On Sat, 05 Oct 2013 15:24:01 -0500, John S
wrote:

The microwave oven test is not very useful. The microwave will test
whatever at about 2450MHz. I doubt he is trying to make a loading coil
for anything near that frequency.

Actually, it's very useful. In my admittedly limited experience,
anything that survives the microwave oven test, will usually work
nicely at HF frequencies. Those that get warm in the oven, might
work ok. Those that melt, burn or explode, will probably not work
very well at HF. While testing at 1000 times the frequency, and 30
times the power, might be considered overkill, it does yield some
useful information.

Incidentally, the loss tangent changes over frequency on many
materials. See table at:
http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_5.html

There are other resources for that information. Please search.

Well, there's the loss tangent tables for various materials.
http://www.rfcafe.com/references/electrical/dielectric-constants-strengths.htm
Is that what you mean? The problem here is that the ABS or PVC coil
form is hollow. There's only a little plastic and plenty of air. If
the PVC tube were thin enough, it might be considered air core.

You are correct. But, the losses (percentage-wise) will be the same
barring heating effects.

The losses are fairly small, but the effects on the material at
different power levels quite different. For example, a 1dB power loss
at the 5 watt level will produce about 1 watt of heat. That same 1dB
loss at 150 watts will produce 30 watts of heat, which will probably
melt the coil form.

It wouldn't be air core considering that it would be over
wood (dry and waterproofed) or PVC pipe.

For a hollow PVC or ABS pipe, it's mostly air core. (For a solid wood
coil form, it's all wood with some absorbed water.) I'm not sure how
to calculate the effective dielectric constant of a hollow plastic
pipe. Probably by measuring the inductance of a surrounding coil with
and without the pipe, and calculating what dielectric constant was
necessary to produce the change. Unfortunately, that doesn't help
calculate the combined losses or loss tangent.

Most posters here do not state all of the facts initially. That's
because most of their ideas are still brewing in the brain and some of
the details are not formalized. It is the reason we ask for other
people's inputs. Cut him some slack and continue to ask how you can help.

Of course. However, I post far too many "answers" in far too many
newsgroups and mailing lists to remember everyones situation. If I'm
expected to spend my time answering a question or solving a problem, I
expect to be provided with:
1. What problem are you trying to solve? A one line description is
sufficient.
2. What do you have to work with? (Equipment, site limitations,
available test equipment, numbers, numbers, numbers).
3. What have you done so far and what happened?

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

On 10/5/2013 3:52 PM, Irv Finkleman wrote:
Thanks John,

I do require the structure be relatively strong or I
would wind the coil, put epoxy glue strips along it
to make it like AirDux and the like.

Cheers and 73,
John KD5YI



Here's a picture of a coil I built years ago using 40 ft Radio Shack
Aluminum Ground wire. It comes coiled at about 8". My coil is about 8" x
8". I'm making an educated guess that it's about 150uh.

http://s395.photobucket.com/user/Qma...c1dd8.jpg.html
I drilled spaced holes in 1/2" pvc pipe and then split it on a band saw
and clamped the wire between the pieces. Need more strength add more pvc
clamps. There are other ways.

I just went to the radio shack website looking for the ground wire, I
have one and it's catalog number 15-035, BUT, I can't find it on their site.
Hmm, I see one on Ebay, $14.99 including shipping
http://www.ebay.com/itm/NEW-Radio-Sh...-/281117465242




Mikek

On 10/4/2013 8:48 PM, Irv Finkleman wrote:
I wonder how much difference it would make if I were to
build a loading coil on a piece of 3''x3" wood? It would be
very easy and I could suspend the winding above the wood
form with plastic dowel glued on each corner of the wood.

I could also make a similar coil using PVC pipe. Even in that
case the winding would have a somewhat rectangular form
factor.

It wouldn't be air core considering that it would be over
wood (dry and waterproofed) or PVC pipe.

I do require the structure be relatively strong or I
would wind the coil, put epoxy glue strips along it
to make it like AirDux and the like.

Any comments or suggestions??

Irv VE6BP







Interesting postings. An old friend of mine, Don, K7hsj, and his wife
recently moved to an assisted living center in Bend, Oregon. He was very
concerned about still being able to get on the air. He approached the
management about a wire from their third floor apartment to a pine tree
several hundred feet away. They were very enthusiastic about his
continuing ham operation and agreed to help if they could. Several of
Don't friends from Bend helped get the wire up.

