Coil Dope
 

I read that old 78 LP's broken into pieces & mixed with a particular solvent
was used as coil dope. Does anybody remember which solvent was used & how
affective it was?

Coil Dope
 

On Mon, 09 Feb 2009 16:47:15 GMT, "Spin"
wrote:

I read that old 78 LP's broken into pieces & mixed with a particular solvent
was used as coil dope. Does anybody remember which solvent was used & how
affective it was?

Coil dope can be made from polystyrene packing peanuts dissolved in
acetone. Q-Dope is some kind of cellulose polymer broken down in the
same solvents. If you're planning on making your own, it does take
several days and plenty of agitation to produce a suitable sticky
mess.

The very old 78 rpm records were originally made from Bakelite, which
is quite resistant to chlorinated hydrocarbon solvents. During WWII,
Vinyl records appeared as a substitute for Bakelite. It's easy to
tell the difference. Bakelite is thermosetting plastic and is
unaffected by acetone. Vinyl is thermoplastic and is softened by
acetone.

My guess is that whomever suggested dissolving records wanted to trick
you into breaking your 78 rpm records. (Note: I'm sloooooly
transcribbling my record collection to various digital formats).

You don't state what you're trying to accomplish. If it's cleaning
the Q-Dope off old coils, acetone softens it nicely. Wipe clean and
you're done.


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

Coil Dope
 

I read that old 78 LP's broken into pieces & mixed with a particular solvent
was used as coil dope. Does anybody remember which solvent was used & how
affective it was?

78s were often made of shellac, and the usual solvent for shellac is
denatured alcohol. I believe that some other 78s were made from
cellulose acetate... for this material I believe that acetone would be
a usable solvent.

My understanding is that commercial Q-dope uses polystyrene, dissolved
in a suitable solvent.

According to an article by Barry Ornitz WA4VQZ (the text is at
http://yarchive.net/electr/coil_dope.html), a very acceptable coil
dope can be home-brewed by dissolving ordinary polystyrene "packing
peanuts" in either toluene or acetone (the latter is less toxic).

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Coil Dope
 

Jeff Liebermann wrote:
Coil dope can be made from polystyrene packing peanuts dissolved in
acetone.

Beware; this produces significant quantities of styrene monomer,
a known carcinogen.

Coil Dope
 

Clifford Heath wrote:
Jeff Liebermann wrote:
Coil dope can be made from polystyrene packing peanuts dissolved in
acetone.

Beware; this produces significant quantities of styrene monomer,
a known carcinogen.
only in Canadian rats

Coil Dope
 

On Tue, 10 Feb 2009 10:09:17 +1100, Clifford Heath
wrote:

Jeff Liebermann wrote:
Coil dope can be made from polystyrene packing peanuts dissolved in
acetone.

Beware; this produces significant quantities of styrene monomer,
a known carcinogen.

That seems to be debatable:
http://www.styrenemonomer.org/3.5.html
Of course, that comes from the Styrene Products Association, which
might be slightly biased.



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

Coil Dope
 

"Dave Platt" wrote in message
...
I read that old 78 LP's broken into pieces & mixed with a particular
solvent
was used as coil dope. Does anybody remember which solvent was used & how
affective it was?

78s were often made of shellac, and the usual solvent for shellac is
denatured alcohol. I believe that some other 78s were made from
cellulose acetate... for this material I believe that acetone would be
a usable solvent.

My understanding is that commercial Q-dope uses polystyrene, dissolved
in a suitable solvent.

Toluene.

According to an article by Barry Ornitz WA4VQZ (the text is at
http://yarchive.net/electr/coil_dope.html), a very acceptable coil
dope can be home-brewed by dissolving ordinary polystyrene "packing
peanuts" in either toluene or acetone (the latter is less toxic).

Thanks for mentioning this archive Dave. I strongly suggest that before
anyone tries making their own Q-dope, they read ALL the safety information
given there. And yes it really does take several weeks for the "cotton
balls" to fully dissolve.

What I think that "Spin" was referring to was that early pressings were
made from cellulose acetate. Acetone would be the solvent of choice here.
I was not aware that phenol formaldehyde thermoset resins were ever used
for records, but if you find any, they won't dissolve in anything!

As for the worry that when Styrofoam is dissolved in a solvent, styrene is
released - forget about it. Styrene is rather volatile and has a VERY
distinctive odor. You would smell it if more than a trace amount were left
in the peanuts. Polystyrene does not depolymerize by dissolving it in a
solvent.

Devcon's Duco Cement is nitrocellulose dissolved in acetone with a little
camphor as a plasticizer and with small amounts of isopropanol and
1-methoxy-2-propanol acetate thrown in for good measure. If you only need
a few ounces of Q-dope, Duco Cement is a suitable substitute.

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.

--
73, Dr. Barry L. Ornitz WA4VZQ

[transpose digits to reply]

Coil Dope
 

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.

I recall you and some other folks posting some very good information
about RTV, the general thrust of which was that there's a very wide
range of formulations, so results might vary a lot from what I measured.

---------------

Spurred by recent comments and questions on this newsgroup, I made
some inductors last weekend and measured them. Results follow.

Toroidal Inductor Measurements

Roy Lewallen, W7EL
December, 1998


Test Equipment

Inductance: GR 1606-A impedance meter. Stray series impedance was
removed by initial calibration. Stray shunt capacitance was separately
measured and removed mathematically. Repeatability is within about +/-
2%. No attempt was made to establish accuracy.

Q: A home-made fixture was used. This is simply an air-variable
capacitor which the inductor is connected across. Coupling into and
out of the fixture with signal generator and oscilloscope is done with
very small capacitors. The Q is calculated from the center frequency
and 3 dB bandwidth. Use of frequency counter, built-in oscilloscope
voltmeter, and switchable 3 dB pad allow repeatability of about +/-
2%. Checks against a commercial Q meter show agreement within a few
percent.

All measurements were made at 10 MHz.

Experiment 1: Coatings

Several identical inductors were fabricated, then coated with various
compounds. Inductance and Q were measured before and after coating.
The inductors were wound on Micrometals T-50-6 cores (Carbonyl SF
material, relative permeability 8.5) with 25 turns of #22 wire. This
just fits on a single layer.

Ind. # Uncoated Coated Coating
L(uH) Q L(uH) Q

1 2.54 281 2.54 284 None (control)
2 2.52 286 2.54 218 Duco cement
3 2.51 267 2.52 265 Standard RTV
4 2.52 280
5 2.54 279 2.55 255 Clear hot melt glue
6 2.48 268 2.55 164 "Sealing tape"
7 2.51 283 2.51 262 Paraffin
8 2.55 262
9 2.56 281 2.59 278 GE Silicone II
10 2.50 283
11 2.51 277

Notes (by inductor number):

Unless otherwise noted, coatings covered the entire core and winding,
extending more than a wire diameter beyond the outside of the wire,
and the center of the core was filled.

