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On 7/5/23 7:58 AM, Mike wrote:

After all that debate about PVC I've just discovered that my coil former is actually ABS ...
Apologies!

Ohh. Black ABS? As in Drain Waste Vent (DWV) pipe?

The black is from carbon black as a pigment - yeah, as in resistors
Also, most DWV is what is known as "cellular" which means that the walls are actually foamed ABS, with smooth ABS skin on them. Makes it nice and lightweight, since it doesn't have to hold pressure.

Some is lossy, some isn't.

After all that debate about PVC I've just discovered that my coil former is actually ABS ...

Apologies!

--
Mike

Thanks for all your comments, Jim. I think I've seen different dissipation factor values for PVC depending on filler amount. I believe I used values for pure PVC, but I can't remember. In any event, with other dielectrics so readily available, I think PVC pipe should be avoided. By the way, cardboard is the lossiest dielectric my program lists. I included it for the oatmeal boxes builders traditionally used for crystal sets.

Some dielectrics like PVC are lossier at HF than UHF and some show the opposite behavior. That's why I think the microwave oven test can be very misleading.

Brian

On Tuesday 04 July 2023 02:54:32 pm Jim Lux wrote:

On 7/4/23 11:16 AM, WB2UAQ wrote:

Mike and Alan,
I measured the loss factor for PVC and it was about 0.005 or so at 1 kHz. I did more measurements at RF but will have to go back to old note books. I made a simple fixture to test a number of plastics. I rebuilt a coil that plugs into a BC-610 transmitter and from that sprung all kinds of questions about dielectrics. Many local guys are using 3D printers and using PLA, I think it is called. They printed out a plate of it for me to test. I would not say that all of this material is made equally and permitivity and loss factor are probably not well controlled. Won't be able to get back to this for awhile as it is Independence Day and a lot going on to take care of this week. Can only say right now that none of this plastic seemed to jump out as being a terrible dielectric. I also tested plate glass because back in the early days of radio capacitors for spark transmitters used what I think was regular glass available at that time.

PVC pipe has two potential problems as a coil form (based on experience
of folks building tesla coils, so 100-500 kHz):
1) it's hygroscopic so the dielectric loss varies with the water content
- nylon has the same problem, BTW.
2) most pipe is made from recycled material, and it can have metal
fragments and other debris in it. The specs for pipe are about holding
pressure and being "safe for drinking water", not dielectric properties.

Tesla coil folks solve #1 by drying it and then coating with something
like lacquer, glyptal, or urethane

#2 is a bit trickier - it's not like you can take a 4 foot long piece of
6" pipe and throw it in the microwave and see if it arcs or has hot spots.

One V/U dual-band antenna that I used for a while was totally enclosed in PVC. But it was a particular kind, my brother made it and he had to get this specific kind to not have the pipe affect the antenna much. I did indeed get out with it, reaching as far as 80 miles (!) with the output of a Baofeng...


--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin

On 7/4/23 12:24 PM, Brian Beezley wrote:

On Tue, Jul 4, 2023 at 11:54 AM, Jim Lux wrote:

PVC pipe has two potential problems as a coil form (based on experience of
folks building tesla coils, so 100-500 kHz):
1) it's hygroscopic so the dielectric loss varies with the water content

I asked Google AI whether PVC is hygroscopic. Here, in part, is what it said
Polyvinyl chloride (PVC) is a hygroscopic powder material. Hygroscopic substances can take and hold moisture from the surroundings.
PVC is non-hygroscopic, meaning it does not absorb moisture internally into the pellet. However, moisture can be collected on the surface of the pellet.
Other non-hygroscopic polymers include polypropylene, polystyrene, and polyethylene.
I thought that was an interesting distinction. Google AI generates very useful summaries, but I don't fully trust it yet, so I searched onward. I found two more references that said PVC is not hygroscopic.
I'm sure your remark about Tesla coils is based on practical experience. Any idea why it might differ from what these references say?

Probably the structure and composition of PVC pipe - unlike a pure bar of PVC, pipe (and must plastic products) are a combination of PVC and some fillers to get the right mechanical properties, color, etc. For instance, in larger sizes it might actually be a foam with solid inner and outer surfaces.

The measurements of loss were with actual secondary coils measured over time with both swept Q measurements and ring down tests (put an impulse in and see how it decays). They put it in environments where the humidity was high (garage or barn on rainy days, I believe) and then when it was dried (warm dry air)

There was also a comparison with other materials - Cardboard tubes (def hygroscopic), acrylic tubes (clear, so no filler), etc.

