Don't get hung up on the length issue. I use a 23' whip and get as good
as perfomance and any of my friends with insulated backstays. I believe the
specs say that 23' is the min length that can be tuned by the AT-140. Any
length beyond that doesn't gain that much additional performance.
Doug, k3qt
s/v Callista

"David Swindon" wrote in message
...
I am in the final stages of building a 38' steel ketch and am currently
looking at the installation of a SSB system (Icom M802 / AT-140). I have
read back through the forum postings and gained some good knowledge,
however
am wondering if anyone can help out with some the problems specific to a
ketch rig.

My boat (a Roberts Offshore 38) has a main mast 38' off the deck, and
mizzen
28' off the deck. This gives me a total backstay length of about 42', and
a
triatic about 14' long. My plan is to rig the main mast with twin
backstays
(i.e. the backstay is split right from the top of the mast).

I realise that the longer the antenna the better, however the backstay
runs
quite close the shrouds of the mizzen mast near the deck, and so I figure
I
would probably need to place my lower insulator 6' off the deck (what is
the
minimum clearance between the antenna and another shroud to avoid
coupling?). I've seen recommendations saying the top insulator should be
3'
from the mast head (any comments??). This would leave me with an effective
antenna length of about 33'. I guess what I am trying to gauge is what
effect all of the other rigging around it will have on performance (being
a
steel boat all of this other rigging will be grounded). Is there a gain to
be made by insulating the triatic and linking this to the backstay
antenna??? What is your judgement on wether this will be an adequate
antenna
system??? One suggestion that I have had is to rig a whip antenna off the
stern and use a change-over switch to manually select either the backstay
or
whip depending on the frequency for transmission . . . I much prefer the
idea of just using the backstay. Any comments would be much appreciated.