Inductances within about 0.3 uH and Q's within less than about 5
should be considered equal.

1. Inductor Q was measured several times over several days to
establish repeatability. Results were 280, 281, 283, 286, 284. (The
apparent trend is interesting, but not conclusive.)
2. Devcon Duco(R) Cement, allowed to dry for 24 hours. Although a
generous coating was applied, the dried coating was less than a wire
diameter in thickness, and the center of the core wasn't filled.
3. Dap Dow Corning 100% Silicone Sealant, Clear, allowed to cure for
24 hours. This is standard acetic-acid (vinegar) curing RTV.
5. Stanley All Purpose GlueSticks, claimed set time 25-30 seconds.
These are nearly clear, translucent white, and not tan or brown
colored.
6. This was some stuff I got surplus. It's a black, sticky, rubbery
compound something like Coax Seal, but may be of entirely different
composition. It's in the form of a thick tape. It's soluble in naphtha
(and the solution dyes everything black it gets on), but acetone
doesn't touch it.
7. Household canning paraffin. (I don't know what it's called in
Britain, but I'm not referring to the liquid -- kerosene to us -- you
call paraffin. This is a common wax made from petroleum.)
9. GE Silicone II Household Glue & Seal, Clear. This is a
non-acetic-acid curing RTV. Allowed to cure for two days. Still just a
little soft even after this much curing.
11. This is the same core as #6. After the coated #6 was measured, the
core was cleaned, the winding cut off, the core further cleaned, then
a new winding put on.

Comments:

I had made some measurements years ago, but couldn't locate the
results. I recall that standard RTV was poor (lowered Q noticeably)
but that an industrial non-acetic-acid curing RTV was good. The
results with standard RTV in this test were striking. Either a) the
formulation of standard RTV has changed over the years, b) there are
major differences among brands, or c) my memory is faulty.

I recall from my earlier tests that epoxy was quite poor, but this has
to be qualified after the experience with RTV. There's a huge number
of different types of epoxy, and some may be much worse than others. I
might test some in the future, but didn't during this test.

I intend to test Q-dope in the future, but didn't have any on hand.

Conclusions:

Of the materials tested, both types of RTV stand out as having a
negligible effect on inductor Q. Hot melt glue and paraffin have a
small enough effect that they should be tolerable for many
applications. Duco cement seriously degrades Q, even in a much thinner
layer than the other coatings. The "sealing tape", tested out of
curiosity, shows just how great a degradation can be caused by a poor
coating.

None of the coatings made much of a change in apparent inductance.
This implies that the reduction in Q is due primarily to dielectric
loss rather than simple increase in capacitance due to the material's
dielectric constant.

Note the difference in inductance and Q between inductors 6 and 11,
which were wound on the same core. Apparently physical differences in
the windings (perhaps such as tightness and conformance to the core,
or uniformity of turn spacing) are a major contributor to differences
between inductors. All the cores used in the test were ordered at the
same time, so they may have come from the same batch and have
relatively little variation. On the basis of just the comparison
between numbers 6 and 11, it's entirely possible that most of the
variation between inductors in this experiment is due to winding
differences. The variation might be less if smaller wire with less
stiffness is used.

Experiment 2: Turn Spacing

I believe it's well established that even a partial second layer can
greatly reduce the Q of a toroidal inductor. But I had recently heard
that optimum Q is achieved when the first layer isn't quite full, but
rather has about a 30 degree gap in the winding, to reduce the
capacitance between winding ends. To test this, I wound 23 turns of
#22 wire on a T-50-6 core, and measured the Q with the turns pushed
close together to make a gap (of about 30 degrees), and then spread to
evenly distribute the turns completely around the core. Measured 10
MHz Q's were 272 and 284, respectively. (Inductances were 2.21 and
2.11 uH.) This one test doesn't by any means exhaust all the
possibilities of core geometries, permeabilities, number of turns, and
wire size, all of which may play a role. But if there's any advantage
to leaving a gap, I believe it would be a small one. And in at least
one case, it's slightly better not to.

Another test was run using 10 turns of the same size wire on the same
core. With the turns pushed together (the winding covering less than
half the core), Q was 213, L was 841 nH. With the turns spread evenly
around the core, Q was 209 but the L had dropped to 505 nH. I reasoned
that a more fair comparison would be with a winding of about the same
inductance as the original close-spaced one. This required 15 turns
when distributed around the core, and resulted in a Q of 257 and L of
924 uH. Here again, the Q is best when the turns are evenly
distributed. Note that type 6 powdered iron has a very low relative
permeability (8.5), so results might be different with
higher-permeability materials. However, this is the material I usually
use for high-Q inductors at HF, so I'm most interested in how it's
affected.

Experiment 3: "Regressive" Winding

In the past, I've found what I thought was a moderate improvement in Q
by "regressively" winding an inductor. To do this, you wind half the
turns in the normal manner. Then you pass the wire through the hole,
but to the opposite side of the inductor (with it ending up beside the
first turn), then completing the winding from the vicinity of the
first turn back toward the origination of the crossover. The result is
an inductor with the two leads coming from points directly opposite
each other. Stray capacitance is allegedly reduced by keeping the ends
of the winding apart. An inductor wound in this manner with 25 turns
of #22 wire measured Q = 285, L = 2.48 uH. This Q is on the high side,
and the L on the low side, of the uncoated inductors measured in
Experiment 1. I didn't try comparing with a standard winding on the
same core, since the same number of turns wound on the same core at
different times (e.g., inductors 6 and 11 in Experiment 1) were shown
to come out differently from each other. My conclusion is that any Q
improvement due to "regressive" winding is slight. Another claim for
"regressive" winding is that it eliminates the "single turn" effect of
toroidal inductors. A normal toroid will couple into its surroundings
as though it consists of a single turn the size of the core. In the
"regressively" wound inductor, there are two half-turns in opposite
directions, so coupling should be reduced. I haven't tested this in
any way, but it may be an argument in favor of the method. The
relatively long wire of the crossover turn would contribute to
coupling, however.

I'll undertake more experiments and measurements as time permits. I'd
love to hear from anyone who has made either supporting or
contradictory quantitative measurements.

Roy Lewallen, W7EL

Coil Dope
 

"Roy Lewallen" wrote in message
treetonline...
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.

I recall you and some other folks posting some very good information
about RTV, the general thrust of which was that there's a very wide
range of formulations, so results might vary a lot from what I measured.

---------------

Spurred by recent comments and questions on this newsgroup, I made
some inductors last weekend and measured them. Results follow.

