BC796D and (maybe weirdly designed) P25 systems

[Jay911]

I'm involved in a thread in the Atlantic/Maritimes forum of the Canada section of the forums regarding helping a fellow scan the new P25 system in his province. Some/enough of the system is in the DB as "Newfoundland Provincial Radio" in the Newfoundland province in the Canada section of the DB.

The system in question seems to be running strangely. All sites have a control channel and at least one voice channel - that's not the odd part. What is, is, on at least one of the voice channels (the only one, in many cases), when there is no voice grant/subscriber audio in progress, the channel is constantly sending what I am calling "dead air" in P25 CAI mode. For all intents and purposes, the scanner (in conventional or frequency search mode) appears to "lock up" on the voice channel frequency, displaying the appropriate NAC for the site, with no audio issuing from the speaker.

I have programmed this system manually into my HP1, my 396XT, and my PSR500, and none of them are having any problems. The guy in the other thread, though, has a BC796D, and is having a hell of a time getting it to work. I do believe he's fairly new to trunking, and I've stepped him through the programming as best as I can by looking at the BC796D owners' manual PDF and not having an actual 796 with me. Reportedly he is still having the scanner 'hanging' on the voice channel when there is no voice traffic. I thought maybe a previous attempt where he programmed them as conventional frequencies had been left in the scanner, but I'm pretty sure he's doing a full reset before any attempt at programming (by hand).

Two questions:

(a) Anyone had a 796 successfully programmed on a modern P25 FDMA system? I can't imagine that it wouldn't work, even though it's a fairly old scanner.

(b) Anyone ever witnessed a system like this, where the VC broadcasts constantly? What is the reason for this? The system still rotates the CC on a regular basis too.. I just don't get the point of running the VC constantly - even if it was an attempt to foil scanners, it would fail because it's locking on the actual voice channel, and thus people can hear everything.

 

[Viper43]

There is one before I heard of doing this and it was thought it was done to keep people from scanning it, they would get tired of hearing nothing and give up. Of course another possibilty is the squelch is open on the scanner...anything is possible I guess.

 

[mikewazowski]

I had no luck getting the Metrolinx system working on a 796T.

I would guess that Digital End Code Detect would help.

 

[Jay911]

It's not a case of the squelch being open. Any scanner tuned to the frequency in a conventional format would stop on this frequency because it's transmitting constantly - but it's transmitting P25 data, so scanners that can decode P25 translate it as fully quiet audio. Someone listening in analog mode would hear a constant 'braaap' sound which never goes away.

I was wondering about Digital End Code but waiting til I got back to Calgary where my 796 is, to check it out. Of course I don't have a P25 system at home to test it on..

 

[kb0nly]

I spoke with this individual as well.. He was having a heck of a time programming it and updating firmware.

The last he asked me was that the database doesn't show the base frequencies and step for that system. So i assume he still doesn't have it programmed correctly for the system in question.

Enabling the end code detect should help also.

I have two 796's and monitor a few different trunked systems with them, no problems whatsoever.

 

[Jay911]

He has the two frequencies we have found for his area. There may be one or two more voice channels, but the past history on this system makes me think it's unlikely.

Base (according to my HP1, and Unitrunker) is 150.8, step is 5 kHz, and to the best of my knowledge there's no offset. I've suggested he keep the default configs in the 796 as I'm led to believe that the P25 signal will provide the necessary information to the radio. I'm not experienced with systems that require base/step/offset values; if he does input 150.8 and 5 kHz for the step (or "spacing" as the 796 calls it), what does he put in for the offset channel? Leave it at 380, set it to 0? Something else entirely? As an example, LCN 1004 is 155.820, which is 150.8 plus (1004*.005). To me, that implies that the offset should be zero. Is that right or wrong?

 

[mikewazowski]

I'm not sure the 796 has the smarts required to pull the bandplans from the control channel.

That was the problem I ran into.

The offset could not be set properly as the scanner was looking for a Type II offset starting at 380.

 

[SCPD]

you do need a base plan for 796D for non 800mhz p25 systems. I had a 796D programed for a VHF
P25 system here in Nebraska. The scanner did not 'download' the base plan from the control channel like the newer scanner does. I also had the same results on a UHF P25 system.
I did not get the scanner to track either system. The VHF system was probably due to no voice traffic. The UHF system did have encrypted voice traffic but the scanner failed to track the system. Even with encrypted voice the 796D should follow the system and open the squelch as the scanner does not skip over encrypted communications like newer scanners.
Has anyone gotten a 796D to work on a non 800mhz P25 system?

 

[kb0nly]

you do need a base plan for 796D for non 800mhz p25 systems. I had a 796D programed for a VHF
P25 system here in Nebraska. The scanner did not 'download' the base plan from the control channel like the newer scanner does. I also had the same results on a UHF P25 system.
I did not get the scanner to track either system. The VHF system was probably due to no voice traffic. The UHF system did have encrypted voice traffic but the scanner failed to track the system. Even with encrypted voice the 796D should follow the system and open the squelch as the scanner does not skip over encrypted communications like newer scanners.
Has anyone gotten a 796D to work on a non 800mhz P25 system?

Both of my 796's work great on the South Dakota State Radio system which is VHF P25 Trunked. You just have to put in the base plan and your set. So i think the guys problem is he still doesnt have the scanner programmed correctly with the base plan.

 

[SCPD]

The south dakota system in not a true P25 system (9600 baud). According to the database it is a type2 system with digital voice (3600 baud).
We are talking about a true P25 system (9600 baud).

 

[kb0nly]

The south dakota system in not a true P25 system (9600 baud). According to the database it is a type2 system with digital voice (3600 baud).
We are talking about a true P25 system (9600 baud).

Yeah for now.... Its going to be changing.

I monitor ARMER as well with my 796's which is 800Mhz though, but 9600 P25.