Roy Lewallen, W7EL, wrote:
Dr. Barry L. Ornitz wrote:
. . .
Roy Lewallen, W7EL, dipped a number of coils in various materials
(RTV silicone, epoxy cement, Q-dope, hot melt adhesive, etc.) a
while back and then measured their losses with a Q-meter. If Roy
can find his old article, perhaps he can post it again.

Great memory, Barry! It was posted on Dec. 16, 1998. A copy of
the original posting follows. I didn't do any other experiments as
I said I would, and I've gotten very little confirming or
contradictory feedback.

Thanks Roy, but reading your article, I have concluded that my memory is
somewhat faulty. I had thought that cellulose nitrate had low dielectric
losses, but it turns out that what I was really thinking of was clear
fingernail polish which is made from a mixture of cellulose acetate,
cellulose acetate propionate, and cellulose acetate butyrate. These
cellulose esters are still not excellent radio frequency insulators, but
they do a better job than cellulose nitrate.

I have recently been working on an introductory paper for electrical
engineers on the mechanical and electrical properties of polymeric
plastics. The following paragraph from the paper explains the basis for a
polymer's electric properties.

"The electrical properties of a polymer are due to the structure of the
polymer both microscopically and macroscopically. Most polymers are
dielectrics (insulators) as opposed to metals where electrons can move
freely. In polymers, the electrons are tightly bound to the polymer
backbone through covalent bonding which resists the movement of electrons.
Not all polymers behave the same when an electric potential is applied to
them. This difference in behavior allows plastics to be classified as
polar or non-polar. Polar plastics do not have fully covalent bonds
leading to a slight imbalance in the electrical charge of the molecule. In
polar plastics, dipoles are created by an imbalance in the distribution of
electrons and in the presence of an electric field these dipoles will
attempt to move slightly to align with the field. Because of the temporal
element of the movement of the dipoles, the frequency of the applied field
strongly affects the motion of the dipoles. In non-polar plastics, the
molecules are symmetric and the bonds are fully covalent. No dipoles are
present to align with the electrical field. However the electric field
does move the electrons slightly in the direction of the applied field;
this is known as electron polarization. This movement is effectively
instantaneous and the effect of frequency on the dielectric properties of
non-polar plastics is quite small. Non-polar plastics tend to be excellent
insulators and have low dielectric constants and low dielectric losses
making them useful for the dielectrics in capacitors. Polar plastics, at
low frequencies, have enough time for the dipoles to align with the
external field. At higher frequencies, the dipoles do not have enough time
to fully align. The result is a decrease in the dielectric constant with
frequency. The hindrance to the movement to the dipoles, a form of
internal friction, causes heat to build up in the polymer. This increased
dielectric loss is the operating principle behind radio frequency heating
and microwave ovens."

From their atomic structure polyethylene [PE], polytetrafluoroethylene
[PTFE, Teflon], and polystyrene [PS] are nonpolar plastics with low
dielectric constants of 2.3, 2.1, and 2.6 respectively. Of these, only PS
readily dissolve in solvents.

The repeating unit of cellulose, a natural polymer, has three hydroxyl
groups which may be substituted with inorganic or organic acids. When
nitric acid is used, cellulose nitrate is produced. Cellulose trinitrate,
the explosive, has three nitrate groups per repeating unit. The ester used
in lacquers and Duco cement is not fully nitrated with a degree of
substitution between 2 and 3. Because of the nitro groups, which are quite
polar, cellulose nitrate has higher dielectric losses than the esters made
with organic acids. These esters are much more lossy than true nonpolar
polymers, but less lossy than very polar plastics like polyvinyl chloride
[PVC].

So for a coil dope with low dielectric losses, I suggest polystyrene
dissolved in acetone or toluene. Clear nail polish will work in a pinch,
but it might be better to use hot melt adhesive, or paraffin wax. If you
can wait a day or more for it to cure, some of the room temperature
vulcanizing silicone products work well too.

--
73, Dr. Barry L. Ornitz WA4VZQ Text in Quotes:
Copyright 2009 B. L Ornitz

[transpose digits to reply]

On Feb 10, 9:00*pm, "Dr. Barry L. Ornitz"
wrote:
Roy Lewallen, W7EL, wrote:
Dr. Barry L. Ornitz wrote:
. . .
Roy Lewallen, W7EL, dipped a number of coils in various materials
(RTV silicone, epoxy cement, Q-dope, hot melt adhesive, etc.) a
while back and then measured their losses with a Q-meter. *If Roy
can find his old article, perhaps he can post it again.