Toroidal Inductor Measurements

Roy Lewallen, W7EL
December, 1998


Test Equipment

Inductance: GR 1606-A impedance meter. Stray series impedance was
removed by initial calibration. Stray shunt capacitance was separately
measured and removed mathematically. Repeatability is within about +/-
2%. No attempt was made to establish accuracy.

Q: A home-made fixture was used. This is simply an air-variable
capacitor which the inductor is connected across. Coupling into and
out of the fixture with signal generator and oscilloscope is done with
very small capacitors. The Q is calculated from the center frequency
and 3 dB bandwidth. Use of frequency counter, built-in oscilloscope
voltmeter, and switchable 3 dB pad allow repeatability of about +/-
2%. Checks against a commercial Q meter show agreement within a few
percent.

All measurements were made at 10 MHz.

Experiment 1: Coatings

Several identical inductors were fabricated, then coated with various
compounds. Inductance and Q were measured before and after coating.
The inductors were wound on Micrometals T-50-6 cores (Carbonyl SF
material, relative permeability 8.5) with 25 turns of #22 wire. This
just fits on a single layer.

Ind. # Uncoated Coated Coating
L(uH) Q L(uH) Q

1 2.54 281 2.54 284 None (control)
2 2.52 286 2.54 218 Duco cement
3 2.51 267 2.52 265 Standard RTV
4 2.52 280
5 2.54 279 2.55 255 Clear hot melt glue
6 2.48 268 2.55 164 "Sealing tape"
7 2.51 283 2.51 262 Paraffin
8 2.55 262
9 2.56 281 2.59 278 GE Silicone II
10 2.50 283
11 2.51 277

Notes (by inductor number):

Unless otherwise noted, coatings covered the entire core and winding,
extending more than a wire diameter beyond the outside of the wire,
and the center of the core was filled.

Inductances within about 0.3 uH and Q's within less than about 5
should be considered equal.

1. Inductor Q was measured several times over several days to
establish repeatability. Results were 280, 281, 283, 286, 284. (The
apparent trend is interesting, but not conclusive.)
2. Devcon Duco(R) Cement, allowed to dry for 24 hours. Although a
generous coating was applied, the dried coating was less than a wire
diameter in thickness, and the center of the core wasn't filled.
3. Dap Dow Corning 100% Silicone Sealant, Clear, allowed to cure for
24 hours. This is standard acetic-acid (vinegar) curing RTV.
5. Stanley All Purpose GlueSticks, claimed set time 25-30 seconds.
These are nearly clear, translucent white, and not tan or brown
colored.
6. This was some stuff I got surplus. It's a black, sticky, rubbery
compound something like Coax Seal, but may be of entirely different
composition. It's in the form of a thick tape. It's soluble in naphtha
(and the solution dyes everything black it gets on), but acetone
doesn't touch it.
7. Household canning paraffin. (I don't know what it's called in
Britain, but I'm not referring to the liquid -- kerosene to us -- you
call paraffin. This is a common wax made from petroleum.)
9. GE Silicone II Household Glue & Seal, Clear. This is a
non-acetic-acid curing RTV. Allowed to cure for two days. Still just a
little soft even after this much curing.
11. This is the same core as #6. After the coated #6 was measured, the
core was cleaned, the winding cut off, the core further cleaned, then
a new winding put on.

Comments:

I had made some measurements years ago, but couldn't locate the
results. I recall that standard RTV was poor (lowered Q noticeably)
but that an industrial non-acetic-acid curing RTV was good. The
results with standard RTV in this test were striking. Either a) the
formulation of standard RTV has changed over the years, b) there are
major differences among brands, or c) my memory is faulty.

I recall from my earlier tests that epoxy was quite poor, but this has
to be qualified after the experience with RTV. There's a huge number
of different types of epoxy, and some may be much worse than others. I
might test some in the future, but didn't during this test.

I intend to test Q-dope in the future, but didn't have any on hand.

Conclusions:

Of the materials tested, both types of RTV stand out as having a
negligible effect on inductor Q. Hot melt glue and paraffin have a
small enough effect that they should be tolerable for many
applications. Duco cement seriously degrades Q, even in a much thinner
layer than the other coatings. The "sealing tape", tested out of
curiosity, shows just how great a degradation can be caused by a poor
coating.

None of the coatings made much of a change in apparent inductance.
This implies that the reduction in Q is due primarily to dielectric
loss rather than simple increase in capacitance due to the material's
dielectric constant.

Note the difference in inductance and Q between inductors 6 and 11,
which were wound on the same core. Apparently physical differences in
the windings (perhaps such as tightness and conformance to the core,
or uniformity of turn spacing) are a major contributor to differences
between inductors. All the cores used in the test were ordered at the
same time, so they may have come from the same batch and have
relatively little variation. On the basis of just the comparison
between numbers 6 and 11, it's entirely possible that most of the
variation between inductors in this experiment is due to winding
differences. The variation might be less if smaller wire with less
stiffness is used.

Experiment 2: Turn Spacing

I believe it's well established that even a partial second layer can
greatly reduce the Q of a toroidal inductor. But I had recently heard
that optimum Q is achieved when the first layer isn't quite full, but
rather has about a 30 degree gap in the winding, to reduce the
capacitance between winding ends. To test this, I wound 23 turns of
#22 wire on a T-50-6 core, and measured the Q with the turns pushed
close together to make a gap (of about 30 degrees), and then spread to
evenly distribute the turns completely around the core. Measured 10
MHz Q's were 272 and 284, respectively. (Inductances were 2.21 and
2.11 uH.) This one test doesn't by any means exhaust all the
possibilities of core geometries, permeabilities, number of turns, and
wire size, all of which may play a role. But if there's any advantage
to leaving a gap, I believe it would be a small one. And in at least
one case, it's slightly better not to.

Another test was run using 10 turns of the same size wire on the same
core. With the turns pushed together (the winding covering less than
half the core), Q was 213, L was 841 nH. With the turns spread evenly
around the core, Q was 209 but the L had dropped to 505 nH. I reasoned
that a more fair comparison would be with a winding of about the same
inductance as the original close-spaced one. This required 15 turns
when distributed around the core, and resulted in a Q of 257 and L of
924 uH. Here again, the Q is best when the turns are evenly
distributed. Note that type 6 powdered iron has a very low relative
permeability (8.5), so results might be different with
higher-permeability materials. However, this is the material I usually
use for high-Q inductors at HF, so I'm most interested in how it's
affected.

