Bruce,
this is a lift of Budgetmarine's site which carries notes in pdf
form:

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~
Coaxial Cable
Coax cable transfers your radio transmitter's energy to the antenna.
It is precisely made, with the impedance matched to VHF-radios.
Bigger cable diameter results in less signal loss.We carry three kinds
of coaxial cable that are suitable for your VHF: RG-58, RG-8U, and
RG-8X. Use the RG-58 for short runs only, the RG-8X for runs up to
60' (18m) and the low loss RG-8U for longer runs. Note that splicing
co-ax cable can result in dramatic losses - by a factor of 10 if
done poorly or with improper connectors.

Coax Size vs Signal Loss
Cable Diameter Loss / 100’ Length for 3dB loss
RG-58 0.195" 6.1dB 49’
RG-8X 0.245" 4.5dB 66’
RG-8U 0.410" 2.7dB 111’
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ `

That strikes a fairly common sense note. But remember,
cable characteristics of the same nominal type vary, and some are more
delicate than others, and more susceptible to UV, and damp......

....but to answer your question:
25 watts into 80 ft of RG-8X (using the specs given above which
apply at VHF) implies 50% loss at 66 ft, and there's another 10% over
the remaining 14 ft --so about 10 watts get into the antenna.

(Could you hoist the whole radio up the stick? It would boost output
power to more than double if you just ran audio and power up 80 ft!
- Jest kidding...)

Their RG8U numbers give an 80 ft loss of about 36% leaving
16 watts available for the antenna.

Here's the thing:
You probably could not notice the difference between 16 watts and 10
watts emitted. So I suggest you avoid the aggravation of going with
the thicker stuff.

Brian W


On Sat, 17 Jan 2004 20:21:41 -0500, "McCampbell"
wrote:

Brian
The RG 8x has stranded core and a solid insulator. What you are saying is
it will be good but not perfect. If I have a 25 watt VHF transmitter, I
should expect ??? wattsoutput at the end of an 80' wire. I am trying to
decide if I should go through the aggrivation of the thicker wire or accept
a loss in power. I need to find a 10' piece of the GTO-15 for my Icom
700pro.
Thanks
Bruce
"Brian Whatcott" wrote in message
.. .
GTO-15 is a single conductor (often 14 gage stranded) rubber
insulated pvc clad unshielded cable used for neon signs and ignition
wires.

It is chosen for its 15 kVolt insulation, which can handle most any
3 - 30 Mhz transmitter signals, which may involve high voltages,
but it is unshielded.

If the RG-8X you have in mind has stranded conductor and foam
insulation, this will have a much lower working voltage
(they seem to rate between 300 volts and 1500 volts).

The people who get hot under the collar about foam insulation have a
point; you can easily wipe out transmitter range by treading on that
stuff just once. It is inevitably more delicate than solid insulation.

In a marine environment, it is reasonable to go for durability
where total runs are reasonably short.

It's true that a hundred feet of cable up a tall mast can give away a
lot of transmitter power at VHF and UHF; much more so at higher
frequencies still, and you might want to consider a well secured and
protected lower loss cable type there.
In general, if the cable type you have been using has
been satisfactory, that's the first option at renewal time.

Above all, you don't pick a regular co ax for GPS antennas, where the
losses mount rapidly.
Hope this helps somewhat, without making too many people mad.
I do have the FCC license to fool with these radio/radar installations
commercially, for what its worth.

Brian W

On Sat, 17 Jan 2004 17:06:09 -0500, "Bruce"
wrote:

I am looking at the Ancor brand RG-8x which has tined stranded core.
Could
I also use this type wire for the 10' run from my SSB tuner to the
backstay?
What I had on the SSB was GTO-15???
Thanks
Bruce