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.

 

[mayidunk]

What you are hearing is the third harmonic of that AM station's carrier frequency. Since, according to your last post, that station is broadcasting at 1050 kHz (or 1.05 MHz), then if you multiply it by three, you'll get 3.15 MHz, which according to what you wrote in your first post, is the SW frequency that you're hearing it on.

The reason why that High Pass filter isn't working is because that transmitter is actually transmitting that third harmonic carrier, along with the main carrier frequency being transmitted. Usually harmonics don't have nearly as much power as the main transmitter frequency because the antenna and the transmitter aren't tuned to transmit at that frequency. That's why these are called spurious emissions, or "spurs." However, if you're close enough to the antennas you'll still pick them up! And since that spurious carrier signal is also Amplitude Modulated, your SW radio will demodulate that harmonic carrier signal just as your AM radio demodulates the transmitter's main carrier signal, though being an harmonic, it usually demodulates it as more distortion and noise than anything, so it usually won't sound good at all.

If you're interested, here's the link to an online, RF harmonics calculator:

RF Harmonics Calculator | formula,equation for RF Harmonics

This page covers RF Harmonics calculator.The formula/equation for this RF Harmonics calculator is also mentioned.The frequencies which are integer multiple of input frequencies are known as harmonic frequencies.

www.rfwireless-world.com

 

[hanlonmi06]

That's help info, thank you!

I literally reverse engineered this 'calculator' a couple weekends ago and I kind of forgot to post. I spun the dial and have found spurs all the way up past 15mhz on the primary radio/antenna that prompted all this. I can replicate the test on other radio/antennas and essentially get the same result. If I'm on my tower repairing/installing/maintaining anything I can look to my south east and see the marker lights on the towers for the station. Daytime is a bit rough as, according to online sources they are at 10kw. The nighttime power does drop and I can tell a difference.

In this scenario, is this to be expected to have legible spurs nearly 20mhz up the band at this range, 2.7miles to be precise?

 

[mayidunk]

I'm glad I could be of help. You might also be able to help yourself, as well as that station by contacting them about this, as they may not be aware of it happening. Their transmitter tossing spurs like that indicates that they, indeed, have a problem that must be looked at. I'm sure they would be more than happy to hear from you, as they can then figure out what's causing it, and fix it before something worse can possibly happen. Their transmitter tossing spurs could be an indication of something failing. Letting them know about this now just might prevent a more damaging failure from occurring down the road!

 

[hanlonmi06]

I suppose that is ultimately what I am trying so suss out. I do not want to waste a professionals time. I don't want to be the hobbyist who is now upset because they moved close to their transmitter site and is now butt hurt because of "interference".

So this was two fold, to learn more about the phenomenon I am experiencing, and then if there is something to be done, either on my end with a filter or if this indicates a reasonable cause to reach out to the station. Personally, I think it would be really cool to meet the station engineer!

As an aside, back in college, the local AM/FM station assistant engineer was my advisor and I got to tag along one night to the station and get a tour of the whole thing. Ill never forget standing near the main mast tuning shack and waving a florescent bulb around while the transmitter was still on. Mind- blown...lol

 

[mayidunk]

Actually, you'd be doing them a big favor! I'm not sure if your in the US, but FCC regs (47 CFR Part 73) pretty much stipulate that they cannot allow spurious emmissions that directly interfere with other radios at frequencies outside of their assigned carrier frequency. This describes what is going on with you. If they continue tossing those spurs, the FCC can, and will, shut them right down until they get it fixed!

Don't worry about them thinking of you as a pesky amateur operator who moved in too close to their antennas. Instead you'll be saving them a lot of heartache. Who knows, the station manager might even take you out to lunch!

Just call them ASAP, don't put it off. They, and you, will be glad you did.

 

[dlwtrunked]

What you are hearing is the third harmonic of that AM station's carrier frequency. Since, according to your last post, that station is broadcasting at 1050 kHz (or 1.05 MHz), then if you multiply it by three, you'll get 3.15 MHz, which according to what you wrote in your first post, is the SW frequency that you're hearing it on.