Experiment 3: "Regressive" Winding

In the past, I've found what I thought was a moderate improvement in Q
by "regressively" winding an inductor. To do this, you wind half the
turns in the normal manner. Then you pass the wire through the hole,
but to the opposite side of the inductor (with it ending up beside the
first turn), then completing the winding from the vicinity of the
first turn back toward the origination of the crossover. The result is
an inductor with the two leads coming from points directly opposite
each other. Stray capacitance is allegedly reduced by keeping the ends
of the winding apart. An inductor wound in this manner with 25 turns
of #22 wire measured Q = 285, L = 2.48 uH. This Q is on the high side,
and the L on the low side, of the uncoated inductors measured in
Experiment 1. I didn't try comparing with a standard winding on the
same core, since the same number of turns wound on the same core at
different times (e.g., inductors 6 and 11 in Experiment 1) were shown
to come out differently from each other. My conclusion is that any Q
improvement due to "regressive" winding is slight. Another claim for
"regressive" winding is that it eliminates the "single turn" effect of
toroidal inductors. A normal toroid will couple into its surroundings
as though it consists of a single turn the size of the core. In the
"regressively" wound inductor, there are two half-turns in opposite
directions, so coupling should be reduced. I haven't tested this in
any way, but it may be an argument in favor of the method. The
relatively long wire of the crossover turn would contribute to
coupling, however.

I'll undertake more experiments and measurements as time permits. I'd
love to hear from anyone who has made either supporting or
contradictory quantitative measurements.

Roy Lewallen, W7EL

I seem to recall reading that Styrene had the best dielectric properties of
the plastics.

I did some similar experiments building 1/4 wave spikes in a BNC connector
for 2m HTs and found that glues would heat up from the RF. Clear epoxy
worked best and JB weld, Pipe dope, Silicone sealers and Hot glue were poor
performers. I still have some fiberglass tape that I use for torroids.

Coil Dope
 

Jim Higgins wrote:
On Tue, 10 Feb 2009 10:09:17 +1100, Clifford Heath
Beware; this produces significant quantities of styrene monomer,
a known carcinogen.
No it doesn't. It's purely a dissolution process with no chemical
reaction.

Glad to hear it - I forget who scared me off using a batch I made
and held on to, unable to decide how to even dispose of it.

Coil Dope
 

JB wrote:

I seem to recall reading that Styrene had the best dielectric properties of
the plastics.

I did some similar experiments building 1/4 wave spikes in a BNC connector
for 2m HTs and found that glues would heat up from the RF. Clear epoxy
worked best and JB weld, Pipe dope, Silicone sealers and Hot glue were poor
performers. I still have some fiberglass tape that I use for torroids.

Of common plastics, Teflon, polyethylene, styrene, and polypropylene
have the lowest RF loss. However, others can be perfectly adequate for
some applications.

Roy Lewallen, W7EL

Coil Dope
 

"Roy Lewallen" wrote in message
treetonline...
JB wrote:

I seem to recall reading that Styrene had the best dielectric properties
of
the plastics.

I did some similar experiments building 1/4 wave spikes in a BNC
connector
for 2m HTs and found that glues would heat up from the RF. Clear epoxy
worked best and JB weld, Pipe dope, Silicone sealers and Hot glue were
poor
performers. I still have some fiberglass tape that I use for torroids.

Of common plastics, Teflon, polyethylene, styrene, and polypropylene
have the lowest RF loss. However, others can be perfectly adequate for
some applications.

Roy Lewallen, W7EL

Actually made good working ladder line from bell wire from the Science dept.
and plastic spoons from the lunchroom for the school radio club station.
The ugliest, goofiest looking projects always seem to work the best.

Coil Dope
 

Having read Roy's impressive measurement results, I would like to
interject a word of caution about the use of RTV's in electronic
applications.

As Roy states, many RTV sealants and adhesives use a curing process that
releases acetic acid (vinegar).
These should be used with care in electronic applications as the acetic
acid can, and does, cause corrosion on metallic surfaces in the vicinity
of the curing RTV.

Coils constructed with a medium to heavy gauge of wire are unlikely to
suffer from this but any inductors employing fine gauge wire can fail
due to corroded (broken) turns resulting from contact with the acetic
acid. The effect is not immediately apparent and can take months or
years before a problem arises.

Application of acid curing RTV should also be avoided to any component
in an assembled electronic device that has switch contacts or plug and
socket contacts in the immediate vicinity, for the same reason.

Electronic grade RTVs do not use an acid curing process and have been
developed to avoid the above problems.

Derek (ex Dow Corning employee)


In message tonline,
Roy Lewallen writes
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.

I recall you and some other folks posting some very good information
about RTV, the general thrust of which was that there's a very wide
range of formulations, so results might vary a lot from what I measured.

---------------

Spurred by recent comments and questions on this newsgroup, I made
some inductors last weekend and measured them. Results follow.

Toroidal Inductor Measurements

Roy Lewallen, W7EL
December, 1998


Test Equipment

Inductance: GR 1606-A impedance meter. Stray series impedance was
removed by initial calibration. Stray shunt capacitance was separately
measured and removed mathematically. Repeatability is within about +/-
2%. No attempt was made to establish accuracy.

Q: A home-made fixture was used. This is simply an air-variable
capacitor which the inductor is connected across. Coupling into and
out of the fixture with signal generator and oscilloscope is done with
very small capacitors. The Q is calculated from the center frequency
and 3 dB bandwidth. Use of frequency counter, built-in oscilloscope
voltmeter, and switchable 3 dB pad allow repeatability of about +/-
2%. Checks against a commercial Q meter show agreement within a few
percent.

All measurements were made at 10 MHz.

Experiment 1: Coatings

Several identical inductors were fabricated, then coated with various
compounds. Inductance and Q were measured before and after coating.
The inductors were wound on Micrometals T-50-6 cores (Carbonyl SF
material, relative permeability 8.5) with 25 turns of #22 wire. This
just fits on a single layer.

Ind. # Uncoated Coated Coating
L(uH) Q L(uH) Q

1 2.54 281 2.54 284 None (control)
2 2.52 286 2.54 218 Duco cement
3 2.51 267 2.52 265 Standard RTV
4 2.52 280
5 2.54 279 2.55 255 Clear hot melt glue
6 2.48 268 2.55 164 "Sealing tape"
7 2.51 283 2.51 262 Paraffin
8 2.55 262
9 2.56 281 2.59 278 GE Silicone II
10 2.50 283
11 2.51 277

Notes (by inductor number):

Unless otherwise noted, coatings covered the entire core and winding,
extending more than a wire diameter beyond the outside of the wire,
and the center of the core was filled.

Inductances within about 0.3 uH and Q's within less than about 5
should be considered equal.

