non-insulated backstay on metal boat
 

I read the following on another forum and have a few questions
regarding same:

"I don't know anyone else doing this and I really don't know why since
it saves money and works great. Everybody should know that with a
metal boat there is no reason to use backstay insulators at all. With
a good ground plane, you can use a ground-fed antenna. Take the
antenna coax, run the shield to the rail (or railing if properly
grounded) and then run the center of the coax up about 6 feet to the
grounded backstay. I use spacers about 2 inches long to space the wire
off the backstay and keep it from flapping around. Most people will
think it is direct short to ground but when you remember the signal is
AC and not DC it makes more sense. If you find one band won't tune
with your tuner, try moving the wire on the backstay up or down 6
inches until it works OK. It's not my idea; aircraft having been doing
it for years since they have such a difficult time getting an antenna
mounted. I am using a MFJ manual tuner and and receive and transmit as
good as anyone with
this rig. No expensive insulators, and no screwing around with
temporary antennas. "

Does this sound like a good idea?

Could the end feed be from the other end (top of the mast) with the
tuner inside the mast (to avoid a wire from the deck to the backstay?

Cheers, Jim

non-insulated backstay on metal boat
 

wrote in message
ups.com...
I read the following on another forum and have a few questions
regarding same:

"I don't know anyone else doing this and I really don't know why since
it saves money and works great. Everybody should know that with a
metal boat there is no reason to use backstay insulators at all. With
a good ground plane, you can use a ground-fed antenna. Take the
antenna coax, run the shield to the rail (or railing if properly
grounded) and then run the center of the coax up about 6 feet to the
grounded backstay.
...
Could the end feed be from the other end (top of the mast) with the
tuner inside the mast (to avoid a wire from the deck to the backstay?

If the backstay is also electrically connected to the mast, you could even
feed the mast istelf form the inside.

Meindert

non-insulated backstay on metal boat
 

wrote:
I read the following on another forum and have a few questions
regarding same:

"I don't know anyone else doing this and I really don't know why since
it saves money and works great. Everybody should know that with a
metal boat there is no reason to use backstay insulators at all. With
a good ground plane, you can use a ground-fed antenna. Take the
antenna coax, run the shield to the rail (or railing if properly
grounded) and then run the center of the coax up about 6 feet to the
grounded backstay. I use spacers about 2 inches long to space the wire
off the backstay and keep it from flapping around. Most people will
think it is direct short to ground but when you remember the signal is
AC and not DC it makes more sense. If you find one band won't tune
with your tuner, try moving the wire on the backstay up or down 6
inches until it works OK. It's not my idea; aircraft having been doing
it for years since they have such a difficult time getting an antenna
mounted. I am using a MFJ manual tuner and and receive and transmit as
good as anyone with
this rig. No expensive insulators, and no screwing around with
temporary antennas. "

Does this sound like a good idea?

Could the end feed be from the other end (top of the mast) with the
tuner inside the mast (to avoid a wire from the deck to the backstay?

Cheers, Jim


Technically, this is known as a gamma
match.

Maybe better than feeding the mast at
the top, you might feed one of the
shrouds instead. If the bottom end is
not grounded, simply place the tuner
between ground and the bottom of the
shroud. Often this will allow placing
the tuner next to the transmitter.

In any case, you may have to experiment
as suggested. I found that sometimes
tuners can't provide an acceptable match
on some frequencies.

Good luck,

Chuck

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

non-insulated backstay on metal boat
 

non-insulated backstay on metal boat
 

non-insulated backstay on metal boat
 

Larry wrote:
wrote in news:1180601311.461858.45960
@r19g2000prf.googlegroups.com:

Does this sound like a good idea?



Well, not really.

I did it with shrouds for a while and it did work, somewhat. I could
tune it but radiation proved less than the insulated backstay when my
captain switched boats. Here's why....

If we feed the backstay (or shrouds) from the insulated-by-fiberglass end
on the stern, the instantaneous antenna current goes, for this instant,
up the backstay and we'll call this radiated wave because of this
current, "in phase". At the top of the backstay, connected to the mast,
the instantaneous current now flows DOWN the mast, OUT OF PHASE with the
backstay current, creating a wavefront that is "out of phase" with the
wavefront created by the backstay.....cancelling lots of it because there
is a significant difference in distance and angle with the backstay.
This creates a radiation pattern that has many small lobes and many deep
nulls, all rotating around as the boat swings, which is not good. The
current will also flow down all the shrouds and forestay, making the
radiation pattern even more complex.

It'll radiate, but not as good as an insulated backstay, which is really
cheap to accomplish.

The foregoing notwithstanding, it is
important to maintain focus on what is
meant by "good" when speaking of radiation.

All of the metal rigging on a sailboat
is in EVERY antenna's near-field.
Currents will be induced in ALL of it
whether grounded or not. The resulting
radiation patterns in the horizontal and
vertical planes will be modified by all
of this rigging.

Only a perfectly vertical radiator on a
boat with no metallic rigging will have
an omnidirectional pattern in the
horizontal plane. Backstays, whips,
etc., will all have non-uniform
radiation to some degree in the
horizontal plane. For antennas with
elements that are neither perpendicular
to the sea nor parallel to it (like a
backstay), there will be a mix of
horizontally and vertically polarized
radiation with generally different
horizontal and vertical patterns that
vary with frequency.

When feeding the mast at its base (or
via one of the shrouds), with the
forestay and backstay ungrounded, the
stays act as a "capacitative hat" and
make the mast appear longer electrically
than it is physically. Good for the
lower frequencies.

If the stays are grounded at stem and
stern, in the above example, two
vertical "loops" are formed with the
mast common to both. Toss in the shrouds
and modeling is required to gain
insights into the resulting radiation
pattern.




I'd rather be feeding the mast from the bilge with insulators on all
shrouds and stays, myself, using the iron or lead keel as a significant
ground plane, but that's not very practical as it would be hard to
accomplish and even harder to keep from corroding into oblivion. All
boat antennas are a great compromise. It's amazing they radiate on HF at
all...(c;

Larry

Almost anything can be made to radiate
efficiently. A great deal of effort and
sometimes costly hardware is required to
achieve that for some radiators.

Sal****er sure helps low-angle radiation
though.

Chuck



----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----