I've had my all-band-doublet up at 90 feet for over a year now with
ladder-line spacers cut from polycarbonate sheet. Works great, is
kinda pretty in the right light. The polycarbonate is supposed to be
relatively UV-resistant and it seems to be doing pretty good.

But I have a hankering to use wooden insulators next time I put an
antenna up.

The old ARRL handbooks always recommended boiling wooden feedline
spacers in paraffin wax for weatherproofing. I suppose the idea is
that it's water-repellent. Don't know how long this can be expected to
survive weather extremes (ice, heat). In my experiments in my garage,
the wax coating seems to pretty much rub right off with my fingernail,
so I'm not sure how much good it does where the feed wires or tie
wires abrades against it.

Shellac is another option I suppose, but shellac seems to me to be
something like the enamel coating on magnet wire, and having used this
in rooftop antennas in the past I was quite surprised that in the
summer it gets hot enough up there to burn off the enamel.

Spar varnish seems to be the ultimate in wood coatings for weather
resistance.

Any words of wisdom? Or is polycarbonate really the cat's meow?

Having fabricated antenna stuff out of both plexiglass and
polycarbonate over the years, I am very very impressed with
polycarbonate's workability. It does not craze or crack the way that
plexiglass does.

Tim N3QE

The old ARRL handbooks always recommended boiling wooden feedline
spacers in paraffin wax for weatherproofing. I suppose the idea is
that it's water-repellent. Don't know how long this can be expected to
survive weather extremes (ice, heat). In my experiments in my garage,
the wax coating seems to pretty much rub right off with my fingernail,
so I'm not sure how much good it does where the feed wires or tie
wires abrades against it.

I think if you're using an older transmitter - keep up the retro theme by
boiling the wood spacers in parafin like the old book says. (But I would
bake them at 190degrees for an hour to remove all moisture first.)

I would also be tempted (considering your home-making the feed line anyway)
to try what I recall being called "G-line", where on the transmitter end of
the line you keep increasing the spacing then just drop one line - and you
have only one conductor going up.
then of course, you do the same thing at the antenna end, going from
2-conductoe wide spacing to 'normal spacing'.
Experiment.
Report back on how it went.

Tim,
Any of the above. Best? Which lasts longer? Which would you
rather use? What's the difference? Not much.
Have fun.
- 'Doc

Just one word of advice. The vapor of boiling paraffin is extremely
flammable -- I'd guess about like gasoline -- so be extremely careful if
you use the old time method. At the very least I'd do it outside and
over an electric hot plate rather than an open flame.

Roy Lewallen, W7EL

{Note: I tried posting this yesterday but Charter's NNTP server was having
problems.}

"Hal Rosser" wrote in message
. ..

I think if you're using an older transmitter - keep up the retro theme by
boiling the wood spacers in parafin like the old book says. (But I would
bake them at 190degrees for an hour to remove all moisture first.)

I would also be tempted (considering your home-making the feed line
anyway) to try what I recall being called "G-line", where on the
transmitter end of the line you keep increasing the spacing then just drop
one line - and you have only one conductor going up. then of course, you
do the same thing at the antenna end, going from 2-conductor wide spacing
to 'normal spacing'.

G-line, more correctly known as Goubau line, is not practical for use in the
HF range. It is generally limited to UHF frequencies and above due to the
physical size of the "launchers" which generate a surface wave along the
line. For details, see: Geog Goubau, "Surface waves and their Application
to Transmission Lines," Journal of Applied Physics, Volume 21, Nov. (1950).

What I believe Hal is talking about was the early practice of using a single
wire from the transmitter to connect to an essentially horizontal antenna.
Of course that single wire did not behave as a transmission line, but rather
became part of the antenna working against ground. In many cases this wire
became the actual antenna with the horizontal portion acting as capacitive
loading. The resulting antenna pattern is often quite distorted from that
expected of the dipole. A good ground is needed on the transmitter, yet
problems of RF in the shack are common.

