If you can't contribute anything positive to this question, then stay out of
it, with your trash!

I have a 10m base loaded mag mount antenna, that I had to put a piece of
felt over the magnet as not to scratch a new vehicle.

When I did this I apparently changed the capacitance between the mag mount
and the roof of the vehicle. Someone suggested that I might want to replace
the felt with either a large balloon or a large prophylactic as it is
thinner and the capacitance would then return to almost where it should be.

Positive comments only!

John Doe wrote:

... Someone suggested that I might want to replace
the felt with either a large balloon or a large prophylactic as it is
thinner and the capacitance would then return to almost where it should be.

Positive comments only!

Using the latter, at least you would insure the antenna would NOT become
preggers! :-)

Positive regards,
JS

"John Doe" wrote in message
...
If you can't contribute anything positive to this question, then stay out
of it, with your trash!

I have a 10m base loaded mag mount antenna, that I had to put a piece of
felt over the magnet as not to scratch a new vehicle.

When I did this I apparently changed the capacitance between the mag mount
and the roof of the vehicle. Someone suggested that I might want to
replace the felt with either a large balloon or a large prophylactic as it
is thinner and the capacitance would then return to almost where it should
be.

Positive comments only!

John

I would have thought that the felt would make the mag mount more likely to
slip against the roof. You might not get any scratches, but you probably
would be minus one antenna at the end of a fast drive.

I have had good results using strips of insulating tape or adhesive backed
plastic type materials, similar to the stuff they print stickers on covering
the magnet. For best results, you want a soft resiliant type of plastic,
something that wont slip against the roof metal. Or have a look for some of
that plastic sheet that sticks to glass and smooth surfaces and is used to
secure licence or insurance details to car windscreens. That should protect
your paintwork and be removable at a moments notice. A favourite trick for
mincab or unlicensed cab drivers is to cover the antenna base with a stout
sandwich bag and secure it in place with a plastic tie wrap. Take the
antenna off the roof and no traces left behind.

Any of the above methods should work okay and they will all be a lot thinner
than a piece of felt.

Mike G0ULI

John Doe wrote:
Positive comments only!

I use aluminum foil.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
et...
John Doe wrote:
Positive comments only!

I use aluminum foil.
--
73, Cecil http://www.w5dxp.com

At least one dualband magmount, no longer offered by MFJ, came with an
aluminum foil bottom. I have used several of them and seen no adverse
effect on the paint -- and I whiz along at highway speeds a lot.

On Nov 3, 5:54 pm, "John Doe" wrote:
If you can't contribute anything positive to this question, then stay out of
it, with your trash!

I have a 10m base loaded mag mount antenna, that I had to put a piece of
felt over the magnet as not to scratch a new vehicle.

You are wasting your time trying to protect the paint when using a
magnetic mount. Grit will find its way under your magnet, and within
a year of normal driving, you will have scratched paint. Take a deep
breath, get out the hole saw or metal punch, and punch a hole in your
new car. Your radio will be happier and so will you as the paint
around your antenna will not be subjected to the inevitable damage
caused by magnet mounts. BTW, before anyone says anything about
lowering the value of the vehicle, I've sold and traded-in multiple
vehicles with holes punched in them, and not once has anyone ever said
a word about the holes. When I trade it in, I just put in a rubber
plug and no one notices.


When I did this I apparently changed the capacitance between the mag mount
and the roof of the vehicle. Someone suggested that I might want to replace
the felt with either a large balloon or a large prophylactic as it is
thinner and the capacitance would then return to almost where it should be.

Positive comments only!

However, if you have committed yourself to using a magnetic mount, I
would suggest using ultra thin vinyl sheeting, this should give you
enough grip to keep it on the vehicle. Nevertheless, anything that
you use is going to require that you retune the antenna, a longer whip
may be also be required because of the decreased capacitance.

73, Dloyd

On Nov 3, 9:27 pm, Dloyd Lavies wrote:
On Nov 3, 5:54 pm, "John Doe" wrote: If you can't contribute anything positive to this question, then stay out of
it, with your trash!

I have a 10m base loaded mag mount antenna, that I had to put a piece of
felt over the magnet as not to scratch a new vehicle.

You are wasting your time trying to protect the paint when using a
magnetic mount. Grit will find its way under your magnet, and within
a year of normal driving, you will have scratched paint. Take a deep
breath, get out the hole saw or metal punch, and punch a hole in your
new car. Your radio will be happier and so will you as the paint
around your antenna will not be subjected to the inevitable damage
caused by magnet mounts. BTW, before anyone says anything about
lowering the value of the vehicle, I've sold and traded-in multiple
vehicles with holes punched in them, and not once has anyone ever said
a word about the holes. When I trade it in, I just put in a rubber
plug and no one notices.

When I did this I apparently changed the capacitance between the mag mount
and the roof of the vehicle. Someone suggested that I might want to replace
the felt with either a large balloon or a large prophylactic as it is
thinner and the capacitance would then return to almost where it should be.

