Merged Control Channels

[ht396jm]

Couldn't find any discussions on this after a forums search....

In theory, would there be any issue in "merging" control channels from three different sites within a p25 trunked system whose NAC's are all the same? Or if the NAC's were different, merging them into a single site and setting the NAC to search mode? I'm monitoring the NJICS statewide p25 system, and the sites in my area are all assigned the same NAC.

Thanks in advance.

 

[ofd8001]

If you are using Uniden scanners (and Whistler may be the same), the scanner stops on the first control channel it hears and does its "thing". It then disregards any other frequencies for the site. If there is more than one site, it goes on to the next and repeats the process. If there is only one site, the scanner goes on to the next system and so on.

That means the second and third control channel frequencies, as active as they may be, with be disregarded. So you will miss anything associated with them, as in sites two and three.

NACs don't matter, if I understand correctly.

 

[ht396jm]

So (correct me if i'm wrong please) what you're saying is..... If i have multiple individual sites on a system, and combine those sites' control channels into a single site, I would be missing the same amount of traffic if I had kept them as individual sites?

 

[GTR8000]

You'll potentially be missing more traffic. A lot more, in fact.

If you "combine" all three site control channels into a single "site" in your programming, the scanner is simply going to land on the first one it finds active and will remain there. Whichever site's control channel it lands on, that's the site you'll be decoding.

So let's say for example you're in range of the West Orange simulcast (774.78125), the Ramapo site (770.95625), and the Alpine site (769.70625). If you program all three of those control channels into a single "site" in the scanner, as soon as you start scanning, it's going to stop on the very first one it comes upon. Doesn't really matter which one it stops on, because it's going to simply stay there decoding only that site, unless it has a reason to move to another (signal drops out, etc.)

In order to have the scanner check all three sites, they need to be programmed separately so that it will dwell on each site for X amount of time, then move on to the next, then the next, etc. It will cycle around all three sites looking for activity. The default dwell time is probably around 2 seconds per site. Unless of course it finds activity, at which point it'll remain at that site until the activity ceases, then it continues the cycle.

Here's the bottom line when it comes to systems like the NJICS that have multiple sites: you're never going to be able to catch all of the activity by scanning multiple sites with a single scanner/receiver. Especially when some talkgroups are normally only carried on certain sites. You may only get the Passaic County Sheriff on the Ramapo site, but not Alpine. Likewise, you may only get the PIP PD on Ramapo or Alpine, but not West Orange. And so on.

So unless you happen to be lucky and find that one of those sites is carrying most of the talkgroups you're interested in, your only choice is to continue to scan multiple sites and deal with the inevitable missing of traffic as the scanner moves from site to site. If it's checking West Orange and Ramapo while a transmission on the PIP PD talkgroup is happening on Alpine, you're going to miss some/all of that transmission. That's just how it works.

The only solution to drastically reducing missed traffic is to use multiple scanners/receiver...one for each site.

 

[marksmith]

The above was a very well stated response and exactly correct.

By putting 3 sites of control channels in one site you are determining you only want to listen to (probably) one site. Scanners only check for one control channel per site (since that is how many there should be).

If this is the only system you are scanning, it will stick on the first control channel it finds. It will never even look for another. Therefore you have reduced yourself to one site's activity.

If you are scanning more than one system, after it checks the first control channel for activity, whether it finds some or not, after the hold or dwell time on that system it will go to the next and ignore any second control channels you have entered.

The reason I said probably above is that you could find a situation where it grabs a different control channel (and thus site) when it leaves and comes back to that system on next scan pass. If it does, thst one control channel will take, and ignore the other two. If you are scanning that system only, then the first control channel to hit will be the only one.

The reasons why it might grab a different control channel on a subsequent pass is not controlled by the user. Things like interference would be the cause.

Bottom line. If you want to scan 3 sites, program them as 3 sites and use the radio the way it is supposed to work. Your method will not work on any Uniden or Whistler radio or their predecessors.

Mark
SDS100&200/536/436/WS1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others

 

[ht396jm]

My understanding of how control channels/sites works in relation to each other was completely off. Thanks for the insight! Much appreciated

 

[marksmith]

My understanding of how control channels/sites works in relation to each other was completely off. Thanks for the insight! Much appreciated

No problem.

It's not a simple concept, especially if you are new to trunking systems.

That's the reason Radio Reference forums are great.

Mark
SDS100&200/536/436/WS1095/996p2/996xt/325p2/396xt/psr800/396t/HP-1/HP-2 & others

 

[ht396jm]

....... With all that being said....... Would there be any benefit to separating each control channel into a single site? For example if there were 2 control channels and 1 alternate in one site location, would there be any benefit to making 3 separate sites?

 

[GTR8000]

....... With all that being said....... Would there be any benefit to separating each control channel into a single site? For example if there were 2 control channels and 1 alternate in one site location, would there be any benefit to making 3 separate sites?

No. A site can only have one control channel active at a time. Don't get fooled by the fact that multiple frequencies per site are flagged as "control capable" in the database, that simply indicates that those frequencies can be used as the control channel at any given time, however only one will be active at a time. The rest can be used for voice/data if the system is configured as such.

 

[ofd8001]

Best bet is to not overthink this too much. The database was set up by some pretty brilliant minds in the scanning world to work best with scanners. Rely on their wisdom because efficiency is an important thing to them too.