduce it until the noise floor dancing stops.

But indeed, if the problem is severe, then additional bandpass filtering may help.  

Mike Webb KC0YHM

Thanks Chris. I dont have any issues on 40 or 80 m.
Today was the aha day....I was able to verify that my noise was associated with the AM on 15mhz. I was also able to document that when radio havanna went away around 11am E... so did my noise.... So..do you believe the bpf represents the simplest solution?

ctate243

No problem. FWIW, Ken is right, the WNB will cause issues like this as well, but assuming you have it on for a reason.. if so I would try a bpf.  the preselectors in the newer radios could solve this as well.  the 6300 doesnt have preselectors making you susceptible to out of band qrm... US AM can also be a problem on 160m.

Mike Webb KC0YHM

Ken.. I would call it severe. I need to find a remedy if possible. I can only operate on 20m at this time and they are making it tough for me to keep my headset on! ;->

Ken - NM9P

Try turning WNB completely off. Then add all the attenuation you have on the rig and see if the problem improves. If not, check you coax connections and other antenna connections. You may have a loose connection that is rectifying their signal creating signal distortion inside your own system. I remember about 4 years ago Tim telling of someone who had a bad lightning arrester that was causing all sorts of intermodal/overload type symptoms. Once it was replaced, things cleared up. (I think this may have been on a 160 inverted L and local AM stations were tearing him up.) Le us know what you find.

Mike Webb KC0YHM

That is good information.
I'll ask my brother in law to do a connection check JIC....he can check the easy ones for me...I wont be able to do it personally for a few months...I operate remote 95% of the time. I live in Naples Fl in the winter and Bloomington MN in the summer...neither location allows towers and yagis so my station is built in rural Farmington MN...at a location I rent.
Thanks Ken