Great memory, Barry! It was posted on Dec. 16, 1998. A copy of
the original posting follows. I didn't do any other experiments as
I said I would, and I've gotten very little confirming or
contradictory feedback.

Thanks Roy, but reading your article, I have concluded that my memory is
somewhat faulty. *I had thought that cellulose nitrate had low dielectric
losses, but it turns out that what I was really thinking of was clear
fingernail polish which is made from a mixture of cellulose acetate,
cellulose acetate propionate, and cellulose acetate butyrate. *These
cellulose esters are still not excellent radio frequency insulators, but
they do a better job than cellulose nitrate.

I have recently been working on an introductory paper for electrical
engineers on the mechanical and electrical properties of polymeric
plastics. *The following paragraph from the paper explains the basis for a
polymer's electric properties.

"The electrical properties of a polymer are due to the structure of the
polymer both microscopically and macroscopically. *Most polymers are
dielectrics (insulators) as opposed to metals where electrons can move
freely. *In polymers, the electrons are tightly bound to the polymer
backbone through covalent bonding which resists the movement of electrons..
Not all polymers behave the same when an electric potential is applied to
them. *This difference in behavior allows plastics to be classified as
polar or non-polar. *Polar plastics do not have fully covalent bonds
leading to a slight imbalance in the electrical charge of the molecule. *In
polar plastics, dipoles are created by an imbalance in the distribution of
electrons and in the presence of an electric field these dipoles will
attempt to move slightly to align with the field. *Because of the temporal
element of the movement of the dipoles, the frequency of the applied field
strongly affects the motion of the dipoles. *In non-polar plastics, the
molecules are symmetric and the bonds are fully covalent. *No dipoles are
present to align with the electrical field. *However the electric field
does move the electrons slightly in the direction of the applied field;
this is known as electron polarization. *This movement is effectively
instantaneous and the effect of frequency on the dielectric properties of
non-polar plastics is quite small. *Non-polar plastics tend to be excellent
insulators and have low dielectric constants and low dielectric losses
making them useful for the dielectrics in capacitors. *Polar plastics, at
low frequencies, have enough time for the dipoles to align with the
external field. *At higher frequencies, the dipoles do not have enough time
to fully align. *The result is a decrease in the dielectric constant with
frequency. *The hindrance to the movement to the dipoles, a form of
internal friction, causes heat to build up in the polymer. *This increased
dielectric loss is the operating principle behind radio frequency heating
and microwave ovens."

From their atomic structure polyethylene [PE], polytetrafluoroethylene
[PTFE, Teflon], and polystyrene [PS] are nonpolar plastics with low
dielectric constants of 2.3, 2.1, and 2.6 respectively. *Of these, only PS
readily dissolve in solvents.

The repeating unit of cellulose, a natural polymer, has three hydroxyl
groups which may be substituted with inorganic or organic acids. *When
nitric acid is used, cellulose nitrate is produced. *Cellulose trinitrate,
the explosive, has three nitrate groups per repeating unit. *The ester used
in lacquers and Duco cement is not fully nitrated with a degree of
substitution between 2 and 3. *Because of the nitro groups, which are quite
polar, cellulose nitrate has higher dielectric losses than the esters made
with organic acids. *These esters are much more lossy than true nonpolar
polymers, but less lossy than very polar plastics like polyvinyl chloride
[PVC].

So for a coil dope with low dielectric losses, I suggest polystyrene
dissolved in acetone or toluene. *Clear nail polish will work in a pinch,
but it might be better to use hot melt adhesive, or paraffin wax. *If you
can wait a day or more for it to cure, some of the room temperature
vulcanizing silicone products work well too.

--
73, Dr. Barry L. Ornitz *WA4VZQ * * * * * * * * * * * Text in Quotes:
Copyright 2009 B. L Ornitz

[transpose digits to reply]

I believe what you are describing is Duco cement the kind that I used
to use to build model cars.
Is that stuff still around? I think they took it off the market
because of the glue huffers. If it is still around it should make
excellent coil dope.

Jimmie.

"JIMMIE" wrote in message
..
{snip - in the early days of Usenet, many sites would not allow messages
where the quoted text was longer than the new text; it is still considered
bad manners to do this}
I believe what you are describing is Duco cement the kind that I
used to use to build model cars.
Is that stuff still around? I think they took it off the market
because of the glue huffers. If it is still around it should make
excellent coil dope.

Duco Cement is made by the Permatex division of ITW/Devcon. It has not
been taken off the market, but in some communities its sale is restricted
to keep it away from children.

