In article ,
"Steve (another one)" wrote:

Dear Folks,

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.
Could someone please suggest an equivalent, or at least a description !

Also if the ground connection has to be broad copper strip because RF
won't run down a wire like a conventional dc current, how can the
antenna be wire ? Doesn't RF have to run along the cable to the base of
the antenna and then up the antenna wire itself ? I'm confused !

Thanks for your help.

Steve


Others have covered the GTO-15 question, very well.

There are a number of reasons that copper strap is used for RF Grounding
in the Maritime Radio Installations. One being, that it is desireable
for the RF Ground to have the lowest possible Impedance at the
transmitted frequency.

Two being, that it is desirable that the surface area of the RF Ground
System be as large as practicable, to maximise coupling to the seawater.

Three being, That RF flows on the surface of the conductor, and more
surface area means lower impedance on the Ground.

The antenna wire isn't supposed to couple into the seawater, but into
the ethos, so it should have the least surface area as can practically
handle the RF Current of the transmitter and be tuned to resonance by
the tuner, and as low of resistance as practicable, so that RF Current
can propagate along it's length.

Bruce in alaska Gary S. can chime in anytime on this.....
--
add a 2 before @

On Wed, 26 May 2004 03:42:24 GMT, Bruce in Alaska
wrote:

In article ,
"Steve (another one)" wrote:

Dear Folks,

What is the recommended wire to connect my insulated backstay to my
AT-120 tuner ? I see references to GTO15 for this purpose in American
publications, but no-one here in the UK seems to know what GTO15 is.
Could someone please suggest an equivalent, or at least a description !

Also if the ground connection has to be broad copper strip because RF
won't run down a wire like a conventional dc current, how can the
antenna be wire ? Doesn't RF have to run along the cable to the base of
the antenna and then up the antenna wire itself ? I'm confused !

Thanks for your help.

Steve


Others have covered the GTO-15 question, very well.

There are a number of reasons that copper strap is used for RF Grounding
in the Maritime Radio Installations. One being, that it is desireable
for the RF Ground to have the lowest possible Impedance at the
transmitted frequency.

Two being, that it is desirable that the surface area of the RF Ground
System be as large as practicable, to maximise coupling to the seawater.

Three being, That RF flows on the surface of the conductor, and more
surface area means lower impedance on the Ground.

The antenna wire isn't supposed to couple into the seawater, but into
the ethos, so it should have the least surface area as can practically
handle the RF Current of the transmitter and be tuned to resonance by
the tuner, and as low of resistance as practicable, so that RF Current
can propagate along it's length.

Bruce in alaska Gary S. can chime in anytime on this.....


Hi Bruce,

The diameter of the antenna wire is not too important. Actually the
larger it is the less resistive loss it has and less power will be
wasted in heat. But unless the antenna is significantly shorter than a
quarter wavelength that loss is negligible in the antenna as the
radiation resistance (radiation resistance is where the power goes to
be radiated) is usually much higher than the resistive loss of the
wire.

However in a very short antenna the radiation resistance can be only
an ohm or a few ohms. Then the resistance of the wire would be a
larger percentage and the heat loss would be greater thus warranting a
larger diameter wire.

Otherwise a larger diameter wire has the advantage of greater
bandwidth for given tuner settings. But the difference between #10 and
# 16 would probably not be noticeable.

As you well know, in the case of the ground system as we have said
many times before, it needs to be as short as possible or it becomes
part of the antenna and radiates. "The antenna starts at ground".
Anything above ground is antenna.

Regards
Gary

Gary Schafer wrote in
:


The diameter of the antenna wire is not too important. Actually the
larger it is the less resistive loss it has and less power will be
wasted in heat. But unless the antenna is significantly shorter than a
quarter wavelength that loss is negligible in the antenna as the
radiation resistance (radiation resistance is where the power goes to
be radiated) is usually much higher than the resistive loss of the
wire.

The diameter of the antenna wire is very important in the antenna's
BANDWIDTH. Go by the CG shore station and look at how WIDE the conical
monopole antenna is:
http://www.tpub.com/content/et/14092/css/14092_35.htm
The whole reason for the wide cone of these broadband HF antennas is to
make it look as if the conductor were several FEET across to the RF from
the feedpoint.

