Fuel tanks and SSB counterpoise.

[Glenn Ashmore]

In the process of laying up the hull I incorporated a couple hundred sq.
ft of bronze bug screen to serve as a counterpoise. In addition two
runs of 2" copper foil run down the center of the hull to the keel area.
Capacitors between the foil and the keel bolts isolate any DC from
getting back into the counterpoise. That is probably enough but as I am
installing two aluminum tanks, I wonder how kosher it would be to tie
them into the counterpoise with more capacitors.

It would add another 14 sq ft of coupling area but would it be
introducing other problems?




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Dennis Gibbons]

I concur. I have internal ballast, so I drilled in and tapped in a bronze
bolt to attach the foil. I had no problems on the most recent Marion to
Bermuda Race.

 

[Bruce Gordon]

Glenn, I think you are overdoing it....I just have a copper strap from
the ground of the antenna tuner to one keel bolt (external lead keel)
and when I tested the syste,after installation (in New York), I got a
55 report from a ham in NW Spain. The only time Herb (Southbound II)
did not hear me loud and clear was because my copper strrap had become
corroded/
john N2ZOA/MM

Getting one or two reports of "5 by 5" doesn't mean anything other than
the band was open, on that frequency, at that time. Years ago this type
of reporting was used to sell SSB Radio's all the time. When just
finishing up an install, the tech would call KMI, WOO, or WOM on 12 Megs
(or whatever band was open at thte time) and get a "Radio Check" for the
customer. The band was open and a .5 watt radio connected to a "Wet
Noodle" would do as well. BIG SCAM, means nothing.

What one really needs is a REAL, across the bands Field Insensity
Reading, and Grounding Network Impedance vs Frequency Plot. These are
not as important for a Metal Hulled Vessel as the grounding system is
usually the hull and is mostly suffienct in and of itself. On wood or
plastic hulls where RF Grounding is usually the limiting factor on
antenna efficency, it is the RF Ground that is Most Impartant, and
the lower the frequency the more ground it takes to support the antenna
system.

Bruce in alaska

--
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

 

[maxlynn]

Okay, here's another question on antenna configuration. I have just gone
through the pricing out of backstay insulators, and received the suggestion
that a good, less expensive alternative would be to substitute a Kevlar
backstay for the rod that I have presently, and wind a piece bare of wire
around the Kevlar, up to near the masthead as an antenna. It is
significantly less expensive, and the Kevlar has the advantage of being
stronger and lighter than the wire.

Anyone know of any disadvantages to this approach??

 

[Tom Dacon]

This doesn't address your antenna question specifically, but I have to say
that the idea of replacing a stainless wire backstay with rope just creeps
me out. Sure Kevlar, in the appropriate size, could be stronger and still
lighter than the wire, but its long-term durability raises some significant
questions. The lifetime of stainless steel 1x19 and rod is well understood,
as is the response to shock loading; I doubt that the same could be said for
Kevlar. Your backstay's a pretty important rigging component - I wouldn't be
inclined to screw around with it. You might also consider the long-term cost
of more frequent replacement of the Kevlar, versus the cost of the wire and
insulators for about a twenty-year lifetime expectancy of the SS wire and
insulator combination.

I'm not against Kevlar in standing rigging per se, although I'd be inclined
to use it in a "supporting role", so to speak. In fact, I'm thinking of
replacing my 7x19 SS wire running backstays on my 41' 3/4-rigged sloop with
Kevlar the next time I re-rig, not so much to save weight as to keep down
the chafing on my spreaders when the running backstays are housed at the
after shrouds. I just wouldn't use in in a single-point-of-failure
application such as the backstay.

Tom Dacon

 

[Glenn Ashmore]

Composite stays are the big thing with multihull sailors but when I
checked it out for monohulls it seems that stretch will be a problem.
High tech line seems to be strong enough but it evidently still
stretches more than stainless wire.

