On Wed, 26 May 2004 03:42:24 GMT, Bruce in Alaska
wrote:

In article ,
"Steve (another one)" wrote:

Dear Folks,

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.
Could someone please suggest an equivalent, or at least a description !

Also if the ground connection has to be broad copper strip because RF
won't run down a wire like a conventional dc current, how can the
antenna be wire ? Doesn't RF have to run along the cable to the base of
the antenna and then up the antenna wire itself ? I'm confused !

Thanks for your help.

Steve


Others have covered the GTO-15 question, very well.

There are a number of reasons that copper strap is used for RF Grounding
in the Maritime Radio Installations. One being, that it is desireable
for the RF Ground to have the lowest possible Impedance at the
transmitted frequency.

Two being, that it is desirable that the surface area of the RF Ground
System be as large as practicable, to maximise coupling to the seawater.

Three being, That RF flows on the surface of the conductor, and more
surface area means lower impedance on the Ground.

The antenna wire isn't supposed to couple into the seawater, but into
the ethos, so it should have the least surface area as can practically
handle the RF Current of the transmitter and be tuned to resonance by
the tuner, and as low of resistance as practicable, so that RF Current
can propagate along it's length.

Bruce in alaska Gary S. can chime in anytime on this.....


Hi Bruce,

The diameter of the antenna wire is not too important. Actually the
larger it is the less resistive loss it has and less power will be
wasted in heat. But unless the antenna is significantly shorter than a
quarter wavelength that loss is negligible in the antenna as the
radiation resistance (radiation resistance is where the power goes to
be radiated) is usually much higher than the resistive loss of the
wire.

However in a very short antenna the radiation resistance can be only
an ohm or a few ohms. Then the resistance of the wire would be a
larger percentage and the heat loss would be greater thus warranting a
larger diameter wire.

Otherwise a larger diameter wire has the advantage of greater
bandwidth for given tuner settings. But the difference between #10 and
# 16 would probably not be noticeable.

As you well know, in the case of the ground system as we have said
many times before, it needs to be as short as possible or it becomes
part of the antenna and radiates. "The antenna starts at ground".
Anything above ground is antenna.

Regards
Gary