wrapping ssb antenna on kevlar backstay

[Steve (another one)]

Dear all

May I pick-up on something mentioned in response to my earlier question.

It was suggested that running a wire up a kevlar backstay is a simple
soultion and avoids having to insulate a piece of conventional rigging.
This sounds very sensible to me and plan to try it, it avoids having to
mess with exposed connections to a wire backstay.

However then Bruce in alaska said:

Then just helical wrap the antenna wire
around the Kevlar Backstay and have a really nice "Fully Loaded >Antenna
with alot of electrical length......

Could someone (Bruce perhaps?) explain this. Would I gain performance by
simply wrapping the wire ? Is no of turns per length of backstay
critical ? Is 'core' diameter critical ?

Thanks

Steve

 

[Glenn Ashmore]

Actually, Kevlar and similar arimids have a dielectric constant range of
3.5 to 4.5 compared to plexiglass at 2.6 to 3.5.

I looked up the Kevlar website at:
http://www.dupont.com/kevlar/whatiskevlar.html

One interesting thing it says is:

"Low Electrical Conductivity"

What's interesting is what it DOESN'T say...NO electrical conductivity.

Food cooking in my microwave oven has "low electrical conductivity", too,
as it converts microwaves into heat.

Most interesting topic. Dupont doesn't mention anything else as they try
to sell the stuff.

Larry

--
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 Pogson]

Dear all

May I pick-up on something mentioned in response to my earlier
question.

It was suggested that running a wire up a kevlar backstay is a simple
soultion and avoids having to insulate a piece of conventional
rigging. This sounds very sensible to me and plan to try it, it
avoids having to mess with exposed connections to a wire backstay.

However then Bruce in alaska said:

Could someone (Bruce perhaps?) explain this. Would I gain performance
by simply wrapping the wire ? Is no of turns per length of backstay
critical ? Is 'core' diameter critical ?

Thanks

Steve

Whilst Kevlar rope has high tensile strength and low weight, they fail to
mention that it weakens rapidly under flexion, i.e. it should never be
knotted or doubled back on itself, as when seizing around a snall-diameter
thimble.

I would think that poses several problem when using as a backstay, unless
some kind of patent terminals are available.

Our Kevlar main halyard parted quite suddenly and without warning at the
thimble a few years ago, and I resolved to go back to wire-spliced
pre-stretched polyester in future.



Remove "nospam" from return address.

 

[Max Lynn]

I am the one who posted re the kevlar backstay. I implemented it and used
the setup on a recent Mexico trip. I can only tell you that my rig was
probably the best in the fleet of several boats. A lot of racing sailboats
are switching their rod or wire backstays to Aramid at this time. The
weight savings is dramatic, and the cost is roughly half of what a backstay
with insulators would cost. It's interesting that with all the expertise on
antennas in this group none sees fit to answer your original question, but
rather they choose to critique a proven rigging advance.

 

[Gary Schafer]

While I don't know much about the properties of kevlar, electrical or
physical, if it has good electrical properties at the RF frequencies
involved then it should work ok.

As far as wrapping the wire around it, I would use a very long wrap.
Not many turns. While more turns will probably make an excellent
antenna for the low frequencies, 2 and 4 mhz, it will hinder the
higher frequencies. The coil will act as a choke at the higher
frequencies and not allow them to pass. It will effectively make a
rather short antenna at the higher frequencies.

When the old 2 mhz marine antennas were made they had a wound coil in
the fiberglass whip. It performed much better on 2 mhz than a straight
whip with no coil. But it was next to useless on frequencies above 4
mhz as the coil effectively disconnected the upper part of the antenna
on the higher frequencies.

With the higher frequencies in common use now you will never see one
of those loaded antennas in service anymore. Unless it is a dedicated
2 mhz antenna and there are other antennas for the other frequencies.
That is the best of both worlds.

Regards
Gary

 

[Bruce in Alaska]

Dear all

May I pick-up on something mentioned in response to my earlier question.

It was suggested that running a wire up a kevlar backstay is a simple
soultion and avoids having to insulate a piece of conventional rigging.
This sounds very sensible to me and plan to try it, it avoids having to
mess with exposed connections to a wire backstay.