Multiple, parallel conductors are also used to increase antenna wire
apparent diameter in broadband rhombic antennas such as:
http://www.smc-comms.com/rhombic_antenna.htm

To quote the text:
"The simple one wire system has a bandwidth of approximately 2: 1, however
SMC have wide experience in the design of this type of antenna and are
able to offer arrays with 1, 2 or 3 wires per leg to give a bandwidth of up
to 4: 1 and, by careful design, gains of 22 dBi are possible."


However in a very short antenna the radiation resistance can be only
an ohm or a few ohms. Then the resistance of the wire would be a
larger percentage and the heat loss would be greater thus warranting a
larger diameter wire.

Huh?? ANY antenna under 1/4 wavelength long exhibits HIGHER and HIGHER
impedance the SHORTER it gets. The first low impedance of a wire antenna
occurs when its radiator (against a ground, artificial or real) is 1/4
wavelength long. A very short antenna, i.e. a 6' whip on the handrail, has
a very HIGH impedance as frequency decreases on the HF band. That's why we
use an L network to match it to 50 ohms....coil in series, cap to ground to
lower its impedance.


Otherwise a larger diameter wire has the advantage of greater
bandwidth for given tuner settings. But the difference between #10 and
# 16 would probably not be noticeable.

True, that's why we use multiple parallel conductors above.

As you well know, in the case of the ground system as we have said
many times before, it needs to be as short as possible or it becomes
part of the antenna and radiates. "The antenna starts at ground".
Anything above ground is antenna.


Actually, in a plastic boat, the radiation from the ground strap is useful
radiation. You've just moved the FEEDPOINT up the radiating element above
the sea. My feedpoint is about 4.8' above ground on Lionheart. It's
signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil,
most of Western Europe on 40 meters and 20 meters. Works pretty good!

73, Larry W4CSC

On Wed, 09 Jun 2004 00:00:34 -0000, Larry W4CSC
wrote:

Gary Schafer wrote in
:


The diameter of the antenna wire is not too important. Actually the
larger it is the less resistive loss it has and less power will be
wasted in heat. But unless the antenna is significantly shorter than a
quarter wavelength that loss is negligible in the antenna as the
radiation resistance (radiation resistance is where the power goes to
be radiated) is usually much higher than the resistive loss of the
wire.

The diameter of the antenna wire is very important in the antenna's
BANDWIDTH. Go by the CG shore station and look at how WIDE the conical
monopole antenna is:
http://www.tpub.com/content/et/14092/css/14092_35.htm
The whole reason for the wide cone of these broadband HF antennas is to
make it look as if the conductor were several FEET across to the RF from
the feedpoint.

Multiple, parallel conductors are also used to increase antenna wire
apparent diameter in broadband rhombic antennas such as:
http://www.smc-comms.com/rhombic_antenna.htm

To quote the text:
"The simple one wire system has a bandwidth of approximately 2: 1, however
SMC have wide experience in the design of this type of antenna and are
able to offer arrays with 1, 2 or 3 wires per leg to give a bandwidth of up
to 4: 1 and, by careful design, gains of 22 dBi are possible."


However in a very short antenna the radiation resistance can be only
an ohm or a few ohms. Then the resistance of the wire would be a
larger percentage and the heat loss would be greater thus warranting a
larger diameter wire.

Huh?? ANY antenna under 1/4 wavelength long exhibits HIGHER and HIGHER
impedance the SHORTER it gets. The first low impedance of a wire antenna
occurs when its radiator (against a ground, artificial or real) is 1/4
wavelength long. A very short antenna, i.e. a 6' whip on the handrail, has
a very HIGH impedance as frequency decreases on the HF band. That's why we
use an L network to match it to 50 ohms....coil in series, cap to ground to
lower its impedance.


Otherwise a larger diameter wire has the advantage of greater
bandwidth for given tuner settings. But the difference between #10 and
# 16 would probably not be noticeable.

True, that's why we use multiple parallel conductors above.

As you well know, in the case of the ground system as we have said
many times before, it needs to be as short as possible or it becomes
part of the antenna and radiates. "The antenna starts at ground".
Anything above ground is antenna.


