The Radio Information Board

I am using TK 840 as my radio base station, my antenna is about 35 feet high, and i am using LMR 400, after 8-10 miles i get a lot of static, i was wonder what do i need to do to get further and better quality? there aren't a lot of tall building around me and i am using 450-470 band. I am about to buy a TKR 820 desktop repeater, would that make any difference? i am 6' 1/4 wave mobile antenna on the cars that i talk to and my base antenna is omni directional. thank you

If your antenna height is 35' and the terrain is smooth, the theoretical distance to the "radio horizon" (distance your antenna can "see") is 8.4 miles. Actual coverage is usually somewhat greater than this but I would say 10-12 miles with some noisy reception beyond about 8 miles is the best you could expect.

If you replace the base with a repeater operating on the same antenna, it will actually be somewhat worse because of the insertion loss of the repeater duplexer.

To increse coverage significantly you would need to either:

Increase antenna height to 100' (theoretical coverage extended to about 15 miles or more).

OR

Lease space on a tower at a good high location for a remote base or repeater or lease service on a shared community repeater.

Antenna height is the key to coverage. Increasing transmitter power or antenna gain has a minimal effect. Doubling power or antenna gain at the base will only produce a barely perceptible improvement. Since you are only using 1/4 wave antennas on the mobiles, upgrade to good 5db gain mobile antennas would help.