If you do decide to use wood spacers, acrylic urethane varnish applied to
dry wood will last the longest and have the best ultraviolet resistance.
Shellac, a natural product, actually has a surprisingly good ultraviolet
resistance too. While boiling the wood in paraffin wax is authentic, be
very careful as Roy, W7EL, points out. The flash point of typical paraffin
wax is approximately 380 to 390 F. Use a double boiler with water in the
lower boiler to melt the wax keeping it well below the flash temperature.
Be very careful as the hot wax causes very bad burns. Work outdoors and
keep a fire extinguisher handy. If you have a local source of bamboo,
consider using it as it is light and often free.

I have made open wire line using poly(ethylene terephthalate) tensile test
bars liberated from the trash where I worked. These PET "dog biscuits"
worked well in this application as PET has good resistance to UV and is
extremely tough.

73, Barry WA4VZQ

Thanks, Barry on helping to wake up my recollections. I had forgotten that
the increasingnes of the spacing of the conductors go into multiple
wavelengths, which as you reminded us, is not practical for HF frequencies.
But for 2-meters and above, it may be worth a try.
The Bamboo suggestion sounds good, by the way. I used to use 300-ohm
twinlead because of the light weight because I wanted the antenna up as high
as possible, and more weight made it droop.

"NoSPAM" wrote in message ...
{Note: I tried posting this yesterday but Charter's NNTP server was having
problems.}

G-line, more correctly known as Goubau line, is not practical for use in
the
HF range. It is generally limited to UHF frequencies and above due to the
physical size of the "launchers" which generate a surface wave along the
line. For details, see: Geog Goubau, "Surface waves and their Application
to Transmission Lines," Journal of Applied Physics, Volume 21, Nov.
(1950).

What I believe Hal is talking about was the early practice of using a
single
wire from the transmitter to connect to an essentially horizontal antenna.
Of course that single wire did not behave as a transmission line, but
rather
became part of the antenna working against ground. In many cases this
wire
became the actual antenna with the horizontal portion acting as capacitive
loading. The resulting antenna pattern is often quite distorted from that
expected of the dipole. A good ground is needed on the transmitter, yet
problems of RF in the shack are common.

73, Barry WA4VZQ

But I have a hankering to use wooden insulators next time I put an
antenna up.

The old ARRL handbooks always recommended boiling wooden feedline
spacers in paraffin wax for weatherproofing. I suppose the idea is
that it's water-repellent. Don't know how long this can be expected to
survive weather extremes (ice, heat). In my experiments in my garage,
the wax coating seems to pretty much rub right off with my fingernail,
so I'm not sure how much good it does where the feed wires or tie
wires abrades against it.


Hi.
I think some Thompson's water seal would be a good substitute for the
boiling paraffin wax. I think the Thompson's is wax dissolved in
kerosene or Diesel. I have been putting two coats on some posts going
into the ground.

Paul

Tim Shoppa wrote:

...
Shellac is another option I suppose, but shellac seems to me to be
something like the enamel coating on magnet wire, and having used this
in rooftop antennas in the past I was quite surprised that in the
summer it gets hot enough up there to burn off the enamel.

Spar varnish seems to be the ultimate in wood coatings for weather
resistance.
...
Tim N3QE

If those ancient OT's heard you state the above, after desiring
materials better than dehydrated wood with hydrocarbons for
preservatives, as their insulators ... well, just suffice it to say,
they'd strike you up the side of the head, HARD! grin

Regards,
JS

In article ,
"Hal Rosser" wrote:

Thanks, Barry on helping to wake up my recollections. I had forgotten that
the increasingnes of the spacing of the conductors go into multiple
wavelengths, which as you reminded us, is not practical for HF frequencies.
But for 2-meters and above, it may be worth a try.
The Bamboo suggestion sounds good, by the way. I used to use 300-ohm
twinlead because of the light weight because I wanted the antenna up as high
as possible, and more weight made it droop.

"NoSPAM" wrote in message ...
{Note: I tried posting this yesterday but Charter's NNTP server was having
problems.}

G-line, more correctly known as Goubau line, is not practical for use in
the
HF range. It is generally limited to UHF frequencies and above due to the
physical size of the "launchers" which generate a surface wave along the
line. For details, see: Geog Goubau, "Surface waves and their Application
to Transmission Lines," Journal of Applied Physics, Volume 21, Nov.
(1950).

