In message , k4kqz
writes

'Jeff[_15_ Wrote:
;795578']-

Which is valid at the microwave oven frequency. Might be relevant at
HF, or more likely, not.

tom
K0TAR-

It is highly unlikely that a material that is OK at 2GHz will be worse
at HF.

Jeff

Actually, a material can be perfectly fine at microwave frequencies and
bad at HF. And vice versa. The microwave oven test should only be
considered a *very rough* indication of material suitability.

Care to suggest one or two examples of materials where RF losses are
higher at HF?
--
Ian

On 31.8.2012 22:04, Wimpie wrote:
El 31-08-12 20:07, Dave Platt escribió:
In ikabel.net,
wrote:

Problem exists how to get reliable insulation to split driven element
and support rod which is exposed to RF voltage ?
Fiberglass is told to be sensitive creating conductive coal brigdes
which creates true resistive short at driving point ? (at least one
fiberglass tubing is done so... gap was 2 inches )

Assuming power of about 1 kW and a HW dipole (say 60 Ohms), the
voltage will be about 350Vp. I can hardly imagine that a plastic gap
of 0.05m will degrade to failure because of tracking.

On the other hand, if the original poster is attempting to drive this
antenna off-resonance, with open-wire feedline and a wide-
impedance-range transmatch / "antenna tuner", then it's entirely
possible that the feedpoint will sometimes be "looking into" a much
higher impedance, and that a matched drive will result in very high
voltages at the feedpoint. Even a coax-feed antenna might have this
problem, I suppose, if the split element is being driven by something
like a delta match which has a relatively high impedance-
transformation ratio.

From what I see in a short Google-search, fiberglass *can* be
hygroscopic, depending on what resin was used to bind the fiberglass.
A fiberglass rod which was made with a somewhat-hygroscopic resin
(e.g. polyamide) might tend to behave badly in the face of high RF
voltages, whereas a rod made with a non-hygroscopic resin might be
fine unless dirty or wet.


Hello Dave,

Thanks for de addition. During the simple voltage calculation my mind
said: "what if VSWR is really bad".

With 1 kVp over 0.05m I would not expect problems. You are right,
Polyamide (Nylon) is bad for RF and as far as I know, isn't fully UV
resistant without additives.

Once I had a nylon bolt in the field of a tuning capacitor running close
to breakdown over about 3mmm. The bolt produced lots of smoke within
some seconds and broke down. Changing from PA to PE solved the problem.

Assuming 50% glass fill factor and effective loss factor of 0.2 (so Q of
the glass/PA composite material is just 5), I would expect a dissipation
in the range of 4 Watts at 1 kVp and 10 MHz in a 1.5 Inch thick massive
rod. Maybe Kba can provide us some additional info on the working
voltage across the gap (and frequency).

When using epoxy or polyester fiberglass, loss will be significantly less.


Thanks for all comments, ... some new approaches have arisen... to
eliminate possible risks and troubles before they exist...

This problem is dual, both electrical and mechanical as insulator in the
element gap is under quite high mechanic stress...
This is future OWA antenna split driven element... will be used at HF...

This previous fiberglass problem wasn't instant, it developed slowly
after several years of succesful use ( and weather effects, moisture
etc. ) so probably the reason was only the moisture, dust and dirt
layers in the inner surface of the insulator.
Insulator was round fiberglass tube of 65mm diameter and around one
meter long, used as center of 7MHz antenna feed element ( 60mm diam.),
the outer surface of the tube was weather ( and UV ) protected and water
proof, but the 5 cm gap inside the tube was not entirely though element
ends were not in open air... some moisture do condensate always inside
the element... I guess...

Measured impedance was quite low, 25 ohms resistive near resonance, so
probably voltages have been also low at one kw power level.

I cannot tell the exact fiberglass grade that was used, probably it was
green FR4 or other strong quality as mechanical stress was high in the
insulator and long and heavy 7MHz element halves loaded the insulator
center.
This fiberglass insulator tube finally got to a ohmic short and didn't
recover.

Later this insulator was replaced with another type and problems
disappeared.

.. . .

Now one other future split driven OWA antenna has been under plan ...
but there are the same mechanical stress problems as element center gap
should ( ? ) have center support rod but it exposes also to all weather
effects... in this case element diameter will be 25 mm...
So insulation in the gap should be good but material should be also
something capable handling bending moment of the element halves...