The reason why that High Pass filter isn't working is because that transmitter is actually transmitting that third harmonic carrier, along with the main carrier frequency being transmitted. Usually harmonics don't have nearly as much power as the main transmitter frequency because the antenna and the transmitter aren't tuned to transmit at that frequency. That's why these are called spurious emissions, or "spurs." However, if you're close enough to the antennas you'll still pick them up! And since that spurious carrier signal is also Amplitude Modulated, your SW radio will demodulate that harmonic carrier signal just as your AM radio demodulates the transmitter's main carrier signal, though being an harmonic, it usually demodulates it as more distortion and noise than anything, so it usually won't sound good at all.

If you're interested, here's the link to an online, RF harmonics calculator:

RF Harmonics Calculator | formula,equation for RF Harmonics

This page covers RF Harmonics calculator.The formula/equation for this RF Harmonics calculator is also mentioned.The frequencies which are integer multiple of input frequencies are known as harmonic frequencies.

www.rfwireless-world.com

Harmonics can also be generated from the fundamental by other loosely contacting metal near the transmitting antenna or other non-linear conductors in the antenna paths when there is a strong signal. (I used to receive an aeronautical beacon on 362 kHz that was nearby by putting a diode in series with the antenna and tuning to 724 kHz (this was a long time ago before receivers were easily found to tune 362 kHz.)
Two things to look at (he/his - original poster:
1. Does he use any lightning protection. Some of those use diodes. Try removing that.
2. If he travels mobile around with your current receiver or another, how does the signal change. Is it strongest near the transmitter or somewhere else?
3. What is his receiver and antenna?

 

[hanlonmi06]

US resident, S.E. Michigan area.

dlwtrunked- i was unsure if you were directing those points to me, but if so:

-The lightning protection that would be in play in my tests are the in-line gas tube discharge style, i am not aware of any diodes present in those devices.

-The only traveling test I performed was while driving home from work one day with my Alinco DX70/Tarheel II antenna tuned to 3.150. As I got into the area near my house I didn't pick anything up. I have about 170ft of driveway from the road to my garage. As I pulled into my driveway I still detected nothing, but as I approached the house, the station suddenly came up in signal and was nearly fully quieting when parked on the pad at the house. I really haven't had time to drive around the area and see if there are detectable nulls or peaks or anything, but it was really weird going less than 200ft and going from detecting nothing to +20 on the signal bars and full quieting/no static.

-i get the same phenomenon on multiple radios and antennas. all similar detections on the harmonics of 1050.

I am searching for contact info today and I will send an email as a start.

 

[dlwtrunked]

US resident, S.E. Michigan area.

dlwtrunked- i was unsure if you were directing those points to me, but if so:

-The lightning protection that would be in play in my tests are the in-line gas tube discharge style, i am not aware of any diodes present in those devices.

-The only traveling test I performed was while driving home from work one day with my Alinco DX70/Tarheel II antenna tuned to 3.150. As I got into the area near my house I didn't pick anything up. I have about 170ft of driveway from the road to my garage. As I pulled into my driveway I still detected nothing, but as I approached the house, the station suddenly came up in signal and was nearly fully quieting when parked on the pad at the house. I really haven't had time to drive around the area and see if there are detectable nulls or peaks or anything, but it was really weird going less than 200ft and going from detecting nothing to +20 on the signal bars and full quieting/no static.

-i get the same phenomenon on multiple radios and antennas. all similar detections on the harmonics of 1050.

I am searching for contact info today and I will send an email as a start.

Your 2nd traveling item is important. This would indicated a good likelihood your problem is originating on your property somehow. Any large metal objects on your property. Are there other antennas present?(what are they connected to?). If you disconnect any other unused antennas and see if it makes a difference? I you can get the signal on a small loop, direction finding may help. This is the sort of problem where any/all remote possibilities should be considered. Good luck and let us know if you find the cause.

 

[mayidunk]

Harmonics can also be generated from the fundamental by other loosely contacting metal near the transmitting antenna or other non-linear conductors in the antenna paths when there is a strong signal. (I used to receive an aeronautical beacon on 362 kHz that was nearby by putting a diode in series with the antenna and tuning to 724 kHz (this was a long time ago before receivers were easily found to tune 362 kHz.)
Two things to look at (he/his - original poster:
1. Does he use any lightning protection. Some of those use diodes. Try removing that.
2. If he travels mobile around with your current receiver or another, how does the signal change. Is it strongest near the transmitter or somewhere else?
3. What is his receiver and antenna?

