I haven't come across this, but I've heard from about 5 guys who have had this problem just in the last few days. Apparently at the end of a transmission they will hear something completely different on the same talkgroup. For example, a 31 div cop is talking on 31, but immediately after he finishes you'll hear an ambulance on 31 division's band - or sometimes you'll just hear dead air. The only way to clear it is to hit the scan button, but it will occur again within minutes. This hasn't happened to me and I've even tried to duplicate it without success. Any thoughts?
Toronto SmartZone issues
- Thread starter yorkphotog
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Yes,I have noticed this on my BC245XLT where you must program in every voice channel.
There are two "problem" freq.'s that I have noticed, one being 862.4875 and the other one 861.4625.
When I noticed the talkgroup number hanging , I'd hit the DATA button on the key pad which will show the offending freq. flashing in the display. It's got to the point that I just lock those two freq.'s out and that seems to solve the hanging problem.
They must have older scanners because my 2096 just has CC and ACC's programmed in and I don't see it lingering on any tx's.
There are two "problem" freq.'s that I have noticed, one being 862.4875 and the other one 861.4625.
When I noticed the talkgroup number hanging , I'd hit the DATA button on the key pad which will show the offending freq. flashing in the display. It's got to the point that I just lock those two freq.'s out and that seems to solve the hanging problem.
They must have older scanners because my 2096 just has CC and ACC's programmed in and I don't see it lingering on any tx's.
exkalibur
Member
I'm going to guess that for whatever reason, those channels aren't transmitting the end code properly, which is what your scanner uses to determine it's time to return to the control channel. I wonder -- if you have end code detect turned off, what is the timeout value for returning to the control channel?
rc1990
Member
I hear the same thing when I listen to the Toronto Police Online Feed. For what reason would an ambulance go on a Police TG. I thought they had their own TGs
I re-read my post and see an error.
You actually hit the LIMIT key rather than the DATA key when checking the frequency of a stagnant talkgroup.
I don't think I can do anything about end code detect.
You actually hit the LIMIT key rather than the DATA key when checking the frequency of a stagnant talkgroup.
I don't think I can do anything about end code detect.
Jay911
Silent Key (April 15th, 2023)
Is this on scanners or pro radios too?
I have actually heard similar stuff on Calgary's system on both my scanner and my pro radio for my volunteer FD (programmed by the official techs, of course). A specific talkgroup when used on the Airport tower will "bleed over" onto other talkgroups on an adjacent tower on occasion, after that talkgroup's traffic has ended. I haven't looked into it enough to determine if it's adjacent frequencies or something like that.
I have actually heard similar stuff on Calgary's system on both my scanner and my pro radio for my volunteer FD (programmed by the official techs, of course). A specific talkgroup when used on the Airport tower will "bleed over" onto other talkgroups on an adjacent tower on occasion, after that talkgroup's traffic has ended. I haven't looked into it enough to determine if it's adjacent frequencies or something like that.
gopherit
Member
I have had the same on my scanner as well. I hear EMS on a Div. band. also open carrier usually from the north tower.
exkalibur
Member
I can assure you that a "real" radio doesn't do this.
Its my guess that the scanner is (for whatever reason) not picking up the end code, therefore it doesn't know to revert back to the control channel. Because of the nature of trunked systems, as soon as one comm is done on a freq, you could (and will) have a totally unrelated comm on that frequency immediatly after the previous one.
If your scanner holds for whatever reason, it'll pick up the unrelated comm.
Its my guess that the scanner is (for whatever reason) not picking up the end code, therefore it doesn't know to revert back to the control channel. Because of the nature of trunked systems, as soon as one comm is done on a freq, you could (and will) have a totally unrelated comm on that frequency immediatly after the previous one.
If your scanner holds for whatever reason, it'll pick up the unrelated comm.
slicerwizard
Member
This form of tailgating is more likely to occur when a site is busy (e.g. a channel gets reassigned just as a comm drops). If you're doing your testing in the wee hours (at Weston/401, perhaps...), you're far less likely to see it. Locations with high noise floors may interfere with end code detection, so park next to a low cell site...
Some RF channels may be weaker/noisier or picking up crap from your PC/WiFi/whatever. Perhaps the audio levels or filtering at the site is a bit different between channels. Discriminator tap recordings of the tailgating would provide definitive answers.
BTW, I've had the same thing happen once in a while on my 246T and 396 while monitoring 3C08. It's fairly rare though.
Nobody said that EMS radios were using PD talkgroups.
Depends on the system. Older ones do it all the time. The folks at ADT kept freaking out when the controller periodically failed to send the end code (verified with flat audio recordings) after their transmissions and some other 1F20 customer would get assigned to the voice channel that all of the ADT radios were still monitoring. They wanted to know why someone else was using "their channel" - I just ran TRUNK88 in their dispatch center and showed them that there was no "their channel". Watching 28 jammed channels in the middle of the day was a real eye opener for them. It explained the short busies, the differences in audio on some channels and the tailgating.
And I told them that they should be less concerned about the guys they could hear using the channel after them (which was really just an annoyance), and more concerned about who might be hearing ADT when an ADT radio tailgated some other talkgroup on a voice channel, since that meant their "secret" comms were being heard by some other user group. Of course, they never knew when that happened. So ADT hearing others = annoyance only; others hearing ADT = out of sight / out of mind = not a problem. After the demo, they never complained about tailgaters again - yay...
Heterodyne
Member
What exactly is the end code, Andrew... is it a subaudible tone on the voice channel, or a command sent through the control channel?
Jammin_Jay
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It all depends on the level of RF that is recieved at the site. If the site can identify the end code at a certain weakness level of RF, and below that it cant. How is the control channel supposed to identify a TG's end of tranmission when it can't pick up the signal at an identifiable RF level.
The end code is broadcast on the voice channel by the voice repeater.
slicerwizard
Member
Yes, it's a repeating 10101100 data pattern that's sent for about 650 ms.
http://home.ica.net/~phoenix/wap/TRUNK88/END-CODE.WAV
Nothing is sent on the control channel when a group or private call ends; the periodic late entry OSWs just stop. It's a pain (for a decoding application) to accurately determine when a voice comm ends, since the rate at which late entries are sent can vary from system to system, and even from one second to the next.
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