I suggested that since the building was fairly new, they probably used
steel studs to partition the rooms and they all had to be connected to
the electrical ground wire of the building wiring. So he used the screw
in the center plate of an outlet cover as ground.

His 75 meter signal is MUCH louder than when he was at home with a
dipole antenna. He got an auto tuner and works most HF bands, now.

So, to make a long story short, try the electrical outlet ground for
your rig. It may work fine for you, also.

73 and good luck
Paul, KD7HB

On Saturday, October 5, 2013 7:44:30 PM UTC-5, Jeff Liebermann wrote:
On Sat, 05 Oct 2013 15:24:01 -0500, John S

wrote:



The microwave oven test is not very useful. The microwave will test

whatever at about 2450MHz. I doubt he is trying to make a loading coil

for anything near that frequency.



Actually, it's very useful. In my admittedly limited experience,

anything that survives the microwave oven test, will usually work

nicely at HF frequencies. Those that get warm in the oven, might

work ok. Those that melt, burn or explode, will probably not work

very well at HF. While testing at 1000 times the frequency, and 30

times the power, might be considered overkill, it does yield some

useful information.

I had always heard that if one were to use PVC, the gray type was
the best vs the white. I've used gray PVC for mobile whip loading
coils for years and never really noticed any real problems.
But, I do not run high power, and 100w is the max I run.
I've always had good results with the antennas, and noticed no
noticeable performance loss vs say an open type bug catcher coil.
There may be some, but it's small enough not to be a problem.

When I first started using the gray PVC, I stuck it in the
microwave with a glass of water, and it did not get warm at all.
I have heard the white PVC can be more of a problem.

On 10/5/2013 4:14 PM, Ralph Mowery wrote:
"Irv Finkleman" wrote in message
...
Hi Jeff, and thanks for your reply.

To begin with I run QRP (5W on a Yaesu ft-817ND).
I have limited workshop space (my desk in a senior's villa), but
lots of my old tools.

I was comparing a wood coil with an air wound coil.
I should have said ABS rather than PVC, and I am
well aware of dielectric losses although I don't worry
about them too much as even 5W minus the losses will
keep me on the air. I'm not overly concerned about
Q as long as I can get a signal out!

My main concern was with winding a loading coil on
a square form, and I was just wondering how much
effect that would have.


After this discussion I think I'll go ABS, and with
the aid of some epoxy may even slip it off the
pipe and go air core supporting the coil off to the
side of the whip mounting. Remember the old
'Gotham Vertical' antennas (1956 Handbook ads)?

Lots of sutff cut out..

I ran a quick and dirty check for you. I took about 8 turns of about #22
wire and a 100 pf capacitor. Wound the wire around a piece of 1/2 inch PVC
pipe that is about 7/8 inch outside diameter. I made a parallel circuit of
the two. Put it on a HP 8924c set as a spectrum generator and tracking
generator.

It resonated about 13.08 mhz and had a relative loss of -46.46 db. Took it
off the form and resonated about 13.14 with a loss of -47.0 db back on the
pvc and it went back to the first number.
I did not have a piece of wood that would exectally fit it,but one that was
close. Resonated at 13.05 mhz and loss of -46.94.

All in all, I doubt there would be enough loss or change to make any
differance. The small loss and frequency change could just be the spreading
of the coil slightly and the loss could be how close the leads are to each
other.

For running the 5 watts like you are, I don't see any problems with
changing the forms on the low bands. I doubt that even at 100 watts it
would have any noticable effect.

Excellent work, Ralph. This is very useful information. Many thanks!

73,
John

On 10/6/2013 2:32 AM, wrote:
On Saturday, October 5, 2013 7:44:30 PM UTC-5, Jeff Liebermann wrote:
On Sat, 05 Oct 2013 15:24:01 -0500, John S

wrote:



The microwave oven test is not very useful. The microwave will test

whatever at about 2450MHz. I doubt he is trying to make a loading coil

for anything near that frequency.