This doesn't address your antenna question specifically, but I have to say
that the idea of replacing a stainless wire backstay with rope just creeps
me out. Sure Kevlar, in the appropriate size, could be stronger and still
lighter than the wire, but its long-term durability raises some significant
questions. The lifetime of stainless steel 1x19 and rod is well understood,
as is the response to shock loading; I doubt that the same could be said for
Kevlar. Your backstay's a pretty important rigging component - I wouldn't be
inclined to screw around with it. You might also consider the long-term cost
of more frequent replacement of the Kevlar, versus the cost of the wire and
insulators for about a twenty-year lifetime expectancy of the SS wire and
insulator combination.

I'm not against Kevlar in standing rigging per se, although I'd be inclined
to use it in a "supporting role", so to speak. In fact, I'm thinking of
replacing my 7x19 SS wire running backstays on my 41' 3/4-rigged sloop with
Kevlar the next time I re-rig, not so much to save weight as to keep down
the chafing on my spreaders when the running backstays are housed at the
after shrouds. I just wouldn't use in in a single-point-of-failure
application such as the backstay.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[maxlynn]

Okay, now that you have given your opinion on Kevlar as a backstay, how
about addressing the original question - i.e., is there any conceptual
problem with wrapping a bare copper wire around it and using it for an
antenna? Has anyone done this?

And, oh by the way, how would you feel about using Kevlar as a substitute
for 1x19 in steering cables? Would it shock you to know that many boats are
using Kevlar in this highly critical application? And have been doing it
successfully for over ten years now? Use as a backstay is pretty mundane
by comparison. And others have been using it for a similar period as
backstay material. And contrary to what you suggest, the lifetime and other
properties of Kevlar are well understood.

 

[Glenn Ashmore]

More elegant would be to use a single braid Vectran. It would take some
patience but you could feed the wire up through the core. I still see
several potential problems.

The first is the termination. Arimids and other high tech lines like
PBO require equal tension on all fibers to maintain rated strength.
Small eye splices will cut strength considerably. Special terminations
that pot the fibers inside a hollow steel fitting are available but cost
more than an insulator and must be factory installed.

The second is stretch. No matter how high the modulus of the fiber,
braided line will creep. The Kevlar 49 stays on boats like the Volvo
Ocean 70's is parallel fiber inside a polyethylene cover. A backstay
cost as much as a pretty decent crosscut mainsail.

BTW, composite steering cables are rarely Kevlar. With the exception of
Technora, arimid fibers have a tendency to chafe against each other when
the line is routinely flexed under tension as around steering sheaves.
Vectran and Technora are the preferred fibers for that application.

Okay, now that you have given your opinion on Kevlar as a backstay, how
about addressing the original question - i.e., is there any conceptual
problem with wrapping a bare copper wire around it and using it for an
antenna? Has anyone done this?

And, oh by the way, how would you feel about using Kevlar as a substitute
for 1x19 in steering cables? Would it shock you to know that many boats are
using Kevlar in this highly critical application? And have been doing it
successfully for over ten years now? Use as a backstay is pretty mundane
by comparison. And others have been using it for a similar period as
backstay material. And contrary to what you suggest, the lifetime and other
properties of Kevlar are well understood.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Tom Dacon]

Okay, now that you have given your opinion on Kevlar as a backstay, how
about addressing the original question - i.e., is there any conceptual
problem with wrapping a bare copper wire around it and using it for an
antenna? Has anyone done this?

The original question (Glenn's), has to do with extending the SSB foil
lattice to the fuel tanks. In response to that, the consensus of the sources
I've referenced for my SSB ground system is that running the foil to the
tops of the tanks is a good thing to do. I've done this on my tanks, and
merely laid the foil on top of the tank surface with an adhesive bonding
agent (it was probably Sikaflex). I don't believe there's any need for an
electrical bond, since induction should do the job nicely.

Tom Dacon

 

[Bruce in Alaska]

I don't believe there's any need for an
electrical bond, since induction should do the job nicely.

