Antenna cable?

krj <joyner_k RemoveThis @bellsouth.net> wrote in news:S6heh.23081$T6.392
@bignews5.bellsouth.net:

> A 25W VHF at 156 mhz with 40 ft of RG-58 will have 15.819W at the
> antenna. With RG-8X it will be 16.741W. With RG-8U it will be 19.859W.
> Assuming a VSWR of 1.3
> krj
>
>

OK, so here's a little reality check......

Stop by any Radio Shack and look closely at the S-meter on any CB radio
in the shop.

http://www.smeter.net/slc/signal/strengths.php

It doesn't matter this is VHF or HF or whatever. 6db is one S-unit.....

So, 1 s-unit drop is 1/4 the power (1/2 the voltage) of the field,
approximately. This might be important on HF where noise is a factor,
but not VHF because it's LINE OF SIGHT.

From a 50' 3db sailboat antenna, 25 watts = 50W ERP at 50'. 15 watts =
30W ERP at 50'. In BOTH cases, the signal at the RADIO HORIZON is
significantly more than is necessary for solid comms unless you're behind
a 60' wall of seawater (in a trough in 30' seas) which puts the other
station over your radio horizon every 10 seconds and radio is somewhere
down the list of priorities at that moment.

The only place on VHF where 1 S-unit might be a factor is around a busy
marina city where the marina has a 50' tower he shouldn't and a 25W radio
I think should be a violation of his license. It just creates havoc at
distance. Marinas need walkie talkie licenses ONLY. If you want to
reserve a slip, call them on the cellphone, not Ch16. A few of the old
public correspondence channels ought to be converted to marina channels
and they should be restricted to it so boaters can listen to 16 WITHOUT
all those dock calls, which makes you want to turn the volume down from
the constant calling....The 1 S-unit might make a small difference trying
to get an emergency declared when some big Hatteras is calling about a
slip....at 25 watts, of course.

Every marina radio in Charleston is setting on 25 watts. Check yours,
unannounced, and take a sample in your area. Ask the teenaged girl
behind the desk if she sees an H or L on the little screen. She'll have
no idea what it means or how to change it. She's not allowed to do
anything like that....

RG-8X or RG-58A/U or RG-8 (3/4") or RG-17A/U (1.5") won't make a hoot's
difference on the air......to another boat on the horizon.....It's
physics.

Larry is correct. 40' of rg58 with a matched antenna will have about
2db of loss on the marine band. This is nothing to be concerned about.
Nobody can tell, with there ears, the difference between the rg58 vice
LMR400. Use the rg58 and use BNC connectors. You can cut the antenna
cable as short as you want because you are adding another 40' length of
cable. Most laymen just don't understand the relationship between power
output and field strength.

Eric