From: John De Armond
Subject: Re: RADIO RANGE - was One-rate nightmare
Date: Thu, 29 Jun 2000 02:22:33 -0400
> W F Sill wrote:
> > Communicating with a repeater is a special case, and the Oz is right
> > that there will be times when additional power will bring up a
> > repeater that you can't otherwise use.
> > Q: Why, O Wizard?
> > A: Because the repeater squelch is deliberately set high enough to
> > prevent weak signals from getting through!
> There's one other reason (that I don't think has been mentioned)
> why increasing the power may make a difference when using a
> repeater (or a cell site, for that matter) - frequently, the
> repeater is running drastically more power than the mobile
> or handheld rig.
And yet another reason. Many repeaters around here use tone gated
squelch. It works as follows: The receiver has a PL tone decoder
that opens the squelch and keys the transmitter. This is
conventional. We have to use it for resource management due to
there being so many repeaters around high population areas.
However, we* didn't want to emulate the pricks out West who have a
stroke if some stranger uses "his" repeater so we didn't want to
have the PL screen out anyone who stumbled across our frequency. So
we arranged the PL decoder to simply change the setting of the
squelch circuit so that without PL present, it takes a strong
received signal (typically about 25-30db SINAD) to open the
squelch. Thus, if you have a strong signal but don't know the PL
frequency, you can still use the repeater as long as your signal is
strong enough to fully quiet the receiver. We programmed our
controller to change the squelch tail beep to alert us that a non-PL
user was on. Someone would usually pop up and tell him what PL tone
to use before he fell out of full quieting range. A lot of power on
the visiting user's rig would sure make a difference under these
*I'm proud to be the evangelist who pushed this concept in the
Atlanta area. It worked so well on our little club's repeater that
it was adopted by many other operators.
Getting back to cellphones, more power helps because the base
station controls the user's transmitter power and will continue
commanding up the power to maintain S/N until it can't anymore. The
more power you have in reserve, the farther you can talk.
The issue is also more complex than just power. Since a few feet of
RG-58 acts like a dummy load for 860 mhz RF, any benefits a 3 watt
rig have will be negated if the thing has to work through several
feet of coax cable. One must also remember that the coax cable loss
is symmetrical - it attenuates just as much on receive as on
transmit. Under the circumstances of a bag phone working through
long coax, a 300 mw portable phone will likely out-perform it.
OTOH, a properly installed 3 watt phone kicks ass! I had a
Panasonic 3 watt system permanently mounted in my Bimmer in the
early days of cellular service. It mounted under the rear shelf and
had oh, a foot or so of RG-213 feeding the thru-hole center-fed half
wave whip on the rear deck. That setup smoked. Before they had
coverage up I-75, I could continue using the phone almost to
Cartersville coming out of Atlanta. My portable would work barely
half the distance. Around atlanta, there was no concept of building
or multipath fade. It sounded just like a land line. I remember
many times having to tell clients to cut it short because I was on
(expensive) cellular - they couldn't tell otherwise.
The mention of using a Yagi is a good one, provided the coax is kept
short. Even 10 feet of RG58 will kill the signal. Some company
used to make (maybe still does) a nice little yagi that sat on an
about 2 ft tall stick of rigid coax that screwed directly into the
TNC connector of a bag phone. I had a friend who had one. We could
go up on the mountains in Tellico Plains TN and get cell service all
the way from Atlanta, over 80 miles away.