Actually, it's very useful. In my admittedly limited experience,

anything that survives the microwave oven test, will usually work

nicely at HF frequencies. Those that get warm in the oven, might

work ok. Those that melt, burn or explode, will probably not work

very well at HF. While testing at 1000 times the frequency, and 30

times the power, might be considered overkill, it does yield some

useful information.

I had always heard that if one were to use PVC, the gray type was
the best vs the white. I've used gray PVC for mobile whip loading
coils for years and never really noticed any real problems.
But, I do not run high power, and 100w is the max I run.
I've always had good results with the antennas, and noticed no
noticeable performance loss vs say an open type bug catcher coil.
There may be some, but it's small enough not to be a problem.

When I first started using the gray PVC, I stuck it in the
microwave with a glass of water, and it did not get warm at all.
I have heard the white PVC can be more of a problem.


The guys that build high Q inductors for crystal radios use
styrene pipe couplers.
http://www.genovaproducts.com/docs/P...og.pdf#page=37
Note: S prefix denotes styrene.
I see references to both Lowes and Home depot having these in stock.
I think styrene will deform at a lower temperature than PVC.
Mikek

Lovely work Mike -- a bit more than I require but I'll keep it
in mind. Thanks!

Irv VE6BP

"amdx" wrote in message
...
On 10/5/2013 3:52 PM, Irv Finkleman wrote:
Thanks John,

I do require the structure be relatively strong or I
would wind the coil, put epoxy glue strips along it
to make it like AirDux and the like.

Cheers and 73,
John KD5YI



Here's a picture of a coil I built years ago using 40 ft Radio Shack
Aluminum Ground wire. It comes coiled at about 8". My coil is about 8" x
8". I'm making an educated guess that it's about 150uh.

http://s395.photobucket.com/user/Qma...c1dd8.jpg.html
I drilled spaced holes in 1/2" pvc pipe and then split it on a band saw
and clamped the wire between the pieces. Need more strength add more pvc
clamps. There are other ways.

I just went to the radio shack website looking for the ground wire, I
have one and it's catalog number 15-035, BUT, I can't find it on their
site.
Hmm, I see one on Ebay, $14.99 including shipping
http://www.ebay.com/itm/NEW-Radio-Sh...-/281117465242




Mikek

On Sun, 6 Oct 2013 00:32:22 -0700 (PDT), wrote:

I had always heard that if one were to use PVC, the gray type was
the best vs the white. I've used gray PVC for mobile whip loading
coils for years and never really noticed any real problems.
But, I do not run high power, and 100w is the max I run.
I've always had good results with the antennas, and noticed no
noticeable performance loss vs say an open type bug catcher coil.
There may be some, but it's small enough not to be a problem.

When I first started using the gray PVC, I stuck it in the
microwave with a glass of water, and it did not get warm at all.
I have heard the white PVC can be more of a problem.

http://lists.contesting.com/_towertalk/2006-12/msg00091.html

I ran tests at 2.4GHz about 15 years ago. The plan was to use PVC
pipe as a 2.4GHz antenna radome. While heating is obviously not an
issue at 1 watt, even small losses and detuning were deemed
intolerable. I couldn't measure any difference between grey or white
as long as the pipe was the same thickness. However, things went awry
when I tried to build prototypes out of a mix of different brands of
white PVC pipe. The dielectric constant was all over the map causing
the resonance point to move around. After determining that even a
single supplier can't keep their electrical characteristics
consistent, we switched to the more expensive fiberglass tubing and
lived happily thereafter.

Another potential problem with a base loaded vertical is not power,
but voltage. At 5 watts, there's not going to be much voltage across
the coil. At 150 watts, it might arc. No calcs today. Gotta run and
watch the solar satellite outage today.
http://en.wikipedia.org/wiki/Sun_outage

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

That's all good info Paul, but with the aid of some ferrite cores and
the like I plan to steer clear of any possible signal entering the
local wiring.

After I've been on the air for a bit, if I find that I'm not causing
any problems, I may run another rig I have (Yaesu ft-857D) and
use a bit more power.

In the meantime, I just want to get a signal out and see what
I can do with 5 watts and assorted attempts at balcony verticals
and later magnetic loops.