Now the latest plan is try to move the mechanic load away from the
center support rod to element support plate which could be much longer
in length... then the element center stress is expected to be lower
across the gap...

Then also the element clamps have more separation as this support plate
is also again FR4...
Secondly the element halves will be insulated from the clamps so there
will be less risk of this FR4 plate becoming conductive...
Insulation between element and clamps could be thin straps of teflon
sheet...

Best might be if the fiberglass center support rod can taken totally out
or be of round teflon bar... good insulator, low friction, probably air
particles etc. don't stick on it easily...

Teflon feels tough but elastic, so in the stress point it's not much
use, but probably functions as a vibration damper in the gap... assuming
the element support plate does not transfer element end bending effects
due to wind load directly to element center gap...

Anyway it's going to be interesting to see how these precautions
will actually work... in both at mechanical and electrical
reliability... hopefully in both.

tnx oh6io

On Thu, 30 Aug 2012 21:49:15 +0300, KBa wrote:

Problem exists how to get reliable insulation to split driven element
and support rod which is exposed to RF voltage ?
Fiberglass is told to be sensitive creating conductive coal brigdes
which creates true resistive short at driving point ? (at least one
fiberglass tubing is done so... gap was 2 inches )

How to improve insulation ? Ptfe-shield over fiberglass rod, heat shrink
tubing, varnish layer ?

tnx oh6io

In a past life, I helped design marine radios. As others have
mentioned, there are different flavors of fiberglass, some of which
are not really suitable for outdoor or high humidity applications.

Instead of trying to fix fiberglass, you might consider machinable
glass ceramics.
http://www.matweb.com/Search/MaterialGroupSearch.aspx?GroupID=301
Something like material:
http://www.matweb.com/search/datasheet.aspx?matguid=848bdecf89b74ef986925162e6a 6255e&ckck=1
http://www.corning.com/assets/0/965/989/1081/1397D5E7-018E-4CF4-A34C-6814B815BCAC.pdf

It's sufficiently strong to handle antenna elements, but was also
somewhat brittle. RF characteristics are superb. 9.4Kv/mm is not
going to arc. However, you won't like the prices. A 1" dia 6" long
rod will cost you $150.
http://www.astromet.com/MacorPriceSheet2010.pdf
For ham radio, nothing but the best.

Otherwise, there's always the traditional dry pine dowel soaked in
bees wax.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

KBa Inscribed thus:

Best might be if the fiberglass center support rod can taken totally
out or be of round teflon bar... good insulator, low friction,
probably air particles etc. don't stick on it easily...

Teflon feels tough but elastic,

Be aware that Teflon will cold flow !

--
Best Regards:
Baron.

On 1.9.2012 19:20, Jeff Liebermann wrote:
On Thu, 30 Aug 2012 21:49:15 +0300, KBa wrote:

Problem exists how to get reliable insulation to split driven element
and support rod which is exposed to RF voltage ?
Fiberglass is told to be sensitive creating conductive coal brigdes
which creates true resistive short at driving point ? (at least one
fiberglass tubing is done so... gap was 2 inches )

How to improve insulation ? Ptfe-shield over fiberglass rod, heat shrink
tubing, varnish layer ?

tnx oh6io

In a past life, I helped design marine radios. As others have
mentioned, there are different flavors of fiberglass, some of which
are not really suitable for outdoor or high humidity applications.

Instead of trying to fix fiberglass, you might consider machinable
glass ceramics.
http://www.matweb.com/Search/MaterialGroupSearch.aspx?GroupID=301
Something like material:
http://www.matweb.com/search/datasheet.aspx?matguid=848bdecf89b74ef986925162e6a 6255e&ckck=1
http://www.corning.com/assets/0/965/989/1081/1397D5E7-018E-4CF4-A34C-6814B815BCAC.pdf

It's sufficiently strong to handle antenna elements, but was also
somewhat brittle. RF characteristics are superb. 9.4Kv/mm is not
going to arc. However, you won't like the prices. A 1" dia 6" long
rod will cost you $150.
http://www.astromet.com/MacorPriceSheet2010.pdf
For ham radio, nothing but the best.

Otherwise, there's always the traditional dry pine dowel soaked in
bees wax.

