"David Swindon" wrote in message
...

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).

We use a tuner mounted on the rail of the pushpit. The antenna is tied off
to the rail beside the tuner and basically looks like and inverted 'L'. We
use a flag hoist on the mizzen and then the antenna is run to the peak of
the main mast. The mainmast end, ends about three feet from the main and the
antenna is adjusted to clear the mizzen about the same as it runs down to
the tuner. The overall length is 28 feet.

Leanne
s/v Fundy

A number of issues have been raised here
that deserve some further comment.

Regarding RF coupling to the standing
rigging, don't be overly concerned. You
will be coupled to the rigging no matter
where you place the antenna. Some
geometries will doubtless be worse than
others, but it will be difficult to
predict in advance. Moreover, such
coupling is not necessarily a bad thing.
It is just a difficult thing to model
and thus more of an unknown.

Regarding antenna length, more is not
necessarily better and may be worse! But
whether worse or better, changing the
length of an antenna may make it
different. For example, if you are
crossing oceans and want reliable skip
communication over great distances, you
want low radiation angles. A
quarter-wave or 5/8-wave vertical will
be your best choice. That would be about
16 feet in length at 14 MHz. Make your
antenna 32 feet long and you have a
half-wave vertical with very little
low-angle radiation at 14 MHz, but at 7
MHz and below, low-angle radiation will
be plentiful.

Which is better depends on your
objectives. Operating near the coast,
you may find that higher radiation
angles produce shorter skip zones to
your advantage.

Were your boat fiberglass or wood
instead of steel, it is possible that a
horizontal antenna laid on the deck
would outperform any vertical antenna
for high radiation angle communications
with a range of say 400 miles. Think
about maintaining solid ssb contact with
boats scattered throughout the Bahamas,
for example. With vertical antennas such
a task would be quite difficult.

Start out your planning with some
consideration of which distances are
most important. From that, move to which
frequencies and radiation angles provide
the appropriate skip zones to achieve
those distances, and from there,
consider antenna options that further
those objectives.

Good luck

Chuck

"Chuck" wrote in message
ink.net...
A number of issues have been raised here that deserve some further comment.

Regarding RF coupling to the standing rigging, don't be overly concerned.
You will be coupled to the rigging no matter where you place the antenna.
Some geometries will doubtless be worse than others, but it will be
difficult to predict in advance. Moreover, such coupling is not
necessarily a bad thing. It is just a difficult thing to model and thus
more of an unknown.

This is my experience.

Regarding antenna length, more is not necessarily better and may be worse!
But whether worse or better, changing the length of an antenna may make it
different. For example, if you are crossing oceans and want reliable skip
communication over great distances, you want low radiation angles. A
quarter-wave or 5/8-wave vertical will be your best choice. That would be
about 16 feet in length at 14 MHz. Make your antenna 32 feet long and you
have a half-wave vertical with very little low-angle radiation at 14 MHz,
but at 7 MHz and below, low-angle radiation will be plentiful.

I think the OP mentioned an automatic tuner. From my experience
both the ICOM and SGC tuners require at least 23'. Not sure how a
longer antenna fairs. Shorter will definitely not tune well.


Good luck

Chuck

In article ,
"Doug Dotson" wrote:

I think the OP mentioned an automatic tuner. From my experience
both the ICOM and SGC tuners require at least 23'. Not sure how a
longer antenna fairs. Shorter will definitely not tune well.

As I posted eslewhere, autotuners have some very specific flaws
that keep them from having optimum preformance. 23' isn't near
long enough for ANY reasonable comm's below 8Mhz. The tuners
get get VERY lossy as input capacitance is increased, in order to tune
short antennas.

Bruce in alaska
--
add a 2 before @

Antennas are really a lot like boats: No
boat will do everything well and no
antenna will either. Boats and antennas
that try to do everything usually fail
across the board.

FWIW, SGC-237, -230, and -231 tuners
need 23 feet only to tune from 1.6 MHz
to 3.3 MHz. Above 3.3 MHz, these SGC
tuners require only eight (8) feet.

The Icom AH-4, for example, needs 23
feet only to tune down to 3.5 MHz, but
will tune from 7 MHz up with Icom's
AH-2b whip (8.2 feet long).

But it doesn't matter what lengths the
tuners require if there is no desire to
operate in that frequency range, and
chances are excellent that recreational
boaters will not be found at the very
low frequencies.

As has been pointed out, some antenna
lengths will be more taxing for an
autotuner than other lengths. Your
objective is not to make life easier for
your tuner, especially when doing so may
move you farther from your real needs.
You may not even need a tuner! Your
objective is to achieve your
communication goals.

You might give some thought to posting
on one of the cruising newsgroups to ask
experienced cruisers for their thoughts
on things like "if you had only one
frequency to operate on, what would it
be? Among other things, that might be
the basis for an antenna you can stow
for emergencies. But tell them where and
how you'll be cruising and what you want
the ssb for (email, emergencies,
boat-to-boat communication, etc.) Then
return to the antenna design questions.

