It is all BS
First; Don't believe the mileage claims of any manufacturer, even
Motorola. The specifications which make a difference are not published
by most of the FRS and GMRS manufacturers.

There are important considerations used to calculate the BEST CASE range
of a portable radio, however it is unavailable for independent evaluation.

1. Antenna gain or loss (usually a loss for a handheld) NEVER PUBLISHED
2. Receiver sensitivity SELDOM PUBLISHED
3. Transmitter power SOMETIMES PUBLISHED, BUT MISLEADING

The above values figure into the "system gain" and can be used to
estimate "best case" line of sight communications" when you factor in
"free space loss" for the distance. But this only works mountain top to
mountaintop!, the path is always worse than free space loss when there
are obstructions like hills, buildings or foliage. I have never seen any
manufacturer other than ICOM provide receiver sensitivity values, no
manufacturer will tell you the antenna gain/(loss), but if you know the
FCC certification number, you might be able to figure it out to some
degree from FCC records.

4. Receiver selectivity (immunity from interference on adjacent
channels) NEVER PUBLISHED
5. Receiver intermodulation (immunity from interference and overload
from multiple off frequency transmitters) NEVER PUBLISHED

These two above reveal how well a receiver will work in an urban or
suburban environment, or even when on a hilltop amongst broadcast
towers. None of the manufacturers want you to know how bad their
receivers behave with respect to the above. If the receiver is prone to
getting interference, your range diminishes rapidly.

6. Transmitter current drain
7. Receiver current drain
8. Operating time

These you need to know if you plan to use the radios on disposable
batteries over an extended time. Don't buy an FRS or GMRS radio unless
you can power it from AA batteries (AAA's suck!)! Operating time is
calculated on a duty cycle like: 10% transmit, 10% receive, 80% standby.
To improve on operating time, the ICOM IC-4008A and IC-4088A FRS radios
publish these specs and their radios are equipped with a battery saver
feature so you can go days with the same set of batteries.

Joe


Pdigmking wrote:

I'm looking at these GMRS motorolas, one is a t6510xmrs and another is a
t5520. Here's the thing: both have a power output of one watt, but one
claims to have a distance range of 8 miles, and the other 5. Is this BS or
what? Why would one 1 -watt radio have more range than another 1 watt
radio? They both have the same size antenna.

Paul.



--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"

The Lost Deep Thoughts By: Jack Handey
Before a mad scientist goes mad, there's probably a time
when he's only partially mad. And this is the time when he's
going to throw his best parties.