The above doesn't take into account that we are dealing with
impedance in the frequency domain. By not having an good
electrial bond, you induce capacative coupling to additional
surface area for your RF Ground, That means that this coupling is
frequency sensative, and then the RF Grounding System will react
significantly different depending on the frequency being transmitted.
Autotune Antenna Couples have very specific tuning firmware, and this
code doesn't react very well to a highly variable Rg Ground impedance.
They are designed to operate against a FLAT RF Ground Impedance,
and the more bumps in the RF Gropund impedance the harder the tuner
has to work to tune the antenna, and the more phantom, and quirky
Low SWR points that the tuner will find, and lock on to.

Bruce in alaska

 

[Larry Demers]

When I could not tune out the ground impedance bumps, I installed a cheap
manual antenna tuner in the ground circuit leg. Then I got perfect
impedance matches at all frequencies into a long ground wire. This was in
addition to the normal automatic antenna tuner for the antenna. Tuning
was simple. Just adjust the ground tuner until the SWR was down to the
lowest you could get.

Larry DeMers

 

[Bruce in Alaska]

It
worked well, but not any better than the 23' fiberglass whip mounted to
the transome.

At what frequency? All Frequencies? A 23' fiberglass whip is
a VERY short antenna at 2182Khz, and m ost autotuners will not
even get a tuned Indication with such an antenna system.

Bruce in alaska

 

[Bruce in Alaska]

When I could not tune out the ground impedance bumps, I installed a cheap
manual antenna tuner in the ground circuit leg. Then I got perfect
impedance matches at all frequencies into a long ground wire. This was in
addition to the normal automatic antenna tuner for the antenna. Tuning
was simple. Just adjust the ground tuner until the SWR was down to the
lowest you could get.

Larry DeMers

If your going to use a manual tuner in the ground system, and have to
readjust it for every large frequency change, why would you not just put
the manual tuner on the antenna and just do manual tuning??? Kind of
redudndent isn't it. The whole point of a autotuner is so that the
operator doen't have to know or understand what the tuner is doing.
That, and so appliance operators could install their own SSB Radio's
systems and cut the Marine Electronics Tech's out of their Installation
Money. Same thing, as when the FCC changed the rules for Radar
Installations, by users, only with many more consequencies.

Bruce in alaska

 

[Gary Schafer]

Since no one answered your question,,
Yes it would be a problem winding a wire around the line. That is if
you make very many turns of the wire. It will act like a choke to the
RF and only the very bottom part of the "coil" of wire will be
effective as an antenna. The rest of it will be electrically
disconnected as far as the RF is concerned due to the inductance of
the choke that you have made.

This is of course at the higher frequencies. It may work fairly well
at 2182.

The old AM whip antennas that were used on 2 and sometimes on 4 mhz
and not on higher frequencies had a center loading coil wound on them.
This increased their efficiency over just a straight whip and putting
all the loading coil in the antenna tuner. With the coil higher up on
the antenna it provided a little higher feed point impedance and
resulted in a more efficient antenna. This worked well when only 2 and
4 mhz was involved. But when higher frequencies are fed to such an
antenna that loading coil that worked wonders on the low frequencies
acts like a choke at the higher frequencies and effectively
disconnects everything above the coil, including part or most of the
coil. You then have only a very short antenna working for you making
it very inefficient.

You could fasten a straight piece of wire to the kevlar and it should
work fine.

Regards
Gary

 

[Ron Thornton]

The coil in the center of an antenna is not a choke it is just an
inductor that electrically lengthens the antenna. This method is used
well above 2-4 mhz in mobile radio. It is not used much above VHF
because a full wave length is already relatively small.

Ron

 

[Gary Schafer]

The coil in the center of a marine antenna that is designed to be used
on 2 mhz is indeed a choke at anything above 7 mhz or so. It is not
intended to be such but that is what it is when the antenna is used
above its intended range. All of the antenna above the coil is
electrically disconnected from the lower part of the antenna. You
could physically remove that upper portion and notice little if any
difference at higher frequencies.

That is the reason that type of antenna is not used on any system that
operates above 4 mhz. A straight whip (no coil involved) is the only
thing that will work satisfactorily in a multi band system. (trap
antenna being the exception)

Those old antennas with the loading coil in them perform much better
on 2 mhz than the straight whip antenna of the same physical length
but they are very poor on the higher bands as part of the antenna is
not there electrically. It is then a very short antenna at the higher
frequencies.

