Originally Posted by gh2
I cannot hear the repeaters 30 miles away on a scanner.
In another direction I can hear repeaters 30 miles away.
Will the receive range be about the same as a scanner?
You're asking for specific answers, but specific answers are virtually impossible with the information given. Range is determined by:
minus transmitter feedline loss
plus antenna gain
minus free space loss (determined by frequency and distance)
minus additional path losses
plus receive antenna gain
minus receiver feedline loss
The remaining signal must be greater than the receiver threshold (sensitivity).
We have transmitter power. We can calculate free space loss based on 30 miles. There are too many other missing pieces to determine the range. The fact that you can hear repeaters 30 miles in one direction, but not 30 miles in another is good evidence that other factors (those additional path losses) exist.
So, let's do this... Assume a 30 mile unobstructed path, 5 watt portables, unity gain antennas, and 0.25 uv sensitivity. I'm converting to db because it makes the math simple.
Transmitter power = 37 dbm (5 watts at 50 ohms)
minus transmitter feedline loss = 0 db (portable antenna)
plus antenna gain = 0 db (portable antenna)
effective radiated power= tx power plus antenna gain +37 dbm
minus free space loss -119.2 (30 miles, 450 mhz)
minus additional path losses 0 db (free space, line of site)
plus receive antenna gain= 0 db (portable antenna)
minus receiver feedline loss = 0 db (portable antenna)
received signal strength= -82 dbm (ERP minus pathloss plus RX antenna gain)
receiver threshold= -119 dbm (0.25 uv at 50 ohms)
This path has a 37 db margin. That's a perfect path, not taking into account any losses other than free space path loss. In reality, there WILL be additional losses, we just don't know what they are, therefore can't adequately predict performance, based on what you've given us. BTW, the fact that the path loss is equal to the receiver threshold is purely coincidental, but it makes the already simple math even simpler.
But let's stretch the distance to see where the fade margin goes to zero...
That would require that the received signal level be reduced to the receiver threshold, or -119 dbm (.25 uv at 50 ohms). That value would be
-119 dbm minus 37 db, or -156 db of total path loss required. That distance (at 450 MHz) is about 2100 miles. The only place you'll get that kind of range from a pair of 5 watt portable radios will be in space.
Because we don't know what all the other losses are... terrain, vegetation, buildings, radio performance, weather, antenna patterns, etc. etc. etc. just plan on something less than that. You see why asking a simple question like "what is the range of radios" is close to impossible to answer without detailed information?