Hi Joe
thank`s for the input. The MFJ-4416B seems to be a really good idea to
solve the voltage problem.
I`m using a LDG tuner, a little bit modified, but in general something
like the SGC.
For your 10m problem ... the problem is that on an antenna you have
voltage and current waves and the length of the antenna will effect the
possibilities of the waves on the antenna, the point of load to the
antenna will be effected by the current and voltage wave and will have,
to try to explain it simpel, the result of different resistance simple
to say R[Ohm]= U [V] /I [A]. Due to the fact that every different wave
length on an antenna will have different wave forms of U and I on the
antenna, you might have the problem to have too high restistance
(depending on the tuner, most of them have a max resistance of 600-850
Ohms which they are able to match) or, too low restistance, I don`t know
any tuner able to match under 5 Ohms. For your situation with the 10m
band the only solution is to make the antenna longer or shorter or to
try to move the point of load on the antenna to get into a situation
either to reduce the resistance or to make the resistance higher as
let`s say 5 Ohms.
It`s not a problem to measure this. I`m using a "noise bridge" to
figure out what`s going on. Very simple to use, the bridge will be
coupled between receiver and antenna, the interesting frequency will be
fixed at the receiver and than the potentiometer (maybe also a variable
capacitor) will be used at the bridge to find the minimum point of noise
in the receiver. Knowing the resistance of the potentiometer and knowing
the capacity of the capacitor will give you the exact reactive part of
impedance and the real restistance.
In case of my antenna in the 40m band or exactly to say at 7.02 Mhz
the resistance is nearly 0 [Ohm] and no chance to match this. Only
possibilitie is to change the antenna to leave the situation of extremly
low resistance in the bands to transmitt. That`s why I`ve got the idea
to make the antenna longer and to make a bridge with a relay at the
upper insulator.
What I saw by running the NEC software was a very interesing effect.
At 80m the result only with insulated antenna was -.7 dBi as max output,
with the whole rig 3,93 dBi. On 40m band, impossible due low resistance
at insulated antenna, 16.7 dBi at whole rigg in max. At 20m band,
insulated 14.2 dBi max but only 1.2 dBi for whole rigg. 15m band nearly
same procedure 8.96 dBi insulated and 1.5 dBi whole rigg. 10m band 8.92
dBi insulated and 12.4 dBi whole rigg.
That`s why I have to insulate for 20m and 15m band and to use a relay.
The high performance of the antenna with a huge ammount of dBi is
based on really directed signals. It`s very interesting to see the
effect of the total rigging and the way of directed signals. For the 80m
band it`s a direction more to aft, 40m band more forward direction, all
other bands will be extremly effected and directed to port and starboard.
best regards
Peter
Am 12.01.2013 14:25, schrieb Joe Della Barba:
I use insulators in my backstay and an SGC auto-tuner. So far it has
matched every frequency I have tried it on, which would be every ham
and marine band between 1.8 and 30 MHz. This definitely includes 40
meters. The only tricky area seems to be 10 meters. I can get a better
tune some days by tuning at 26 MHz and locking the tuner and then
going to 10 meters. Not sure exactly why?? I haven't tried it myself,
but I have heard of people only using the bottom insulator on the
backstay and letting the tuner load the whole rig with ground strap
run the tuner to the base of the mast.
Anyway, for the low voltage issue, you can try this:
http://www.mfjenterprises.com/Product.php?productid=MFJ-4416B
You can see my TS-440 here:
http://www.dellabarba.com/sailing/rh1.jpg and here
http://www.dellabarba.com/sailing/isabelchart.jpg
Joe Della Barba
Coquina C&C 35 MK I
N3HGB
------------------------------------------------------------------------
*From:* CnC-List [mailto:cnc-list-boun...@cnc-list.com] *On Behalf Of
*Colomba
*Sent:* Friday, January 11, 2013 6:49 PM
*To:* cnc-list@cnc-list.com
*Subject:* Re: Stus-List HAM radio on board
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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