It's all about capacity. The Virginia system doesn't have the same capacity as the VIPER system does. Because VIPER has so many more site that cover a smaller area (footprint), they don't have to share those sites with a larger geographic area. Because Virginia is using VHF, which has a larger footprint (just based on free-space propagation), they would have to significantly increase the number repeaters at each site to even get close to the capacity of VIPER. This is the same reason cellular sites are much lower and closer together in high population areas because of all the users.
Check to see who is on the Virginia system and compare that to who is on the North Carolina system and I think you'll see a difference.
I was primarily referring to the geographic coverage in Virginia. Amazing it only requires 61 sites, which is of course due to increased free-space propagation. Number of subscribers was not in my thoughts since I was asking why not 150 MHz in western NC. Virginia maybe could add 800 MHz sites in metropolitan areas if they wanted to add subscribers there and get the increased density.
I certainly understand Cellular Radio and free-space propagation. None of this explains why 150 MHz cannot be used in the mountain counties.
There may be other technical or cost considerations we are not aware of, that surely the Viper Engineers are. Is it just cost? There seems to be an officer safety issue if loss of low band coverage is not addressed.
If NC does not maintain low band, what will be the solution for the mountain coverage?
This is what I was thinking.
I was wondering why 150 MHz could not be a solution since they need to buy more radios, and they could buy multiband to add to the fleet. The major cost would be adding 150 MHz to the existing sites. 800 Mhz and 150 MHz transceivers could be used on the same sites utilizing different trunk channels. If a radio is only 800 Mhz capable it just uses an existing ID for"Trp F Dist 2" and for 150 Mhz a different ID with maybe the name of "Trp F Dist 2V", or whatever. Same traffic on both. The multiband radio could use either and also be compatible in the rest of the state where 800 MHZ is used.
Except for major metropolitan areas, site density is not as much the concern, but site coverage is.
NC requires 220 sites due to free-space propagation and not capacity. Monitoring sites in NC it is obvious they are very under utilized. NC is very rural compared to other states that probably would have to have a high density of sites to provide enough channels using limited range per site. NY and NJ certainly comes to mind.
Wake county is covered by 6 sites and Durham by 4. Not huge numbers where the number of subscribers is so high. Cellular traffic has a much higher utilization of time slot per channel than 2 way traffic on a trunked system, and cellular has much higher subscriber numbers per geographic area. Trunked systems usually would not need as much channel capacity as cellular for the same number of subscribers. In trunked systems, adding channels up to the max is more often the consideration for increased capacity than adding sites as long as the sites can cover the geographic area. Cellular is usually the other way around due to such high subscriber density. Which as you pointed out, is the reason for limited range and high site density. Cellular sites are certainly engineered to cover a footprint. Many are not even omnidirectional, especially in metropolitan areas. Sites in rural areas are at higher points, sites in metro areas not nearly as high.
It would be interesting to see how they address the coverage issue without low band. I would imagine maintaining low band for safety will be far cheaper than anything I suggested using 150MHz on Viper. Why not keep it? There are still plenty of low band radios available new. There was a big drop in supply years ago. Now seems the options are much better. Vertex certainly makes good radios.
Vertex Standard | vx-5500 Low band radios need repeaters so they are still making low band transmitters and receivers.
https://midlandusa.com/product/71-0100a-analog-transceiver/