In article
,
Bil wrote:

I am starting to think of replacing the standing rigging of my cutter-
rigger monohull. The current rigging includes an insulated length of
the backstay (insulators top and bottom) which I use as the antenna of
my SSB transceiver (an ICOM M710 RT with an ICOM ATU).

A dock idler reckons that I could get a superior antenna by only using
a single insulator on the backstay - just the bottom insulator. That
would mean that the upper portion of the backstay, the mast, the
shrouds, and the forestays would all be parts of the antenna.

That dock idler reckons the ATU would tune the whole rig. And that
more metal in the antenna is effectively better.

Is this madness? Heresy? Or makes sense?

Cheers

Bil

If you listen to this Yahoo, you will get exactly what you paid for....
NOTHING.... On most plastic (Non Metal) hulls, the antenna design is not
the limiting factor in Antenna Efficiency. The Limiting Factor is ALWAYS
your RF Ground System, for the antenna. Autotuners are a fair compromise
in getting good antenna efficiency, HOWEVER that make the assumption,
and it is a BIG Assumption, that the RF Ground system is LOW Impedance,
across the entire Frequency Spectrum used by the Transmitter in question.
Take it from one who has spent a career (35+ Years) as a Marine
Radioman, doing systems design, and installations, all over the North
Pacific, your RF Ground is significantly more important than whatever
you decide to stick up in the air. With ALL the above, noted, Autotuners
have some significant limitations, in just what they can tune, while
maintaining efficiency. The electrical 1/2 Wave Point of the antenna,
is where a Marconi Antennas impedance goes to infinity, and AutoTuners
get really wonky as you approach this area, and usually have a dead spot
that is 500 Khz wide around that frequency, where they can NOT tune,
even with a perfect RF Ground. When designing an antenna system for a
specific vessel, determining just where to place this Dead Zone in the
Radio's Spectrum is a Major Criteria. for strictly Marine Applications,
I always like to use 7.250 Mhz, for that, because it is in the middle of
the 40 Meter Ham Band, and very few commercial Mariners are Hams, so it
was nice. Non-commercial vessels are much more likely to have a Ham
aboard, and 40 Meters is a popular Ham band for Mariner Hams so that
just doesn't work, and some other Frequency needs to be used. some of
the ceaper Autotuners do NOT do well with over 3/4 wavelength antenna
Frequency Tuning, as the Phase Detector systems weren't designed to give
adequate Phase outputs in these cases, and this causes the Autotuner to
not find a good tuning setup. If the RF Ground has impedance bumps at
different frequencies, then these will also cause the autotuner to find
frequencies that it can't find tuning setups for, as well.
It is much easier for one to use a Manual Tuner, with some selectable
fixed Capacitance, on both Input and Output Circuits, and a good Roller
Inductor, for a tuner and make a Log of the settings for any particular
Frequency used. But that is just my opinion, and your milage may
vary.....

--
Bruce in alaska
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