FM radio interference on Guard 121.5

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Gator596

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So after months of problem free listening, my local FM rock station on 97.7fm is now suddenly stomping on 121.5 and locking up my scanner. I have to lock the freq out, which sucks, because I occassionally heard some good stuff on it.
I have a few questions I'd like help with...
1) Is this normal, or have I mis-diagnosed the problem? Could it be someone's cordless speakers I'm hearing?
2) My preliminary research points me towards a notch filter to fix this issue. Can anyone suggest a good one?
I'm running a bcd996xt with a d130j on a 35ft tower.
Thanks in advance,
 
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737mech

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FM filter

So after months of problem free listening, my local FM rock station on 97.7fm is now suddenly stomping on 121.5 and locking up my scanner. I have to lock the freq out, which sucks, because I occassionally heard some good stuff on it.
I have a few questions I'd like help with...
1) Is this normal, or have I mis-diagnosed the problem? Could it be someone's cordless speakers I'm hearing?
2) My preliminary research points me towards a notch filter to fix this issue. Can anyone suggest a good one?
I'm running a bcd996xt with a d130j on a 35ft tower.
Thanks in advance,
I think you will be very pleased with the fm scanner filter from PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts works wonders for me.
 

kb2vxa

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Uh oh, a filter may or may not solve your problem, the really big clue is it's a NEW problem. The filter will block the main carrier of the FM station but not the new signal on 121.5 which very well could be a spurious emission from one of the transmitter's frequency multiplier stages, a tower bonding issue or ground fault. Simply put, it sounds like a fault has developed in the transmitter plant the station's chief engineer should know about and investigate before somebody complains to the FCC which takes a VERY dim view of interference to aviation frequencies.

I well may be off the beam on this but better safe than sorry, contact the CE and work with him/her to confirm or deny my suspicion. You'll be doing the both of you a great favor and with luck there's a Cushman Station Monitor or spectrum analyzer kicking around the station.

Another possibility is YOU have a bonding/grounding issue, a common problem that causes local interference but process of elimination first, the transmitter plant and the FCC is the greater issue. If it turns out to be clean you have a real hair puller on your hands we can go into later if necessary.
 

Gator596

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Uh oh, a filter may or may not solve your problem,....
Another possibility is YOU have a bonding/grounding issue, a common problem that causes local interference but process of elimination first, the transmitter plant and the FCC is the greater issue. If it turns out to be clean you have a real hair puller on your hands we can go into later if necessary.
Thanks for the great advice de Warren. My set up is less than 6mos old so I don't think it is me. Will contact the local station CE this week - they will probably be interested to know that there are people out there who are paying attention.
Am also going to get a PAR filter just on general principles.
Thanks everyone!
 

kb2vxa

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OK, I'm curious to see where this thing goes. BTW, "de" is CW shorthand for "this is". Normally the exchange would be (your callsign) de KB2VXA but here I have it arranged as a sig line.
 

majoco

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"de" is French for "from" :)

You'll hear all sorts of shorthand on CW - "es" for "and" (Spanish) plus all the usual "tnx fr rpt ur fb 2 bcnu ltr" stuff
 
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mikepdx

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it sounds like a fault has developed in the transmitter plant the station's chief engineer
should know about and investigate before somebody complains to the FCC
I think I'd exhaust all other possibilities before
contacting the station, Industry Canada or Transport Canada.

Presenting data obtained from an "economically built",
uncalibrated consumer scanner surrounded by many
other potentially RF noisy home electronics devices isn't exactly gospel.

Use another receiver (or two) to verify (if you really, really want to troubleshoot).
Preferably a Part 87 transceiver or some other well designed commercial receiver.

Since 121.5 is monitored worldwide, I'd suspect that
if harmful interference in occuring in a certain area, the powers to be
on the aviation side would know about it in very short order.

I see you're using an outside antenna way up there.
Sometimes using an outside antenna not only brings in
the desired freq, but also a lot of yuk.

Good luck Gator!
 
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Gator596

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I contacted the station Engineer. He got back to me right away, and is doing some checks. Will let you know how it ends up. Thanks for the advice everyone!
 

jim202

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So after months of problem free listening, my local FM rock station on 97.7fm is now suddenly stomping on 121.5 and locking up my scanner. I have to lock the freq out, which sucks, because I occassionally heard some good stuff on it.
I have a few questions I'd like help with...
1) Is this normal, or have I mis-diagnosed the problem? Could it be someone's cordless speakers I'm hearing?
2) My preliminary research points me towards a notch filter to fix this issue. Can anyone suggest a good one?
I'm running a bcd996xt with a d130j on a 35ft tower.
Thanks in advance,
My guess is that your having an issue with intermod. Just what is causing it will be the question. You know 2 of the frequencies. Trying to find the third or fourth is the problem. If it has just started to happen, I would ask if the FM station has made any changes that would change it's effected radiated power that would make the problem worse. If you have a cell site near by, it could be a mix from them that is part of the issue. Don't forget that you could have an image in the scanner that is picking up some other frequency causing the problem.
 

Gator596

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Turns out that the interference vanished as quickly as it came. The station engineer was extremely attentive to the problem, and in the end it was probably not his station that caused the problem. He was very helpfull with a lot of suggestions and a solid offer to get back in touch with him if the problem comes up again. He said he enjoys playing "sherlock Holmes" with this sort of thing. It is always good to know there are professionals out there.
 

kb2vxa

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THAT'S GREAT! I've known radio people from Mike R. Phone to his Aunt Enna and many engineers in between, most are quite friendly and open to any helpful outside observations. I made that suggestion because there are things outside the scope of babysitting a transmitter and that's one of them. Your comments tell me just where his mind is and it's a good thing. Hey guy, have you considered the fact you just made a friend and a valuable friend at that? He can teach you things about radio and I don't mean maybe!

You never know, maybe it was on his end. Maybe lightning hit the tower and welded that corroded joint? (;->)
 
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