Regards
Gary

 

[Ron Thornton]

Well I guess if I tried to push 30 mhz thru a 2 mhz transmitter you
could call the transmitter a choke too. But in reality it ain't and
the coil in the middle of an antenna ain't either. What you describe as
a choke is a tuning inductor, the choking is an inconsequential behavior
of the tuning at a frequency the antenna was never designed to operate
at.

Ron

 

[Gary Schafer]

If it acts like a choke it must be a choke. :>)

Regards
Gary

 

[Bruce in Alaska]

The coil in the center of a marine antenna that is designed to be used
on 2 mhz is indeed a choke at anything above 7 mhz or so. It is not
intended to be such but that is what it is when the antenna is used
above its intended range. All of the antenna above the coil is
electrically disconnected from the lower part of the antenna. You
could physically remove that upper portion and notice little if any
difference at higher frequencies.

That is the reason that type of antenna is not used on any system that
operates above 4 mhz. A straight whip (no coil involved) is the only
thing that will work satisfactorily in a multi band system. (trap
antenna being the exception)

Those old antennas with the loading coil in them perform much better
on 2 mhz than the straight whip antenna of the same physical length
but they are very poor on the higher bands as part of the antenna is
not there electrically. It is then a very short antenna at the higher
frequencies.

Regards
Gary

Just a few comments here on this thread.......

Gary is right on in his assesment of the operation of the end feed
loaded antenna. The coil does indeed act as a choke on frequencies
higher than 4XResonant. In the "Old Days" we used Morad 2800 and 3600
loaded whips with 15 to 35 ft of wire below them as antennas in the
MF Frequency Range. They were just great below 5 Mhz, and not half
bad above that as the coil only choked off the upper 102" whip and
the coil itself, and left the bottom 10ft of antenna and 35 Ft of
wire as an antenna for the HF Ranges above 5 Mhz. This 45 Ft of
antenna did just fine as an antenna in those ranges as it would be
tuned (Fixed tuned antenna tuner era) as 3/4 Wavelength at these higher
frequencies. today's autotuners have a similar tuning firmware routine
that adds output Capacitance untill it finds the 3/4 Wavelength point.
They don't do as good of job as a Fixed tuned tuner due to the step size
and the sense circuits, but they will get close, and be fairly effecent.
The trick to make this type of antenna work is to get some wire under
the antenna, so that you have an effective antenna length once the coil
chokes off, as the frequency rises. Most of the North Pacific Fishing
Fleet uses this type of antenna system for MF, and HF, comms.

Bruce in alaska

 

[Bruce in Alaska]

Well I guess if I tried to push 30 mhz thru a 2 mhz transmitter you
could call the transmitter a choke too. But in reality it ain't and
the coil in the middle of an antenna ain't either. What you describe as
a choke is a tuning inductor, the choking is an inconsequential behavior
of the tuning at a frequency the antenna was never designed to operate
at.

Ron

Ron, Ron,

Loaded Whips, are just that, wires with a big coil in the middle, that
effectivly lengthen the antenna. They are designed to be 1/4 Wavelength
at the Designed Frequency. ( Morad 2800 & 3400 ect) these can be
resonated as 3/4 Wavelenth at higher HF Frequencies very easily by
adding output shunt capacitance in the tuner. The coil does decouple
the antenna above it at something near 4X Designed Resonance. These
type of antennas have been around in Marine Radio for 50 years, and
Eddie Zanbergen RIP (Chief Engineer @ Morad) designed, built, and sold
them throughout the world, and the properties of Impedance vs Frequency
are well documented for them over the years. After one tunes the old
fixed tuned Antenna Tuners, common in the Marine Radio Service for 20
or 30 years, you get a feel for how they tune and how they work. They
DO tune up very well, and ARE as effecent as any other Marine Antenna
System. Been there, Done that, on hundreds of vessels from 20' to 1200'.


Bruce in alaska