How does trunked scanning work in a Uniden?

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Anderegg

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Yeah, I know, it monitors the control channels and goes where it is told.....but more technically, and explanation of the following if possible.

1: Hold time: Scans the control channel for the time specified in this setting. How is this scan taking place? I know in conventional you have the so many channels per second, but on trunking, how does this work? Are the available talkgroups in a system loaded into RAM then matched against control channel data? Does a 1 or 2 second hold time make any difference as long as a scanned talkgroup gets a channel grant within the specified system hold time? Also, if you have a scanner dedicated to one specific system, would setting the hold time to the longest possible option decrease the chance of missing the beginning of a transmission while the system "resets" itself at the expiration of the hold time?

2: Delay time: I am noticing that once the delay time expires for a talkgroup, scanning moves on to the next system immediately. Does the previously discussed system hold time count off while receiving a transmission, so that if the RX goes past the amount of hold time, then it would go right to the next system?

3: Motorola end code: As it pertains to delay time. When I have end code enabled, and delay set to 0, the scanner begins scanning instantly as soon as the audio drops. If end code were turned off, would the delay time begin when the repeater drops, or still when the audio ends?

I decided against getting a 436HP, so I am working to make my little 396XT work as well as possible now. :)

Paul
 

UPMan

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1. I trunking, this is how long it dwells on the control channel. It is not actually scanning frequencies, it is watching the channel grants and channel updates that are being issued to see if any TGID of interest is active at that site.

2. Yes, hold time is total time on the system, even during voice calls.

3. If end code is off, then the scanner must rely on squelch drop to know that the current comms are over. On a busy system, there might not be a squelch drop between two different comms, resulting in your hearing unwanted traffic with mislabeled descriptions.
 

JamesO

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Would be interested in understanding this a bit more as well.

Seems some of my systems tend to camp out on a "System" longer than I would expect.

This may be due to multiple "Sites" in the database.

So what happens lets say you have a System with Multiple sites, each site may have had a all frequencies entered. How does the scanner react if an additional Site is scanned and the control channel cannot be picked up/locked on to? Does the radio function as a conventional scanner, looking for the control channel to attempt to lock onto it? If so, how long will the scanner function in a conventional mode looking for the control channel?

I am also starting to think that on trunked systems when the scanner is stopping on a talk group but there is not audio and the scanner is stopped for a while, this may be due control channel errors of some sort?

I was playing around with my HP1 with recently using the Discovery and Analyze modes and noticed in some of the reports that there were a lot of lines indicating Errors.
I assume these errors confuse/tie up the scanner in an attempt to decode and properly follow a trunked system?

I expect many of these errors to be caused by either multisite simulcast multipath distortion and/or questionable signal quality of the control channel?
 

UPMan

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On each enabled site, the scanner looks for a control channel (fraction of a second). When found, the scanner dwells on that control channel for a minimum of about 2 seconds (the time it takes for the control channel to cycle through all site activity). Then, it moves on to the next site. If no control channel is detected after checking all frequencies, it moves on to the next site.
 

Anderegg

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UPMan, does the amount of talkgroups actively scan enabled make any difference to the scanner and it's ability to receive them as long as they get a grant during the hold time monitor of the control channel? I wouldn't want to put so many "maybe they will talk one day" talkgroups in a system If that would endanger missing an active talkgroup coming alive.

Oh yeah, I tried turning end code off on analog, and began getting a very non Motorola like squelch tail at frequency drop......doh!

Thanks!

Paul
 

Anderegg

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On each enabled site, the scanner looks for a control channel (fraction of a second). When found, the scanner dwells on that control channel for a minimum of about 2 seconds (the time it takes for the control channel to cycle through all site activity). Then, it moves on to the next site. If no control channel is detected after checking all frequencies, it moves on to the next site.
This brings up another question I forgot to ask. Does keeping only ONE control channel frequency unlocked in the list make dealing with receiving faster for the scanner? In my neck of the woods, it is very rare for the control channel to switch. If it does, I simply press hold, then scroll through and unlock whatever is control channeling! From looking at my 396 moving from system to system, it seems to remember the last received CC frequency, because they always pops on the screen right away as the new system comes up.

Paul
 

UPMan

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P: The number of TGID's programmed into a trunked system will not in any way affect scan speed.

A: I cannot see how locking out site channels would create any improvement worth the trouble. The scanner always checks the last known control channel first (and even if it didn't it would take only a few score milliseconds to acquire it).
 
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