The most trashed FM signal I've ever seen, spanning 800+ kHz...how does this happen?

[RomanPort]

Hello! My apologies if this is in the wrong place, I wasn't sure where to post it.

While scanning through the FM band yesterday, I noticed the most trashed FM signal I've ever seen. This station is licensed to be broadcasting at 99.3 MHz but it's signal is "repeated" across 99.1, 99.5, 99.7, and I'm even hearing interference on the 100 kW station at 99.9 MHz.



At first I figured that this was my SDR overloading somehow, but I could confirm the same thing in my car stereo and the radio on my desk. My car was even locking onto stereo on 99.7, 400 kHz away from where the station should be! Below is a video of it on both my SDR and my car.

Just out of curiosity, does anyone know how something like this would even happen? And how it's gone at least 24 hours completely unnoticed, even when the frequency adjacent to the one they're supposed to be on sounds better than their normal frequency? I'm just baffled how something like this can happen. I've purposefully avoided identifying the station, as I suspect that isn't allowed here, but it's just 250 watts about 3.5 miles away.

Thanks!

 

[SomeRadioGuy]

Hello! My apologies if this is in the wrong place, I wasn't sure where to post it.

While scanning through the FM band yesterday, I noticed the most trashed FM signal I've ever seen. This station is licensed to be broadcasting at 99.3 MHz but it's signal is "repeated" across 99.1, 99.5, 99.7, and I'm even hearing interference on the 100 kW station at 99.9 MHz.

View attachment 2212

At first I figured that this was my SDR overloading somehow, but I could confirm the same thing in my car stereo and the radio on my desk. My car was even locking onto stereo on 99.7, 400 kHz away from where the station should be! Below is a video of it on both my SDR and my car.

Just out of curiosity, does anyone know how something like this would even happen? And how it's gone at least 24 hours completely unnoticed, even when the frequency adjacent to the one they're supposed to be on sounds better than their normal frequency? I'm just baffled how something like this can happen. I've purposefully avoided identifying the station, as I suspect that isn't allowed here, but it's just 250 watts about 3.5 miles away.

Thanks!

you did a poor job of not identifying it.. RDS shows in your picture and your location shows in your signature.

FYI: Failures happen, even with the best of them... and Klove has a number you can call 1 800 525 LOVE and report this stuff.

 

[PTBoardOp94]

It's not necessary for a broadcaster to have equipment on site to verify the operation of their transmission system, let alone continuously monitor it. The only requirement is to shut down the transmitter if interference is reported.

 

[ZantennaG1]

This reminds me of the "K-love on 91.2 FM" fiasco in Twin Falls, Idaho back in 2013. Their actual transmitter on 92.9 had so many issues (being way off frequency included), that they just canned that transmitter and came back on a different one.

 

[Cowboy78]

Hi there...This is really bizarre. I can't even imagine a transmitter staying on the air if in fact that's what its output looks like! We do frequent transmitter proofs and remotely monitor our signals pretty vigilantly, but things do happen. It's unlikely it's leaving the transmitter that way, but I've seen stranger things! More likely would be something localized causing the issue. PM me the call letters and your location and I'll give it a look.

As always, if you ever notice a K-LOVE or Air1 signal operating improperly, please don't hesitate to call our 24/7 NOC at 800-525-6373.

--
Shane Toven
Senior Broadcast Engineer
Educational Media Foundation (K-LOVE/Air1)

 

[Cowboy78]

I looked into this a bit further and gave the signal a listen remotely with a monitoring receiver on-site...

While it doesn't sound as good as I would expect, I'm not hearing the mirrored modulation above and below the carrier that you are seeing. All transmitter readings look normal as well.

In any case, I'll have the local engineer investigate further to see if something else is going on here.

Thanks,
--Shane

 

[ZantennaG1]

Glad an EMF rep is actually on here to respond to our questions. You're the best, and I'll be tuned in!

 

[Schroedingers Cat]

I've noticed these spurs cropping up on other stations, like the spur on one side +0.3 MHz from the licensed frequency. Years ago, I heard some asymmetric sidebands, and the engineer told me that the resonant cavity was detuned. Could this also be caused by errant audio processing? There was an AM station on 1290-and yes it was WHGR before Clear Channel turned the license in, at the same site as WUPS 98.5. It had spurs at ~99.8 and ~97.2. One of the assistant engineers at Family Life Radio told me that something was interfering with WUGN on 99.7. I figured it out and he had the problem fixed. But those were symmetrical spurs.

 

[Kelly A]

Hello! My apologies if this is in the wrong place, I wasn't sure where to post it.

While scanning through the FM band yesterday, I noticed the most trashed FM signal I've ever seen. This station is licensed to be broadcasting at 99.3 MHz but it's signal is "repeated" across 99.1, 99.5, 99.7, and I'm even hearing interference on the 100 kW station at 99.9 MHz.

There could be something wrong, probably not 800kHz worth. But just remember, you're making an assumption based on what amounts to measurements with a toy. All of your other claims using this SDR against stations have been wrong, so not sure why you think this is anything different.

Just out of curiosity, does anyone know how something like this would even happen?

It likely isn't.

 

[Cowboy78]

I've noticed these spurs cropping up on other stations, like the spur on one side +0.3 MHz from the licensed frequency. Years ago, I heard some asymmetric sidebands, and the engineer told me that the resonant cavity was detuned. Could this also be caused by errant audio processing? There was an AM station on 1290-and yes it was WHGR before Clear Channel turned the license in, at the same site as WUPS 98.5. It had spurs at ~99.8 and ~97.2. One of the assistant engineers at Family Life Radio told me that something was interfering with WUGN on 99.7. I figured it out and he had the problem fixed. But those were symmetrical spurs.