Keep to it!

Chuck

As Bruce says, "tuners get very lossy with short antennas". But that
is not the only problem with short antennas. The antenna and ground
system become very lossy with short antennas. Below 1/4 wavelength the
radiation resistance of the antenna drops drastically. It can be less
than an ohm. That equates to very high losses. The antenna system in
those cases may be only a few percent efficient.

It is far better to have a longer antenna that gives a much higher
radiation resistance even if it may not be the optimum length as far
as radiation pattern is concerned. If you can't get the power to the
antenna the radiation pattern doesn't much matter. You still won't get
out very well.

On a typical boat the radiation pattern is going to be far from ideal
with whatever length antenna you have due to all the surrounding
objects on the boat.

The difference in radiation patterns between a 1/2 wavelength and 5/8
wavelength antennas are minimal. About the only real difference is the
feed point impedance they present.

As far as antennas greater in length than a quarter wavelength, they
start to produce multiple lobes in the pattern. Which on a boat may
not be a bad thing. As you mention, sometimes higher angles are
desired depending on the distance trying to be covered.

A longer antenna on a typical boat is most always going to be more
efficient than a short antenna even if the longer antenna produces
multiple pattern lobes.

Regards
Gary



On Tue, 09 Nov 2004 00:29:53 GMT, Chuck wrote:

Antennas are really a lot like boats: No
boat will do everything well and no
antenna will either. Boats and antennas
that try to do everything usually fail
across the board.

FWIW, SGC-237, -230, and -231 tuners
need 23 feet only to tune from 1.6 MHz
to 3.3 MHz. Above 3.3 MHz, these SGC
tuners require only eight (8) feet.

The Icom AH-4, for example, needs 23
feet only to tune down to 3.5 MHz, but
will tune from 7 MHz up with Icom's
AH-2b whip (8.2 feet long).

But it doesn't matter what lengths the
tuners require if there is no desire to
operate in that frequency range, and
chances are excellent that recreational
boaters will not be found at the very
low frequencies.

As has been pointed out, some antenna
lengths will be more taxing for an
autotuner than other lengths. Your
objective is not to make life easier for
your tuner, especially when doing so may
move you farther from your real needs.
You may not even need a tuner! Your
objective is to achieve your
communication goals.

You might give some thought to posting
on one of the cruising newsgroups to ask
experienced cruisers for their thoughts
on things like "if you had only one
frequency to operate on, what would it
be? Among other things, that might be
the basis for an antenna you can stow
for emergencies. But tell them where and
how you'll be cruising and what you want
the ssb for (email, emergencies,
boat-to-boat communication, etc.) Then
return to the antenna design questions.

Keep to it!

Chuck

In article ,
Gary Schafer wrote:

As Bruce says, "tuners get very lossy with short antennas". But that
is not the only problem with short antennas. The antenna and ground
system become very lossy with short antennas. Below 1/4 wavelength the
radiation resistance of the antenna drops drastically. It can be less
than an ohm. That equates to very high losses. The antenna system in
those cases may be only a few percent efficient.

It is far better to have a longer antenna that gives a much higher
radiation resistance even if it may not be the optimum length as far
as radiation pattern is concerned. If you can't get the power to the
antenna the radiation pattern doesn't much matter. You still won't get
out very well.

On a typical boat the radiation pattern is going to be far from ideal
with whatever length antenna you have due to all the surrounding
objects on the boat.

The difference in radiation patterns between a 1/2 wavelength and 5/8
wavelength antennas are minimal. About the only real difference is the
feed point impedance they present.

As far as antennas greater in length than a quarter wavelength, they
start to produce multiple lobes in the pattern. Which on a boat may
not be a bad thing. As you mention, sometimes higher angles are
desired depending on the distance trying to be covered.

A longer antenna on a typical boat is most always going to be more
efficient than a short antenna even if the longer antenna produces
multiple pattern lobes.

Regards
Gary

Exactly, Doug says he does fairly well on 80 and 40 Meters with
a 23' whip and an autotuner. We take him at his word, but if he
would figure out how to increase that to 50' or 75', there is a GOOD
chance that he would do better, and even in poorer band conditions.
It doesn't take much power or antenna to communicate if the band is
open, to where you want to talk, on the frequency that your using.
Try that if the bands isn't so hot and the time of day is against
you, with a Very Marginal antenna system. Yea, I know most pleasure
boaters have never heard of Marine Frequencies below 4Mhz, but up
here in Alaska we have been using 1.6Mhz and 2.0Mhz - 4Mhz Marine
frequencies for years, and very suscessfully, even on Poor Band Years.
I have used 3261Khz for Maritime Comms for 35 years, and worked my
Fleet Vessels, with 65% completion of Comms, rate on a daily basis.
You will not get that kind of connectitvity, with a 23' antenna,
on your Maritime Mobile Stations. In the "Good Old Days", the previous
generation of Alaskan RadioMen used to work 1630Khz consistantly
every night for intercompany Comms.