Actually, in a plastic boat, the radiation from the ground strap is useful
radiation. You've just moved the FEEDPOINT up the radiating element above
the sea. My feedpoint is about 4.8' above ground on Lionheart. It's
signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil,
most of Western Europe on 40 meters and 20 meters. Works pretty good!

73, Larry W4CSC


Oh oh, here we go again. :)

Remember I said that the radiation resistance drops as the antenna
gets shorter. That is the reason the losses go up with a shorter
antenna. Higher current in the antenna and loading coil means more I
squared R loss.

(radiation resistance is equal to the equivalent resistor that would
dissipate the same amount of power that is being radiated) Lower
radiation resistance requires more current for the same amount of
power verses a higher radiation resistance and less current.

The reactance does indeed get higher the shorter the antenna is. With
an antenna shorter than a quarter wave length as you know it looks
like a capacitor. (capacitive reactance) The less capacitance (shorter
antenna) the higher the reactance. The coil in series provides an
equal but opposite inductive reactance to cancel the capacitive
reactance in the antenna.

That leaves only the radiation resistance to feed power to. The coil
AC resistance (not reactance now)is then effectively in series with
the radiation resistance of the antenna. The same current must flow in
both the antenna and coil losses. While the antenna radiates most of
the power it gets, the coil dissipates power in heat equal to the I
squared R loss in the coil.

The capacitor to ground on the other side of the coil and part of the
coil form an L network to match the impedance to the feed line.

Actually we could say that the L network portion really matches the
radiation resistance plus the coil resistance to the feed line.
Because when the coil reactance and antenna reactance are equal we
have resonance and the only component left is purely resistive.

The high reactance in the antenna causes the voltage to go high. But
there is also a phase shift due to the reactance. So the current is
not in phase with the voltage developed across the reactance. That is
why the voltage is high.

Regards
Gary

"Larry W4CSC" wrote

Actually, in a plastic boat, the radiation from the ground strap is useful
radiation. You've just moved the FEEDPOINT up the radiating element above
the sea. My feedpoint is about 4.8' above ground on Lionheart. It's
signal strength 5, readability 8 in Moscow, Belarus, UAE, Japan, Brazil,
most of Western Europe on 40 meters and 20 meters. Works pretty good!

Larry, we've probably had the details of this antenna system in pieces
across various posts, but would you mind putting in one place here? Sounds
like an intersting and well thought out setup.

Thanks,

Jack

"Jack Painter" wrote in
news:Vlxxc.5736$5B2.5631@lakeread04:

Larry, we've probably had the details of this antenna system in pieces
across various posts, but would you mind putting in one place here?
Sounds like an intersting and well thought out setup.

Thanks,

Jack

It isn't very fancy, actually. The Icom AT-140 tuner is screwed to the top
of the aft cabin just aft of the mizzen mast, which is deck stepped. The
HV RF output post is about 8" from the base of the insulated backstay on
the main and a short, smoothly bent piece of #12 Copperweld antenna wire is
hose clamped to the Amel's backstay jack out of the way of the winch handle
socket. The insulator is about a ft from the mast at the top and every
time I look up there I want an insulator on each end of the triatic stay
with an interconnecting Copperweld wire connecting the top of the backstay
antenna to the center of the insulated triatic to make it a capacitor hat
on top of the 50' sloping vertical for the lower frequency bands. If it
ever goes back into the yard for demasting, it will have it...(c; But, for
now, it just has the backstay.

When Geoffrey got the boat, the previous owner reported poor performance
(he was a ham, too) from the backstay antenna, which I traced down to
loading from the stainless cable topping lift on the large main boom,
sucking off the signal to the mast because when the boom was centered, it
was only a few inches from the backstay. Not good. So, we changed the
stainless to nylon and now no metal gets near the antenna, no matter where
the boom is set. Signal reports came up a LOT!

