PSR500, Talk group transmissions come thru as control channel noise

[GrumpyAeroGuy]

If this has been asked before, I apologize.

THis problem is confined only to the Ohio MARCS... and began happening only a short time ago.

SOmetimes---there appears to be no ryme or reason to it that I can detect--- the scanner will begin to receive a talk group on OH MARCS, and voice is coming thru with high quality. Then, towards the end of the transmission, it is like someone throws a magic toggle switch somewhere, and I hear what I interpret to be the sound of an analog trunking control channel. This will tail on for a while, then I hear the response to the original traffic, usually OK. SOmetimes however, the response is a combo between high quality voice and the control channel sound. I may have read in previous posts around here that folks refer to this as the "motor boat" sound, which it kinda, indeed, sounds like.

At times (90+% of the time), this same talk group is flawless. But, every now and then, I get the control channel sound.

What is happening here? Anyone have a theory?

 

[mikey60]

If you were to listen to a voice channel on an analog scanner, you would hear what pretty much sounds like a control channel. For some reason, the scanner is switching from digital mode to analog mode on that voice channel. Do you have a strong signal on that system?

Mike

 

[GrumpyAeroGuy]

If you were to listen to a voice channel on an analog scanner, you would hear what pretty much sounds like a control channel. For some reason, the scanner is switching from digital mode to analog mode on that voice channel. Do you have a strong signal on that system?

Mike

That particular talk group, if I were to classify it, is probably the one that comes in weakest of them all (this is REALTIVELY speaking, of course, as, generally, this system is very well monitored by my PSR500). As this is an MARCS system, I have several sites programmed, and the tower pushing THIS signal is most likely the weakest of the three....

 

[mikey60]

Ok, Then my guess would be that it's losing enough of the signal that the scanner can't pick up the sync data on the voice channel, and switches to analog mode. Strictly a guess on my part. The system I monitor is a P25 control channel, so it's pretty much locked on Digital when I monitor it.

Mike

 

[GrumpyAeroGuy]

If you were to listen to a voice channel on an analog scanner, you would hear what pretty much sounds like a control channel...
Mike

On a side note, I was wondering about that issue generically too, on occasion. I never tried to monitor a digital system with a non digital scanner to see what you hear and do not hear for the curiosity of it.

So THAT'S what happens. You hear motor boats instead of voice... interesting and thanks for answering that question buried in the back of my mind as well.