However then Bruce in alaska said:

Could someone (Bruce perhaps?) explain this. Would I gain performance by
simply wrapping the wire ? Is no of turns per length of backstay
critical ? Is 'core' diameter critical ?

Thanks

Steve

Gary has a valid point in that a tightly wound helical wire will tend
to trap out the higher frequencies in the HF range. One thing to
remeber however, is that if the band is open it doesn't take as efficent
of antenna to communicate on these Higher Frequencies, and if the band
is closed, no amount of antenna tuning or fooling around is going to
allow communications. Where as on MF Frequencies, one needs all the
length one can get for an efficent antenna, and the band is what it is,
and really doesn't change much as far as open or closed, except for Day
and Night. Better distances at night than during the day. A good
compromise would seem to be a resonate 1/4 Wave at say 3200 Khz would
allow for far efficency at 2182 Khz, by wrapping the helical windings
tighter at the top of the antenna, give a reasonable length of wire
on the lower part to resonate with the tuner at 12 Mhz, 16 Mhz, and 22
Mhz.

Bruce in alaska

 

[engsol]

Oh boy..here we go...<laughing>.... see below....

Gary has a valid point in that a tightly wound helical wire will tend
to trap out the higher frequencies in the HF range. One thing to
remeber however, is that if the band is open it doesn't take as efficent
of antenna to communicate on these Higher Frequencies, and if the band
is closed, no amount of antenna tuning or fooling around is going to
allow communications. Where as on MF Frequencies, one needs all the
length one can get for an efficent antenna, and the band is what it is,
and really doesn't change much as far as open or closed, except for Day
and Night. Better distances at night than during the day. A good
compromise would seem to be a resonate 1/4 Wave at say 3200 Khz would
allow for far efficency at 2182 Khz, by wrapping the helical windings
tighter at the top of the antenna, give a reasonable length of wire
on the lower part to resonate with the tuner at 12 Mhz, 16 Mhz, and 22
Mhz.

Bruce in alaska

Bruce has an excellent point re the windings...but I see a problem.
Given a kelvar backstay length, how would one compute the
pitch of the wrap? A turn every 6 inches for the first 2/3rds? Then
every 2-3 inches for the remainder? Ouiji board?

This topic is so interesting to me that short of buying a network analyzer,
(I'll be honest, I can't afford one), I'm determined to figure out what
simple test equipment I can use to evaluate various configurations,
and then test them.
Any ideas?
Norm B

 

[Bruce in Alaska]

Oh boy..here we go...<laughing>.... see below....

snipped for brevity

Bruce has an excellent point re the windings...but I see a problem.
Given a kelvar backstay length, how would one compute the
pitch of the wrap? A turn every 6 inches for the first 2/3rds? Then
every 2-3 inches for the remainder? Ouiji board?

This topic is so interesting to me that short of buying a network analyzer,
(I'll be honest, I can't afford one), I'm determined to figure out what
simple test equipment I can use to evaluate various configurations,
and then test them.
Any ideas?
Norm B

Actually most of the work in this area was done by Ed Zanbergen, while
he was Principal Partner and Chief Engineer of MORAD Electronics in
Seattle, Wa. MORAD antennas are the defacto standard for commercial
vessels in the North Pacific. They build some of the most rugged and
effective antennas in the Marine Mobile Radio Service. Ed is long since
gone to the Great Radioroom in the Sky, but his legacy is still around
and being produced by MORAD today. When I was a beginner in this bizz,
I worked for Northern Radio Co. which had a shop next door to Morad,
and Ed and I became very good friends. I still have some custom antennas
that he built for me, specifically for MF/HF Coast Station installations
in alaska. I don't know if any of his notes were ever published, but
he spent 40 years designing antennas in these Radio Services.

One of the better designs that Ed built for me was a pair of matched
Helically Loaded Whips that were resonate at 3300Khz. I mounted them at
60 Ft in a Dipole configuration, with PhosBronze feedwire, connected at
the end of the 15 Ft Base tubes. Then feeding down to an Experimental
SEA 1612B Autotuner that has twin tuning boards driven by a single CPU/
Sensor System, so that both dipole legs are effectivly tuned by the
autotuner. This antenna can be heard, evey summer on the Marine Freqs
as KWO-70/WDT-59 and operations on all Marine Bands from 2003Khz
to 25 Mhz.

Bruce in alaska