Larry wrote:
krj 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.


These days, an s-unit may turn out to be as small as 3 or 4 dB. Can't go
by the S-meters.

The important comparison for coax is the difference in cable losses in
dB. If the difference between two alternatives is on the order of 1 or 2
dB, it is not likely to be noticeable.

I don't think I saw any comments on foam insulation problems. With sharp
bends, the foam compresses and changes the impedance of the cable
resulting in higher vswr and losses. For sharp bends (less than 6 inch
radius) avoid the foam.

Chuck

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