Directly beneath the tuner, in the support for the deck stepped mast, are
several storage holes I can put wires into. So, I got a #8 battery wire,
black of course, and put a ring terminal to fit the ground post on the
tuner on one end. As straight as I could, I routed it down through the
openings in the mount into the engine compartment which is right under the
mast. Directly under the tuner, too, is the DC shunt used for the ampere-
hour meter on the house batteries under the shunt. This great ground, to
the big 700 AH house batteries against the hull, and the whole house ground
system, is tied in at the shunt, then the cable drops straight down to the
engine block for more grounding and capacitive coupling through the hull.
Antenna current came way up as did signal reports from this installation.
Dropping a bare Copperweld wire over the side I use for even more grounding
while underway at sea, I measure only about 1.5 ohms from the bare wire
laying on the bottom of the marina and this ground connection above.
Something's got a great connection to the ocean down there. I musta got
lucky.

That's it. The radio is grounded to a ground strap Amel installed behind
the panel behind the chart table. It's a common ground strap where all my
instrumentation, navigation and communications is tied with small wire.
There is a direct connection between that strap at the nav station and the
engine block and house ground, too. I like to think it may bypass some
static hits, but haven't been through any on this boat....yet. Let's not
rush the testing of this theory.

Larry W4CSC

"Larry W4CSC" wrote

It isn't very fancy, actually. The Icom AT-140 tuner is screwed to the
top
of the aft cabin just aft of the mizzen mast, which is deck stepped. The
HV RF output post is about 8" from the base of the insulated backstay on
the main and a short, smoothly bent piece of #12 Copperweld antenna wire
is
hose clamped to the Amel's backstay jack out of the way of the winch
handle
socket. The insulator is about a ft from the mast at the top and every
time I look up there I want an insulator on each end of the triatic stay
with an interconnecting Copperweld wire connecting the top of the backstay
antenna to the center of the insulated triatic to make it a capacitor hat
on top of the 50' sloping vertical for the lower frequency bands. If it
ever goes back into the yard for demasting, it will have it...(c; But,
for
now, it just has the backstay.

When Geoffrey got the boat, the previous owner reported poor performance
(he was a ham, too) from the backstay antenna, which I traced down to
loading from the stainless cable topping lift on the large main boom,
sucking off the signal to the mast because when the boom was centered, it
was only a few inches from the backstay. Not good. So, we changed the
stainless to nylon and now no metal gets near the antenna, no matter where
the boom is set. Signal reports came up a LOT!

Directly beneath the tuner, in the support for the deck stepped mast, are
several storage holes I can put wires into. So, I got a #8 battery wire,
black of course, and put a ring terminal to fit the ground post on the
tuner on one end. As straight as I could, I routed it down through the
openings in the mount into the engine compartment which is right under the
mast. Directly under the tuner, too, is the DC shunt used for the ampere-
hour meter on the house batteries under the shunt. This great ground, to
the big 700 AH house batteries against the hull, and the whole house
ground
system, is tied in at the shunt, then the cable drops straight down to the
engine block for more grounding and capacitive coupling through the hull.
Antenna current came way up as did signal reports from this installation.
Dropping a bare Copperweld wire over the side I use for even more
grounding
while underway at sea, I measure only about 1.5 ohms from the bare wire
laying on the bottom of the marina and this ground connection above.
Something's got a great connection to the ocean down there. I musta got
lucky.

That's it. The radio is grounded to a ground strap Amel installed behind
the panel behind the chart table. It's a common ground strap where all my
instrumentation, navigation and communications is tied with small wire.
There is a direct connection between that strap at the nav station and the
engine block and house ground, too. I like to think it may bypass some
static hits, but haven't been through any on this boat....yet. Let's not
rush the testing of this theory.

Larry W4CSC

Sounds great Larry, Thanks. Seen in a Univ of Florida study, paraphrased:

1. All boats can be struck by lightning, protected or not, and
2. Protected boats and unprotected boats both suffer damage when hit, and
3. Unprotected boats suffer significantly more damage than protected boats.

It sounds like you and Lionheart are well protected.

