I have been researching SSB installation issues and am left with a couple of
questions.

First, antenna installation. I intent to use a long wire through a tuner to
operate on HF. I intend to use an insulated shroud (I have a cat with no
backstay) with a short feed from the tuner. I have always believed that the
feed wire should be seaparated from the rigging before it reaches the
connection point to reduce capacitive reactance. I have accomplished this
in the past with 2" spacers holding the wire off of the shroud until it
reached the connection point. Recently, I read a credible opinion that
separation of an inch or two is irrelevant at high frequencies because to
eliminate all capacitive reactance the seaparation would have to be meters.
The capacitive reactance that does exist can be accomodated with the tuner.
If this is true I would prefer to directly attach a long insulated wire to
the shroud - perhaps tape it over a 25 foot length. It would be out of the
way, safe from rf burn risk and would not require the installation of
rigging isolators which introduce mechanical weakness and expense.

My second set of questions relate to ground plane/counterpoise installation
but I'll hold of on those quetions for the moment.

Thanks for your help.

Hello Jerry,

I'm not sure I understand exactly what you want to
do. It seems you want to simply use the shroud as
a support for an insulated wire, which would be
your antenna. This would allow you to avoid a
direct (DC) connection between the antenna wire
and the shroud. I think that if the shroud were
non-conducting, your idea would work well. If the
shroud is metal, which is most likely, then I
believe you will transfer energy to the shroud
which in turn will radiate and provide a means of
producing RF burns.

A better solution might be to slip some rubber or
teflon tubing over the shroud up to a height of
say six feet. You might slit the tubing to allow
attachment without disconnecting the shroud. Then
you could attach your short feed length of wire
from the tuner directly to the shroud and you're
in business. Do the same on the other shroud and
it may even look nice.

If that is not attractive, you could run a length
of nylon or dacron line from someplace on the hull
to the mast (or use a flag halyard) and pull an
insulated wire antenna up to some pre-determined
height that way. You will still get some coupling
into the rigging from any antenna anywhere on the
boat. Usually (but not always) there is little
danger of RF burns. One advantage of this
technique is that you can get the antenna to be a
quarter wave at some desired frequency--an option
not available with the shroud antenna.

Have I missed the boat? Hope that helps.

Chuck


Jerry Peters wrote:
I have been researching SSB installation issues and am left with a couple of
questions.

First, antenna installation. I intent to use a long wire through a tuner to
operate on HF. I intend to use an insulated shroud (I have a cat with no
backstay) with a short feed from the tuner. I have always believed that the
feed wire should be seaparated from the rigging before it reaches the
connection point to reduce capacitive reactance. I have accomplished this
in the past with 2" spacers holding the wire off of the shroud until it
reached the connection point. Recently, I read a credible opinion that
separation of an inch or two is irrelevant at high frequencies because to
eliminate all capacitive reactance the seaparation would have to be meters.
The capacitive reactance that does exist can be accomodated with the tuner.
If this is true I would prefer to directly attach a long insulated wire to
the shroud - perhaps tape it over a 25 foot length. It would be out of the
way, safe from rf burn risk and would not require the installation of
rigging isolators which introduce mechanical weakness and expense.

My second set of questions relate to ground plane/counterpoise installation
but I'll hold of on those quetions for the moment.

Thanks for your help.

Hi Chuck,

No you didn't miss the boat but I need to clarify. My intent is to have a
permanent long wire antenna installed without having to "break" the rigging
with insulators. I know I can haul a wire up with a halyard but I want it
permanently available. I think that the most out of the way place to
permanently raise a longwire is along the shroud. I'm not very worried
about rf burn because I can be careful and/or insulate the shroud at the
level that is likely to be touched. I am more concerned about loss of
effective power due to reactive interaction with the grounded shroud.

Any thoughts?


Hello Jerry,

I'm not sure I understand exactly what you want to
do. It seems you want to simply use the shroud as
a support for an insulated wire, which would be
your antenna. This would allow you to avoid a
direct (DC) connection between the antenna wire
and the shroud. I think that if the shroud were
non-conducting, your idea would work well. If the
shroud is metal, which is most likely, then I
believe you will transfer energy to the shroud
which in turn will radiate and provide a means of
producing RF burns.

A better solution might be to slip some rubber or
teflon tubing over the shroud up to a height of
say six feet. You might slit the tubing to allow
attachment without disconnecting the shroud. Then
you could attach your short feed length of wire
from the tuner directly to the shroud and you're
in business. Do the same on the other shroud and
it may even look nice.

If that is not attractive, you could run a length
of nylon or dacron line from someplace on the hull
to the mast (or use a flag halyard) and pull an
insulated wire antenna up to some pre-determined
height that way. You will still get some coupling
into the rigging from any antenna anywhere on the
boat. Usually (but not always) there is little
danger of RF burns. One advantage of this
technique is that you can get the antenna to be a
quarter wave at some desired frequency--an option
not available with the shroud antenna.

Have I missed the boat? Hope that helps.

Chuck

Aha!

