Site Question

[K0MSM]

Yesterday, while trying out my new SDS100 on a road trip, I noticed that it was picking up traffic from ISP on the new Greene County ISICS site at Seven Hills Park. I picked up the traffic while I was in Boone County, close to Ogden. Traditionally, I've been getting my ISP traffic from the Boone County "Ames/Woodward Simulcast" system, because the Seven Hills Site seemed to be still in development. So naturally, I was excited to see some traffic on it!

When I go home, I turned off Boone County on my 200 to see if I would start picking up traffic from Seven Hills. After a couple of hours of monitoring... nothing. Lots of hits, as normal, on Greene County's conventional system, but nothing at all on the ISICS system. Turned Boone County back on, and bingo - ISP comes back from the Ames/Woodward site. So...

Could it be that they were just testing the Seven Hills site for a little while yesterday? Or, is there possibly some other reason that I'm overlooking for this behavior?

Sean

 

[kslager]

Yesterday, while trying out my new SDS100 on a road trip, I noticed that it was picking up traffic from ISP on the new Greene County ISICS site at Seven Hills Park. I picked up the traffic while I was in Boone County, close to Ogden. Traditionally, I've been getting my ISP traffic from the Boone County "Ames/Woodward Simulcast" system, because the Seven Hills Site seemed to be still in development. So naturally, I was excited to see some traffic on it!

When I go home, I turned off Boone County on my 200 to see if I would start picking up traffic from Seven Hills. After a couple of hours of monitoring... nothing. Lots of hits, as normal, on Greene County's conventional system, but nothing at all on the ISICS system. Turned Boone County back on, and bingo - ISP comes back from the Ames/Woodward site. So...

Could it be that they were just testing the Seven Hills site for a little while yesterday? Or, is there possibly some other reason that I'm overlooking for this behavior?

Sean

The way I understand things, some talk group's are setup to not transmit on the tower if there there's no provisioned radio connected to the tower.

For example, if there is a car accident in Greene County, and Life Flight goes en route, you won't hear it. But as Life Flight nears, their radio might switch to the Greene County tower and you will then here them reporting on the ground and airborne again. As they get closer to Des Moines, their radio would most likely switch back to a tower there, and your Life Flight traffic goes away again.

 

[BinaryMode]

Site affiliations.

Here in Northern CO I sometimes hear traffic from the Denver area because someone is affiliating with a tower here and the tower allows the affiliation. Some towers do not allow the affiliation. It's all dependent on how the repeater is programed.

You have to think of a P25 trunked system like a cellphone system. You "affiliate" with the nearby cell site as you move and get handed over to the next site.

Also note, like cell sites, all the towers are connected via copper, fiber or microwave link...

Edit-

There's an Ogden, Utah, too.

Edit 2-

Looks like there a at least 12 Ogden's.

 

[thatoneiowan]

I went to school in the Iowa Ogden that's why I can't do math

op what talkgroups were hitting on the new site, law 3b or whatever district? radio testing? how do we know it was DPS? what kind of traffic were you hearing, sounds like it was routine? maybe set it up during whenever they do shift change and see if the 10-41s come thru

 

[K0MSM]

Ogden, Iowa.

The traffic was from ISP Districts 3 & 4. They must have been running some tests, because I've heard nothing on that site since except for some local traffic (possibly Jefferson PD) in the wee early morning hours a couple of days ago. I hadn't yet enabled recording on my SDS200 so I don't know what it was. But I fixed that now.

I suspect they're still doing some tests on the site.

I keep my SDS100 running at my desk, and only on the Greene County site, so if there's anything else that comes up, it'll catch my attention.

Sean

 

[CastleBravo1954]

Ogden, Iowa.

The traffic was from ISP Districts 3 & 4. They must have been running some tests, because I've heard nothing on that site since except for some local traffic (possibly Jefferson PD) in the wee early morning hours a couple of days ago. I hadn't yet enabled recording on my SDS200 so I don't know what it was. But I fixed that now.

I suspect they're still doing some tests on the site.

I keep my SDS100 running at my desk, and only on the Greene County site, so if there's anything else that comes up, it'll catch my attention.

Sean

You might look into an SDR Scanner. They're cheaper and more versatile.

 

[K0MSM]

You might look into an SDR Scanner. They're cheaper and more versatile.

I found the problem shortly after this post. Turns out it with the splitter I was using to bring my discone into my radio room for my wx radio, 3 scanners, and SDR dongle. For some reason, it was attenuating the freqs used for my local site. (But not others.) So, once I took that out of the equation, everything worked fine. And continues to do so.

The SDS 200 gets the signal first before anything else. Then the splitter feeds the rest, and everyone is currently happy. (The SDS 200 is the only radio that cares about the 700 MHz range.)

Sean

 

[sempai]

The way I understand things, some talk group's are setup to not transmit on the tower if there there's no provisioned radio connected to the tower.

For example, if there is a car accident in Greene County, and Life Flight goes en route, you won't hear it. But as Life Flight nears, their radio might switch to the Greene County tower and you will then here them reporting on the ground and airborne again. As they get closer to Des Moines, their radio would most likely switch back to a tower there, and your Life Flight traffic goes away again.

i have a question:

is this facilitated by automation? is it inherent to the way p25 is provisioned and deployed? i.e. is this usually the case, or was it implemented to reduce unnecessary traffic being hauled due to geography that was service-impacting?

as for using an SDR the SDS100/200 are an SDR platform aren't they? i assume it was intended to be rtl-sdr or something like that since Cheaper was mentioned 😆

 

[maus92]

The behavior is by design in a multicast trunking radio system; it is not because the system is "P25" specifically. Older trunking system technologies (EDACS / Smartnet) also behave in similar ways. The reason is to conserve finite frequency resources that can be used elsewhere. The logic is that if no end user is operating within the footprint of a particular site, then there is no reason to transmit their tg traffic from that site. This reduces the number of frequencies required to support normal traffic levels on a particular site.

Each multicast tower has a site controller (either a piece of hardware, or more recently software running on a server container) that determines what tgs are transmitted from the site. The controller knows when a user enters its service area because their radio (subscriber) registers with with the site and tells it what tg it is using. The site controller is connected to the radio network via some flavor of backhaul (microwave, fiber or copper) and monitors all tgs in use in its zone. The controller knows what traffic to forward (transmit) based on the subscribers registered with the site and the tgs it is using. The system is more complicated than this, but this gives you an idea about how the technology works.