1. Inductor Q was measured several times over several days to
establish repeatability. Results were 280, 281, 283, 286, 284. (The
apparent trend is interesting, but not conclusive.)
2. Devcon Duco(R) Cement, allowed to dry for 24 hours. Although a
generous coating was applied, the dried coating was less than a wire
diameter in thickness, and the center of the core wasn't filled.
3. Dap Dow Corning 100% Silicone Sealant, Clear, allowed to cure for
24 hours. This is standard acetic-acid (vinegar) curing RTV.
5. Stanley All Purpose GlueSticks, claimed set time 25-30 seconds.
These are nearly clear, translucent white, and not tan or brown
colored.
6. This was some stuff I got surplus. It's a black, sticky, rubbery
compound something like Coax Seal, but may be of entirely different
composition. It's in the form of a thick tape. It's soluble in naphtha
(and the solution dyes everything black it gets on), but acetone
doesn't touch it.
7. Household canning paraffin. (I don't know what it's called in
Britain, but I'm not referring to the liquid -- kerosene to us -- you
call paraffin. This is a common wax made from petroleum.)
9. GE Silicone II Household Glue & Seal, Clear. This is a
non-acetic-acid curing RTV. Allowed to cure for two days. Still just a
little soft even after this much curing.
11. This is the same core as #6. After the coated #6 was measured, the
core was cleaned, the winding cut off, the core further cleaned, then
a new winding put on.

Comments:

I had made some measurements years ago, but couldn't locate the
results. I recall that standard RTV was poor (lowered Q noticeably)
but that an industrial non-acetic-acid curing RTV was good. The
results with standard RTV in this test were striking. Either a) the
formulation of standard RTV has changed over the years, b) there are
major differences among brands, or c) my memory is faulty.

I recall from my earlier tests that epoxy was quite poor, but this has
to be qualified after the experience with RTV. There's a huge number
of different types of epoxy, and some may be much worse than others. I
might test some in the future, but didn't during this test.

I intend to test Q-dope in the future, but didn't have any on hand.

Conclusions:

Of the materials tested, both types of RTV stand out as having a
negligible effect on inductor Q. Hot melt glue and paraffin have a
small enough effect that they should be tolerable for many
applications. Duco cement seriously degrades Q, even in a much thinner
layer than the other coatings. The "sealing tape", tested out of
curiosity, shows just how great a degradation can be caused by a poor
coating.

None of the coatings made much of a change in apparent inductance.
This implies that the reduction in Q is due primarily to dielectric
loss rather than simple increase in capacitance due to the material's
dielectric constant.

Note the difference in inductance and Q between inductors 6 and 11,
which were wound on the same core. Apparently physical differences in
the windings (perhaps such as tightness and conformance to the core,
or uniformity of turn spacing) are a major contributor to differences
between inductors. All the cores used in the test were ordered at the
same time, so they may have come from the same batch and have
relatively little variation. On the basis of just the comparison
between numbers 6 and 11, it's entirely possible that most of the
variation between inductors in this experiment is due to winding
differences. The variation might be less if smaller wire with less
stiffness is used.

Experiment 2: Turn Spacing

I believe it's well established that even a partial second layer can
greatly reduce the Q of a toroidal inductor. But I had recently heard
that optimum Q is achieved when the first layer isn't quite full, but
rather has about a 30 degree gap in the winding, to reduce the
capacitance between winding ends. To test this, I wound 23 turns of
#22 wire on a T-50-6 core, and measured the Q with the turns pushed
close together to make a gap (of about 30 degrees), and then spread to
evenly distribute the turns completely around the core. Measured 10
MHz Q's were 272 and 284, respectively. (Inductances were 2.21 and
2.11 uH.) This one test doesn't by any means exhaust all the
possibilities of core geometries, permeabilities, number of turns, and
wire size, all of which may play a role. But if there's any advantage
to leaving a gap, I believe it would be a small one. And in at least
one case, it's slightly better not to.

Another test was run using 10 turns of the same size wire on the same
core. With the turns pushed together (the winding covering less than
half the core), Q was 213, L was 841 nH. With the turns spread evenly
around the core, Q was 209 but the L had dropped to 505 nH. I reasoned
that a more fair comparison would be with a winding of about the same
inductance as the original close-spaced one. This required 15 turns
when distributed around the core, and resulted in a Q of 257 and L of
924 uH. Here again, the Q is best when the turns are evenly
distributed. Note that type 6 powdered iron has a very low relative
permeability (8.5), so results might be different with
higher-permeability materials. However, this is the material I usually
use for high-Q inductors at HF, so I'm most interested in how it's
affected.

Experiment 3: "Regressive" Winding

In the past, I've found what I thought was a moderate improvement in Q
by "regressively" winding an inductor. To do this, you wind half the
turns in the normal manner. Then you pass the wire through the hole,
but to the opposite side of the inductor (with it ending up beside the
first turn), then completing the winding from the vicinity of the
first turn back toward the origination of the crossover. The result is
an inductor with the two leads coming from points directly opposite
each other. Stray capacitance is allegedly reduced by keeping the ends
of the winding apart. An inductor wound in this manner with 25 turns
of #22 wire measured Q = 285, L = 2.48 uH. This Q is on the high side,
and the L on the low side, of the uncoated inductors measured in
Experiment 1. I didn't try comparing with a standard winding on the
same core, since the same number of turns wound on the same core at
different times (e.g., inductors 6 and 11 in Experiment 1) were shown
to come out differently from each other. My conclusion is that any Q
improvement due to "regressive" winding is slight. Another claim for
"regressive" winding is that it eliminates the "single turn" effect of
toroidal inductors. A normal toroid will couple into its surroundings
as though it consists of a single turn the size of the core. In the
"regressively" wound inductor, there are two half-turns in opposite
directions, so coupling should be reduced. I haven't tested this in
any way, but it may be an argument in favor of the method. The
relatively long wire of the crossover turn would contribute to
coupling, however.

I'll undertake more experiments and measurements as time permits. I'd
love to hear from anyone who has made either supporting or
contradictory quantitative measurements.

Roy Lewallen, W7EL

--
Derek R. Smith.

Coil Dope
 

I have seen hams use silicon sealant to fill a UHF connector before
screwing it together. The idea is to keep out water. (The connection is
also taped or sealed with Coax seal). Is this a good idea?

Bob W8ERD

Coil Dope
 

JB wrote:

Actually made good working ladder line from bell wire from the Science dept.
and plastic spoons from the lunchroom for the school radio club station.
The ugliest, goofiest looking projects always seem to work the best.


Sweet! Any pictures?

- 73 de Mike N3LI -

Coil Dope
 

"Bob Dixon" wrote in message
...
I have seen hams use silicon sealant to fill a UHF connector before
screwing it together. The idea is to keep out water. (The connection is
also taped or sealed with Coax seal). Is this a good idea?

Bob W8ERD


NO!

The silicone will impair the connection, the dielectric, makes a fumbling
mess and usually causes the tape to come off. Just tightly wrap with
electrical tape and tie off the loose end. It will outlast the coax. Unless
the antenna itself is prone to leak into the connector.

Coil Dope
 

Probably not a good idea.

Silicone Grease would be much less harmful to the connector and be much
easier to undo, when the time comes.