I remember a night of terrible line squalls that wrecked several yachts in
Block Island Salt Harbor. I had stayed up on deck with gear on as I knew it
was coming as I returned from a night on the town. It was worse than any
summer line squall should have been! By the time I roused my family the
winds had the entire harbor dragging anchor. Anyne who has been there can
imagine the panic of watching your Out Island 41 heading toward mega-million
yachts both dragging along with you, and lining the docks for a busy
weekend. The Westerbeke diesel with one anchor could not hold us, and I went
forward to set a second anchor and lots of chain with it. I think there must
have been hundreds of lightning srtikes all around us without any break
between them. Night turned to day, and that helped avoid touching shrouds
while on deck. Everything around us seemed to be getting hit, and of course
it was one of those moments when (at least I) thought I was going to die
from lightning at any moment. But the second anchor and the diesel held us
just short of one of the hundred-footers at the outer docks. In the
aftermath, we heard there was a lot more damage from collisions than from
lightning, and that is amazing considering how many yachts I saw get struck
that night.

Best,

Jack

"Jack Painter" wrote in
news:16syc.157$Jk5.41@lakeread02:

outer docks. In the aftermath, we heard there was a lot more damage
from collisions than from lightning, and that is amazing considering
how many yachts I saw get struck that night.

I've read the webpage from FL. Very interesting research. The mast looks
tall when you're standing at the bottom of it looking up, but in the
overall height of a thunderstorm FIVE MILES HIGH, our masts are like a
dimple on the dining room table, and not much of a "target".

I was at the transmitter shack of WRJA-TV, the PBS station in Sumter, SC,
visiting an old friend who was chief engineer, Bill Jones, one night. We
were building the first weather radio repeater after Bill had applied for,
and gotten, an FCC license for that band to simply repeat the signal from
Columbia, SC's weather station to the local Sumter area which had trouble
hearing it. We made it out of kit ham radio repeater boards from VHF
Engineering in Binghamton, NY, as we had a local repeater.

A huge thunderstorm cell moved across Sumter and actually went THROUGH the
1800' WRJA-TV tower while we watched out the back door as lightning went
SIDEWAYS 10 miles in the cloud just to hit that big 1800' ground rod
sticking up out of the table-flat terrain of eastern Sumter County. I'm
standing there watching the light show and suddenly Bill taps me on the
shoulder and hands me a big yellow rain coat, saying, "Come on. I wanna
show you something neat." We followed the huge hardline coaxial cables
from the 35KW TV transmitter out to the base of the antenna and Bill says,
"You're standing in the safest place in Sumter County. There is a cone of
protection against being hit by lightning provided by my tower and you're
now standing in the middle of it. Hang onto the tower leg and feel the
current going through it." I burned my hand a couple of times as the huge
BOOMs went off over my head a thousand feet up. The huge bridge cables
JUMPED from the surge of electrical EMP hit them, many times. The lights
went out and we had to go back in the building to reset the transmitters
when the power came back on.

Though the "tower" on the sailboat is very short, in comparison, I like to
think that if you have a proper grounding system, like the professor
describes on his webpages, you are also in a tiny cone where the blast will
mostly be shunted AROUND you, which is why your car is so safe in a
thunderstorm. The current surge that kills goes AROUND the the steel body
of the car....Steel ships and boats do that....Plastic, not so good.

Larry

On Fri, 11 Jun 2004 20:27:40 -0400, "Jack Painter"
wrote:

I remember a night of terrible line squalls that wrecked several yachts in
Block Island Salt Harbor.

======================================

Would that have been in the summer of '74 by any chance? I was
halfway between Mystic, CT and BI that year when we got hit by the
mother of all line squalls just after dark.

In article ,
Gary Schafer wrote:


Hi Bruce,

The diameter of the antenna wire is not too important. Actually the
larger it is the less resistive loss it has and less power will be
wasted in heat. But unless the antenna is significantly shorter than a
quarter wavelength that loss is negligible in the antenna as the
radiation resistance (radiation resistance is where the power goes to
be radiated) is usually much higher than the resistive loss of the
wire.

However in a very short antenna the radiation resistance can be only
an ohm or a few ohms. Then the resistance of the wire would be a
larger percentage and the heat loss would be greater thus warranting a
larger diameter wire.

Otherwise a larger diameter wire has the advantage of greater
bandwidth for given tuner settings. But the difference between #10 and
# 16 would probably not be noticeable.

As you well know, in the case of the ground system as we have said
many times before, it needs to be as short as possible or it becomes
part of the antenna and radiates. "The antenna starts at ground".
Anything above ground is antenna.

Regards
Gary

Yep, absolutly right Gary.


Bruce in alaska
--
add a 2 before @