In article ,
Brian Whatcott wrote:

Oh my! Anonymous poster, it was *YOUR* suggestion that an RF ground
of 200 sq ft of mesh under the (external hull) gel-coat was required
for a satisfactory RF ground at HF.

It was the original poster's suggestion of an elevated mesh that
caught your interest, not mine.

As you asked about antenna testing, I should mention that
a supercomputer is not really necessary: there is a handy dandy
gadget ( from MFJ ) which combines several RF test functions like
antenna bridge, SW ratio etc. It ran about $200 as I recall. I
satisfy myself with an LC meter these days - which gets one into the
ball park at $100.
eBay has an MFJ noise bridge at $25 currently.


Hmmm...the capacitance to ground of a few objects in my vicinity runs
about 45 pF per sq ft. Like me, standing on carpet It is just
possible a hi level ground screen of 200 sq ft might get you 200 X 45
pF = 9000 pF

At 3 MHz that would put the capacitive reactance at
1/2pi.f.C ohms = 6 ohms. Not that great. The actual value might
well be quite a bit higher than that.
But that's just me measuring with an instrument, rather than you
guessing how poor it is.
Another thing: the conductivity of sea water does not vary all that
much - it doesn't have much impact on capacitance. But there I go
again, actually measuring things!

Regards

Brian Whatcott
p.s. I have an FCC GROL+rdr. You?

I am not so "Anonymous" as you would think. There are, certainly, folks
who know who "Me" really is. Some even post here.

I didn't "Say or State" that the above WAS required. I stated that "200
sq ft" would certainly provide a "Low Impedance Wideband RF Ground, on
plastic hulled vessles floating in Salt Water." I also introduced the
discreditied concept of "copper screen in the overhead" into the thread,
if you would go back and actually read the whole thread.

Your testing tools seem to be of the consumer variety. Some one should
teach you a bit about modern RF Antenna Design & Testing Tools, one of
these days. Most compitant folks use both RF Network Analysers, and, or
an Antenna Impedance Bridge feeding a Spectrum Analyser with a Tracking
Sweep Generator. Best you come back after you learn to use the tools,
that "the Big Boys" use.

It is just possible that you don't have much of a clue about MF/HF
Marine Antenna Systems and RF Grounds aboard Vessles.

The above statement about some mythical capacitive reactance at 3 Mhz
really shows that your way out of your league in this dicussion. There
are few 3 Mhz Marine Frequencies, (Mostly in alaskan waters) and most
non-commercial MF/HF Marine Radio Users rarely use any below the Maritime
Mobile 4 Mhz Band. There are many 1.6Mhz, 2.0 - 3.3 Mhz, Marine
Frequnecies used in alaska, by commerical users, and a daily basis, and
have been for many years. When was the last time you actually operated,
or for that matter installed, a Private Coast Station, using any
frequency at all, or for that matter any Maritime Mobile Station of any
kind. I operate a Private Coast/ Alaska Public Fixed Station, on a
daily basis, that I designed and installed 20 years ago, and communicate
with vessels all over the North Pacific. Tell us all, about your great
experience in Marine Communications.

The conductivity of Seawater isn't in dispute in this thread on it's
own, what is in dispute seems to be how it compares to fresh water, RF
Grounds used in MF Commercial Radio Stations, and other mediums. What
you fail to understand is that capacative coupling to SeaWater is
extremely Frequency Sensitive, and to design an effective Low Impedance,
"Wideband" RF Ground on a plastic, or cellulose hulled vessel, requires
a very effective coupling to the Seawater over a Wide Frequency Range.
That is the crucks of the problem.

Again, "It is the RF Ground, sonny, the RF Ground"...


Me 1st Class RadioTelegraph, with Seatime Endorsement, Radar
Endorsement, and, wait for it.... Aircraft Endorsement...

On Mon, 01 Aug 2005 20:23:23 GMT,
the not so anonymous Me wrote:
///
Most compitant folks use both RF Network Analysers
///
Me

Whatever you say, Me....

Actually, I am getting this vast sense of relief, that the big boys
are throwing a little abuse my way. I was feeling *so* left out.

:-)

Brian W

"Me" wrote:

There are few 3 Mhz Marine Frequencies, (Mostly in alaskan waters)
and most non-commercial MF/HF Marine Radio Users rarely use any below
the Maritime Mobile 4 Mhz Band.

I don't claim to be any sort of expert, but on the radio course I took, we
learned that 2182 kHz is "the international distress, safety and calling
frequency for radiotelephony". As far as I can see that is well below 4MHz,
and commonly used even outside Alaska.

-Heikki

In article ,
Heikki wrote:

"Me" wrote:

There are few 3 Mhz Marine Frequencies, (Mostly in alaskan waters)
and most non-commercial MF/HF Marine Radio Users rarely use any below
the Maritime Mobile 4 Mhz Band.

I don't claim to be any sort of expert, but on the radio course I took, we
learned that 2182 kHz is "the international distress, safety and calling
frequency for radiotelephony". As far as I can see that is well below 4MHz,
and commonly used even outside Alaska.

-Heikki



Actually you will find that in the USA, 2182 Khz is not used along our
Coasts for the simple reason that it's daytime coverage (Groundwave)
is easily covered by Remote Base VHF Highsite Radio Systems. This is
different then most of the European Countires as they tend to have
significantly less coastline to monitor, and usally it can be done with
just one or two stations in any country. All High Seas Distress Radio
Systems are now based on the IMO GMDSS Convention, which feature
multiple Maritime Radio Frequencies in the HF Band. In the USA 2182.0
Khz isn't even monitored on a regular basis by human ears. For the
North Pacific, 4125.0 Khz is moniotred by human ears, from Kodiak,
Hawii, and Comox BC on a 24/7 basis.


Me who understands the difference between the book,
and reality.....