Derek

In message
, Bob
Dixon writes
I have seen hams use silicon sealant to fill a UHF connector before
screwing it together. The idea is to keep out water. (The connection is
also taped or sealed with Coax seal). Is this a good idea?

Bob W8ERD

--
Derek R. Smith.

Coil Dope
 

On Feb 11, 12:40*pm, Bob Dixon wrote:
I have seen hams use silicon sealant to fill a UHF connector before
screwing it together. The idea is to keep out water. (The connection is
also taped or sealed with Coax seal). Is this a good idea?

Bob W8ERD

I like to grease the threads with silicon dielectric grease to keep
water from wicking up the threads but I have seen people pack N
connectors full of it before screwing them together and cant say it
did any harm. I am am a big fan of wiping down a connector with Deoxit
before puting it together.

I heard that Marvel Mystery Oil works as well as Deoxit. Has anyone
else ever heard of this?

Jimmie

Coil Dope
 

On Feb 11, 7:04*am, "Derek R. Smith"
wrote:
Having read Roy's impressive measurement results, I would like to
interject a word of caution about the use of RTV's in electronic
applications.

As Roy states, many RTV sealants and adhesives use a curing process that
releases acetic acid (vinegar).
These should be used with care in electronic applications as the acetic
acid can, and does, cause corrosion on metallic surfaces in the vicinity
of the curing RTV.

Coils constructed with a medium to heavy gauge of wire are unlikely to
suffer from this but any inductors employing fine gauge wire can fail
due to corroded (broken) turns resulting from contact with the acetic
acid. The effect is not immediately apparent and can take months or
years before a problem arises.

Application of acid curing RTV should also be avoided to any component
in an assembled electronic device that has switch contacts or plug and
socket contacts in the immediate vicinity, for the same reason.

Electronic grade RTVs do not use an acid curing process and have been
developed to avoid the above problems.

Derek (ex Dow Corning employee)

In message tonline,
Roy Lewallen writes



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.

I recall you and some other folks posting some very good information
about RTV, the general thrust of which was that there's a very wide
range of formulations, so results might vary a lot from what I measured.

---------------

Spurred by recent comments and questions on this newsgroup, I made
some inductors last weekend and measured them. Results follow.

* * * * * *Toroidal Inductor Measurements

* * * * * * * * *Roy Lewallen, W7EL
* * * * * * * * * *December, 1998

* * * * * * * * * *Test Equipment

Inductance: GR 1606-A impedance meter. Stray series impedance was
removed by initial calibration. Stray shunt capacitance was separately
measured and removed mathematically. Repeatability is within about +/-
2%. No attempt was made to establish accuracy.

Q: A home-made fixture was used. This is simply an air-variable
capacitor which the inductor is connected across. Coupling into and
out of the fixture with signal generator and oscilloscope is done with
very small capacitors. The Q is calculated from the center frequency
and 3 dB bandwidth. Use of frequency counter, built-in oscilloscope
voltmeter, and switchable 3 dB pad allow repeatability of about +/-
2%. Checks against a commercial Q meter show agreement within a few
percent.

All measurements were made at 10 MHz.

* * * * * * * Experiment 1: Coatings

Several identical inductors were fabricated, then coated with various
compounds. Inductance and Q were measured before and after coating.
The inductors were wound on Micrometals T-50-6 cores (Carbonyl SF
material, relative permeability 8.5) with 25 turns of #22 wire. This
just fits on a single layer.

Ind. # * Uncoated * * * *Coated * * * * Coating
* * * L(uH) * Q * * * L(uH) * Q

1 * * *2.54 * *281 * * 2.54 * *284 * * None (control)
2 * * *2.52 * *286 * * 2.54 * *218 * * Duco cement
3 * * *2.51 * *267 * * 2.52 * *265 * * Standard RTV
4 * * *2.52 * *280
5 * * *2.54 * *279 * * 2.55 * *255 * * Clear hot melt glue
6 * * *2.48 * *268 * * 2.55 * *164 * * "Sealing tape"
7 * * *2.51 * *283 * * 2.51 * *262 * * Paraffin
8 * * *2.55 * *262
9 * * *2.56 * *281 * * 2.59 * *278 * * GE Silicone II
10 * * 2.50 * *283
11 * * 2.51 * *277

Notes (by inductor number):

Unless otherwise noted, coatings covered the entire core and winding,
extending more than a wire diameter beyond the outside of the wire,
and the center of the core was filled.

Inductances within about 0.3 uH and Q's within less than about 5
should be considered equal.

1. Inductor Q was measured several times over several days to
establish repeatability. Results were 280, 281, 283, 286, 284. (The
apparent trend is interesting, but not conclusive.)
2. Devcon Duco(R) Cement, allowed to dry for 24 hours. Although a
generous coating was applied, the dried coating was less than a wire
diameter in thickness, and the center of the core wasn't filled.
3. Dap Dow Corning 100% Silicone Sealant, Clear, allowed to cure for
24 hours. This is standard acetic-acid (vinegar) curing RTV.
5. Stanley All Purpose GlueSticks, claimed set time 25-30 seconds.
These are nearly clear, translucent white, and not tan or brown
colored.
6. This was some stuff I got surplus. It's a black, sticky, rubbery
compound something like Coax Seal, but may be of entirely different
composition. It's in the form of a thick tape. It's soluble in naphtha
(and the solution dyes everything black it gets on), but acetone
doesn't touch it.
7. Household canning paraffin. (I don't know what it's called in
Britain, but I'm not referring to the liquid -- kerosene to us -- you
call paraffin. This is a common wax made from petroleum.)
9. GE Silicone II Household Glue & Seal, Clear. This is a
non-acetic-acid curing RTV. Allowed to cure for two days. Still just a
little soft even after this much curing.
11. This is the same core as #6. After the coated #6 was measured, the
core was cleaned, the winding cut off, the core further cleaned, then
a new winding put on.

Comments:

I had made some measurements years ago, but couldn't locate the
results. I recall that standard RTV was poor (lowered Q noticeably)
but that an industrial non-acetic-acid curing RTV was good. The
results with standard RTV in this test were striking. Either a) the
formulation of standard RTV has changed over the years, b) there are
major differences among brands, or c) my memory is faulty.

I recall from my earlier tests that epoxy was quite poor, but this has
to be qualified after the experience with RTV. There's a huge number
of different types of epoxy, and some may be much worse than others. I
might test some in the future, but didn't during this test.

I intend to test Q-dope in the future, but didn't have any on hand.

Conclusions:

Of the materials tested, both types of RTV stand out as having a
negligible effect on inductor Q. Hot melt glue and paraffin have a
small enough effect that they should be tolerable for many
applications. Duco cement seriously degrades Q, even in a much thinner
layer than the other coatings. The "sealing tape", tested out of
curiosity, shows just how great a degradation can be caused by a poor
coating.