Now I understand. I suspect that taping an
insulated wire to the shroud would be equivalent
to attaching the wire directly to the shroud. Why
not just do that instead? You could connect at a
shroud backing plate bolt inside the hull,
perhaps. It is cleaner and requires no hole in the
hull.

The fiberglass hull is a good insulator and so
your signal is not likely to be shorted to the
water. If your shroud is actually in the water,
you probably won't be using the radio.

What kind of antenna that gives you is not easy to
characterize. If the shroud connects to the mast
at a spreader, then you have a kind of gamma
matched vertical, with the mast being the antenna
and the other shroud and the forestay acting like
a capacity hat. Regardless of how it is
characterized, it works and works well, IF you can
load it!

On some bands, the shroud will load easily and
well, while on others, you may encounter some very
high reactances that will challenge a lot of
tuners. I think the extreme reactances may be a
result of the gamma matching not being what you
would choose if you could locate the spreader
anywhere on the mast. You might have to add an
external capacitor or inductor to your tuner on
some bands. But maybe not.

Try it. Many boats have used that system for years
with no problems at all and with performance at
least as good as the more common insulated
backstay (or shroud). Obviously, the shroud you
feed should not be grounded at the hull end. It is
ok if the mast is grounded at its base.

If you decide to try it, let the group know how it
works for you. Good luck.

Chuck

Jerry Peters wrote:
Hi Chuck,

No you didn't miss the boat but I need to clarify. My intent is to have a
permanent long wire antenna installed without having to "break" the rigging
with insulators. I know I can haul a wire up with a halyard but I want it
permanently available. I think that the most out of the way place to
permanently raise a longwire is along the shroud. I'm not very worried
about rf burn because I can be careful and/or insulate the shroud at the
level that is likely to be touched. I am more concerned about loss of
effective power due to reactive interaction with the grounded shroud.

Any thoughts?



Hello Jerry,

I'm not sure I understand exactly what you want to
do. It seems you want to simply use the shroud as
a support for an insulated wire, which would be
your antenna. This would allow you to avoid a
direct (DC) connection between the antenna wire
and the shroud. I think that if the shroud were
non-conducting, your idea would work well. If the
shroud is metal, which is most likely, then I
believe you will transfer energy to the shroud
which in turn will radiate and provide a means of
producing RF burns.

A better solution might be to slip some rubber or
teflon tubing over the shroud up to a height of
say six feet. You might slit the tubing to allow
attachment without disconnecting the shroud. Then
you could attach your short feed length of wire
from the tuner directly to the shroud and you're
in business. Do the same on the other shroud and
it may even look nice.

If that is not attractive, you could run a length
of nylon or dacron line from someplace on the hull
to the mast (or use a flag halyard) and pull an
insulated wire antenna up to some pre-determined
height that way. You will still get some coupling
into the rigging from any antenna anywhere on the
boat. Usually (but not always) there is little
danger of RF burns. One advantage of this
technique is that you can get the antenna to be a
quarter wave at some desired frequency--an option
not available with the shroud antenna.

Have I missed the boat? Hope that helps.

Chuck

In article ,
"Jerry Peters" wrote:

I have been researching SSB installation issues and am left with a couple of
questions.

First, antenna installation. I intent to use a long wire through a tuner to
operate on HF. I intend to use an insulated shroud (I have a cat with no
backstay) with a short feed from the tuner. I have always believed that the
feed wire should be seaparated from the rigging before it reaches the
connection point to reduce capacitive reactance. I have accomplished this
in the past with 2" spacers holding the wire off of the shroud until it
reached the connection point. Recently, I read a credible opinion that
separation of an inch or two is irrelevant at high frequencies because to
eliminate all capacitive reactance the seaparation would have to be meters.
The capacitive reactance that does exist can be accomodated with the tuner.
If this is true I would prefer to directly attach a long insulated wire to
the shroud - perhaps tape it over a 25 foot length. It would be out of the
way, safe from rf burn risk and would not require the installation of
rigging isolators which introduce mechanical weakness and expense.

My second set of questions relate to ground plane/counterpoise installation
but I'll hold of on those quetions for the moment.

Thanks for your help.



Jerry,
You have designed the system correctly for most situations by having
the feedline standing off the grounded part of the shroud line, to
eliminate a big output capacitance for the tuner to deal with. The
addition of external Capacitance to modern autotuners will cause them to
"Thrash around" a lot more while trying to tune anywhere close to the
1/2 wave resonace of the antenna. Autotuners just don't have the brains
to do this tuning job well if they are presented with external output
capacitance. I would worry more about that than having a crewperson
"burned by RF" while transmitting. It just doesn't happen if the crew
is properly trained and instructed. On most plastic vessels they just
become part of the antenna and detune things a bit, because they aren't
really grounded if they are just standing on the deck, and happen to
grab the antenna shroud while the transmitter is active.

Goggle this group for a complete course on designing a LOW IMPEDANCE
RF Ground System for MF?HF Operations.


Bruce in alaska
--
add a 2 before @