Estimating (Very Roughly) Coverage Area

[Dave_D]

Hi all,

Is there a general-purpose chart or formula for the coverage area of a system, given the transmitter's power and frequency? Forget geography, obstructions, sun spots, etc. I'm just looking for the estimated working range of a system. [Per my previous threads, I'm mapping systems by lat/long and radius into my GPS-aware scanner.]

Most of the systems I'm mapping operate in the 800 Mhz spectrum and employ a 100 watt transmitter. Do I tell the scanner that this system has a 10, 20, 30 or 50 mile radius?

Thank you!

Dave

 

[n4voxgill]

10 should give you a good signal. 20 will drop out if you get behind a hill or obstruction. 30 is not realistic, but you may get some signal. FCC limits most systems to a weak signal 3 miles beyond the city limits.

 

[N_Jay]

10 should give you a good signal. 20 will drop out if you get behind a hill or obstruction. 30 is not realistic, but you may get some signal. FCC limits most systems to a weak signal 3 miles beyond the city limits.

Good rougth estimate (given the sparce information)

However the 3 mile rule is only for NPSPAC 800 MHz channels.

 

[Dave_D]

Thanks, guys!!!

How 'bout 150 Mhz at 100 watts? Same thing?

Dave

 

[Rayjk110]

150 MHZ at 100w, depending on height, can cover a whole county. It does over here. Actually our local FD Gets interference from a FD 1 county down on a 90w repeater ontop of a building on the same freq.

 

[SCPD]

There was a formula running around, I think its was something like antenna height times distance to horizon plus .5. I don't quite remember....

 

[Al42]

Horizon (in miles) = sqr(antenna height in feet) * 1.17.

Signals tend to go farther than the horizon (knife-edge refraction, reflection) and less than the horizon (path loss, obstructions), but adding the horizon distance of the two antennas (receiving and transmitting) gets you, if not in the ballpark, at least in the same zip code.