None of the coatings made much of a change in apparent inductance.
This implies that the reduction in Q is due primarily to dielectric
loss rather than simple increase in capacitance due to the material's
dielectric constant.

Note the difference in inductance and Q between inductors 6 and 11,
which were wound on the same core. Apparently physical differences in
the windings (perhaps such as tightness and conformance to the core,
or uniformity of turn spacing) are a major contributor to differences
between inductors. All the cores used in the test were ordered at the
same time, so they may have come from the same batch and have
relatively little variation. On the basis of just the comparison
between numbers 6 and 11, it's entirely possible that most of the
variation between inductors in this experiment is due to winding
differences. The variation might be less if smaller wire with less
stiffness is used.

* * * * * * * Experiment 2: Turn Spacing

I believe it's well established that even a partial second layer can
greatly reduce the Q of a toroidal inductor. But I had recently heard
that optimum Q is achieved when the first layer isn't quite full, but
rather has about a 30 degree gap in the winding, to reduce the
capacitance between winding ends. To test this, I wound 23 turns of
#22 wire on a T-50-6 core, and measured the Q with the turns pushed
close together to make a gap (of about 30 degrees), and then spread to
evenly distribute the turns completely around the core. Measured 10
MHz Q's were 272 and 284, respectively. (Inductances were 2.21 and
2.11 uH.) This one test doesn't by any means exhaust all the
possibilities of core geometries, permeabilities, number of turns, and
wire size, all of which may play a role. But if there's any advantage
to leaving a gap, I believe it would be a small one. And in at least
one case, it's slightly better not to.

Another test was run using 10 turns of the same size wire on the same
core. With the turns pushed together (the winding covering less than
half the core), Q was 213, L was 841 nH. With the turns spread evenly
around the core, Q was 209 but the L had dropped to 505 nH. I reasoned
that a more fair comparison would be with a winding of about the same
inductance as the original close-spaced one. This required 15 turns
when distributed around the core, and resulted in a Q of 257 and L of
924 uH. Here again, the Q is best when the turns are evenly
distributed. Note that type 6 powdered iron has a very low relative
permeability (8.5), so results might be different with
higher-permeability materials. However, this is the material I usually
use for high-Q inductors at HF, so I'm most interested in how it's
affected.

* * * * * * * Experiment 3: "Regressive" Winding

In the past, I've found what I thought was a moderate improvement in Q
by "regressively" winding an inductor. To do this, you wind half the
turns in the normal manner. Then you pass the wire through the hole,
but to the opposite side of the

...

read more »- Hide quoted text -

- Show quoted text -

Ive see the center conductor of RG214 dissolved through with RTV. The
corrosion on the associated Al/Cu joint was likewise disgusting.

Jimmie

Coil Dope
 

JIMMIE wrote:

Ive see the center conductor of RG214 dissolved through with RTV. The
corrosion on the associated Al/Cu joint was likewise disgusting.

Jimmie

And I've used the acetic acid-curing variety many times on bare copper
(wire and PC board traces) and aluminum, and not a hint of corrosion
when it was cut off long after. Besides the wide variety of
formulations, there may be other factors at work causing the
corrosiveness to vary so much.

Roy Lewallen, W7EL

Coil Dope [silicon vs. silicone, DeOxit vs. Marvel Mystery Oil]
 

"JIMMIE" wrote in message
...
On Feb 11, 12:40 pm, Bob Dixon wrote:
I have seen hams use silicon sealant to fill a UHF connector
before screwing it together. The idea is to keep out water. (The
connection is also taped or sealed with Coax seal). Is this a
good idea?

Bob W8ERD

I like to grease the threads with silicon dielectric grease to
keep water from wicking up the threads but I have seen people pack
N connectors full of it before screwing them together and cant say
it did any harm. I am am a big fan of wiping down a connector with
Deoxit before putting it together.

Please people, use the correct spelling. Silicon is an element with
a melting point of 1410 to 1414°C (2570 to 2577°F) depending on the
reference. Silicone grease is a low molecular weight polydimethyl
siloxane polymer. It is hydrophobic (does not wet with water) and
is often used to lubricate rubber and other items that are
incompatible with hydrocarbon greases. Its main use with electrical
connectors is its lubricating properties and water repellency.

I heard that Marvel Mystery Oil works as well as Deoxit. Has
anyone else ever heard of this?

DeOxit is 95% petroleum naphtha with 5% of a proprietary
ingredient. Caig tends to try to keep the secret ingredient
secret. I cannot say for sure but I suspect it might be tocopherol
(Vitamin E). Marvel Mystery Oil is a mixture of naphthenic
hydrocarbons (motor oil), mineral spirits (naphtha), and 1,2-
dichlorobenzene (a chlorinated solvent). From the smell, it is
likely to contain a small amount of methyl salicylate (oil of
wintergreen). So I would say they are quite different. Besides,
the chlorinated solvent is not the best thing to use around
polyethylene and is especially bad around vinyl.

--
73, Dr. Barry L. Ornitz WA4VZQ

[transpose digits to reply]

Coil Dope
 

In message ,
Roy Lewallen writes
JIMMIE wrote:
Ive see the center conductor of RG214 dissolved through with RTV.
The
corrosion on the associated Al/Cu joint was likewise disgusting.
Jimmie

And I've used the acetic acid-curing variety many times on bare copper
(wire and PC board traces) and aluminum, and not a hint of corrosion
when it was cut off long after. Besides the wide variety of
formulations, there may be other factors at work causing the
corrosiveness to vary so much.

Roy Lewallen, W7EL

I think you've been lucky (or are maybe mistaken about it being
acid-curing).

I have used silicone grease, but WD40 is more-readily available. It also
wets better, and creeps into the hidden nooks and crannies. I give
everything a good dowsing before and after assembly, assemble, wipe off
the surplus WD40, and seal with stretched self-amalgamating tape. Such
assemblies from over 30 years ago give every indication of lasting until
I am no longer in a position to be interested in amateur radio.
--
Ian

Coil Dope
 

In article ,
Ian Jackson wrote:

I have used silicone grease, but WD40 is more-readily available. It also
wets better, and creeps into the hidden nooks and crannies. I give
everything a good dowsing before and after assembly,

Wouldn't that tend to *increase* water infiltration rather than reduce
it?

grin

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Coil Dope
 

I have used silicone grease, but WD40 is more-readily available. It also
wets better, and creeps into the hidden nooks and crannies. I give
everything a good dowsing before and after assembly,

At one time I thought silicone grease would save wear on N connectors until
I used the spray on wattmeter slugs and found it completely insulated the
shell contact. I since found it caused an SWR hump on N connectors even if
it were just a spot on the threads.

Coil Dope [threads on N connectors]
 

"JB" wrote in message
...

