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

wrote:
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

Thank you Eric.

Well, as a layman I'd have to agree with you there.
That's why I asked all these silly questions.
(a little knowledge is a dangerous thing)

And thanks for the reply about the antenna cable length.
That 3' tail is a problem to deal with neatly.
The instructions that came with the antenna mentioned something like
an 8" minumum bend radius - but at the top of the mast ???

If I can trim it short things work out a lot mo better.

I went into Rat Shack and found a 50' RG58 package with PL259
connectors on
both ends for about $23.

Still have to get it through the deck, but hey - making progress here,
boss.

I photographed my neighbors deck connections (Catalina 27) and put it
at

http://www.home.earthlink.net/~cavel...es/deckpin.jpg

Anybody have a source for these things?

As a side issue, earthlink seems to have lost the news server (again)
so I
crawled in via google groups.

My email address is

Thanks for all the help guys,

Richard

On Fri, 08 Dec 2006 19:02:42 GMT, cavelamb himself
wrote:

krj wrote:

Might make a good mizzen mast?
Unstayed???

There is a good calculator for coax losses at

http://www.ocarc.ca/coax.htm

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

Like many people have said, 15 or 20 watts and you cannot hear the
difference. It is antenna height that matters as far as range is
concerned. Masthead installation means antenna us way up, but hard to
fix if something goes wrong. And most likely extra connectors, as you
would need to detach the antenna when you take your mast down.

My VHF antenna is only some 3 meters above deck. Permanent
installation and therefore less maintenance problems. Coast guard
stations 20-30 nautical miles away come in strong since they have
antennas way up in tower, and I can hear and work anything within
visible horizon. If you dont go far offshore, this is enough for
emergency communcations etc.

Well, considering all aspects of this, RG8 foam core - WELL SEALED
might be the best choice for me.

Foam is great for fixed installations such as your ham radio antenna
at home. But I wouldnt use foam for boating installations. Any bends
etc, and center could eventually short circut with shield.

Now, how to seal up the connectors?

Adhesive lined heat shrink may be fine for the top one, but the
deck connector? That one has to come apart occasionally.

I used just electrican´s tape with masthead antenna installation on my
previous boat. Takes is few minutes to seal up in spring and take off
in fall. If connectors corrode, you can clean the surface or even
replace them every few years. Leave somewhere a few extra inches of
cable so you can replace connectors.

But make sure you seal cable and connector so that water will not
enter cable. Its not a disaster if contact surface corrodes a bit,
but any leak and coax will be filled with water. Still OK to your DC
meter, but water in cable spells very high losses in HF and VHF,
nothing like in line loss calculations when different cable types vere
compared. Cable filled with water is better thrown away.

Mika






--
----------------------------------------------------
Haluatko lähettää postia? Vaihda osoitteen
eka (vai oliko se toka?) numero vitonen numeroksi
kahdeksan...
----------------------------------------------------

Iv'e used NewMar's Thru-dex fittings for years. They are a bit pricey
so also take a look at Blue Sea cable clams for about half the price.

http://www.rapidresponsemarine.net/b...-Fittings.html

http://www.consumersmarine.com/modpe...&i=920048&aID=

Both of these allow you to drill a hole large enough for your
connector but still give a good seal.

Eric

cavelamb wrote:

Still have to get it through the deck, but hey - making progress here,
boss.

I photographed my neighbors deck connections (Catalina 27) and put it
at

http://www.home.earthlink.net/~cavel...es/deckpin.jpg

Anybody have a source for these things?

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

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----