Hi Fred
of cause, basic idea is to use only an auto-tuner ... but, if you look
at the possibilities, on 7 MHZ ( 40m band) there will be no chance for
any auto-tuner to match the aft stay (on the C&C 34 with 12.7m isolated
aft stay length, other length of cause may be possible).
To illustrate the problem i.e. 80m band (3,5-3,8 Mhz) ... aft stay
isolated, far field pattern: max. -0.7 dBi, losses in the antenna tuner
app. 50%, 30° vertical angle. Aft stay connected to the whole rigging
the far field: max 3.93 dBi; losses in the antenna tuner 2%, with a
vertical angle of 60°, which means nearly an optimum for long distance
connections.
Main problem for HF connections on a sailing boat is, during sailing I
have only app. 12.5V meaning something about 60W output, but 15A. Ok, I
can use an Amplifier to increase output, say to 300 W or something, no
problem, but in this case I would use app. 60A or something like that.
For sailing conditions inacceptable. Result in my point of view is, to
optimize the antenna. If I`m able to send out really with 60 W and have
only 2% losses, than everything is fine. With 100W output I had contact
to stations up to 3000 sm away, on sea, with salt water enviroment 60W
should doing same due to much better ground conditions.
For the relay in the circurit, no, it`s not really a big thing.
Looking to what`s going on on this point, only 0.6V and 2A (on 80m band
with 100W, the others I have to check, but I do not expect really high
voltage or current), so a 12 V rellay with 16A should do this job easily.
best regards
Peter
Am 11.01.2013 23:19, schrieb Frederick G Street:
Peter -- on this side of the pond, it's common to use a
completely-isolated backstay for the antenna. I'd be concerned about
getting RF burns if you don't isolate at the top (using the mast and
the rest of the stays/shrouds as antennas); and depending on your
transmit power, you'd need quite a large relay to switch the
mast/rigging in or out of the circuit anyway.
Are you using an antenna tuner between the radio and the antenna?
Most SSB installations I'm familiar with use an auto-tuner along with
the fully-isolated backstay.
See if this helps: http://www.yachtcom.info/backstay/index.html
Fred Street -- Minneapolis
S/V Oceanis (1979 C&C Landfall 38) -- on the hard in Bayfield, WI :^(
On Jan 11, 2013, at 4:08 PM, Colomba <colo...@peter-gottwald.de
<mailto:colo...@peter-gottwald.de>> wrote:
Good day
last October I made my ham radio licence. Whatever, hard stuff.
Of cause my main idea is to bring the ham radio onto Colomba (C&C34)
and I`m wondering ho to install the antenna. Perhaps someone had same
idea and some solutions.
In the moment I`m modelling the boat incl. rigging with 4nec2 and the
results are interesting ... and a little bit confusing. Up to now I
made two setups of antennas, one separate on the stern with max 8m
long wire in a glasfibre tube, app. 10° showing aft from the
vertical. I`m not very pleased to have such antenna, much to
complicated for mooring etc. Also it seems that this antenna will not
work without a huge ammount of losses even if matched by an antenna
tuner.
The other possibility is to use the aft stay. It`s isolated, so in
general no problem. But, it`s funny ... isolated no chance to match
it on 40m band, 80m is possible but not really good. 20,15 and 10m
are working. Than I`ve tried to use the aft stay without an isolation
in the top. Result was interesting. 80m working good, 40m perfect, 20
and 15m do not work, 10m excellent. That the 10m is working coupled
to the whole rigg is realy surprising me. My idea is now to place a
relais in the top to have a circurit with the rigg or to isolate the
aft stay. Of cause, under all circumstances I have to match the
antenna with an automatic tuner, but I want to reduce losses in the
tuner as much as possible.
Perhaps someone has his/her own experience and can give me some
advices. If someone is interesting in the nec file, please give me a
note.
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