Positive comments only!

However, if you have committed yourself to using a magnetic mount, I
would suggest using ultra thin vinyl sheeting, this should give you
enough grip to keep it on the vehicle. Nevertheless, anything that
you use is going to require that you retune the antenna, a longer whip
may be also be required because of the decreased capacitance.

73, Dloyd

Try some 3mil Teflon, Teflon has a very high capacitive coefficent.

Jimmie

JIMMIE wrote:

Try some 3mil Teflon, Teflon has a very high capacitive coefficent.

I'm afraid you're misinformed. The dielectric constant of PTFE Teflon is
2.1, or just about twice that of air. Quite a few plastics are higher
(e.g. Mylar at 3.2 and PVC around 3.5), and many materials, such as
those used for capacitors, have dielectric constants that are a lot
higher (e.g., barium titanate at 1500 - 2000). Of course, a lot of the
latter aren't physically suited for this application. A long time ago, I
had trouble with microstrip line dispersion in a high speed delay line
compensation network design. So I chose Teflon for the substrate
material because of its *low* dielectric constant. The previous design
was on an alumina substrate having a dielectric constant of about 10.

The capacitance of two parallel plates is directly proportional to the
dielectric constant and the plate surface area, and inversely
proportional to the plate spacing. So putting 0.1 inch of Teflon between
the plates gives you the same capacitance as putting the plates 0.05
inch apart with air between.

This isn't to say that Teflon might not be a good choice. It's a very
low loss material, and chemically very inert. It's soft so won't
scratch, but it's slippery which might be a disadvantage. It's also
subject to cold flow, but there probably won't be enough pressure for
that to be a problem.

Roy Lewallen, W7EL

Roy Lewallen wrote:
JIMMIE wrote:

Try some 3mil Teflon, Teflon has a very high capacitive coefficent.

I'm afraid you're misinformed. The dielectric constant of PTFE Teflon is
2.1, or just about twice that of air. Quite a few plastics are higher
(e.g. Mylar at 3.2 and PVC around 3.5), and many materials, such as
those used for capacitors, have dielectric constants that are a lot
higher (e.g., barium titanate at 1500 - 2000). Of course, a lot of the
latter aren't physically suited for this application. A long time ago, I
had trouble with microstrip line dispersion in a high speed delay line
compensation network design. So I chose Teflon for the substrate
material because of its *low* dielectric constant. The previous design
was on an alumina substrate having a dielectric constant of about 10.

The capacitance of two parallel plates is directly proportional to the
dielectric constant and the plate surface area, and inversely
proportional to the plate spacing. So putting 0.1 inch of Teflon between
the plates gives you the same capacitance as putting the plates 0.05
inch apart with air between.

This isn't to say that Teflon might not be a good choice. It's a very
low loss material, and chemically very inert. It's soft so won't
scratch, but it's slippery which might be a disadvantage. It's also
subject to cold flow, but there probably won't be enough pressure for
that to be a problem.

Roy Lewallen, W7EL

It was a joke. I actually tried it on my wifes car, she wouldnt let me
drill a hole. The antenna stayed on about 3 minutes, just long enough
for her to get out of the neighborhood and get up to about 45MPH, then
it slid off and scratched the side of her car.Slipperiness is a BIG
disadvantage.

Jimmie

In message . com,
JIMMIE writes

Roy Lewallen wrote:
JIMMIE wrote:

Try some 3mil Teflon, Teflon has a very high capacitive coefficent.

I'm afraid you're misinformed. The dielectric constant of PTFE Teflon is
2.1, or just about twice that of air. Quite a few plastics are higher
(e.g. Mylar at 3.2 and PVC around 3.5), and many materials, such as
those used for capacitors, have dielectric constants that are a lot
higher (e.g., barium titanate at 1500 - 2000). Of course, a lot of the
latter aren't physically suited for this application. A long time ago, I
had trouble with microstrip line dispersion in a high speed delay line
compensation network design. So I chose Teflon for the substrate
material because of its *low* dielectric constant. The previous design
was on an alumina substrate having a dielectric constant of about 10.

The capacitance of two parallel plates is directly proportional to the
dielectric constant and the plate surface area, and inversely
proportional to the plate spacing. So putting 0.1 inch of Teflon between
the plates gives you the same capacitance as putting the plates 0.05
inch apart with air between.

This isn't to say that Teflon might not be a good choice. It's a very
low loss material, and chemically very inert. It's soft so won't
scratch, but it's slippery which might be a disadvantage. It's also
subject to cold flow, but there probably won't be enough pressure for
that to be a problem.

Roy Lewallen, W7EL

It was a joke. I actually tried it on my wifes car, she wouldnt let me
drill a hole. The antenna stayed on about 3 minutes, just long enough
for her to get out of the neighborhood and get up to about 45MPH, then
it slid off and scratched the side of her car.Slipperiness is a BIG
disadvantage.


Use RUBBER.
--
Ian