Well, hmmm...
There seems to be several alternatives to fiberglass... and several
grades of it...

Just thinking of how glass ceramics may behave under bending force...
Element center gap is under very small vibration (wind load) and element
static load stresses the insulator center... it bends slighly depending
how elastic is the material...
Fiberglass have some elasticity... it's not brittle... on the other hand
there could be support limiting the bar bending or the element halves
might have more than two clamping points... so the center gap would
be steady...

Actually I had in mind using extra varnish layers on fiberglass after
processed to diameter and then boiling it in bee wax...
This is still the plan b or c.

tnx oh6io

El 01-09-12 18:13, KBa escribió:
On 31.8.2012 22:04, Wimpie wrote:
El 31-08-12 20:07, Dave Platt escribió:
In ikabel.net,
wrote:

Problem exists how to get reliable insulation to split driven
element
and support rod which is exposed to RF voltage ?
Fiberglass is told to be sensitive creating conductive coal brigdes
which creates true resistive short at driving point ? (at least one
fiberglass tubing is done so... gap was 2 inches )

Assuming power of about 1 kW and a HW dipole (say 60 Ohms), the
voltage will be about 350Vp. I can hardly imagine that a plastic gap
of 0.05m will degrade to failure because of tracking.

On the other hand, if the original poster is attempting to drive this
antenna off-resonance, with open-wire feedline and a wide-
impedance-range transmatch / "antenna tuner", then it's entirely
possible that the feedpoint will sometimes be "looking into" a much
higher impedance, and that a matched drive will result in very high
voltages at the feedpoint. Even a coax-feed antenna might have this
problem, I suppose, if the split element is being driven by something
like a delta match which has a relatively high impedance-
transformation ratio.

From what I see in a short Google-search, fiberglass *can* be
hygroscopic, depending on what resin was used to bind the fiberglass.
A fiberglass rod which was made with a somewhat-hygroscopic resin
(e.g. polyamide) might tend to behave badly in the face of high RF
voltages, whereas a rod made with a non-hygroscopic resin might be
fine unless dirty or wet.


Hello Dave,

Thanks for de addition. During the simple voltage calculation my mind
said: "what if VSWR is really bad".

With 1 kVp over 0.05m I would not expect problems. You are right,
Polyamide (Nylon) is bad for RF and as far as I know, isn't fully UV
resistant without additives.

Once I had a nylon bolt in the field of a tuning capacitor running
close
to breakdown over about 3mmm. The bolt produced lots of smoke within
some seconds and broke down. Changing from PA to PE solved the problem.

Assuming 50% glass fill factor and effective loss factor of 0.2 (so
Q of
the glass/PA composite material is just 5), I would expect a
dissipation
in the range of 4 Watts at 1 kVp and 10 MHz in a 1.5 Inch thick massive
rod. Maybe Kba can provide us some additional info on the working
voltage across the gap (and frequency).

When using epoxy or polyester fiberglass, loss will be significantly
less.


Thanks for all comments, ... some new approaches have arisen... to
eliminate possible risks and troubles before they exist...

This problem is dual, both electrical and mechanical as insulator in the
element gap is under quite high mechanic stress...
This is future OWA antenna split driven element... will be used at HF...

This previous fiberglass problem wasn't instant, it developed slowly
after several years of succesful use ( and weather effects, moisture
etc. ) so probably the reason was only the moisture, dust and dirt
layers in the inner surface of the insulator.
Tracking (forming of conductive (carbon) path) is mostly a slow
process that may take years to develop to failure, so this sound
strange (if creepage is the root cause).


Insulator was round fiberglass tube of 65mm diameter and around one
meter long, used as center of 7MHz antenna feed element ( 60mm diam.),
the outer surface of the tube was weather ( and UV ) protected and
water proof, but the 5 cm gap inside the tube was not entirely though
element ends were not in open air... some moisture do condensate
always inside the element... I guess...

This changes the story when moisture can enter the inner side of the
tube and may stay there. I assumed you used a massive rod for
mechanical strength. At the inner side you don't have the cleaning
effect due to rain, wind, precipitation, etc. Could there be salt
built-up (due to seeping water that evaporates slowly)?

You mentioned it is 1 m long, that is really a large creepage
distance! Assuming about 5mm wall thickness and fully conducting
inner side of the tube, radial field strength (350V) will be in the
50V/mm range, well below permissible levels to avoid insulation
failure at MHz frequencies in FR4 material.

It would be nice to inspect such a failed tube to figure out how the
tracking took place, because I have now idea.




Measured impedance was quite low, 25 ohms resistive near resonance, so
probably voltages have been also low at one kw power level.

I cannot tell the exact fiberglass grade that was used, probably it
was green FR4 or other strong quality as mechanical stress was high in
the insulator and long and heavy 7MHz element halves loaded the
insulator center.
This fiberglass insulator tube finally got to a ohmic short and didn't
recover.

Later this insulator was replaced with another type and problems
disappeared.

. . .

Now one other future split driven OWA antenna has been under plan ...
but there are the same mechanical stress problems as element center gap
should ( ? ) have center support rod but it exposes also to all
weather effects... in this case element diameter will be 25 mm...
So insulation in the gap should be good but material should be also
something capable handling bending moment of the element halves...

Now the latest plan is try to move the mechanic load away from the
center support rod to element support plate which could be much longer
in length... then the element center stress is expected to be lower
across the gap...

Then also the element clamps have more separation as this support plate
is also again FR4...
Secondly the element halves will be insulated from the clamps so there
will be less risk of this FR4 plate becoming conductive...
Insulation between element and clamps could be thin straps of teflon
sheet...

Best might be if the fiberglass center support rod can taken totally
out or be of round teflon bar... good insulator, low friction,
probably air particles etc. don't stick on it easily...

Teflon feels tough but elastic, so in the stress point it's not much
use, but probably functions as a vibration damper in the gap... assuming
the element support plate does not transfer element end bending effects
due to wind load directly to element center gap...

Anyway it's going to be interesting to see how these precautions
will actually work... in both at mechanical and electrical
reliability... hopefully in both.

Besides mechanical cracks that may provoke solid insulation breakdown,
carbon trace forming (tracking) over wheather exposed plastic surfaces
is the most likely problem, so I think you should try to maximize the
creepage path. As E-field strength in the insulation materials will be
low, you don't need low loss materials.

Thanks for sharing the info on the insulator failure!


--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

El 01-09-12 22:10, Wimpie escribió:
El 01-09-12 18:13, KBa escribió:
On 31.8.2012 22:04, Wimpie wrote:
El 31-08-12 20:07, Dave Platt escribió:
In ikabel.net,
wrote:

Problem exists how to get reliable insulation to split driven
element
and support rod which is exposed to RF voltage ?
Fiberglass is told to be sensitive creating conductive coal brigdes
which creates true resistive short at driving point ? (at least one
fiberglass tubing is done so... gap was 2 inches )

Assuming power of about 1 kW and a HW dipole (say 60 Ohms), the
voltage will be about 350Vp. I can hardly imagine that a plastic gap
of 0.05m will degrade to failure because of tracking.

On the other hand, if the original poster is attempting to drive this
antenna off-resonance, with open-wire feedline and a wide-
impedance-range transmatch / "antenna tuner", then it's entirely
possible that the feedpoint will sometimes be "looking into" a much
higher impedance, and that a matched drive will result in very high
voltages at the feedpoint. Even a coax-feed antenna might have this
problem, I suppose, if the split element is being driven by something
like a delta match which has a relatively high impedance-
transformation ratio.

From what I see in a short Google-search, fiberglass *can* be
hygroscopic, depending on what resin was used to bind the fiberglass.
A fiberglass rod which was made with a somewhat-hygroscopic resin
(e.g. polyamide) might tend to behave badly in the face of high RF
voltages, whereas a rod made with a non-hygroscopic resin might be
fine unless dirty or wet.


Hello Dave,

Thanks for de addition. During the simple voltage calculation my mind
said: "what if VSWR is really bad".

With 1 kVp over 0.05m I would not expect problems. You are right,
Polyamide (Nylon) is bad for RF and as far as I know, isn't fully UV
resistant without additives.

Once I had a nylon bolt in the field of a tuning capacitor running
close
to breakdown over about 3mmm. The bolt produced lots of smoke within
some seconds and broke down. Changing from PA to PE solved the
problem.

Assuming 50% glass fill factor and effective loss factor of 0.2 (so
Q of
the glass/PA composite material is just 5), I would expect a
dissipation
in the range of 4 Watts at 1 kVp and 10 MHz in a 1.5 Inch thick
massive
rod. Maybe Kba can provide us some additional info on the working
voltage across the gap (and frequency).

When using epoxy or polyester fiberglass, loss will be significantly
less.


Thanks for all comments, ... some new approaches have arisen... to
eliminate possible risks and troubles before they exist...

This problem is dual, both electrical and mechanical as insulator in
the
element gap is under quite high mechanic stress...
This is future OWA antenna split driven element... will be used at
HF...

This previous fiberglass problem wasn't instant, it developed slowly
after several years of succesful use ( and weather effects, moisture
etc. ) so probably the reason was only the moisture, dust and dirt
layers in the inner surface of the insulator.
Tracking (forming of conductive (carbon) path) is mostly a slow
process that may take years to develop to failure, so this **doesn't** sound
strange (if creepage is the root cause).


Insulator was round fiberglass tube of 65mm diameter and around one
meter long, used as center of 7MHz antenna feed element ( 60mm diam.),
the outer surface of the tube was weather ( and UV ) protected and
water proof, but the 5 cm gap inside the tube was not entirely though
element ends were not in open air... some moisture do condensate
always inside the element... I guess...

This changes the story when moisture can enter the inner side of the
tube and may stay there. I assumed you used a massive rod for
mechanical strength. At the inner side you don't have the cleaning
effect due to rain, wind, precipitation, etc. Could there be salt
built-up (due to seeping water that evaporates slowly)?

You mentioned it is 1 m long, that is really a large creepage
distance! Assuming about 5mm wall thickness and fully conducting inner
side of the tube, radial field strength (350V) will be in the 50V/mm
range, well below permissible levels to avoid insulation failure at
MHz frequencies in FR4 material.

It would be nice to inspect such a failed tube to figure out how the
tracking took place, because I have now idea.




Measured impedance was quite low, 25 ohms resistive near resonance, so
probably voltages have been also low at one kw power level.

I cannot tell the exact fiberglass grade that was used, probably it
was green FR4 or other strong quality as mechanical stress was high in
the insulator and long and heavy 7MHz element halves loaded the
insulator center.
This fiberglass insulator tube finally got to a ohmic short and didn't
recover.

Later this insulator was replaced with another type and problems
disappeared.

. . .

Now one other future split driven OWA antenna has been under plan ...
but there are the same mechanical stress problems as element center gap
should ( ? ) have center support rod but it exposes also to all
weather effects... in this case element diameter will be 25 mm...
So insulation in the gap should be good but material should be also
something capable handling bending moment of the element halves...

Now the latest plan is try to move the mechanic load away from the
center support rod to element support plate which could be much longer
in length... then the element center stress is expected to be lower
across the gap...

Then also the element clamps have more separation as this support plate
is also again FR4...
Secondly the element halves will be insulated from the clamps so there
will be less risk of this FR4 plate becoming conductive...
Insulation between element and clamps could be thin straps of teflon
sheet...

Best might be if the fiberglass center support rod can taken totally
out or be of round teflon bar... good insulator, low friction,
probably air particles etc. don't stick on it easily...

Teflon feels tough but elastic, so in the stress point it's not much
use, but probably functions as a vibration damper in the gap...
assuming
the element support plate does not transfer element end bending effects
due to wind load directly to element center gap...

Anyway it's going to be interesting to see how these precautions
will actually work... in both at mechanical and electrical
reliability... hopefully in both.

Besides mechanical cracks that may provoke solid insulation breakdown,
carbon trace forming (tracking) over wheather exposed plastic surfaces
is the most likely problem, so I think you should try to maximize the
creepage path. As E-field strength in the insulation materials will be
low, you don't need low loss materials.

Thanks for sharing the info on the insulator failure!




--
Wim
PA3DJS
www.tetech.nl
Please remove abc first in case of PM

On Sat, 01 Sep 2012 22:36:52 +0300, KBa wrote:

Just thinking of how glass ceramics may behave under bending force...

Machinable glass ceramic insulators don't behave... they break.
They're great under compression but miserable in tension. So-so in
torsion. All you have to do is make the insulator stronger than the
element it supports. If there's excess force on the element, the
aluminum element will bend rather than the insulator will break.

Element center gap is under very small vibration (wind load) and element
static load stresses the insulator center... it bends slighly depending
how elastic is the material...