At one time I thought silicone grease would save wear on N
connectors until I used the spray on wattmeter slugs and found it
completely insulated the shell contact. I since found it caused
an SWR hump on N connectors even if it were just a spot on the
threads.

I could see where the thin silicone coating might be an insulator to the
low voltages from the wattmeter slubs, but I find the second statement
exceptionally hard to believe. In type N (and even BNC) connectors, the
threads (or the bayonet connection) are not in the RF path. Look close at
either type of male connector and note that there is a coaxial shield
around the center pin. This shield presses against the inside wall of the
jack providing a continuation of the coaxial line. The threads (or the
bayonet connection) merely provides a sturdy mechanical connection. This
what gives the type N and BNC connectors a constant impedance, and what
makes them far superior to UHF connectors. It also allows the use of a
rubber washer to make the connector waterproof.

In one of my instrumentation applications, I had to use N connectors made
of 304 stainless for corrosion resistance and high temperatures. Ceramic
and glass insulation was used within the connectors. The female jacks were
welded in place and rated to withstand pressures of up to 100 PSIG.
Stainless is quite bad about galling, and these connectors cost plenty, so
a silver paste was used to lubricate the threads. One day, I had to make
an "emergency" repair in the field and did not have the silver paste; so I
used PTFE thread seal tape instead. Going back to my lab, I tested a few
connectors with the thread seal tape using a Tek 1502 time domain
reflectometer. Even with several layers of PTFE tape, I was unable to see
any difference in the impedance through the connector. Since the
application was always less than 200°C, we quit using the silver paste.

--
73, Dr. Barry L. Ornitz WA4VZQ

[transpose digits to reply]

Coil Dope [threads on N connectors]
 

Dr. Barry L. Ornitz wrote:

I could see where the thin silicone coating might be an insulator to the
low voltages from the wattmeter slubs, but I find the second statement
exceptionally hard to believe. In type N (and even BNC) connectors, the
threads (or the bayonet connection) are not in the RF path. Look close
at either type of male connector and note that there is a coaxial shield
around the center pin. This shield presses against the inside wall of
the jack providing a continuation of the coaxial line. The threads (or
the bayonet connection) merely provides a sturdy mechanical connection.
This what gives the type N and BNC connectors a constant impedance, and
what makes them far superior to UHF connectors. It also allows the use
of a rubber washer to make the connector waterproof.

In one of my instrumentation applications, I had to use N connectors
made of 304 stainless for corrosion resistance and high temperatures.
Ceramic and glass insulation was used within the connectors. The female
jacks were welded in place and rated to withstand pressures of up to 100
PSIG. Stainless is quite bad about galling, and these connectors cost
plenty, so a silver paste was used to lubricate the threads. One day, I
had to make an "emergency" repair in the field and did not have the
silver paste; so I used PTFE thread seal tape instead. Going back to my
lab, I tested a few connectors with the thread seal tape using a Tek
1502 time domain reflectometer. Even with several layers of PTFE tape,
I was unable to see any difference in the impedance through the
connector. Since the application was always less than 200°C, we quit
using the silver paste.

And, when tightened threads *are* necessary for electrical contact, oil
or light grease often improves conductivity. Thread pressure is adequate
to squeeze the lubricant out from the contact areas, allowing good
metallic contact. And it prevents oxidation or other corrosion of the
contact surfaces when the contacts are moved or vibrate by excluding
air. This holds true for all contacts properly designed to wipe and
contact with sufficient pressure. Quite a few people incorrectly
attribute this improvement to conductivity or some mystical property of
the lubricant, but its real trick is simply to exclude air.

Roy Lewallen, W7EL

Coil Dope [threads on N connectors]
 

In message tonline,
Roy Lewallen writes




And, when tightened threads *are* necessary for electrical contact, oil
or light grease often improves conductivity. Thread pressure is
adequate to squeeze the lubricant out from the contact areas, allowing
good metallic contact. And it prevents oxidation or other corrosion of
the contact surfaces when the contacts are moved or vibrate by
excluding air. This holds true for all contacts properly designed to
wipe and contact with sufficient pressure. Quite a few people
incorrectly attribute this improvement to conductivity or some mystical
property of the lubricant, but its real trick is simply to exclude air.

Roy Lewallen, W7EL

I would be surprised if a lubricant was sufficiently viscous and had
enough 'body' to act as an insulating layer between two parts of
well-tightened a connector.

However, I have personal experience that Araldite can. This was used to
ensure that a reducing bush (PG11 thread to 5/8"), in the wall of the
housing of a CATV amplifier, remained securely in place. On all four
ports, there was absolutely no continuity between the outers of the
connectors and the housing.
--
Ian

Coil Dope [threads on N connectors]
 

Ian Jackson wrote:

I would be surprised if a lubricant was sufficiently viscous and had
enough 'body' to act as an insulating layer between two parts of
well-tightened a connector.

However, I have personal experience that Araldite can. This was used to
ensure that a reducing bush (PG11 thread to 5/8"), in the wall of the
housing of a CATV amplifier, remained securely in place. On all four
ports, there was absolutely no continuity between the outers of the
connectors and the housing.

Araldite seems to be a trade name for a variety of adhesives. There are
certainly materials other than the oil or light grease I was speaking of
which will interfere with continuity, and some of those adhesives are
apparently in that category. Kids, don't apply epoxy to your relay
contacts. Honey and contact cement might not be too good either.

Roy Lewallen, W7EL

Coil Dope [threads on N connectors]
 

"Roy Lewallen" wrote in message
treetonline...
Ian Jackson wrote:

I would be surprised if a lubricant was sufficiently viscous and had
enough 'body' to act as an insulating layer between two parts of
well-tightened a connector.

However, I have personal experience that Araldite can. This was used to
ensure that a reducing bush (PG11 thread to 5/8"), in the wall of the
housing of a CATV amplifier, remained securely in place. On all four
ports, there was absolutely no continuity between the outers of the
connectors and the housing.

Araldite seems to be a trade name for a variety of adhesives. There are
certainly materials other than the oil or light grease I was speaking of
which will interfere with continuity, and some of those adhesives are
apparently in that category. Kids, don't apply epoxy to your relay
contacts. Honey and contact cement might not be too good either.

Roy Lewallen, W7EL

I used to think that too. Good point about the inner shell, but I wonder if
all N's are created equal. That might have tainted my results. The
experiment was encountered in the process of tuning cavities, duplexers and
other filters with a R2001D. I have used oils before but some will rot the
gasketting. Grease or oils will migrate, but Stainless is a problem about
galling. It was a regular thing to have to clean Silver dust and grunge
from the bulkhead female with a q-tip and Isopropyl. The final answer was
to add a sacrificial N male to female adapter to save wear on the Silver
plating.

I also noticed Coffee doesn't make good contact cleaner either. Even with
plenty of sugar (just trying to help).