Just because SGC says their tuner only needs 23ft of wire, doesn't mean
that you can actually talk to anyone with that type of system. By the
way SGC didn't do the design of that autotuner, themselves, they stole
it from SEA, and didn't even change the "CopyWrite Statement" in the
firmware code. All autotuners on the market today, come from the
original design work of Bill Schillb, an engineer for Motorola MF/HF
Systems, at the time. He worked out the basics of the tuning code and
the hardware design. When he left Motorola and came out west to
Seattle, he landed at Northern Radio for s short while, and while there
passed on the basic technology to Bill Forgey, who was Chief Engineer at
Nothern at the time. Both Bill's left Northern Radio just before it
went under, with Forgey taking the whole Design Team with him, and with
Dick Stephens started SEA. (Stephens Engineering Asscoiates) Dick was
the Chief Engineer at Northern before Bill, and his mentor. Bill Forgey
along with Mark Johnson (an ex Northern Tech) designed the first truely
Marine Radio Autotuner which was the SEA1600, using the basics that Bill
Schillb had imparted, and on which, they improved and expanded. The
first autotuner that had Frequency Memory and Instant Band Switching was
the SEA1612, and the B version is what SGC copied for their 23x series
tuners. Icom, Kenwood, Furuno, and the rest are "Johnnie Come Latelys"
in the world of Marine Autotuner design, and basically they reverse
engineered the SEA design and firmware, for their systems.

I was closely associated with these folks as a Traveling Radio Tech for
Northern Radio, before leaving to become Comm Supt. for the largest
Salmon Canner in Alaska. I count all these folks a close friends, even
after all these years, and also while working the Dark Side (I was a
Field Agent for the FCC for five years) of the industry. I also did a
pile of beta testing over the years for SEA, that included most of their
designs for autotuners. Some of the prototypes are still in use today,
in various places in alaska. I designed and installed the first Marine
Autotuner feeding a Dipole Antenna, and that system is still in use
today. Bill, Mark and I designed and built a 1Kw Maritime Mobile Coast
Station that has 8 Control Points, and uses a SEA1612B Autotuner, and
one of a kind Dipole Antenna for MF/HF Frequencies from 1630Khz
thru 30Mhz at the 150W PEP level, and 1Kw on 4Mhz, 6Mhz, 8Mhz, 12Mhz
16Mhz, 22Mhz Marine Frequencies, using another special Dipole Antenna,
from Morad Electronics. This system is still in use today as well, and
has been around for more than 10 years.

I don't usually "Toot my own horn", but I do have considerable practical
experience in this field, as well as a long history in the industry.



Bruce in alaska onetime Fed, and long time Radioman..........

--
Bruce (semiretired powderman & exFCC Field Inspector for Southeastern Alaska)
add a 2 before @
Bruce Gordon * Debora Gordon R.N. Bruce's Trading Post
P.O. Box EXI Excursion Inlet South
Juneau, Alaska 99850 Excursion Inlet, Alaska 99850
www.btpost.net www.99850.net

Hello Gary:

Seems I've simply lost the ability to communicate any more. My point was
that seeking the most efficient antenna (as defined by maximum power
transfer into space) ought not to be the guiding principle. We want
maximum power delivered to the other station. All other things the same,
a higher radiation resistance would mean lower ohmic losses. But all
other things are not the same when antenna length is increased.

Yes, radiation patterns on real boats will differ from radiation
patterns in space. But even on a real boat, a high percentage of energy
is radiated at quite high angles when the antenna is a half-wavelength.
Yes, the half-wave will be more "efficient" in getting energy off the
boat because the radiation resistance is higher than with a shorter
antenna. But if it doesn't get the signal to the other station because
the radiation angle is too high, then it's not really optimal. Look at
some numbers on vertical radiation patterns. You can easily lose 6 db at
useful, low radiation angles by going from a quarter-wave to a
hslf-wave. There is no way you'll ever recover that through the
half-wave's higher radiation resistance, although that high-angle stuff
could actually be a good thing if you're not in the middle of the
Pacific trying to work Europe. And we have not even addressed the
consequences of a sloping antenna on both horizontal and vertical patterns.

No quarrel, of course, with your observation that as the length of an
antenna falls below a quarter-wave, the radiation resistance (and thus
radiated efficiency) falls. Those losses are one of the parameters that
one needs to weigh against other considerations. At the same time, a
reduction of length to say, .2 wavelengths would probably not even be
detectable (i.e., 1 dB). Also, even as the length decreases, the
radiation pattern remains basically that of a quarter-wave antenna.