I'm glad you piped up with this information! It didn't even occur to me to suspect local influences possibly generating harmonics in his receiver. His saying in a later post that he wasn't receiving that station with a portable radio until he actually got near to his house, also sounded a bit strange to me. So, thanks for stepping in, and possibly sparing him, and that station, from a wild goose chase. Hopefully he finds the culprit, or if not, can at least take his receiver to a remote location, and see if he's still getting those spurs.

RF can be wild stuff!

 

[mayidunk]

US resident, S.E. Michigan area.

dlwtrunked- i was unsure if you were directing those points to me, but if so:

-The lightning protection that would be in play in my tests are the in-line gas tube discharge style, i am not aware of any diodes present in those devices.

-The only traveling test I performed was while driving home from work one day with my Alinco DX70/Tarheel II antenna tuned to 3.150. As I got into the area near my house I didn't pick anything up. I have about 170ft of driveway from the road to my garage. As I pulled into my driveway I still detected nothing, but as I approached the house, the station suddenly came up in signal and was nearly fully quieting when parked on the pad at the house. I really haven't had time to drive around the area and see if there are detectable nulls or peaks or anything, but it was really weird going less than 200ft and going from detecting nothing to +20 on the signal bars and full quieting/no static.

-i get the same phenomenon on multiple radios and antennas. all similar detections on the harmonics of 1050.

I am searching for contact info today and I will send an email as a start.

First, I apologize if I sent you on a wild goose chase with this. It just didn't occur to me, at first, that something around the house might have been causing this. However, after reading what dlwtrunked had written, plus the post you made about how you didn't get anything at 3150 on your portable until you got near the house, I have to agree with dlwtrunked, that the spurs may actually be coming from somewhere around your house.

I'm guessing that RF from that AM station may be inducing currents in two loosely connected pieces of metal, causing them to create sparks that are re-radiating the carrier, adding an additional mixing product into the front end of your receiver, which may be causing the spurs to be generated internally.

I'm going to keep watching this thread. Please post with whatever you happen to find.

Edit: After re-reading what I just wrote, I realize that it's probably obvious to everyone that this is likely the case, and that what I just wrote is a bit pedantic. I haven't thought about stuff like this in over 50 years, and I'm kind of re-learning things as I go along. So please excuse me if I'm sounding like a newb, because I kinda am to a degree!

 

[hanlonmi06]

no apologies necessary/no wild goose chases! i had kind of let this slide on terms of a priority and really had to remember that day i drove up with 3.150 tuned on the trucks rig. I'm talking, it went from no indication of anything there to coming right up out of the noise to full quieting as I pulled up to the house. It was stated in the beginning of the thread to do this portable test, but i really now understand the importance of doing this, so if anything I apologies for not heeding the advice sooner.

dlwtrunked- to your point, i do have the tower behind the house and there is definitely an "antenna" farm there.

I think I will start with driving around the area and document the results and kind of keep making closer rings, depending on what I pick up, with the house essentially the bulls eye. Then try to make a plan on how to isolate things if/when i determine the interference is more local to my location, as opposed to actually coming from the AM broadcast site.

 

[mayidunk]

Thanks. And, good luck with the "fox hunt!"

 

[WB5UOM]

You mentioned your location , Im wondering if you are in the direction of maximum radiation. You say you have a Tower, I may have missed it but how tall is it?
It might be acting as a incindental radiator (fcc term) and may be re radiating the signal causing you isdues.
only a guess , but I have had a little experience with AM issues thru the years,as well as having some lmr stuff on a AM tower .
The maximum radiation is looks to be on the map about 350 or so degrees

 

[WB5UOM]

from fcc license info

 

[dlwtrunked]

no apologies necessary/no wild goose chases! i had kind of let this slide on terms of a priority and really had to remember that day i drove up with 3.150 tuned on the trucks rig. I'm talking, it went from no indication of anything there to coming right up out of the noise to full quieting as I pulled up to the house. It was stated in the beginning of the thread to do this portable test, but i really now understand the importance of doing this, so if anything I apologies for not heeding the advice sooner.

dlwtrunked- to your point, i do have the tower behind the house and there is definitely an "antenna" farm there.

I think I will start with driving around the area and document the results and kind of keep making closer rings, depending on what I pick up, with the house essentially the bulls eye. Then try to make a plan on how to isolate things if/when i determine the interference is more local to my location, as opposed to actually coming from the AM broadcast site.

Make sure all grounds for towers/radio are "tight". Then disconnect all antennas except the one you are using. Is there any other large metal objects near like a wire fence or metal roof?