Can someone explain to me how priority scanning works in mixed CONV/LTR/P25 scanning?

[wp3539]

In my county we have a LTR system, numerous conventional VHF channels, a P25 system on VHF and an LTR system on 800 MHz. I'm listening to the following on a PSR-500:

- Local Fire on CONV VHF set to Priority in scanning list (1)
- Local PD on CONV VHF, non-priority in scanning list (1)

- County FD Talkgroup on P25 system set to priority in scanning list (2)
- Neighboring city FD Talkgroup on P25 system set to priority in scanning list (2)
- Neighboring city FD on CONV VHF non-priority in scanning list (2)
- 4 FD TAC and a Fire Marshal Talkgroup on P25 non-priority in scanning list (2)
- 2 neighbor FD Talkgroups on LTR non-priority in scanning list (2)

- EMS on CONV VHF set to Priority in in its own scanning list (3)

- Various PD related channels on P25 non-priority in scanning group (4)
- Various PD related channels on LTR non-priority in scanning group (4)

My questions are:

1) If the scanner stops on a non-priority P25 channel will it jump to a priority P25 channel if it starts transmitting?

2) If the scanner stops on a non-priority LTR channel will it jump to a priority channel on
a) P25?
b) CONV VHF?

3) If the scanner stops on a non-priority CONV VHF channel will it jump to a priority channel on
a) P25?
b) CONV VHF?

It seems like if I disable the CONV priorities and the radio stops on a P25 channel it will stay on it until the transmission is over before it starts checking for other priority traffic. If that is the case why bother setting up priority channels on a P25 system?

It also seems that if I don't have any CONV priority channels and the radio stops on a CONV VHF channel it will not scan the P25 CC until the transmission is over on the CONV channel.

Could someone shed some light as what the best setup would be to scan such a system? I have 2 other VHF radios that I use to monitor the local FD and EMS channels so my biggest importance is to have the two FD channels on P25 be ultimate priorities and be caught no matter what.

Thanks a lot in advance!

 

[DonS]

In my county we have a LTR system, numerous conventional VHF channels, a P25 system on VHF and an LTR system on 800 MHz. I'm listening to the following on a PSR-500:

- Local Fire on CONV VHF set to Priority in scanning list (1)
- Local PD on CONV VHF, non-priority in scanning list (1)

- County FD Talkgroup on P25 system set to priority in scanning list (2)
- Neighboring city FD Talkgroup on P25 system set to priority in scanning list (2)
- Neighboring city FD on CONV VHF non-priority in scanning list (2)
- 4 FD TAC and a Fire Marshal Talkgroup on P25 non-priority in scanning list (2)
- 2 neighbor FD Talkgroups on LTR non-priority in scanning list (2)

- EMS on CONV VHF set to Priority in in its own scanning list (3)

- Various PD related channels on P25 non-priority in scanning group (4)
- Various PD related channels on LTR non-priority in scanning group (4)

My questions are:

1) If the scanner stops on a non-priority P25 channel will it jump to a priority P25 channel if it starts transmitting?

If they're on the same TSYS, then yes. On a P25 system, though, this will only happen during "breaks" in the conversation, where the scanner returns to the control channel to look for the continuing traffic on the non-priority talkgroup. If, during those breaks, a priority talkgroup is seen, it will be monitored instead.

2) If the scanner stops on a non-priority LTR channel will it jump to a priority channel on
a) P25?

No.

b) CONV VHF?

Yes, if the "TGRP Pri Int" item in the GLOB menu is set to "ON".

3) If the scanner stops on a non-priority CONV VHF channel will it jump to a priority channel on
a) P25?

No.

b) CONV VHF?

Yes.

It seems like if I disable the CONV priorities and the radio stops on a P25 channel it will stay on it until the transmission is over before it starts checking for other priority traffic. If that is the case why bother setting up priority channels on a P25 system?

As mentioned above, the scanner will check for priority talkgroups on a P25 trunked system during "breaks" in the conversation.

It also seems that if I don't have any CONV priority channels and the radio stops on a CONV VHF channel it will not scan the P25 CC until the transmission is over on the CONV channel.

Yes. To look for priority talkgroups while monitoring a CONV object would incur a huge audio gap in that CONV object.

Could someone shed some light as what the best setup would be to scan such a system? I have 2 other VHF radios that I use to monitor the local FD and EMS channels so my biggest importance is to have the two FD channels on P25 be ultimate priorities and be caught no matter what.

Unfortunately, there's no way to catch priority talkgroups "no matter what" if you're also scanning conventional channels. To do that would require either a) the huge audio gaps in the CONV objects in order to go look at the trunked system's control channel and wait some noticable amout of time for one of your priority talkgroups to appear or b) a second tuner/receiver that is looking at the control channel(s) of the trunked system(s) whose talkgroup(s) you want to set as "priority".

Here's how the PSR-500/600 handles priority for CONV and TGRP objects:
1. Currently monitoring a non-priority CONV object: periodically tune to any priority CONV objects to check for activity. This can be pretty fast, without too much of "gap" in the non-priority object's received audio. It can slow down noticably (with much larger gaps in the audio) if the priority CONV objects are opening squelch, but not matching any CTCSS/DCS/NAC values programmed.

2. Currently monitoring a non-priority TGRP object:

a) if the "TGRP Pri Int" option is turned ON, periodically tune to any priority CONV objects to check for activity. This can lead to some gaps in the TGRP's audio, since returning to it requires a re-check of the control channel in case the TGRP is either no longer active or on a different voice frequency. It can also have the squelch-related gaps in #1.

b) during breaks in the TGRP's conversation, where the scanner returns to the control channel to look for continued activity on that TGRP, if any priority TGRP activity is seen, monitor it instead

c) on some trunked systems (e.g. Mot 3600 if the system is programmed for it, and LTR for some talkgroups), look at low-speed data on the voice frequency, checking for any priority TGRP information.

 

[wp3539]

DonS, thanks so much for the detailed response, it raises some more questions though...

If they're on the same TSYS, then yes. On a P25 system, though, this will only happen during "breaks" in the conversation, where the scanner returns to the control channel to look for the continuing traffic on the non-priority talkgroup. If, during those breaks, a priority talkgroup is seen, it will be monitored instead.

When do these breaks happen? I thought the P25 system had a 9.6k baud data rate half of which was roughly used for the audio and the other half is used to relay active talkgroup information constantly. I guess I misunderstood how this worked.

1. Currently monitoring a non-priority CONV object: periodically tune to any priority CONV objects to check for activity. This can be pretty fast, without too much of "gap" in the non-priority object's received audio. It can slow down noticably (with much larger gaps in the audio) if the priority CONV objects are opening squelch, but not matching any CTCSS/DCS/NAC values programmed.

This all makes sense to me now. When I had squelch turned all the way to the counterclockwise position scanning was awful slow, now I understand why.

I guess I'll stop monitoring the CONV channels and dedicate this scanner for the P25 system exclusively, that should make it pick up better.

On another note often I see the scanner tune to a P25 TGRP, the display will show the appropriate ID and name. the LED will blink as set but no sound would come out. When would this happen?

Thanks again for the detailed answer. I guess we'll have to wait for a scanner that can scan a P25 control channel constantly while it's also receiving on the P25 or conventional talk channel at the same time. Now that would be pretty awesome.