Pro-164 w/ EDACS

[n1ghtwish]

Forgive me if this is better suited for the EDACS forum, but here's my situation...

I live in Nevada, which has a statewide EDACS system (Nevada Shared Radio System Trunking System, Various, Multi-State - Scanner Frequencies). This system is used by many different agencies, but my primary focus is the Highway Patrol. With a RS Pro-164, I am trying to monitor a talkgroup used by the north eastern area of the state (Elko 2, AFS 05-102). The caveat to this is that I am trying to monitor this talkgroup from a site in a completely different region.

I have programmed in frequencies for several sites in the area that the scanner is located. The scanner trunks these sites just fine and I can pick up talkgroups used in the scanner's area, but even with the bank(s) open, I cannot pick up traffic from the other region.

Now here's the other part of my setup - I have a Harris XG-75 programmed for the state system. The Harris will pick up ANY talkgroup in the entire state from ANY site/tower in the state. When my Harris radio is on and near the scanner, the scanner will pick up traffic from the talkgroup that the Harris is tuned to. It's almost like the scanner is only hearing traffic because the Harris unit is receiving it.

The funny thing is that when I turn off the Harris unit, the Pro-164 will still pick up my target talkgroup for about 30 minutes, and then it's almost as if it forgets what it's supposed to scan and then I get nothing. I have programmed in THAT talkgroup alone, and closed all the banks so that I only get that TG's traffic.

Anyone know how I can get the scanner to continue to receive traffic from that talkgroup without the help of the Harris unit being on?

Thanks!!

 

[Spitfire8520]

The Trunking Basics: Networked Systems on the RadioReference wiki will likely be a good read for you to get the basic overview of what is happening.

Now I'll try to provide a description of what is happening with the system. What is happening is that the sites around you are actually not broadcasting the talkgroup whenever your actual radio is not on. While the system is networked together, an event known as an affiliation need to happen for a specific site to broadcast the audio associated with a specific talkgroup.

An affiliation is your radio telling whatever site it finds that you are interested in listening to a specific talkgroup. This is processed by the system so that it will then route the audio to that site so that it can be heard if it is not already doing so. This happens with each and every radio that is on the system when they are turned on, or when you switch to a different talkgroup. If a site does not have any affiliations to a talkgroup, then it will not broadcast a talkgroup to preserve frequency resources since it knows that no radio is listening to that talkgroup on that site.

You have provided a perfect example of experiencing affiliation first hand. Before you turn on your radio, the nearby sites have no one in the area interested in listening to Elko 2. Whenever you turn on your radio, searches for a site and then affiliates to system and the the Elko 2 talkgroup. The system will then begin airing the talkgroup on that site so that the radio can receive (and transmit) to that talkgroup from its current location. When you turn it off, the system will realize that no one in the area is listening to Elko 2 and stop broadcasting the talkgroup that site (other sites will still have it given that a radio is affiliated to it).

This is an important detail, especially given some of the sites on the system that have very limited frequencies (3 in some cases). One frequency is used as a control channel to communicate with each of the radios, the remaining are the physical frequencies used to transmit talkgroup audio. It can be easily seen that none of the sites on the system can handle every single talkgroup being used at the same time. Rural areas are generally expected to have less users and therefore will have a less frequencies as opposed to other more urban/suburban areas that tend to have more frequencies.

It's almost like the scanner is only hearing traffic because the Harris unit is receiving it.

That is exactly what is happening. A scanner can only receive and never broadcasts anything. In essence, it is basically eavesdropping on the system and has no control to whether or not a talkgroup can be heard on a site. Your Pro-164 is behaving exactly as it should as the system is the deciding that the talkgroup will not be broadcast on the site. A recommendation made to those wanting to monitor a wide area is to program busy sites that are known to carry lots of talkgroups, for example a site located on top of a large mountain/hill that might provide a large footprint. In the end, an actual radio will not notice any of this, but scanners will.

Now, a side note to all of this. Hopefully the users are training regarding using their radios on a large network in regards to keeping their radios on when they roam out of their normal service area. From what you have said, no one in your area uses that talkgroup on a normal basis. When you turn your radio on, you are basically allocating a some of a site's resources to that radio. What this can lead to is increased loading on that particular site as it now is required to find a voice frequency and broadcast that in addition to everything it normally broadcasts. Some sites, especially the rural ones, are not suited for this and can cause a hazardous situation by causing system busies.

You may be familiar with this if you are an actual user on the system. What basically happens is that the site runs out of frequencies and simply has no more that it can use, so it gives whoever is trying to talk a busy tone to let them know to wait it out until it gets the resources to transmit the audio. This is undesirable for everyone involved and therefore it is discouraged to drag talkgroups into different regions.

Now if you are not a typical user of the system, then hopefully you will reconsider using the radio as a means of monitoring the system. While it might allow you to hear whatever you want wherever you want, it is certainly very much frowned upon. It is entirely possible that a public safety user needs to talk and finds himself being blocked due to a rouge radio dragging a talkgroup from a hundred miles away, or even worse if the rouge radio were to transmit and blocks actual users from talking.

Anyone know how I can get the scanner to continue to receive traffic from that talkgroup without the help of the Harris unit being on?

If you haven't read the wall of text above, then the answer would be no.

 

[n1ghtwish]

Spitfire8520,

Thank you so much for taking the time to provide an incredibly detailed write up of what is happening. Your reply has far exceeded my expectations!! Prior to this reply, I did have a basic understanding of the EDACS system, however, I was unaware that not ALL talk groups were availale from ALL sites.

This makes perfect sense, and I suspected something like this was happening, I just couldn't seem to find a technical explanation. Of course the towers near the scanner won't broadcast talk groups not used in that area! Why would they?

I did make sure to try to monitor the sites with the most frequencies (12 and 15) as to not cause any disturbance to the system, and rest assured I will not be using my actual radio to monitor it. I am in fact a user of the system as I work for one of the agencies utilizing it and wouldn't want to interfere with its operation in any way.

Again, thanks for the reply! I guess I'm SOL on this project!

 

[N8IAA]

Being that some of the TGID's are in Mixed mode, when they go digital, you won't hear them. When in Analog mode, you'll hear everything. The fact that the commercial radio, which was made to follow the system exclusively, is going to work better than the 164,
I presume that is what is happening with the explanation you gave.
Larry