What I believe Hal is talking about was the early practice of using a
single
wire from the transmitter to connect to an essentially horizontal antenna.
Of course that single wire did not behave as a transmission line, but
rather
became part of the antenna working against ground. In many cases this
wire
became the actual antenna with the horizontal portion acting as capacitive
loading. The resulting antenna pattern is often quite distorted from that
expected of the dipole. A good ground is needed on the transmitter, yet
problems of RF in the shack are common.

73, Barry WA4VZQ





find some of that oil they soak telephone poles in then coat it
w/sealer

ultimately wood prob wont last as long as some good plastic and
i guess would be heaver stressing the wires more

it will prob still hold more water than a smooth plastic dunno

and prob not have as good insulative prop's but might be moot

"ml" wrote in message
...
In article ,
"Hal Rosser" wrote:

Thanks, Barry on helping to wake up my recollections. I had forgotten
that

{snip}

find some of that oil they soak telephone poles in then coat it
w/sealer

ultimately wood prob wont last as long as some good plastic and
i guess would be heaver stressing the wires more

it will prob still hold more water than a smooth plastic dunno

and prob not have as good insulative prop's but might be moot

I consider this a poor suggestion for a number of reasons...

Several methods of wood treatment have been used over the years. The three
main methods used to be pressure treatment with creosote, pentachlorophenol,
or inorganic arsenic salts. These were generally replaced by chromated
copper arsenate. Other treatments involved copper napthenate, zinc
napthenate, and tributyl tin oxide. All of these methods provide fungus
protection and some limited moisture protection.

Creosote, as used for treating wood, is generally coal tar creosote. This
material is distilled from coke oven tar and it contains polycyclic aromatic
hydrocarbons, phenols, and cresols, all of which are quite toxic and most
are either proven or suspected carcinogens.

Pentachlorophenol is registered by the Environmental Protection Agency as an
insecticide (termicide), fungicide, herbicides, molluscide, algaecide,
disinfectant, and as an ingredient in antifouling paint. Stated simply. it
is toxic to just about all life.

Chromated copper arsenate, at one time, was the most widely used wood
treatment. Hexavalent chromium and arsenic in any form are both extremely
toxic, so newer treatments were developed including ammoniacal copper
quaternary. The EPA lists this as a general use pesticide and it is far
less toxic than chromated copper arsenate. Other newer wood treatments used
today are based on borax and other borate salts. These too are less toxic
than the older copper salts.

The oil treatment that "ml" refers to is most likely creosote. However
creosote or any other of the treatments described above will not make the
wood a good electrical insulator for use as spacers in open wire
transmission line. Raw wood or wood treated with any of the metal salts
shows a high dielectric loss. Even pentachlorophenol is not very suitable
as its dielectric constant is around 8 to 10. But then the wood itself
usually has a radio frequency dielectric constant around 10 or more too,
even if completely dried. Increases are seen at frequencies below the MHz
region, and with increasing moisture. The loss tangent of wood also
increases rapidly with moisture content.

The reason that old timers boiled their wood dowels in paraffin wax was
twofold. The first was to completely dry the wood, and the second was to
provide moisture protection. The preservation of the wood against fungus or
termites was generally inconsequential for use as spacers in transmission
lines.

Polyvinyl chloride and chlorinated polyvinyl chloride plastics are
moderately lossy at radio frequencies but are far better than wood in this
respect, and I have seen them used with homebrew transmission lines.
However, from the standpoint of RF losses and ultraviolet radiation damage,
acrylic plastics are my choice as true ladder line insulators.

One suggestion I have is to look at cheap plastic coathangers. These are
about 1/4 inch in diameter and are not vinyl coated wire hangers. Several
insulators can be cut from a single coathanger. Since you can often buy
these hangers for around $1.00 for ten, a few dollars could provide a good
number of insulators. If you don't like the color, spray paint them with
Krylon or another acrylic paint. White will provide the best ultraviolet
resistance. I would limit my wire size to 16 Gauge or smaller as this
plastic is quite brittle.

73, Dr. Barry L. Ornitz WA4VZQ