I probably need to repeat that I have not advocated "shorter" antennas,
"longer" antennas, quarter-wave antennas, half-wave antennas, vertical
antennas, horizontal antennas or much of anthing other than an analysis
of the desired signal paths and the basing of an antenna design and
frequency combination on that analysis. Well, I have also cautioned
against blindly increasing antenna length. Sort of struck me as a
motherhood kind of thing.

Onward . . .

Chuck



Gary Schafer wrote:
As Bruce says, "tuners get very lossy with short antennas". But that
is not the only problem with short antennas. The antenna and ground
system become very lossy with short antennas. Below 1/4 wavelength the
radiation resistance of the antenna drops drastically. It can be less
than an ohm. That equates to very high losses. The antenna system in
those cases may be only a few percent efficient.

It is far better to have a longer antenna that gives a much higher
radiation resistance even if it may not be the optimum length as far
as radiation pattern is concerned. If you can't get the power to the
antenna the radiation pattern doesn't much matter. You still won't get
out very well.

On a typical boat the radiation pattern is going to be far from ideal
with whatever length antenna you have due to all the surrounding
objects on the boat.

The difference in radiation patterns between a 1/2 wavelength and 5/8
wavelength antennas are minimal. About the only real difference is the
feed point impedance they present.

As far as antennas greater in length than a quarter wavelength, they
start to produce multiple lobes in the pattern. Which on a boat may
not be a bad thing. As you mention, sometimes higher angles are
desired depending on the distance trying to be covered.

A longer antenna on a typical boat is most always going to be more
efficient than a short antenna even if the longer antenna produces
multiple pattern lobes.

Regards
Gary



On Tue, 09 Nov 2004 00:29:53 GMT, Chuck wrote:


Antennas are really a lot like boats: No
boat will do everything well and no
antenna will either. Boats and antennas
that try to do everything usually fail
across the board.

FWIW, SGC-237, -230, and -231 tuners
need 23 feet only to tune from 1.6 MHz
to 3.3 MHz. Above 3.3 MHz, these SGC
tuners require only eight (8) feet.

The Icom AH-4, for example, needs 23
feet only to tune down to 3.5 MHz, but
will tune from 7 MHz up with Icom's
AH-2b whip (8.2 feet long).

But it doesn't matter what lengths the
tuners require if there is no desire to
operate in that frequency range, and
chances are excellent that recreational
boaters will not be found at the very
low frequencies.

As has been pointed out, some antenna
lengths will be more taxing for an
autotuner than other lengths. Your
objective is not to make life easier for
your tuner, especially when doing so may
move you farther from your real needs.
You may not even need a tuner! Your
objective is to achieve your
communication goals.

You might give some thought to posting
on one of the cruising newsgroups to ask
experienced cruisers for their thoughts
on things like "if you had only one
frequency to operate on, what would it
be? Among other things, that might be
the basis for an antenna you can stow
for emergencies. But tell them where and
how you'll be cruising and what you want
the ssb for (email, emergencies,
boat-to-boat communication, etc.) Then
return to the antenna design questions.

Keep to it!

Chuck

Well do I have egg on my face!

Gary, you are correct, of course, in stating that there is not a lot of
difference between the vertical radiation patterns of half-wave and
quarter-wave antennas. Surely not the differences I was alluding to.

And so my statements to the contrary were just plain wrong.

While I was writing half-wave, I was thinking of something longer, like
3/4 wave. I should have been more careful and I do apologize.

My point, however, is just as valid. Many sailboats sport 45' backstay
antennas and that is close to 3/4 wavelength in the 15 MHz range. A 3/4
wave antenna has maximum vertical radiation at 45 degrees! I would say a
16- or even an 8-foot whip would be very competitive with such a
backstay antenna at the lower radiation angles needed for transoceanic
communication.

At higher marine frequencies, 3/4 wavelength is obviously even less than
45 feet.

Of course, the 3/4 wave will be efficient and easy on the autotuner.

I'll try to keep my brain in synch with my typing, henceforth.

Chuck

I've been able to do reasonably well on 40 and 80 meters with my
23' whip. I do get more side effects like twinkling lights and sometimes
the LectraSan activates itself

Doug, k3qt
s/v Callista

"Bruce in Alaska" wrote in message
...
In article ,
"Doug Dotson" wrote:

I think the OP mentioned an automatic tuner. From my experience
both the ICOM and SGC tuners require at least 23'. Not sure how a
longer antenna fairs. Shorter will definitely not tune well.

As I posted eslewhere, autotuners have some very specific flaws
that keep them from having optimum preformance. 23' isn't near
long enough for ANY reasonable comm's below 8Mhz. The tuners
get get VERY lossy as input capacitance is increased, in order to tune
short antennas.

Bruce in alaska
--
add a 2 before @