Dispatch using a different input tone for multi-site repeater system?

[mcjones2013]

The frequencies and tones below are just examples.

Let's say an agency has two repeaters on 159.075 PL 192.8, one on the east side, one on the west side. Both use the same input of 155.025.

The field units have 155.025 w/ 67.0 PL for the east side repeater, and 155.025 w/ 162.2 PL for the west side repeater.

When the dispatcher goes out via 155.025, they're using 136.5 PL.

My questions (questions 2 and 3 are based on question 1 being true):

1: Is dispatch using 136.5 PL to key up both repeaters at the same time? Is this creating a simulcast system of sorts without needing the infrastructure to link the repeaters on the back-end? If not to key-up both repeaters, why the seperate tone?

2: Why not have the 136.5 PL in the field unit radios instead of the seperate tones? My guess is because there doesn't appear to be a voter system in place, it could create an issue somewhere?

3: If you were to add, for example, a north repeater, south repeater, central repeater, etc., with how many repeaters can you do this, using this method of seperate input tones for each repeater execept for dispatch who can hit all at once with one tone, before there's issues?

 

[APX8000]

If those repeaters have overlapping coverage areas, that would make a poor mans hot simulcast mess based on the difference in timing. It sounds like they have a receiver on that 136.5 at both sites that tells the controller to key the transmitter at each respective site. This way, the dispatcher doesn't have to guess which repeater the field unit is coming in on, they just key both. But, this is far from a good set up.

 

[kf8yk]

Is this creating a simulcast system of sorts without needing the infrastructure to link the repeaters on the back-end?

Nope, to work properly a true analog simulcast system needs transmitter frequency control, audio amplitude control and audio phase control.

Sometimes you can get away without all the simulcast gear if there is little to no coverage overlap between the two repeaters. If the east & west repeaters are in valleys and have a big mountain between them then you might be able to do it. Simulcast without timing is sometimes called sloppycast.

 

[mcjones2013]

Thanks. Let's say there is a proper simulcast system in place that I'm not aware of (I'm just a scanner listener), and it's activated via 136.5 but in this case it's only for the dispatcher, can there be separate tones set for each site to key-up only that local repeater instead of using the simulcast for field units?

 

[kf8yk]

It's possible, but I can't say I've seen it done that way.

Maybe this system started out as a non-simulcast system with two co-channel standalone repeaters separated by PL tone. Unless the users frequently roam between east & west coverage they may not be in a hurry to reprogram their radios.

The use of many repeaters with the same input/output frequencies and unique PL tones on the input sounds like many of the US Forest Service repeater nets. Could the dispatcher tone just be the default tone they use for a site that covers most of the area & they only switch if the field unit says contact me on site .... mountain? See this Wiki article for an example.

 

[mcjones2013]

Thanks. I'm aware of the forest service method, CAL FIRE does that here, and it's interesting watching them use a different input PL on each dispatch.

I don't think that's the case here, its probably more of your second paragraph but I'll have to investigate more.

 

[ramal121]

No big deal to set up on the repeaters if they have the ability to accept multiple PLs on the input.

Now why would they do this? The only reasonable thing is to make general announcements or possibly dispatches from the dispatchers over a wide area without having to repeat the message multiple times. The same as if they use multi select from the console when it is hardwired to the repeater.

The field units do not need this capability as the main concern is to communicate with dispatch and local units and not to another radio across the service area. If they do indeed need to do this then simulcast then should be used.

As far as overlap areas from multiple repeaters you have to consider this carefully. Will it serve the majority of the area with minimal issues or will the funk be so large that certain users are shut out from a reasonable receive. Places where the signal strengths are pretty much equal will exhibit the most undesirable audio. Away from these areas there will be some heterodyne noise but voice can still be pulled out. Our brains are wonderful filters. This is unlike digital where the receive simply goes away all together.

Not the most ideal way to do things but can be done with minimal infrastructure.

 

[RFI-EMI-GUY]

Yeah a poor mans quasi simulcast system. Far from ideal as units in the overlap are going to have a hard time hearing unless they are in capture. But capture effect is minimal with the narrow band systems these days.

 

[jeepsandradios]

I did a very similar setup on our SAR system in the county uintil funding was found for simulcast equipment. I had 3 repeater sites. Seperate receiver at the sites with a different PL for priority over field units. Repeaters had wireline priority and the stand along dispatch recevier would use the wireline (priority over RF). Worked ok and most of our folks run portables so the few over lap areas weren't as much as issue. Since switched to simulcast Quantars. Field units would use the PL for the local repeater to them. Poor man voting at its best

 

[KAA951]

Our county did this for years with 4 UHF sites at the points of the compass- different PL inputs for each site but the same PL output on all. However, the dispatcher never keyed up more than one of them at a time. Once you got used to it, it wasn’t a big deal and it was much less expensive then trying to build a voting / simulcast system.

They were even using Motorola business repeaters (35-40 watt) instead of the more expensive public safety repeaters (100 watt). When there is no money- you find a way and make due.