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Spot tripping my STL

N

NHRadio

Dear Engineering gods:
I need some advice. I recorded 2 spots for the cluster I work for. On one of the FMs the spot takes down the Moseley PCL 6010 STL. The power and radiate LED's go from green to red muting the station's audio. Levels look good. Ran them through a de-esser. No help. Low pass filter, Uh-uh. Mix into mono, still no joy. Runs on other stations just fine. If I didn't know better I'd think it was some kind of interference...
Anyone ever seen this before? How can I fix it? Thanks!
 
Two things come to mind. Sub-sonic (e.g the old 25 Hz)/Supersonic (>15 KHz). Or the timing on the spot is messing with the time constants on the audio processing chain.
 
Someone a while back posted a similar problem with a Dial Global song. Run it through a 50 Hz high-pass filter - probably some sub-sonic audio in there causing the PLL to unlock.
 
Sub-sonic bass has caused older exciters and stl xmtrs to lock up.Chris'
suggestion should work fine.Yep,when the urban thump came along outdated gear had a tough time passing it.
 
Not to be picky, but I would have said, "high pass at 30 Hz, and low pass at 15 kHz."
 
Not to be picky, but...
Click to expand...
Elephants & dogs could hear it!

We had a DC offset from a Henry digital recorder* do the same thing. Whenever they would play the traffic report recorded on the Henry the STL transmitter AFC would un-lock. Set the HPF to 30 Hz on the Optimod.

(*Really a MACKENZIE MacFi with a Henry sticky lable on it.)
 
AFC is unlocking, most likely from sub-bass that's in the spot somewhere. High pass it at 30Hz, at least. If it's just a few spots, go to 50Hz with a more gentle roll off.

Are you running composite or discrete on it?
 
Make sure your Optimod, Omina or whatever flavor you have in front of the STL has the high-pass filter on.

And I would still filter the two offending spots, and see if that makes the problem go away.
 
The AFC in older 6010 transmitters will unlock with audio lower than about 8Hz. To prevent this, Moseley changed the time constants (via capacitor changes) in newer and factory repaired units.
 
I program a Hip-Hop station... Luckily, my Optimod 8300 has a 30Hz filter in it. I just leave it on (It's off by default on all presets for some reason).

Anytime I setup a digital processor, the first thing I do is turn the 30Hz filter on. I honestly don't understand why that would not be the 'default' setting out of the box. It fixes anything that gets into automation with subsonic noise.
 
Perhaps the designer of the 8300 presets assumed that the STL and exciter would be digital. If no analog AFC is in the air chain, then the 30Hz high pass filter is totally unnecessary. I've heard that the AFC in some consumer receivers can stutter or unlock with excessive bass boost but I've never observed this phenomenon. Besides, high pass filters (or low pass for that matter) produce phase shift around their cutoff frequency and you know what phase shift does to square waves...
 
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