High-pitched whistle in background

[johnbasalla]

I am involved with a 4,000 watt station at 88.3 FM that has been experiencing a slight, but annoying background noise since about January, 2009. We are in a major metropolitan area. We hear a high-pitched whistling sound that appears to be either generated at the transmitter sight or is some sort of interference. It is always there and is noticeable, particularly during very soft passages of music or during talk.
We've received a number of questions and complaints about it. We have done some testing and are sure it is not the STL, and is not being generated from the studio. Has anyone else ever been confronted by such a technical issue? Can anyone share what a good course of action may be in determining and fixing the problem? I thank you in advance.

 

[TheLongArm]

Orban 8000 stereo generators would do that when the PS capacitors dried out. Use to hear that pretty often when there were more old 8000's around.

 

[ChiefEngineer]

Not enough information. STL hop length? Type of stl? Processor ? Have you listened to the audio at studio out of the console, at the input to the exciter?

Turn off he stereo generator and see if the whine goes away. This is the typical power supply problem in a stereo generator.

Pray this isn't HD interference from someone on 88.1 or 88.5.

 

[oldiesstation]

sounds like the SG or something in the exciter.Got any spares you can swap out.any HD's near you?Have you tried turning off the SG?

 

[cgould]

Harris Digit exciters will do that too if the wrong bypass capacitor dries out...

You need to supply more info for anyone to make a halfway educated guess as to where you need to look.
Otherwise, it's a case of everyone shouting random answers at ya like a TV gameshow...


-C

 

[rrsounds]

You need to supply more info for anyone to make a halfway educated guess as to where you need to look.
Otherwise, it's a case of everyone shouting random answers at ya like a TV gameshow...

-C

Yeah, and I was just going to say that a high-pitched whistle usually means the water is ready to make tea. :

 

[littlejohn]

Quick n dirty way to isolate it - unplug the feed from the proc amp to the exciter, and short the exciter input. Goes or stays?
If it goes, unplug the STL feed and short the inputs to the proc amp. Goes or stays?
If it stays, find out what's coming unhung in the exciter, and more info is needed. As someone pointed out, a particxular component failure in a Digit exciter will make this happen.
If it sgoes when the p[roc box is unplugged but returns even with a shorted input, look at the proc amp. Again, more info is needed. Analog Optimods would do this when there was poor bypassing or poor power supply filtering.
Some of the Moseley composite STLs were capable of generating a whine also. There was a paerticular IC which got flaky in them.

 

[johnbasalla]

Thank you all so much! Even the joke about tea is appreciated, as that was cute.
Here is more information that I hope will prove helpful.

Our transmitter is an Energionics Legend 3000. It is not run at full power at 4000 watts.
Our STL is a Moseley. When there is no input into the Moseley, the tone is still there.
We have an Omni-one FM for our equalization, FM generation, and compression. The stereo generator is part of the Omni-One. It's all in one unit.

The noise that we're talking about has been measured at between 11.5 and 12.5 Khz.

 

[TomT]

How old is the exciter? Is it an Energy-Onix as well?

When you say the tone is there with no input to the Moseley I am going to assume you are disconnecting the composite feed from the Omnia One....if you mean you are just cutting the program feed to the Omnia, check the SCA level pot on the back. Understand that some "Ones" were shipped with this pot wide open, which can put some noise--or even a whistle--into the main channel audio.

Go through Little John's tests--short the composite input to the Moseley and see if the tone goes away. If it does, then I would look at the Moseley. If not, go out to the transmitter, and disconnect the composite feed to the exciter. If you still have the tone, I would look at the exciter. If the the Moseley's input is shorted, but the tone is clearly coming from the STL receiver, you may have some kind of interference on your STL channel. Try killing the STL transmitter and see what you hear at the transmitter end.

If it looks like the whistle is coming from the exciter, it's probably time to re-cap the exciter. I've worked on two different vintages of these Energy-Onix exciters recently (circa 92 SST-30 and more recent exciter with the digital display on the front). These fellows run hot, and the caps can dry out--with various anomalies appearing before they completely die.

 

[ChiefEngineer]

Thank you all so much! Even the joke about tea is appreciated, as that was cute.
Here is more information that I hope will prove helpful.

Our transmitter is an Energionics Legend 3000. It is not run at full power at 4000 watts.
Our STL is a Moseley. When there is no input into the Moseley, the tone is still there.
We have an Omni-one FM for our equalization, FM generation, and compression. The stereo generator is part of the Omni-One. It's all in one unit.

The noise that we're talking about has been measured at between 11.5 and 12.5 Khz.

Need to clarify . No input to the Moseley. Follow the previous instructions. Dead carrier into the moseley means nothing unless the audio into the moseley is unhooked. (shorted is even better but unhooked is a start)

The odd thing I see is there is no Moseley model number. Only a few Moseley units allow analog audio inputs.
Most place composite inputs into the moseley. What model is this?

If you have mono audio into a composite or mono system and then run this into a stereo system you create other problems. If this is one of the Moseley digital units I find more junk in their audio due to interference than you would ever believe. Starlink and the earlier versions develop odd problems regularly. An unknown because Moseley can mean many things. Composite/Digital/model?

Because the exciter develops the stereo pilot you have a way to see if this is pilot hash. You can use the controls on the omni one I think to turn the stereo pilot OFF.

Go to the exciter and try this. If the whine leaves the fix then is to place an OMNIA ONE in line for $2500. Your audio will greatly improve.

By not using a defective portion of the exciter and avoiding repair or replacement of the exciter this could be a wash. AND your audio will sound much better than the on board processing.

AGAIN. The issue is how does the audio get to the transmitter. We completely overlooked digital trash in the stl because the type of stl is unknown. It seems possible that the stereo is being generated at the transmitter because digital audio (very susceptible to interference) is being utilized. Please let us know.