It was a long running discussion about "good materials" for secondary forms - partly inspired by radical differences reported with large cardboard Sonotube type forms. Turns out some concrete forms have an aluminum foil layer in them.

probably >10 years ago on Tesla Coil Mailing List.

By the way, I've collected dielectric data for years for use in my coil inductance and Q calculator. The PVC dissipation factor it uses is 0.016 at 1 MHz and 0.0055 at 3 GHz. (This is why testing PVC in a microwave oven does not indicate its HF properties.).

Indeed - and that is kind of weird - *usually* tan d gets bigger as frequency goes up.


My coil inductance and Q calculator logarithmically interpolates these values. PVC is not too bad at HF, but much better dielectrics are readily available. Try any round plastic container from your refrigerator or kitchen cabinet. It is likely to be one of the non-hygroscopic polymers Google mentions. Read the recycling code on the bottom to determine just what it's made of.


Yes - clear plastic is likely to be more like the "handbook" values.

Pipe (or tube), not so much. I was surprised the first time I was turning a piece of white 3" PVC pipe on the lathe to "clean up the surface" and discovered that right below that surface was blotches of gray and black.

Just 4 turns. The idea and constructive details came in 2015 from Jim Giammanco N5IB, the original designer of the PHSNA.

Ignacio

--
Este correo electrónico ha sido analizado en busca de virus por el software antivirus de Avast.
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On Tue, Jul 4, 2023 at 11:54 AM, Jim Lux wrote:

PVC pipe has two potential problems as a coil form (based on experience of
folks building tesla coils, so 100-500 kHz):
1) it's hygroscopic so the dielectric loss varies with the water content

I asked Google AI whether PVC is hygroscopic. Here, in part, is what it said


Polyvinyl chloride (PVC) is a hygroscopic powder material. Hygroscopic substances can take and hold moisture from the surroundings.

PVC is non-hygroscopic, meaning it does not absorb moisture internally into the pellet. However, moisture can be collected on the surface of the pellet.
Other non-hygroscopic polymers include polypropylene, polystyrene, and polyethylene.


I thought that was an interesting distinction. Google AI generates very useful summaries, but I don't fully trust it yet, so I searched onward. I found two more references that said PVC is not hygroscopic.

I'm sure your remark about Tesla coils is based on practical experience. Any idea why it might differ from what these references say?

By the way, I've collected dielectric data for years for use in my coil inductance and Q calculator. The PVC dissipation factor it uses is 0.016 at 1 MHz and 0.0055 at 3 GHz. (This is why testing PVC in a microwave oven does not indicate its HF properties.). My coil inductance and Q calculator logarithmically interpolates these values. PVC is not too bad at HF, but much better dielectrics are readily available. Try any round plastic container from your refrigerator or kitchen cabinet. It is likely to be one of the non-hygroscopic polymers Google mentions. Read the recycling code on the bottom to determine just what it's made of.

Brian

On 7/4/23 11:16 AM, WB2UAQ wrote:

Mike and Alan,
I measured the loss factor for PVC and it was about 0.005 or so at 1 kHz. I did more measurements at RF but will have to go back to old note books. I made a simple fixture to test a number of plastics. I rebuilt a coil that plugs into a BC-610 transmitter and from that sprung all kinds of questions about dielectrics. Many local guys are using 3D printers and using PLA, I think it is called. They printed out a plate of it for me to test. I would not say that all of this material is made equally and permitivity and loss factor are probably not well controlled. Won't be able to get back to this for awhile as it is Independence Day and a lot going on to take care of this week. Can only say right now that none of this plastic seemed to jump out as being a terrible dielectric. I also tested plate glass because back in the early days of radio capacitors for spark transmitters used what I think was regular glass available at that time.

PVC pipe has two potential problems as a coil form (based on experience of folks building tesla coils, so 100-500 kHz):
1) it's hygroscopic so the dielectric loss varies with the water content - nylon has the same problem, BTW.
2) most pipe is made from recycled material, and it can have metal fragments and other debris in it. The specs for pipe are about holding pressure and being "safe for drinking water", not dielectric properties.

Tesla coil folks solve #1 by drying it and then coating with something like lacquer, glyptal, or urethane

#2 is a bit trickier - it's not like you can take a 4 foot long piece of 6" pipe and throw it in the microwave and see if it arcs or has hot spots.