Duco Cement is cellulose nitrate dissolved in acetone. It is plasticized
by a small amount of camphor (probably for historic reasons, camphor was
the plasticizer used in celluloid and pyroxylin around the turn of the 20th
century).

As I stated in the post you quoted, cellulose nitrate is far from the best
radio frequency insulator. Fingernail polish performs slightly better as
an RF insulator but polyvinyl chloride is worse. I still recommend General
Cement commercial Q-dope which is polystyrene dissolved in toluene or
methyl-ethyl-ketone (GC has changed their formulation). You can make your
own inexpensively by dissolving Styrofoam shipping "peanuts" in toluene.
methyl-ethyl-ketone, or acetone. Of these three solvents, acetone is the
safest. Home Depot used to sell all three solvents in the past, but sadly
there is no store near me where I now live.

--
73, Dr. Barry L. Ornitz WA4VZQ

[transpose digits to reply]

On Tue, 10 Feb 2009 21:00:32 -0500, "Dr. Barry L. Ornitz"
wrote:

I have recently been working on an introductory paper for electrical
engineers on the mechanical and electrical properties of polymeric
plastics.
(...)

"The electrical properties of a polymer are due to the structure of the
polymer both microscopically and macroscopically. Most polymers are
dielectrics (insulators) as opposed to metals where electrons can move
freely.
(...)

Argh. Is this really for an introductory (beginning) publication? I'm
either fatally obsolete (the most likely possibility) or materials
have progressed well beyond my 25 year old chemistry experience. Looks
like I'll be doing some more reading to decode the technical terms.
Don't change, as I prefer accurate and complete explanations even if I
don't initially understand them.

I'm partial to seat-of-the-pants testing for RF loss using a microwave
oven. In general, if it gets hot in a microwave oven, it's going to
be lossy. I haven't tried various coil coating formulations and
tapes. However, I have tried various common hardware store plastic
and fiberglass products to find something suitable for a 2.4GHz
antenna radome. The problem was that it was impossible to assign a
numerical value to the RF losses using the microwave oven test. Some
would be hotter or less hot depending on the color (doping). My IR
optical thermometer was also rather sensitive to surface reflectivity,
resulting in additional errors. Still, the stuff that didn't work,
was fairly obvious by the deformation, smell, and sometimes smoke.
Incidentally, I've lost count of how many microwave ovens and toaster
ovens (for glue curing) that I've destroyed.

Thanks much for taking the time to supply the technical detail on
various materials and techniques. I've learned more from your
postings than from the usual uninformed speculative rubbish (such as
what I tend to post).


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

What about contact cement? What i have states it is a "polychlorprene-based
contact cement.

"Dr. Barry L. Ornitz" wrote in message
...
Roy Lewallen, W7EL, wrote:
Dr. Barry L. Ornitz wrote:
. . .
Roy Lewallen, W7EL, dipped a number of coils in various materials
(RTV silicone, epoxy cement, Q-dope, hot melt adhesive, etc.) a
while back and then measured their losses with a Q-meter. If Roy
can find his old article, perhaps he can post it again.

Great memory, Barry! It was posted on Dec. 16, 1998. A copy of
the original posting follows. I didn't do any other experiments as
I said I would, and I've gotten very little confirming or
contradictory feedback.

Thanks Roy, but reading your article, I have concluded that my memory is
somewhat faulty. I had thought that cellulose nitrate had low dielectric
losses, but it turns out that what I was really thinking of was clear
fingernail polish which is made from a mixture of cellulose acetate,
cellulose acetate propionate, and cellulose acetate butyrate. These
cellulose esters are still not excellent radio frequency insulators, but
they do a better job than cellulose nitrate.

I have recently been working on an introductory paper for electrical
engineers on the mechanical and electrical properties of polymeric
plastics. The following paragraph from the paper explains the basis for a
polymer's electric properties.

"The electrical properties of a polymer are due to the structure of the
polymer both microscopically and macroscopically. Most polymers are
dielectrics (insulators) as opposed to metals where electrons can move
freely. In polymers, the electrons are tightly bound to the polymer
backbone through covalent bonding which resists the movement of electrons.
Not all polymers behave the same when an electric potential is applied to
them. This difference in behavior allows plastics to be classified as
polar or non-polar. Polar plastics do not have fully covalent bonds
leading to a slight imbalance in the electrical charge of the molecule.
In polar plastics, dipoles are created by an imbalance in the distribution
of electrons and in the presence of an electric field these dipoles will
attempt to move slightly to align with the field. Because of the temporal
element of the movement of the dipoles, the frequency of the applied field
strongly affects the motion of the dipoles. In non-polar plastics, the
molecules are symmetric and the bonds are fully covalent. No dipoles are
present to align with the electrical field. However the electric field
does move the electrons slightly in the direction of the applied field;
this is known as electron polarization. This movement is effectively
instantaneous and the effect of frequency on the dielectric properties of
non-polar plastics is quite small. Non-polar plastics tend to be
excellent insulators and have low dielectric constants and low dielectric
losses making them useful for the dielectrics in capacitors. Polar
plastics, at low frequencies, have enough time for the dipoles to align
with the external field. At higher frequencies, the dipoles do not have
enough time to fully align. The result is a decrease in the dielectric
constant with frequency. The hindrance to the movement to the dipoles, a
form of internal friction, causes heat to build up in the polymer. This
increased dielectric loss is the operating principle behind radio
frequency heating and microwave ovens."

