AM BCB interference, please explain

hanlonmi06

Member
Premium Subscriber
Joined
Jul 16, 2009
Messages
221
Location
Pittsfield Twp, Michigan
Fox hunt, I like that!

So at this point, I have gathered a few "data points" using my truck setup (alinco dx70/tarheel II) as a sort of field strength meter and listening on 3.150mhz. A sort of pro/con of this is that the TH can be made more and/or less resonant and the DX70 does have a preamp of sorts so depending on how that's arranged i can tune out any semblance of detecting the station up to flat out overloading the crap out of the radio. That said, I have driven around the nearby area and monitored to see what i get.

To answer the question of whether I am in the direction of max radiation: absolutely yes. my home location is definitely directly in the path. more on that in a moment...

To answer how much "metal" is around me: "yes". I have a 36' rohn tower with a 20' tall ground plane at the tippy top so, tower/mast/antenna is pushing 60' tall vertical structure. Tower grounds are bonded to the "grounding electrode" of the service entrance, if that detail matters. The property is 2.5 acres with roughly 2 acres fully fenced in with livestock fencing that's pushing over 1000' linear feet of fencing that does pass within 50 of the tower. Also, there is a fabi-cobbled-Frankenstein 'random long wire' that follows said fence line for roughly 700' that does have a coax feed into the house. Traditional timber structure house with asphalt roofing, aluminum gutters, so yea, there's a lotta "metal" structures to isolate and work through from that perspective.

As for the 4wheel drive field strength meter: imagine the AM transmitter site as the origin at the center point. on a straight line in the direction of max radiation, at 3.7 miles from the transmitter I was able to detect the station on 3.150mhz. On that same line, at 2.7 miles from the transmitter is my home location.

I have been able to detect the station on 3.150mhz in a few other spots around my home location that, for simplicity sake, i would say are all in line with the stations max radiation direction. When i am 'off axis' from that it seems that i cannot detect anything. When passing just shy of a mile directly perpendicular to the transmitter site i did not detect anything.

My assertion at this point is that I can probably predict locations around my area that ill likely pick up an image in the directed beam path. As for my location at home, i really do think that i have a re-radiating phenomena happening as to why when i pull up to the house the station comes right up on the image frequency 3.150. The weather is breaking, so first order of business at home is to do some inspections on the grounding system and make sure from a safety standpoint there's no glaring issues. and from there, try to make some kinda attack plan to ground/isolate things and see if hit the lotto on a perfectly resonate incidental radiator.
 

mayidunk

Member
Joined
Jun 10, 2006
Messages
157
I wonder if the propagation pattern of that AM station is affected by your Rohn tower in some small way? That would be interesting if it did!
 

MikeinDestin

Member
Joined
Nov 21, 2024
Messages
64
Location
Destin, FL
The third harmonic is usually the strongest. If you're ever transmitting on 40M, try listening to your signal on 15M. Of course it's legal to have some harmonics.
 

WB5UOM

Member
Premium Subscriber
Joined
Sep 5, 2022
Messages
466
I think you are on the right track
It probably would be a pain, but removing antennas/tower one at a time might be helpful AND that 700 ft longwire would be my 1st pick to go.
 

EAFrizzle

Member
Premium Subscriber
Joined
Jun 2, 2019
Messages
241
I think you are on the right track
It probably would be a pain, but removing antennas/tower one at a time might be helpful AND that 700 ft longwire would be my 1st pick to go.

I had to give you a 'like' because I agree, but it was painful. But that longwire really is the place to start. Perhaps converting it to a loop or helical loop might help. I'd hate to lose a good antenna if I could avoid it.
 

WB5UOM

Member
Premium Subscriber
Joined
Sep 5, 2022
Messages
466
Well I meant for it to be take it diwn to see if problem goes away..
if thats not it, put it back up
BUT likely they will all have to come down to see for sure.
 
Top