I've seen symmetrical spurs on an FM with certain exciter failures...With modern DSP based exciter designs, however, it's far less common.

As for carrier asymmetry, yes, a filter cavity or antenna (or potentially a PA cavity in a tube rig) that does not have a symmetrical pass band can cause that. I see this occasionally with digital sidebands passing through filters and combiners.

--Shane

 

[valvashon]

K257EP, licensed to Dilworth, MN.

 

[Cowboy78]

It's not necessary for a broadcaster to have equipment on site to verify the operation of their transmission system, let alone continuously monitor it. The only requirement is to shut down the transmitter if interference is reported.

For what it's worth, these signals have pretty extensive monitoring (and are checked regularly by humans)-but even the best monitoring can't catch every possible scenario. Always appreciate reports of any potential issues so we can investigate further.
--Shane

 

[Cowboy78]

Glad an EMF rep is actually on here to respond to our questions. You're the best, and I'll be tuned in!

I'm not on this board frequently, but if someone points out a post to me, I'm always happy to hop in and see what's up.

Like I said, we try to be good citizens on the broadcast spectrum, but things happen-and if in fact there is an issue with a signal, we want to get it corrected as quickly as possible.
--Shane

 

[Cowboy78]

This reminds me of the "K-love on 91.2 FM" fiasco in Twin Falls, Idaho back in 2013. Their actual transmitter on 92.9 had so many issues (being way off frequency included), that they just canned that transmitter and came back on a different one.

That one was before my time-but I've heard the stories! Thankfully most questionable gear that would cause that sort of issue has long since been replaced...
--Shane

 

[ZantennaG1]

That one was before my time-but I've heard the stories! Thankfully most questionable gear that would cause that sort of issue has long since been replaced...
--Shane

That must've been the reason, as my local K-Love (90.9/91.1) and Air1 (89.1/104.1) have not had these issues in recent memory. They occasionally disappear for a few days (for maintenance I assume?) and then come back up. Z of Cheyenne, Wyoming.

 

[RomanPort]

Hi there...This is really bizarre. I can't even imagine a transmitter staying on the air if in fact that's what its output looks like! We do frequent transmitter proofs and remotely monitor our signals pretty vigilantly, but things do happen. It's unlikely it's leaving the transmitter that way, but I've seen stranger things! More likely would be something localized causing the issue. PM me the call letters and your location and I'll give it a look.

As always, if you ever notice a K-LOVE or Air1 signal operating improperly, please don't hesitate to call our 24/7 NOC at 800-525-6373.

--
Shane Toven
Senior Broadcast Engineer
Educational Media Foundation (K-LOVE/Air1)

Thank you very much for your response, I really appreciate it. My apologies if I came off as rude in my initial post, that was not my intention. I will check again later today when I have the chance.

Thanks again for the response. It means a lot!

 

[Kelly A]

Like I said, we try to be good citizens on the broadcast spectrum, but things happen-and if in fact there is an issue with a signal, we want to get it corrected as quickly as possible.
--Shane

My experience is EMF has indeed been good operators. That's why I wouldn't be too concerned about the OP claim. He's posted many times with claims that this or that station is over modulated, or somehow their HD sidebands are out of spec. Problem is: the SDR he's using is an un-calibrated and inaccurate toy.

Without a real spectrum analyzer, what he's posting amount to pretty colored ink blots.

 

[Mikey Radio]

My experience is EMF has indeed been good operators. That's why I wouldn't be too concerned about the OP claim. He's posted many times with claims that this or that station is over modulated, or somehow their HD sidebands are out of spec. Problem is: the SDR he's using is an un-calibrated and inaccurate toy.

Without a real spectrum analyzer, what he's posting amount to pretty colored ink blots.

I'm not trying to debate your comments @Kelly A, but then again, I didn't go back to see what the OP has posted in the past. What I did notice is that, according to his signature at the bottom of the messages he posts, he's an 18 year old college kid. The screenshots he's posted may be all he has at his disposal - maybe some suggestions of other ways he could validate what he's seeing would help him expand his knowledge? IMO at least he's showing a solid interest at his young age, AND he's not just looking at the irregularities he sees (or believes he's seeing) and ignoring them. He's posting here to ask questions, to try and gain knowledge and in the case of this particular discussion thread, someone that can actually check the transmission system and possibly do something to correct any irregularities at that site got involved. IMO this kid should be patted on the back and given a bit of encouragement and direction.

 

[Cowboy78]

Our local field engineer visited the site and discovered a bizarre issue related to the selected audio input. None of us had ever seen anything quite like it, and the transmitter readings otherwise looked great! In any case, the offending equipment has been swapped out and the signal should be back to normal.

A failure mode like this is EXTREMELY rare and difficult to automatically detect remotely. This is a big reason why we visit our sites regularly and carry spectrum analyzers to proof our transmitter installations in the field, but sometimes things happen between those visits!

Once again, always appreciate the reports and happy to investigate.

--
Shane Toven
Senior Broadcast Engineer
Educational Media Foundation

 

[RomanPort]

Our local field engineer visited the site and discovered a bizarre issue related to the selected audio input. None of us had ever seen anything quite like it, and the transmitter readings otherwise looked great! In any case, the offending equipment has been swapped out and the signal should be back to normal.

A failure mode like this is EXTREMELY rare and difficult to automatically detect remotely. This is a big reason why we visit our sites regularly and carry spectrum analyzers to proof our transmitter installations in the field, but sometimes things happen between those visits!

Once again, always appreciate the reports and happy to investigate.

--
Shane Toven
Senior Broadcast Engineer
Educational Media Foundation

Thanks for the response, that is really fascinating! I had checked my SDRs and car ~1 PM this afternoon and still saw the distortion but checking now and it's all well. Any chance you could elaborate on what happened? I'm just curious and really respect your work.