From their atomic structure polyethylene [PE], polytetrafluoroethylene
[PTFE, Teflon], and polystyrene [PS] are nonpolar plastics with low
dielectric constants of 2.3, 2.1, and 2.6 respectively. Of these, only PS
readily dissolve in solvents.

The repeating unit of cellulose, a natural polymer, has three hydroxyl
groups which may be substituted with inorganic or organic acids. When
nitric acid is used, cellulose nitrate is produced. Cellulose trinitrate,
the explosive, has three nitrate groups per repeating unit. The ester
used in lacquers and Duco cement is not fully nitrated with a degree of
substitution between 2 and 3. Because of the nitro groups, which are
quite polar, cellulose nitrate has higher dielectric losses than the
esters made with organic acids. These esters are much more lossy than
true nonpolar polymers, but less lossy than very polar plastics like
polyvinyl chloride [PVC].

So for a coil dope with low dielectric losses, I suggest polystyrene
dissolved in acetone or toluene. Clear nail polish will work in a pinch,
but it might be better to use hot melt adhesive, or paraffin wax. If you
can wait a day or more for it to cure, some of the room temperature
vulcanizing silicone products work well too.

--
73, Dr. Barry L. Ornitz WA4VZQ Text in Quotes:
Copyright 2009 B. L Ornitz

[transpose digits to reply]

Jeff Liebermann wrote:
. . .
I'm partial to seat-of-the-pants testing for RF loss using a microwave
oven. In general, if it gets hot in a microwave oven, it's going to
be lossy. . .

If it gets hot in a microwave oven, it's going to be lossy at 2.4 GHz,
but it isn't necessarily going to be lossy at HF or even VHF. However,
if it *doesn't* get hot in a microwave oven, it's probably pretty low
loss at any frequency up to 2.4 GHz.

There is, of course, a problem with reducing loss to a binary quantity
of "lossy" or "not lossy". A relatively high amount of loss can easily
be tolerated at points of low electric field strength, such as an
insulator at the feedpoint of a half wavelength dipole. On the other
hand, you need very low loss for some other applications like potting
high Q inductors or for feedline insulators when the feedline has a very
high SWR.

Roy Lewallen, W7EL

"Spin" wrote in message
...
What about contact cement? What i have states it is a
"polychlor{o}prene-based contact cement.

The strongly polar chlorine atom in the polymer backbone or polychloroprene
will make your cement lossy at radio frequencies.

--
73, Dr. Barry L. Ornitz WA4VZQ

[transpose digits to reply]

Dr. Barry L. Ornitz wrote:
"Spin" wrote in message
...
What about contact cement? What i have states it is a
"polychlor{o}prene-based contact cement.

The strongly polar chlorine atom in the polymer backbone or
polychloroprene will make your cement lossy at radio frequencies.

And it would be terribly sticky and attract dirt and everything else.

Roy Lewallen, W7EL

" And it would be terribly sticky and attract dirt and everything else"

I could always use it instead of a bug zapper.
!


"Roy Lewallen" wrote in message
ine...
Dr. Barry L. Ornitz wrote:
"Spin" wrote in message
...
What about contact cement? What i have states it is a
"polychlor{o}prene-based contact cement.

The strongly polar chlorine atom in the polymer backbone or
polychloroprene will make your cement lossy at radio frequencies.

".

Roy Lewallen, W7EL

Roy Lewallen wrote:
Dr. Barry L. Ornitz wrote:
"Spin" wrote in message
...
What about contact cement? What i have states it is a
"polychlor{o}prene-based contact cement.

The strongly polar chlorine atom in the polymer backbone or
polychloroprene will make your cement lossy at radio frequencies.

And it would be terribly sticky and attract dirt and everything else.

Roy Lewallen, W7EL

Did anybody mention wax?