Bill Powell wrote: > Thanks for the reply Jim, > > I'm speaking of a mixed user public safety system w/ fire, EMS, 3 PD > zones and emergency management. > > In our system all of the users of a given channel have to be able to > hear and interact with ALL other users on that channel AND the > dispatcher - not what trunking was really designed for: "dumbing down" > radio ops.
Anyone on a talkgroup hears everyone else on the talkgroup. Think of a talkgroup as a 'channel'. So fire has a main dispatch TG, and all FD radios are programmed to power-up on that TG. Everyone will hear everything anyone says on that TG. Then yes, you can have TAC TG's to offload some traffic. Radios can be setup to scan any TG's, and I've heard whole conversations between two users who were on different TG's, and scanning between them! Set the scan delay to zero, and it does work. > Our public safety users are smart enough to know which TAC channel to > use and the circumstances that require it's usse or they wouldn't be > using a radio. Trunking brings nothing to that table. Just that you can have a LOT more of those as needed without having to add actual RF channels, hence licensing issues. A dedicated TG for covert ops, which can be encrypted, special events, like a convention or a big-wig comes to town, the annual 'spud festival', whatever. We're talking THOUSANDS and THOUSANDS of possibilities. > The dispatcher MUST have control at all times - in the "loop" between > what the reperaters hear and what goes out on the air - not connected > as a "user" and competing for air-time. If the dispatcher has a console, it is connected directly to the system, and can have ruthless preemption on any talkgroup the console has privileges for (setup by system admins), just like conventional, only more. It's all in programming. > > Aside from those issues, we have politicians that will not say no when > it doesn't cost them any money. Our dispatchers are up to the task at > the moment but couldn't / wouldn't handle garbage trucks, health > department and all the other non public safety users that would get > added to the system without a thought: politicians are inherently > incapable of rational thought! Dispatchers don't have to be given anything they don't want or need. It's all in programming. They can be given as much or as little as desired. And anything in the console can be muted temporarily at any time. > So - a trunked system would get loaded up with everyone and anyone who > bought a radio and dispatchers and system be damned! It's all in the design and engineering. You determine roughly how may radios and users you will likely have (easier then it sounds), and people that know how can determine how many actual RF channels you need to support them. Statistics are kept in the system that will tell you if you are getting too many "busies", meaning a user tried to access the system and all the channels were busy. On a properly designed system, it should be VERY rare, on the order of less then 5-10 seconds of queuing in 6 months. If there is a big incident, yes it will get busy, but there will be MUCH more traffic passed then there would have been on conventional channels. Oh, and with, I think you said 9 channels you have now, I'll guess you could handle roughly 5-10,000 radios without anyone stepping on anyone else's toes. Oh, and trunking isn't limited to 800 MHz. There are plenty of good systems on VHF and UHF. It's all about licensing correctly. > However, some of the features found in trunked systems would be very > nice to have... > Bp > I don't know of too many ways to get those features and stay analog. MDC, GE-Star, and Fleetsync are pretty much it. P25 will do most everything in conventional that it will do in trunked, but it is digital, and yes, I agree that digital is not appropriate in many, many circumstances the way it is now. Fireground is a prime example of when you should be on ANALOG SIMPLEX. Any place with high background noise should stay analog. At least for now. I'm not very good at explaining things sometimes, and I'm sure there are people much better suited then I to do it as to how it all works and the features.
