AM BCB interference, please explain

[hanlonmi06]

I live about 2.7 miles as the crow flies from an AM BCB transmitter site. They operate at 10kw daytime power and 500w night time power, and
I am literally right in their transmitter pattern according to an online radio locator site. I've noticed what I believe to be harmonics up into the shortwave bands on various radios in different parts of my house, using outdoor antennas. I've established what AM channel it is by listening to the actual AM channel on a little portable and "matching" the garbled audio on the given shortwave frequency, and it does seem to change in intensity as they switch over to night time operation.

I've tried some BCB filters in an attempt to mitigate this. What I noticed on this last attempt was that the filter does in fact knock out the AM band itself pretty well. When I put it in line, the Detroit area blow torch sites of 950 and 760 are pretty well knocked down, and full signal without the filter, however, the interference I hear in the SW bands is more or less still there.

Can anyone shed some light on how harmonics and BCB "interference" works, RF wise? Air quotes on the interference as it is a nuisance to me that Id rather not have but I am absolutely not trying to imply or suggest there is a problem at their transmitter site. It wouldn't be so bad if it wasn't a sports talk only station, lol! Does the harmonic I hear in the SW band actually not get affected if I am using a 1.8mhz HPF because its actually an RF transmission occurring 3.150 MHz for example?

 

[dlwtrunked]

I live about 2.7 miles as the crow flies from an AM BCB transmitter site. They operate at 10kw daytime power and 500w night time power, and
I am literally right in their transmitter pattern according to an online radio locator site. I've noticed what I believe to be harmonics up into the shortwave bands on various radios in different parts of my house, using outdoor antennas. I've established what AM channel it is by listening to the actual AM channel on a little portable and "matching" the garbled audio on the given shortwave frequency, and it does seem to change in intensity as they switch over to night time operation.

I've tried some BCB filters in an attempt to mitigate this. What I noticed on this last attempt was that the filter does in fact knock out the AM band itself pretty well. When I put it in line, the Detroit area blow torch sites of 950 and 760 are pretty well knocked down, and full signal without the filter, however, the interference I hear in the SW bands is more or less still there.

Can anyone shed some light on how harmonics and BCB "interference" works, RF wise? Air quotes on the interference as it is a nuisance to me that Id rather not have but I am absolutely not trying to imply or suggest there is a problem at their transmitter site. It wouldn't be so bad if it wasn't a sports talk only station, lol! Does the harmonic I hear in the SW band actually not get affected if I am using a 1.8mhz HPF because its actually an RF transmission occurring 3.150 MHz for example?

I had similar happen when I lived in CT. Instead of being harmonics, it was inter-modulation ("intermod") cause inside the transmitter by that one's antenna receiving another stations signal that then was mixing with its own signal. When I contacted them, they knew about the problem. Inter-modulation/harmonics can also be caused by loose connected metal near transmitters. In these cases, there is nothing you can do to fix the problem, it is theirs. If that is your case, good luck.

 

[EAFrizzle]

If it's actually a spurious emission above the 1.8 m HPF won't affect it. Have you tried checking for spurs with a portable SW both indoors and out? You may still be having overload problems on an outdoor antenna, even at nighttime power.

If they actually have a problem with their xmtr, I'm sure they'd love to address it.

 

[vagrant]

What model receiver is being used?
What is the coax type and length?
Elaborate on the antenna type and configuration.
What AM BCB filter is being used? What brand/model?
Where is the filter at inline and how far is it inline from the receiver?
Is an amplifier or anything else inline on the coaxial cable?

 

[hanlonmi06]

This all started with noticing the phenomenon on my FT990 that I run for ham as well as swl/lw/mw listening when I moved here in 2016. I had a hpf in and out of line on that setup, across some different sw/ham antennas but generally nothing affected the it. I had more or less accepted that this wasn't really surprising once I realized I'm two miles from a 10kw 4 tower beam directed site.

I set up an FRG7700 on my night stand this past summer and have it on separate antennas. I finally started actually using it a lot only recently, and noticed the same phenomenon, so last night I grabbed a different HPF and put it in line and noticed the same thing, whatever I was hearing in the sw bands was still there with the filter in line, but this time I doubled check on the AM band to make sure it actually did something and the AM band was absolutely suppressed. That got me to wonder more about trying to understand what exactly I was dealing with, ie, your folks' reply with indermod, spurious emissions, so thank you, and...this weekend I hopefully will make time to get the specifics of everything as vagrant highlighted, and do some reading up on those two topics, as well as walk with a portable and see what we get.

Essentially, two totally separate radio/antenna/filter setups resulted in the same continuing to hear 1050khz into the sw bands...

I can at least tell you the filter last night was made by SV1AFN, and was in line right at the FRG7700's uhf port on the back of the radio. The antenna is an older "maple leaf studio" end fed multiband shortwave antenna. It actually works pretty well even though its clearly not pro-grade stuff, and has been in the weather well over a decade now. The "ground side" is actually more of an ariel probably 50' long strung over to a tree in the yard from the feed point balun. The overall average height of the whole antenna is between 15-20 feet high, broad side of antenna is facing the AM transmitter site, and the coax run is probably 75-100' of RG6 tv coax, and no amplification.