P25 Scanning - Frequencies

[brendan3]

Hello all,

I understand that when scanning P25 sites only the control channel frequencies, if available, need only be scanned and the scanner will receive data from the CC to know which specific frequency it needs to tune.

I am curious that in the event of a fail soft, will having all available frequencies in my scanner database for the system sites be beneficial? I understand that the control channel will not work in this mode and hence the system will make all frequencies available.

Thank you,
B

 

[rk911]

I enter all control channels associated with whatever tower(s) I want to monitor. This allows for the routine rotation or maintenance of CC.

 

[KevinC]

Scanners don't "understand" failsoft so it wouldn't help to have them in the CC list. You could put them in conventionally, but seeing how failsoft continually transmits your scanner will lock onto the first frequency it hits. Also, a lot of systems don't have failsoft enabled (I personally don't like it).

 

[GTR8000]

+1 on failsoft sucking. If a system has gotten to the point of failsoft, it can't even maintain site trunking anymore and is in big trouble.

 

[brendan3]

Understood, thanks for the replies. I guess to reword my question, is there any benefit to having all of the frequencies from a site in the scanner besides just the control channel(s)? When would they be used or heard?

 

[GTR8000]

For a Motorola ASTRO 25 (P25) system? No, not if you're 100% certain of which frequencies (up to 4, could be less) are control capable. The traffic (voice/data) frequencies would not be used as control unless the site was reconfigured, which would be very rare for an established system.

Other manufacturers such as L3Harris, Tait, etc. do things a bit different. L3Harris in particular likes to allow any site frequency to be control capable, so the recommendation is to include all site frequencies in the scanner's programming.

There's usually no harm in programming every site frequency into the scanner and letting it figure out which is the control, unless something very weird was done like a nearby site is reusing one of those traffic frequencies for control and you're unlucky enough to be in range of both sites. That would be extremely poor planning and (hopefully) exceedingly rare.

PS - 98% of all Motorola ASTRO 25 systems use the BEE00 WACN, so it's a pretty good indicator of what brand a P25 system is (or isn't) for making the determination.

 

[brendan3]

Thank you for the excellent explanation!

 

[fog]

Understood, thanks for the replies. I guess to reword my question, is there any benefit to having all of the frequencies from a site in the scanner besides just the control channel(s)? When would they be used or heard?

To back up a bit, the list of frequencies you enter is, definitionally, just telling the scanner where to look for the system control channel. Once it finds the control channel, it computes voice traffic frequencies directly. So, entering things which will not be control channels does no good, and arguably does a tiny bit of harm, in that it's one more frequency that has to be checked when looking for the control channel. (But we're probably talking milliseconds of delay.)

You should program all the channels that might be control channels. GTR8000's advice is right on the money.

 

[brendan3]

Thanks. I am programming the San Diego RCS system which has a few simulcast nets among other independent sites. It seems that the database would be maintained pretty accurately because this system is pretty high visibility in the region. With that said I have programmed the known control channels only in hopes to, like you suggest, speed up the scan.

 

[tvengr]

Thanks. I am programming the San Diego RCS system

What scanner are you using?

 

[brendan3]

What scanner are you using?

SDS100

 

[tvengr]

SDS100

That is the tool to do the job. Simulcast will not be a problem.