[Elecraft] New antenna (Definitely OT)

[Ron D'Eau Claire]

And then there's the issue of keeping the "element" sort of the right length
as the water breaks up into globules at the far end, not to mention the
impact of typical winds on it. 

I noticed they demonstrated a version with the water running up a plastic
pipe, but if you're going to do that a copper or aluminum pipe would be much
more efficient.

Ships, having a sea water ground plane all around them, get out extremely
well with short, loaded vertical antennas. The 'standard' today on large
ships is a 22-foot free standing fiberglass "whip" used across the HF bands.
Most ships have two or three of them. Back before CW on MF was dropped from
common use, they typically used a 100+ foot end fed wire on 415-500 kHz.
Even a 150 foot wire on 600 meters was less than 1/10 wavelength, yet with a
few hundred watts ships routinely worked over thousands of miles at night
and hundreds of miles in the daytime using CW. 

The "moral" of the story for us Hams is that a short vertical is exactly as
good as its ground system. 

73, 

Ron AC7AC



-----Original Message-----
On 10/17/2010 1:40 AM, Jan Erik Holm wrote:

> This will go nicely with my K3
> http://www.youtube.com/watch?v=9tIZUhu21sQ

Seawater has electrical conductivity of seven *orders* of magnitude  
lower than copper!

As a quick and dirty check, I created a simple 10m ground plane  
antenna in NEC-4.  Four counterpoises and a vertical radiating element  
that is bottom fed, all of equal lengths, with the counterpoises and  
the feedpoint 1m above seawater (natch!) ground.  All elements 0.5" in  
diameter.

With perfectly conducting elements, the feedpoint impedance is just  
about 35 ohms, with a gain of 4.7 dBi.

When I changed the conductivity of the vertical element to 5 mhos/ 
meter, while keeping the counterpoises as perfectly conducting, the  
computed gain dropped to -8.2 dBi and the feedpoint impedance is  
capacitive at 320 -i*250 ohms.

I.e., something like 13 dB loss compared to using copper elements.

BTW, I could not achieve resonance by extending the length of the  
radiating element --  I guess you will need a KAT500 in addition to  
that KPA500 which you use to make up for the missing 13 dB.

This could make a good water heater.  All that power has to go  
*somewhere* :-).

73
Chen, W7AY