Another interesting thing is how I can feed the antenna through
the door to the balcony. I can't drill holes, but I currently have
a piece of RG-58 squeezed through the closeddoor. Every day I
check to see if anything has happened to it such as migration of
the center conductor to the point where it shorts to the sheild.
I've only been here for a week, but so far so good. I am aware
that there may be an impedance bump, but I'm not at all
concerned -- if I can get one or two watts ERP I'll be more
than happy. My earliest Elmer/Mentor, VE7YY, used to run a half
watt homebrew rig and got all over the place with it although
I think that his tower and beam helped a wee bit!

I'm not desperate, but nearly so, and anxious to get on the
air again. It might take a bit of time, but I hope all the
ideas I have put into setting up the system will work right
the first time. We had a touch of snow last week, and I'm
getting a little beyond the point of enjoying antenna work
outdoors in the winter.

Irv VE6BP

"Paul Drahn" wrote in message
...
On 10/4/2013 8:48 PM, Irv Finkleman wrote:
I wonder how much difference it would make if I were to
build a loading coil on a piece of 3''x3" wood? It would be
very easy and I could suspend the winding above the wood
form with plastic dowel glued on each corner of the wood.

I could also make a similar coil using PVC pipe. Even in that
case the winding would have a somewhat rectangular form
factor.

It wouldn't be air core considering that it would be over
wood (dry and waterproofed) or PVC pipe.

I do require the structure be relatively strong or I
would wind the coil, put epoxy glue strips along it
to make it like AirDux and the like.

Any comments or suggestions??

Irv VE6BP







Interesting postings. An old friend of mine, Don, K7hsj, and his wife
recently moved to an assisted living center in Bend, Oregon. He was very
concerned about still being able to get on the air. He approached the
management about a wire from their third floor apartment to a pine tree
several hundred feet away. They were very enthusiastic about his
continuing ham operation and agreed to help if they could. Several of
Don't friends from Bend helped get the wire up.

I suggested that since the building was fairly new, they probably used
steel studs to partition the rooms and they all had to be connected to the
electrical ground wire of the building wiring. So he used the screw in the
center plate of an outlet cover as ground.

His 75 meter signal is MUCH louder than when he was at home with a dipole
antenna. He got an auto tuner and works most HF bands, now.

So, to make a long story short, try the electrical outlet ground for your
rig. It may work fine for you, also.

73 and good luck
Paul, KD7HB

"Irv Finkleman" wrote in message
...
That's all good info Paul, but with the aid of some ferrite cores and
the like I plan to steer clear of any possible signal entering the
local wiring.

After I've been on the air for a bit, if I find that I'm not causing
any problems, I may run another rig I have (Yaesu ft-857D) and
use a bit more power.

In the meantime, I just want to get a signal out and see what
I can do with 5 watts and assorted attempts at balcony verticals
and later magnetic loops.

Another interesting thing is how I can feed the antenna through
the door to the balcony. I can't drill holes, but I currently have
a piece of RG-58 squeezed through the closeddoor. Every day I
check to see if anything has happened to it such as migration of
the center conductor to the point where it shorts to the sheild.
I've only been here for a week, but so far so good. I am aware
that there may be an impedance bump, but I'm not at all
concerned -- if I can get one or two watts ERP I'll be more
than happy. My earliest Elmer/Mentor, VE7YY, used to run a half
watt homebrew rig and got all over the place with it although
I think that his tower and beam helped a wee bit!

I'm not desperate, but nearly so, and anxious to get on the
air again. It might take a bit of time, but I hope all the
ideas I have put into setting up the system will work right
the first time. We had a touch of snow last week, and I'm
getting a little beyond the point of enjoying antenna work
outdoors in the winter.

Irv you may just be over thinking things. One thought that comes to mind
is to make something similar to the ham stick dipole. You take two mobile
whips and mount them on a plate so you have a horizontal dipole made of
them.

http://www.k7su.com/hsdipole.html

An easy way to home brew something may be to get a few pieces of PVC pipe.
Get a T and don't glue it, but just stick a piece out of each end and make a
loaded dipole out of each side for the band you want to work. Then use the
long side of the T to come down as a support. All this can be broken down
and assembled as needed in a minuit or so. You may be able to get a big
flower pot and fill it with cement with a hole in it so you can place the
vertical pipe.

Too bad that you can not drill about a 3/4 inch hole in the wall and use a
long bulkhead coax connector.