But Lance, you know as well as I, that if someone wanted to learn all they need to do is ask. Going onto some discussion site and accuse stations of poor engineering or violating the rules without enough information or proper test equipment is, in my view, unnecessary. I hire younger folks for tech all the time. But, I hire ones who admit they don't know everything and are willing to learn and equally eager to ask questions.
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iHeart owned station here HD/iBOC transmitter is causing adjacent interference way outside their spectrum. How do I get them to fix it?
- Thread starter pclover
- Start date
Of course I may be in the wrong here. There is a lot that I don't know. As mentioned I'm using hobbyist equipment. Perhaps I've started this thread off on a bad note.
As I mentioned previously last year the Sony XDR and a portable radio both refused to lock into their iBOC sidebands and that awful looking waterfall and spectrum was present. When it worked again the noise was completely gone and clean. It has been for a long time till recently. That's too coincidental for me to think nothing of it.
With that said the noise isn't as bad this time around but it's a similar pattern.
Again, I may be in the wrong and a different issue but I'm going based on the pattern last time.
Is there anything you suggest I should do for better results of the issue I think exists or is everything I own at this point invalid? I have other screenshots and recordings for it being in normal operation but it wasn't the target at the time if that helps at all.
Would be nice if that noise could get cleaned up to last time to free up an empty channel for the upcoming Sproadic-E season. Mainly why I care but it will only be fixed if there is adjacent channel interference.
I debated posting this but I'll go ahead anyways.
Happened to catch KTOM earlier today with the analog carrier and HD transmitter being turned off. If you look at the screenshot when the HD transmitter is briefly turned off you can see the noise I'm talking about disappears. Why this is happening in the middle of the day is beyond me.
This was done with indoor vertical dipole antenna and a SDR Play RSPdx. It's not a RTL-SDR and much better. Obviously indoor noise pickup is a concern here so results may be skewed compared to a outdoor FM yagi which is less noise.
Not sure why the analog carrier and HD transmitter is being turned off like this in the middle of the day.
Of course this is not scientific measurements and just observations.
Not sure what to make of it but hopefully there is some way to get that noise cleaned up that's been gone for a long time. Now that it's back right in time for the Sproadic-E season is frustrating. Any ideas I should try at this point? I'm open ears at this point.
Happened to catch KTOM earlier today with the analog carrier and HD transmitter being turned off. If you look at the screenshot when the HD transmitter is briefly turned off you can see the noise I'm talking about disappears. Why this is happening in the middle of the day is beyond me.
This was done with indoor vertical dipole antenna and a SDR Play RSPdx. It's not a RTL-SDR and much better. Obviously indoor noise pickup is a concern here so results may be skewed compared to a outdoor FM yagi which is less noise.
Not sure why the analog carrier and HD transmitter is being turned off like this in the middle of the day.
Of course this is not scientific measurements and just observations.
Not sure what to make of it but hopefully there is some way to get that noise cleaned up that's been gone for a long time. Now that it's back right in time for the Sproadic-E season is frustrating. Any ideas I should try at this point? I'm open ears at this point.
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Most likely reason is that they are on an auxiliary transmitter that does not have HD Radio installed.
You say that the "analog carrier... off". If that is so, the station would be off the air. FM modulates the frequency, not the carrier. Or do we have another terminology deficiency here?
The RSPdx is a rather cheap SDR, so I would not overly trust its "findings". As its name indicates, it is a "dx" device, not a professional monitor.
Hum... AFIK you could in theory see a similar pattern if it's a shared antenna with a diplexer. Isn't the HD transmitter and FM exciter and RF amp chain if you are high power separate in this case? You could have one on and the other off and vice versa?
This is a case where my knowledge breaks down and I have to ask but I'd figure a separate antenna just for HD would be more expensive and not the most common. Also figure that would present engineering problems having two transmitting antennas so close to each other as well.
In the first screenshot there was no analog RF output for a period of time but there was still HD. I look at FM as the carrier is frequency modulated. If you still have RF but no modulation you'll see a defined line. You'll see other lines if you have Stereo and a RDS subcarrier as well if you have it. Of course this is way oversimplified as it's much more complicated.
Not sure how it's defined when a station has no analog RF output but HD remains on as it's not quite off the air. However, In the second screenshot it was off the air for a brief period of time fully. I guess some kind of reboot?
True, At the end of the day the high end modern spectrum analyzers are mostly SDRs now but obviously factory calibrated and spurs reduced as much as possible. I wish I had a proper spectrum analyzer but those are expensive. Wish I had a friend near by that I could lend one from and calibrated antennas etc.
Probably getting too verbose but why this noise is present again is puzzling and frustrating. If an issue does exist I'm probably the only one that sees it and chasing a uphill battle. Normal listeners wont notice the nosier stereo on other stations. As a sidenote on the Sony XDR i have turning to 93.3 i see several bars on a signal indicator despite there being nothing there. Previously it's showed nothing. Just something I've noticed
The Sony XDRS3HD is one of the best radios available. DXing requires a great radio that can pull a weak signal out of the noise.
A cheap SDR might overload and put spurs all over the spectrum. However, the spurs and intermod would be reduced at a much greater level than the main carrier if you attenuate the signal. If you attenuate 6dB, then the spurs and intermod should drop more than 6dB all else being equal. That’s how you know it’s being generated in the receiver.
