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Could IBOC be getting into my signal?

W

wnmb

It's 7:05 am edt on this 11th of August. Our air monitors at WNMB are providing us with a "white" noise or hiss underneath the audio. I just checked in my car and it sounds the same. Everything in the audio chain here at 900 WNMB in North Myrtle Beach looks nice and clean. There's plenty of power on the STL and so on. Could this be IBOC? I know it happened a coupe of years ago when WLS was running IBOC at 890. Do they have it on again?
 
Hook up an amp and a set of speakers, and wire that amp into every point in your audio chain (console output, processing input, processing output, STL input, STL output, transmitter input) and check each point for that hiss. It could be HD noise from WLS, but you should make sure your own audio chain is in order first before you blame someone/something else.
 
Yep - once again "hair" nails it. I'm assuming here you're monitoring off-air either using a receiver or a modulation monitor with audio output driven by an RF amplifier. In either case if there's IBOC on adjacents the detector will be wide-band enough to pick up the infernal hissing.

Like "hair" says get your engineer to methodically elminate all other possible sources. Then go out into the field away from WMNB's site when you're experiencing the noise phenomenon; take along either or both an FIM-41 and a sensitive communications receiver, preferably one with selective bandwidth.

By rotating the FIM about its axis you should be able to get a bearing on the source of the noise. If it's coming from WLS when you hold the meter at a 90-degree angle from the direction of Chicago, the noise will null out.

There could also be some kind of local noise source such as a bad pole transformer near your station, although I find that much less likely. Bill, didn't you have this happen to you earlier?
 
FYI,

WLS has apparently reversed its long-standing policy of shutting off the infernal hiss generator at night. I've monitored them running IBOC every night this past week.

Very disappointing.
 
The noise began fading away around 8:00 this morning. By 8:35 it was all gone. However, just to check our own chain, by 2 pm today we've gone through everything from the beginning (on air console output) to the pre-processor, STL transmit and receive, Optimod, and final oudio out to transmitter. All clean as a whistle. This did happen to us once before about a year and a 1/2 ago. It certainly could have been some kind of external interference other than an IBOC hiss. Very strange. At the present moment, all receivers sound fine. We listened in the studios and even had people several miles away calling in. All our test gear showed clean audio in the past hour. We'll just hope whatever it was does not show up tonight or tomorrow morning. Now, if we could just do something about program content!!!!
 
Bill said:
The noise began fading away around 8:00 this morning. By 8:35 it was all gone. However, just to check our own chain, by 2 pm today we've gone through everything from the beginning (on air console output) to the pre-processor, STL transmit and receive, Optimod, and final oudio out to transmitter. All clean as a whistle. This did happen to us once before about a year and a 1/2 ago. It certainly could have been some kind of external interference other than an IBOC hiss. Very strange. At the present moment, all receivers sound fine. We listened in the studios and even had people several miles away calling in. All our test gear showed clean audio in the past hour. We'll just hope whatever it was does not show up tonight or tomorrow morning. Now, if we could just do something about program content!!!!
Click to expand...

I predict that the noise will show up again. WLS clearly still has IBOC on tonight (at 2200 EDT, well past their sunset). Since night operation goes against Citadel corporate policy, I would suspect some kind of automation glitch. A similar thing happened at WABC some months ago.
 
That's good news. I was afraid it signaled a change in policy.
 
Sounds like time for some stations to e-mail Son Nguyen at fcc.gov ;) .

Now that I've thought a bit (3rd cup of coffee).....Have you checked your directyional when this is happening?
My first thought was, maybe something happened in the monitoring system, maybe where you sample the RF. But, if it was noticable in the car, then that's out! Could it be that something is intermittently changing in the phasor, the transmission lines, or one of the tower bases?

Next time it happens, put on "MacArthur Park" and go make a complete check of all your base currents and other parameters, plus look at reflected power on the transmitter. Compare them to readings taken again, right after the noise goes away.

Of course, like someone said, it might be some electrical interference. So, maybe a quick drive down the road a half-mile, listening to blank-spots on the band, might turn something up (getting out from under your own towers).
 
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