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High-pitched whistle in background

Unless the interfering STL is using a digital system, you should hear any interfering signal on your STL receiver if you turn off your STL transmitter. Not uncommon in bigger cities to have other STL's on both adjacent and even the same channel. An STL on the same channel is more likely to cause a whistle. The older Moseley receivers (EG: 505 series) were rather broad and may capture adjacent channel signals if the main channel is off, but will quiet down nicely when the system is running properly.

Sometimes two STL systems are set up locally on the same channel because of crowded conditions, but may co-exist happily for years until something changes. Such as a new skyscraper that reflects the STL signal in the wrong direction. Or a studio move by one station without anyone worrying about "minor" details such as frequency coordination.
 
One of our technical people reports that the tone is louder when you are close to the transmitter.

Our transmitter and tower is in an urban/suburban location, across the street from a large shopping mall. The transmitter is in an apartment complex with the tower being on the roof.
 
Uplug the output from the STL receiver. Short the input to the exciter, all of them if there's more than one. There's likely two or three subcarrier inputs and a couple of composite inputs. Short all of them. Does the tone remain, or go away? (Obviously the program will go away, buit it shouldn't take more than a couple of seconds of silence to ascertain whether there's still a tone n the air or not, with no baseband input to the exciter.) Further diagnosis is purely anecdotal till this is resolved.
 
Go to the transmitter site,feed audio directly into the exciter,bypassing the stl completely and see what happens.What is the model number and age on this Moseley?If you still have the tone you know it's the exciter or the xmtr.If it goes away,the stl is the culprit.Tell us more about that antenna setup,height, nearby structures like high power lines.
 
Our tower and antenna is as follows:

Height Above Average Terrain: 256 feet
Height Above Ground Level: 213 feet
Height Above Sea Level: 968 feet

The antenna pattern is Directional, going primarily west.
 
I can absolutely respect the fact that you've come on here asking for help. You've gotten some really good advice.

By this point, if the culprit hasn't been identified...it's time for the person(s) that hold(s) your license to pony up a small amount of money and pay a contract engineer to identify the the problem. I'm really not trying to be a jerk, just being honest.
 
Agreed, Sgeirk.Of all the input offered, the source of that noise should have been found.John, did you do what little john or the rest of us suggested?we're here to help,but you need to follow through.If you don't have spares, you have to isolate until you find the problem.last time i saw anything close to this ,a worn out moseley that should have been refurbed was the culprit and i've heard the afc in the exciter could cause the whine.It could be something in the xmtr ,a bad cable or part picking up rf , a bad cap in the audio section.But once again stay out of the xmtr and fnd someone qualified to do that,not worth your life.You've got guys on here that's been around since the RCA days(scary,isn't it).FREE advice is rare these days.
 
My turn to pile on. Brother John, the engineers on this board are here to help you, but it would have helped if you were more direct.

Like this: is your station WBWC? If so, your "large metropolitan market" -- Cleveland -- is chock-full of insanely-qualified engineers.

Speaking of which, I see that the WBWC website has a person listed as Chief Engineer. This is not the place to get into "I said / he said", but assuming this is your station, have you worked with him regarding this problem? Again, this is not really the place to answer that question... but it is to ask it.

I've worked with volunteer-run stations that broadcast a variety of programming, and I understand that it may be hard to cut through the noise to get attention focused towards a hard-to-hear or hard-to-track issue. What the posters here are suggesting is for you to follow a more "scientific" approach of observation and elimination in order to help your engineer find the problem.

I will give you one "non-invasive" test that you can run: find a fixed receive location no more than about a mile from your transmitter, preferably one with a clear view to the tower (i.e. not in the middle of a mall or other building). A quick search shows a bunch of restaurants surrounding the tower site that should work nicely, and I assume many have lots of glass and handy outlets. Remember the goal is repeatability.

To this location, bring as many FM stereo radios as you can muster. Bring at least one good set of headphones such as a pair of Sony MDR7506's. The problem may not be the hearing of us "old people" (ahem!), but that 12 kHz ain't so easy to replicate via cheap headphones or car speakers. Make sure you are in a location of excellent signal.

Find a time when both WBWC and another station have silent passages, such as between programs. WCPN looks like a good candidate, since they are in talk programming most of the day. I assume you can find a cooperative WBWC DJ to give you some periods of silence.

Now, when both WBWC and the reference station (WCPN) are in silence, switch your test radios between the two frequencies without changing anything else. That last part is important.

Do you hear the tone on every radio, every time? Is it on both stations, just yours, or none? Make it as fair a test as you can.

While you have all this stuff piled out amongst the Wendy's burgers, run one other test: while WBWC is in silence, switch the radios from stereo to mono. Does the tone fully go away, or just slightly or not at all?

Write it all up as simply, clearly and as non-confrontationally as possible, hand it to your engineer, thank him, then walk away from it. You've done all you can do.
 
Dr. Tech:

I agree...the details does match WBWC.

The chief there is a great guy, and knows his stuff. John: I recommend working with him on this. If he is stumped, there are plenty of us here in Cleveland who would be more than willing to lend him a hand troubleshooting.

-C
 
Therer are no NPR HD signals in cleveland around their signal. The closest one is 89.7 coming out of Akron, but that's pretty far from their site.

If this is WBWC, then this is what their neighborhood is looking like:

88.1 WZIP the University of Akron -- no HD signal
88.3 - WBWC
88.7 - WJCU John Carroll University - no HD
88.9 - WSTB - Streetsboro highschool No HD
89.3 - WCSB - no HD
89.7 - WKSU - Kent State University (NPR) - HAS HD
90.3 - WCPN - (NPR) - NO HD
90.9 W21BS - no HD

So, as you can see. The one station with HD is a few channels up, and if there are problems with them, then WBWC wouldn't be the only folks with problems. He really just needs to talk to the Chief.

A thorn in everyone's side here is CIMX 88.7 out of Windsor, Ontario (100Kw). WJCU is directional (2.5 Kw beaming mostly EAST from the east side of town) from WBWC's turf because of that (WBWC, btw is halfway across town on the west side).

-C
 
If this is WBWC 88.3, I picked you up in Cincinnati in 1970 when you had 10 watts...and there was no high pitched whistle then if that helps narrow it down. I almost kept a straight face typing this!
 
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