"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

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 @

"Steve (another one)" wrote in message
...
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

Steve, you have asked about two distinctly different forms of connection
that require equally different conductors. Additionally, within your
grounding questions there also are two different issues, addressed below:

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for RF.
Never improvise with something such as spark plug wires.

2.(a) Grounding: RF

This does not have to be wide surface area copper, but doing so will not
hurt, and it will allow the combination-use of the RF ground connection to
serve as a lightning protection ground. RF ground does not require a dc-
connection to ground, and is often designed to use capacitive coupling to
ground for sailing vessels and other marine applications where isolation for
galvanic protection is adviseable.

2. (b) Grounding: Lightning protection

Also does not require a dc-connection to ground, but may not use low valued
capacitors such as would be acceptable for RF ground. Lightning protection
DOES require the widest surface area possible, this provides a lower
impedance path to ground. But your radio and auto-tuner and other equipment
are most importantly bonded to each other, and that may be of any standard
braid, #8 wire, etc. Only the single connection of all your bonded equipment
to ship's ground must be of the highest surface area possible. If more than
one connection from bonded equipment to ground must be made, then each of
those connections should be wide surface area conductors.

Hope this helps,

Jack Painter
Virginia Beach, VA

"Jack Painter" wrote in message
news:SR2tc.76990$pJ1.75446@lakeread02...

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for
RF.

Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about
200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz) antenna
connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.

Never improvise with something such as spark plug wires.
GTO15 is not sparkplug wire.

2.(a) Grounding: RF

This does not have to be wide surface area copper,

The ground connection has to be as low impedant as possible. Copper strip
has a lower impedance than copper wire with the same cross-section.

Meindert

"Meindert Sprang" wrote in message
...
"Jack Painter" wrote in message
news:SR2tc.76990$pJ1.75446@lakeread02...

1. RF feedline from ATU to antenna.

This should be coaxial cable with dialectric and shielding designed for
RF.

Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of about
200 ohms at 4 MHz) does to a high impedance (several kOhms at 4MHz)
antenna
connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.

Hi Meindert, I don't understand your reasoning there, sorry. And Doug too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same Sunair
ATU that I use, connected to the wire HF antennas. It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners. I have also fed a longwire with that same tuner/coax
combnation, however the longwire was a grounded antenna, and not simlar to a
insulated backstay of a sailboat.

Best regards,

Jack Painter
Virginia Beach,VA

"Jack Painter" wrote in message
newsxstc.52$9h.43@lakeread02...

Hi Meindert, I don't understand your reasoning there, sorry. And Doug
too,
who referenced a steel ship, which is my reference as well. I have seen
hardline (still 50ohm coax) in shipboard installations using the same
Sunair
ATU that I use, connected to the wire HF antennas.

A backstay antenna is relatively short compared to the wavelength. It
therefore has a high impedance. To match it to the 50 ohm of the
transceiver, the impedance has to be transformed by an L-circuit with the
capacitance at the low impedant side to ground and the inductance from the
low impedance "hot" side to the antenna. If you would use coax at the high
impedant antenna side, you get a terrible mismatch. The capacitance of this
pice of coax adds to the L circuit at the wrong side, effectively giving you
a PI circuit which is unable to match the high impedant backstay to the 50
ohms of the transceiver.

It appears (to me) no
different that the ungrounded dipole that I feed with coax from my land
station tuners.

Theoretically no. But your land dipole is probably much longer than a
backstay and therefore has a lower impedance. By the way, does your coax
connect directly to the dipole or do you have a balun (with a possible
impedance transformation wich makes the coax have less influence)?

Meindert

"Meindert Sprang" wrote in
:


Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of
about 200 ohms at 4 MHz) does to a high impedance (several kOhms at
4MHz) antenna connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.


That's just about as bad as neatly tywrapping the wire from the tuner to
the bottom insulator on the backstay to the grounded backstay part UNDER
the bottom insulator. Trying to get them to let that wire HANG away from
everything to lower the capacitance to ground is like trying to get 5200
adhesive that's hardened out of a crack in the decking. They don't care
what it does to the signal output, as long as it looks "neat and tidy".

Larry W4CSC

Normally, when tywrapping the feedline to the backstay below
the insulator, the lower part of the backstay is not grounded. Otherwise
small standoff are used.

Doug. k3qt
s/v Callista

"Larry W4CSC" wrote in message
...
"Meindert Sprang" wrote in
:


Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of
about 200 ohms at 4 MHz) does to a high impedance (several kOhms at
4MHz) antenna connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.


That's just about as bad as neatly tywrapping the wire from the tuner to
the bottom insulator on the backstay to the grounded backstay part UNDER
the bottom insulator. Trying to get them to let that wire HANG away from
everything to lower the capacitance to ground is like trying to get 5200
adhesive that's hardened out of a crack in the decking. They don't care
what it does to the signal output, as long as it looks "neat and tidy".

Larry W4CSC

In article ,
"Doug Dotson" wrote:

Normally, when tywrapping the feedline to the backstay below
the insulator, the lower part of the backstay is not grounded. Otherwise
small standoff are used.

Doug. k3qt
s/v Callista

"Larry W4CSC" wrote in message
...
"Meindert Sprang" wrote in
:


Imagine what 2 meters of coax with a capacity of 200pF ( a "load" of
about 200 ohms at 4 MHz) does to a high impedance (several kOhms at
4MHz) antenna connection: right... almost short circuit it to ground.
NEVER use coax between the ATU and the antenna.


That's just about as bad as neatly tywrapping the wire from the tuner to
the bottom insulator on the backstay to the grounded backstay part UNDER
the bottom insulator. Trying to get them to let that wire HANG away from
everything to lower the capacitance to ground is like trying to get 5200
adhesive that's hardened out of a crack in the decking. They don't care
what it does to the signal output, as long as it looks "neat and tidy".

Larry W4CSC




I liked the idea, I saw here a while back, of using the new Kevlar based
Backstay material, and not worring about having to ground or not. Seemed
like the logical answer to me. Then just helical wrap the antenna wire
around the Kevlar Backstay and have a really nice "Fully Loaded Antenna
with alot of electrical length........


Bruce in alaska
--
add a 2 before @