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.

In article ,
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.

The difference might be real, due to improved receiver sensitivity or
to the use of an antenna which looks the same but has lower losses or
higher gain.

The difference might be illusory, due to differences in the assumed
test conditions (e.g. height of the radios above ground clutter and
obstructions, or just what sort of signal intelligibility qualifies as
an acceptable contact for the purposes of figuring out range).

The difference might be marketingbabble - numbers pulled out of the
air, or out of somebody's bodily orifice, for the sole purpose of
making the radios seem (and sell) better than those of the competition.

Frankly, I suspect that a a 1-watt GMRS radio is likely to achieve
even the lower of these two range figures (5 miles) only under rather
optimistic conditions... e.g. both users are up on the tops of
buildings or hills, with a clear line of sight to the other and with
no obstructions in between the two.

In a typical suburban ground-level setting, I wouldn't count on
getting signals to go more than a mile, and you'd probably have to
walk around a bit to find a location with a clean signal path (direct
or reflected) to the other.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Pdigmking" wrote in message
...
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.

Here's a good site:
http://www.popularwireless.com/gmrsrange.html

Cheers.

Ken

In article , 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-

Both are theoretical values for person-to-person communications over level
ground with no obstructions or reflecting surfaces. Since the
communications path is essentially line-of-sight, slight efficiency
differences in power or antenna gain make little difference. Therefore,
the differences must be based on some assumption that was different when
calculations were made.

For line-of-sight, you can approximate the distance to the radio horizon
for each, and add the two for total maximum range. Suppose a person holds
the handheld radio up to their face, and it is five feet above ground.
The distance to their radio horizon in miles, is approximately the square
root of twice the antenna height in feet, or 3.2 miles. Range to another
similar person would be 6.4 miles under these ideal conditions.

You should see that estimating distance based on different heights can
result in differeing ranges. A height of 3.125 feet (sitting down?) has
range of 5 miles, and a height of 8 feet (basketball player?) has a range
of 8 miles to a similar person.

This approach works fairly well from mountain to mountain or airplane.
Based on power and receiver sensitivity, the limiting range might easily
be greater than a hundred miles. In the real world there are reflections
that cancel signals (Multipath), tall objects that block signals and
vegetation that absorbs them. Person-to-person on typical terrain might
easily be limited to less than one mile.

Fred

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.

Paul;
I will add another angle;
Motorola used to make a low cost mobile radio called the "MOXY". It was
a cheap radio to compete with Japanese brands. Motorola also sold a
somewhat more expensive model called the MAXAR 80 targeting buyers
wanting a high performance dash mounted radio. In the high powered UHF
and VHF models of 30 watts and higher, the MAXAR 80 chassis was used in
both the MAXAR 80, the MAXAR (slightly cheaper) and the dirt cheap MOXY.
All three radios had same guts (a pretty good performer by the way) but
were given a different set of performance specifications. So the guy who
bought the MOXY (which was an ugly radio with a tiny mike!) got just as
good a radio as the buyer of the hyped up MAXAR 80.

It is called specsmanship

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.