Mike and Alan,
I measured the loss factor for PVC and it was about 0.005 or so at 1 kHz. I did more measurements at RF but will have to go back to old note books. I made a simple fixture to test a number of plastics. I rebuilt a coil that plugs into a BC-610 transmitter and from that sprung all kinds of questions about dielectrics. Many local guys are using 3D printers and using PLA, I think it is called. They printed out a plate of it for me to test. I would not say that all of this material is made equally and permitivity and loss factor are probably not well controlled. Won't be able to get back to this for awhile as it is Independence Day and a lot going on to take care of this week. Can only say right now that none of this plastic seemed to jump out as being a terrible dielectric. I also tested plate glass because back in the early days of radio capacitors for spark transmitters used what I think was regular glass available at that time.
73

On Mon, Jul 3, 2023 at 11:24 PM, alan victor wrote:

Excellent Mike. So that is a Qul of 348. I spilt the difference between 6 and
8 ohms... lets say 7... From the appearance of your coil, that seems
reasonable. The material you wound the unit on has a loss tangent. Any idea
what it is? Nice if it were .0005 or better.... Suspect it is not.

It's PVC water pipe.

--
Mike

On 7/3/23 4:13 PM, WB2UAQ wrote:

Alan, How does the loss factor of the dielectric that the coil form is made from impact the magnetic circuit? I have heard others mention this but with no explanation.

Most coils have some parasitic C (it can be quite large). That C has a voltage on it, and a lossy dielectric leads to loss.

Hi Pete.

The inductor is supporting a propagating field. It is both magnetic and electric. You are correct, while the magnetic properties of a core are key to control loss, so are the dielectric properties, as this impacts the electric field. A good way to approach all lumped components is not to consider them as lumped, but as distributed. An L and C are actually transmission line components. Particularly as the frequency increases. So the dielectric loss as it affects a transmission line is really no different in its impact when it supports a coil on an insulating form. Loss in the dielectric contributes a resistive shunt component and reduces the inductor Q. As a rule of thumb, try to use a material whose loss tangent provides a Q value (1/loss tan) of 5 x the inductor alone.

You can change the setting in the menu to display R+jX instead of the default R +inductance/capacitance.

Roger

Alan, How does the loss factor of the dielectric that the coil form is made from impact the magnetic circuit? I have heard others mention this but with no explanation.
Thanks, Pete

Good evening!

I would very much appreciate recommendations on the best version of the NANOVNA that displays reactance values for the markers on the Smith chart, instead of inductance and capacitance.

Thank you very much!

Tom

Excellent Mike. So that is a Qul of 348. I spilt the difference between 6 and 8 ohms... lets say 7... From the appearance of your coil, that seems
reasonable. The material you wound the unit on has a loss tangent. Any idea what it is? Nice if it were .0005 or better.... Suspect it is not.

On Mon, Jul 3, 2023 at 03:27 PM, alan victor wrote:

If difficulty in finding the paper from EDN and the figures, here is a pdf
abbreviated and a test case circuit screen capture. If you are careful in
fixture construction depending on operating frequency, unloaded Q of 350 or
more is easy to obtain. You really need to take care in any Q measurement to
prevent series R losses from accumulating unless you can accurately de-embed
the "stray" R value(s).

Alan

OK I had a go at this with my NanoVNA and got the attached result, which if I follow your calculation correctly equates to Rq = 8.05 ohms.

Coil64 estimates 5.9 ohms which, given the less than ideal test jig I'm using, is not too far off.

Mike


--
Mike

Return it and get a refund. Then go to R & L Electronics and purchase a genuine one. Problem solved!!! PS... This is the very best advise ANYBODY can give you!!!

Alan

I found the article from your earlier link and will give it a go, thanks.

In the meantime I repeated my measurement with NanoVNA-App calibrated for 6401points and got a slightly lower value of 13.6 ohms at resonance.

--
Mike

On Monday 03 July 2023 08:20:00 am DougVL wrote:

I occasionally see them for sale at hamfests. I have gotten a few that way, but I shouldn't have - I haven't used any yet. Not even the big, (relatively) heavy old U.S. military one.
If you look for one that way, be sure that any that you find still has its set of plug-in coils.

I had the thought to get one some time back, and started looking on ebay. It's amazing how many of these units do NOT have any of the coils with them! I know of one guy who took on one of those and proceeded to try and make his own coils, but I'm not feeling that ambitious these days...

I wonder where all of those coils go?

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin