To those that say a few db extra cable loss does not make any
difference consider the following:

Every time you double the height of your VHF antenna you gain 6 db in
signal strength.

6 db signal strength increase at 30 miles accounts for about 3 extra
miles in range.

The amount of loss you have in the cable or because of low antenna
height effects the receiver the same as it does the transmitter.

With an extra 6 db of cable loss you will hear 3 miles less at 30
miles.

When you add antenna height you pick up signal gain from added height
but also increase cable loss due to longer antenna cable length.

There will be a point with a given type of cable that when you double
the height to gain another 6 db you will also lose 6 db in cable loss.
As an example with RG58 at 6 db loss per 100 feet, if you were at 100
feet and went to 200 feet antenna height you would pick up 6 db from
height but would also loose 6 db in additional cable loss.
If you continued to use RG58 it would do no good to increase the
antenna height at that point.

At lower, more practical heights, that are associated with boats the
same problem exists but to a lesser extent. Because you have not
reached the gain / loss (height / cable loss) at lower heights you
still have a gain when you increase antenna height.
But if you use better cable you can realize more of the height
advantage than with higher loss cable.

Remember, every little few db of gain or loss helps. They all add up.

You could reduce your power a few watts and loose a couple of db. You
could use higher loss cable and loose a couple of db. You could mount
your antenna a little lower and loose a few more db. Pretty soon you
have some significant loss. Will you notice the difference in signal
strength when signals are good, no. Can you still talk, sure. Can you
talk as far, no.

To my way of thinking why leave a few db of signal strength laying on
the deck when all you have to do is use a little better cable. That is
probably the cheapest way of all in gaining a few db of signal
strength.

Regards
Gary


On Sun, 18 Jan 2004 06:15:40 -0500, "Bruce"
wrote:

Brian and Gary...good stuff. Now understanding the loss of power, it
would make sense to get an amp (Idon't think it would be legal) or have a
second line run to the spreader on the mizzen.That would drop the run down
to 30' and a corresponding increase in power.
Thanks for you help
Bruce
"Gary Schafer" wrote in message
.. .
This is the same Larry that says that he has a 150 watt VHF amplifier
to switch in the antenna line if he can't be heard.
Yet he recommends using lossy rg58 cable. Old surplus stuff at that!
When cable ages it does not always do so gracefully. The dielectric
breaks down and the losses can be considerably higher than new cable.

For the amount of work involved and the minimal cost of 100 feet of
RG8 type cable, use the best NEW cable.
RG8 with polyethylene insulation is the way to go unless you have a
size restraint. And forget the aluminum wrap shield stuff. You are
asking for trouble in the marine environment with aluminum.
You do not need "high shielding" for a VHF radio.
Foam insulation is not a good idea on a boat though. The center does
migrate at bends. It is also very difficult to install connectors on
foam cable. The heat from the soldering iron melts the insulation
quickly and lets the center wire move to the side. Sometimes even
shorting it.

Regards
Gary


On Sat, 17 Jan 2004 18:53:08 GMT, Brian Whatcott
wrote:

I recommend checking with suppliers' specifications for cable
construction materials: solid or stranded? solid or foam insulation?
%coverage of shield? Tape wrap? Non-acid outer sheath? before
blindly implementing Larry's recommendation below on choosing
cables. Yes: let's call it a reality check.

Brian W



On Sat, 17 Jan 2004 05:54:58 GMT, (Larry W4CSC) wrote:

... 55' mainmast has a Shakespeare 1/2 wave VHF antenna on top
with about 75' of RG-58A/U military surplus cable///
If I had to start from scratch, and couldn't buy a 500' roll of
surplus RG-58A/U for $10 at my local thrift shop...

I recommend using VERY flexible, and reliable,
Polyethelene-cored, finely stranded center conductor RG-58A/U (not
RG-58/U which has a solid center conductor) for your purpose. All
those fancy loss charts mean nothing when the fancy foam cables are
pulled through a sharp turn, somewhere. Hell, you can wind RG-58A/U
in a hangman's noose and it'll still work great! REALITY CHECK!!