Interesting Occurence

[TXFirefighter112]

This post deals solely with the Carrollton TX public safety trunked system as this is the only system Ive ever encountered this, but Im putting it in general scanning both because of what happened and to see if anyone else has had something similar occur.


I just got back from a movie and came into my room to find my Pro-94 playing the good ole machine gun tune of "Motorola Trunked System Control Channel." It was interesting to note though that it HAD NOT exited trunk mode. In fact, it was actually displaying a talkgroup ID. Unfortunately in my haste to cut off the noise I failed to remember the exact talk group ID.

I do remember the first two digits of the number being 16 though. Trouble is, all the talk groups in Carrollton's system begin with a 49, 50, 51 or 52.

I do know for a fact that it was still in trunk mode because I hit "SCAN" instead of "Trunk" to make the noise stop.

So anyone else ever heard of this? Or have an explanation of what it was?

 

[jparks29]

Probably a DATA channel, in trunked systems, data channels can be used instead of dedicated frequencies, it's allocated just like a voice call is, except the rx/tx is data instead of voice... They can be used for MDT's, or even station alerting, even mundane stuff like monitoring water pressure/level.

 

[slicerwizard]

So anyone else ever heard of this? Or have an explanation of what it was?

The scanner just mis-decoded the data coming off the control channel. It thought it saw an indication of a group comm on a specific frequency and when it tuned to that frequency, it found a signal (the control channel you heard), so it stayed there, tuned to the bogus "talkgroup". The control channel might've been part of a different system.

Usually, when scanners mess up control channel decoding, they get directed to random channels that have no signal present, so you never notice the glitch (the scanner sees no RF carrier, so goes right back to the control channel)

It's behaviour like this that leads to newbies announcing that they've just found a new talkgroup on their local system. When pressed on the matter, they admit that there was no meaningful audio heard, but the group ID was being displayed, so it must be valid...

Options like CC-only mode and ID Search / open mode just make the situation worse, since they let the scanner respond to more bogus decodes.

 

[SLWilson]

Ohio MARCS...

The Ohio MARCS system does that occassionally. I don't think it's a problem with your scanner. The scanner prpbably just happened to "miss" whatever it uses to decode the transmission.

With the Pro2096 (they've done a couple of firmware updates & those helped) Ohio's system would act like the frequently, BUT, it was an issue with the scanner not decoding the TG or whatever in a timely manner.

If I reach up & hit scan when it is happening, it DOES go around and hit on the unit talking....

So, I'd say, SNAFU is par for the course.....

Steve/Gallia

 

[spiritwolfpr]

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