I don't expect wind vibration to be much of a problem. The forces are
rather small compared to a flock of overfed birds landing on the
elements or the wind blowing at hurricane force. With a brittle
insulator, an impact with a flying hard object is a real danger.

Fiberglass have some elasticity... it's not brittle... on the other hand
there could be support limiting the bar bending or the element halves
might have more than two clamping points... so the center gap would
be steady...

You haven't supplied any numbers or dimensions, can't do any
calculations.

I don't think you'll have much trouble with the static loads
(including the birds). The wind loading might be a problem depending
on design.

Required reading "The Physical Design of Yagi Antennas" by Dave
Leeson:
http://www.universal-radio.com/catalog/books/0995.html
http://www.realhamradio.com/Download.htm
Ugh... I dunno about these prices:
http://www.alibris.com/booksearch?qwork=5115496
Mo
http://thebont.com/spreadsheets/AnalysisOfAntennaMastStrength.htm
http://www.rotorservice.com/antenna%20wind%20load.htm
http://www.arraysolutions.com/Products/windloads.htm
http://www.sinctech.com/antenna_wind_loading.aspx

Actually I had in mind using extra varnish layers on fiberglass after
processed to diameter and then boiling it in bee wax...
This is still the plan b or c.

Bees wax won't work on fiberglass.

tnx oh6io

Perhaps if you build something really disgusting errr... innovative,
which balances some of the tension on the insulator with a little
compression, try building the yagi elements using wires instead of
tubing using a "cage". The "cage" will increase the effective element
diameter (thus increasing the antenna bandwidth). The "cage" will
also supply some tension to the insulator, which will balance some of
the tension.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 01 Sep 2012 18:00:48 -0700, Jeff Liebermann
wrote:

The "cage" will
also supply some tension to the insulator, which will balance some of
the tension.

Oops. That should read:
The "cage" will also supply some compression to the insulator, which
will balance some of the tension.

http://www.ets-lindgren.com/3104C
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 2.9.2012 4:00, Jeff Liebermann wrote:
On Sat, 01 Sep 2012 22:36:52 +0300, KBa wrote:

Just thinking of how glass ceramics may behave under bending force...

Machinable glass ceramic insulators don't behave... they break.
They're great under compression but miserable in tension. So-so in
torsion. All you have to do is make the insulator stronger than the
element it supports. If there's excess force on the element, the
aluminum element will bend rather than the insulator will break.

Element center gap is under very small vibration (wind load) and element
static load stresses the insulator center... it bends slighly depending
how elastic is the material...

I don't expect wind vibration to be much of a problem. The forces are
rather small compared to a flock of overfed birds landing on the
elements or the wind blowing at hurricane force. With a brittle
insulator, an impact with a flying hard object is a real danger.

Fiberglass have some elasticity... it's not brittle... on the other hand
there could be support limiting the bar bending or the element halves
might have more than two clamping points... so the center gap would
be steady...

You haven't supplied any numbers or dimensions, can't do any
calculations.

Hi Jeff

Ok, very good points... this design may need better tools I have in
hands for the stress checks...

But some numbers... 14MHz tapered element half, symmetric segments,
starting at center 47" (OD 1", ID 0.625"), 24" (OD 0.875",ID 0.619"),
44" (OD 0.75", ID 0.619"),36"(OD 0.625",ID 0.467") and tip 58.7" (OD
0.5", ID 0.494") AL 6082, element wall dimensions are somewhat on a
heavy side at the center segments... so is the weight a little...
Center gap 2" between element halves.

Currently planned support plate dimensions L 15.75" x W 7.87" thickness
0.393" FR4, element clamp positions 2" and 6.88" symmetric along plate
long side, so two clamps for each element half, plate located above
element for partial rain cover... Plate max size 19.6" x 9.8"...
Not yet processed, so no worries for changes...

Much appreciated if you have some dimensioning help for the center
insulator diameter and length ( minimum ) handling the stress...

I may still need to consider FR4 bar covered with shrink tube, but
ceramics are also on a map... but depending on support plate strength
and bending at gap center (or between nearest clamps 2" off the gap
center ) there might be chance to forget whole center bar in the gap...

tnx oh6io


I don't think you'll have much trouble with the static loads
(including the birds). The wind loading might be a problem depending
on design.