A cheap SDR might overload and put spurs all over the spectrum. However, the spurs and intermod would be reduced at a much greater level than the main carrier if you attenuate the signal. If you attenuate 6dB, then the spurs and intermod should drop more than 6dB all else being equal. That’s how you know it’s being generated in the receiver.
Fully agree. I'm tired of reading this kind of language here. Constantly berating people for being "radio nerds" is faintly ridiculous on a radio enthusiasts' and industry discussion forum.
I can't see the problem with the 92.7 signal the poster is flagging up, it looks like a normal HD signal on an SDR waterfall to me, but surely it's better for everyone to just be a bit nicer? As for the signal, these types of consumer SDR receivers are known to get overloaded by strong local FM signals. Until recently, I lived a few miles from a 250,000 watt FM station, and most SDRs (including the SDRplay models) were unusable with noise and images and general crap from the nearby station. That wasn't the station's fault, its signal was clean, but my equipment not being equipped to deal with huge signals. They're designed for DX, not for dealing with strong local FM.
I have this sticker on my laptop, perhaps a bunch need to be ordered for Radio Discussions posters:
Occasionally Frank and I have privately messaged posters when we feel they are a bit "beyond the pale".
This group is, by design, open to radio fans and radio professionals. Occasionally the pros get tired of the same comments, even if they are innocent and based on lack of "inside knowledge" of how radio works. And occasionally the fans get upset when a professional radio person says, "I told you this already, and ten other people did too".
We try not to moderate with the 19th Century "hickory stick" and have a certain degree of tolerance for disagreement. We ask site participants to understand that point.
The problem is it appears the HD output is very noisy from the station for some reason. Normally when you overload SDRs it becomes obvious if you pay attention.
As I've mentioned previously that noise last year was so bad no HD radio would lock onto their HD signal. When i guess they fixed it the noise was gone and HD worked again. Similar noise pattern appeared again after being gone.
I don't believe that is IMD on the SDR. Around 30 miles away from the station and it's 7Kw.
Put some pointers on this image to show what I'm talking about. Happened to catch a time they turned off their HD and Analog for some reason.
At this point concluded there is likely nothing I can do because stuff works and nobody will likely notice there may be an issue.
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Embrace the term nerd. There are lots of 'enthusiasts' of a hobby that aren't offended by the term. Computer nerds, bicycle nerds, car nerds, chess nerds, AI nerds, and yes, radio nerds.
how about Geeks? Are Geeks above or below Nerds in the pecking order?
In my mind that depends. If you go back in history, Fred Blassie's song; 'Pencil Neck Geek' was not very complementary to the term. Fast forward to the 80's, and the term was used to describe early tech pioneers like Bill Gates and Steve Wozniak, so it could be considered complimentary. Then you have the Best Buy service even today, called The Geek Squad.
I used to work at Iheart in Miramar and dealt with their FM transmitters. The noise you are seeing is the result of RTAC (real-time adaptive correction) being off on their HD exciter. When HD carriers and analog are being amplified through the same RF amplifier the non linearity in the amplifier stage will produce IMD products outside of occupied bandwidth. RTAC is a software process on the exciter that takes a sample of this distorted final signal, extracts the distortion products, inverts then and sums them with original clean signal pre-distorting it so that it cancels in the final amplifier stage and the output would become clean. Funny thing, I also used SDR Play RSP1A to monitor and tune HD transmitters into mask compliance. The SDRs work fine for this, as long as it's not overloaded and amplitude scale is linear and accurate. They are probably aware of this problem and likely working on it. You can register on Broacast Engineers facebook group to name and shame this station since there are a bunch of Iheart engineers active on there.
Thank you for the reply.
I've been pulling my hair out here trying to resolve it and was lead to believe that it was my fault. Nobody here has believed this is real so far...
Do you have any iHeart contacts to maybe pass this along? Rather not shame anybody just if it can be resolved if it's their fault would be good.
https://www.nautel.com/content/user...-HD-Radio-Digital-Adaptive-Pre-Correction.pdf Found this and learned something new.
Using an existing antenna I was under the impression HD exciters had their own amp chain that eventually gets fed to a diplexer that combines your analog and digital RF. I guess if you have a shared site with many stations then a combiner. Kind of novel you can feed it al though a single chain and pre-distort it. Though not a new method. Just didn't think about it being applied to HD radio.
I guess this falls in line with OFDM requiring stuff to be extremely linear or bad things happen. Meanwhile Analog FM can be non linear and fine.
That's called high level combining. Allows to add HD signal without replacing old analog transmitter. Another method is to use separate transmit antenna for HD signal. Third option is low level combining where one exciter produces analong FM signal with HD sidebands included that goes on to be amplified by final PA in class AB mode.
I had a similar problem when 710 WOR's IBOC was splattering on everything 50 kHz above and below their carrier. Their engineer blamed it on "front end overload" in my receivers, even though I was 25 miles away.
What eventually solved the problem was a complete rebuild of their transmitter site, when their original one got taken for Meadowlands redevelopment via Eminent Domain and the state of NJ paid for them to build a new one. After then, their IBOC signal was within spec and not splattering any more than is normal for HD (Hiss and Distortion) Radio on AM.
What eventually solved the problem was a complete rebuild of their transmitter site, when their original one got taken for Meadowlands redevelopment via Eminent Domain and the state of NJ paid for them to build a new one. After then, their IBOC signal was within spec and not splattering any more than is normal for HD (Hiss and Distortion) Radio on AM.
Ugh, I hate when they do this. Basically telling you to go away.
In my experience, it's usually good advice.
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