Originally Posted by sepura
1. for a small city about 6 square miles? Would one repeater work for the whole city if it was TXing at 100W 300 feet up? With all flat land.
2. How does a conventional radio system work with many repeaters? Does the signal go to the closest repeater and then it's transmitted back to the main repeater then back to the other radios or?
3. How does a five watt radio reach the repeater? Does the repeater put out a signal that reaches out to the radio?
That's about the dimension of my home town in VA where I was a police/fire dispatcher and a volunteer firefighterback in the 70's-80's. The PD used a UHF system, with the repeater on top of a water tank in the middle of town. Dispatch from HQ was covered by runnung a tranceiver from the board and simply pointing a yagi to the repeater. (the boad had panels for PD1, PD2, FD, and the statewide lo band freq.) The UHF system worked great within town, even on the HT220 HTs.
The FD used a VHF system with the repeater at HQ and the antenna atop a 100' tower. The footprint of this system went well beyond the city, with mobiles able to hit the repeater as much as 20 miles or more out.
What was interesting was that on PD1 - the repeater freq for the police, HQ was like just another mobile unit....the repeater itself was across town. The FD repeater, on the other hand, was at HQ, so i was operating the through the repeater itself. Perhaps this was the optimal set up since we used that freq for the FD alert tones and paging, the tone board fed right into the controller. The downside is that I only heard what mobiles transmitted on FD1 - the repeater channel, because if they went to FD2 - simplex on the mobile RX freq, I could not hear them at HQ. (The undercover cops sometimes used FD2 as a tactical freq, as their conversations were not captured on tape at HQ, lol.)
My ham club's repeater system where I live now in NY is VHF (2m) with one transmitter - antenna on top of a 300'+ tower, and about 5 receive sites around the county. The repeater uses a voting system to determine what signal is selected. The county PD uses a similar system on VHF and there are known dead spots in the county, but this is way more than 6 miles square.
The problem with VHF - in the past and now, is problems with coordination and interference from band openings. Back in the day, my FD in VA often had Camden, NJ booming in. The PD of the county where I live now in NY has had a long running interference issue with a neighbor in NJ. I haven't experienced this on UHF.
If you are the guy in charge of designing a system for your town, you probably need to work with someone who can model your communications requirements (e.g., departments, talk groups, security/encryption, specs like citywide portable reliability, etc.) and topography against various system variables, like band, power, receivers, transmitting antenna height, etc., etc., etc.....not mention your budget!
Sounds like a fun project...enjoy!!