 

[cgould]

I'm assuming "Omni-One" means Omnia One, so I'll chime in assuming that

A couple of quick and dirty things to check to see if it is the Omnia....

1) Disconnect the composite output of the Omnia.One, and see if the tone is still there. If it is gone, that will tell us one of two things....more on that in a moment.

2) If it goes away, Reconnect the composite output and disconnect the audio input. If the tone goes away, then we know the tone is getting into the unit from the program audio feed somehow. Otherwise:

3) Is there anything connected to the SCA input? If so, disconnect and see if the tone is still there. If there is nothing connected to the SCA input, it would not hurt to make sure the control (on the back panel) is turned all the way down to rule out any noise getting in from there somehow.

4) If the tone persists, go to a radio with a mono / stereo switch. See if the tone remains when switched to mono. If so, then you will want to talk to us @ Omnia Audio to help narrow things down further -- ask for Mark Manolio.

5) If the tone is ONLY there in stereo, then the problem (once again) could be anywhere as this can point to STL interference, or maybe a capacitor drying out in the STL or exciter, causing oscillations that are sitting somewhere in the stereo subcarrier region and will only be heard when a stereo radio "opens up" and decodes the area, causing that tone to be heard.

One way to rule out the STL as a problem is to take the processor out to the transmitter site, and see if the tone persists when connected directly to the transmitter...

If you have a backup processor (or can borrow one from a friend in the industry) you can substitute it for your existing one for a moment to see if you still get the tone.

Some ideas for ya -- assuming you have an Omnia.One.

-Cornelius

Thank you all so much! Even the joke about tea is appreciated, as that was cute.
Here is more information that I hope will prove helpful.

Our transmitter is an Energionics Legend 3000. It is not run at full power at 4000 watts.
Our STL is a Moseley. When there is no input into the Moseley, the tone is still there.
We have an Omni-one FM for our equalization, FM generation, and compression. The stereo generator is part of the Omni-One. It's all in one unit.

The noise that we're talking about has been measured at between 11.5 and 12.5 Khz.

 

[johnbasalla]

Thank you so much! I am not an engineer myself and am relaying information from others. I will work as quickly as I can to share more relevent information. I can add this: the transmitter was installed in late 2000/early 2001 and went on-air full time beginning in mid February, 2001.

In relation to our current problem, testing was done with carrier on and no modulation (overnight a Sunday into Monday) and the studio disconnected so as to take that out of the equation.

Respectfully submitted.

 

[oldiesstation]

SO, we can assume the omnia one is at the studio? If so your problem seems like STL,Exciter or xmtr.They have age on them and i would suspect the exciter,CAPS gone south.contact energyonix,they're easy to talk to..you're getting in an area where you need a qualified engineer.Don't KILL yourself over this.It is not worth it.Had a good engineer friend short the interlocks on a xmtr while working on it.He died at age 45.Senseless...Now is not the time to get stupid....

 

[phr8trayn]

Do you happen to be using a Scala brand preamp
in front of the Moseley receiver?
I had one with an oscillation.
When you turned the pilot off on the Optimod
the tone went away. At first led me to believe
Optimod issue.

 

[johnbasalla]

Here is our chain. On-air Board to EAS to Delay to the Omnia-One to STL. We have no Optimod.

 

[frankberry]

The problem could be the AFC (automatic frequency control) loop in your exciter.
Your frequency may have drifted so far that the AFC can't control it. The squeal could be caused by the AFC attempting to lock.
Check the transmitter's frequency. It should be within 2kHz of your assigned frequency.

 

[phr8trayn]

Here is our chain. On-air Board to EAS to Delay to the Omnia-One to STL. We have no Optimod.

Of course you don't have an Optimod. I did. My point was that the STL receiver pre-amp was the source of the whistle in my case.
If you happen to have such a faulty pre-amp in front of you STL receiver, it could possibly be causing the problem.

John writes: "I am not an engineer myself and am relaying information from others"

Ask "others" for a complete detailed description of the air chain from Board to TX. Post it here.

It may help with diagnosis.

 

[syvjeff]

I'm going to toss in another thing to check:

Is this station using subcarriers or Mux? I once worked at a station where the CE changed the remote control settings and feed to the TX via the STL. The Mux channel was flooded with noise from remote control and caused a tone noise to bleed into audio channel.

 

[BobOnTheJob]

I'm going to toss in another thing to check:

Is this station using subcarriers or Mux? I once worked at a station where the CE changed the remote control settings and feed to the TX via the STL. The Mux channel was flooded with noise from remote control and caused a tone noise to bleed into audio channel.

That jogged my memory on something that was semi-common 40+ years ago. Stations that ran a 67khz SCA subcarrier would occasionally have a 9khz whistle. Had something to do with a hetrodyne between the second harmonic of the 38khz stereo subchannel (76khz) & the 67khz SCA. I never knew if it was being transmitted that way or if it was being generated in the receiver. By the time I got knee deep into such issues, it had faded into radio history.

 

[johnbasalla]

We are not using the SCA. Here is more detailed information about our chain.

On-air board - to delay - to processing (Omnia-One FM for FM generation, stereo generator etc...) - STL transmitter. The sound is then microwaved over to the transmitter where the STL receiver receives it. From there it goes to the input of the transmitter (exciter and poweramp).

Looking this over, it does occur to me that there also is a possibility of microwave interference. What is the best way to determine if that's the culprit?

It is quite a high pitched sound, so those with high end hearing loss don't hear it as well, or at all. However our station appeals to young people, and guess whose hearing is amongst the best? (Answer is obvious).

Respectfully, and which much thanks, John Basalla.