"Denny" wrote in message
ps.com...
In my search for knowledge I recently went through a big thrash with
antenna tuners... Because of cost I built my own variable caps... To
keep the size down I experimented with various insulators between the
plates, from air up to glass...

Being that the tuners on 40 and 20 were end matching a half wave
antenna element the circulating tank current was considerable... On
20 meters where the capacitor plates are 1.5" square for resonance the
glass would simply shatter at about 800W for 5 seconds... Plexiglass
would boil internally in roughly 20 seconds leaving this interesting
rippled piece with 'steam' bubbles in the center of the plexi...
Ceramic tiles seemed to work OK, but I didn't find any thin ones
locally and the thick pieces resulted in plates being awkwardly
large...

On 80 meters the glass plates are 4" X 6" and the glass runs barely
above ambient at 2KW...

denny / k8do


An very odd result considering that glass dielectric capacitors are sold
specifically for high rf current use by people such as AVX and the like. I
guess it depends on what type of glass you used. You shouldn't have used
your old lead crystal glasses (;-))

73
Jeff

Thomas & Karen Mitchell wrote:

...
So: I'll stay at 25 when in the car.

-- KG7U
--------------------------------------------------------------------------
Tom Mitchell, Port Angeles, Washington, USA
http://www.olympus.net/personal/kg7u
--------------------------------------------------------------------------

Every engineer, worth his pay, which I know, allow at least a 20% excess
on ratings.

50 X 20% = 10 watts

50 + 10 = 60 watts

I'd run the 65 and examine the glass mount now and then. You'll see if
damage begins and switch lower power.

Warm regards,
JS

"Richard Clark" wrote in message
...
On Mon, 4 Jun 2007 02:43:18 +0100, "Mike Kaliski"
wrote:

Take a deep breath before transmitting with all the controls set to 11...

Hi Mike,

Is the warrantee void within 100 yards of a 50KW AM antenna? Or
howabout those half megawatt LF stations that litter the continent?

73's
Richard Clark, KB7QHC

Richard

It's all about RF actually within the vehicle. The bodywork acts like a
Faraday cage against external influences. But I suspect you know that
already :-)

A couple of years back a lightning bolt hit a field I was driving past
during a storm. The dash completely blanked for 2 seconds and then came back
to life - no other ill effects noted - just as well because the road was
nearly completely under water at that point.

The radio key remote locking can fail if you park too close to a mobile
phone mast, or someone is transmitting on 70 cms nearby, but that's about
it.

As I only operate QRP I hadn't given the matter much thought until I checked
in the vehicle manual and saw a footnote.

Mike G0ULI

"Mike Kaliski" wrote in message
...

"Richard Clark" wrote in message
...
On Mon, 4 Jun 2007 02:43:18 +0100, "Mike Kaliski"
wrote:

Take a deep breath before transmitting with all the controls set to
11...

Hi Mike,

Is the warrantee void within 100 yards of a 50KW AM antenna? Or
howabout those half megawatt LF stations that litter the continent?

73's
Richard Clark, KB7QHC

Richard

It's all about RF actually within the vehicle. The bodywork acts like a
Faraday cage against external influences. But I suspect you know that
already :-)

A couple of years back a lightning bolt hit a field I was driving past
during a storm. The dash completely blanked for 2 seconds and then came
back
to life - no other ill effects noted - just as well because the road was
nearly completely under water at that point.

The radio key remote locking can fail if you park too close to a mobile
phone mast, or someone is transmitting on 70 cms nearby, but that's about
it.

As I only operate QRP I hadn't given the matter much thought until I
checked
in the vehicle manual and saw a footnote.

Mike G0ULI




I had a similar experience with lightning. The lightning hit a tall comm
tower on the side of the road, jumped out the side of the tower, hit the
roof of the truck I was in, and then struck a pine tree on the other side of
the road. The engine diesd and I coasted to the side of the road. After a
few minutes of getting my composurer back together and surveying the damage
I was able to start the truck like nothing had happened. I was expecting all
the electronics to be fried.


Jimmie

Richard Clark wrote:
On Mon, 4 Jun 2007 02:43:18 +0100, "Mike Kaliski"
wrote:


Take a deep breath before transmitting with all the controls set to 11...


Hi Mike,

Is the warrantee void within 100 yards of a 50KW AM antenna? Or
howabout those half megawatt LF stations that litter the continent?


I'd venture that the concern is not so much radiated field (although, in
the nearfield it drops off pretty quick, so a 100W transmitter on a car
might well create larger field strengths than that 50kW AM station.

It's probably more the potential for conducted RF via the radio's power
leads, etc. Imagine that if the chassis of the radio is RF hot,
relative to the car body (oh no, that never happens, no waygrin), so
now you have significant RF current flowing in the vehicle wiring harness.

From a straight field standpoint, it's easy to exceed the ANSI RF field
Maximum Permissible Exposure(MPE) with a 2m transmitter and 50W on a
car. Combination of the limit being lowest, close proximity to the
radiator, etc. (I seem to recall the limit is reached at about 1 meter
away from a groundplane/whip antenna at 50W, albeit at 100% duty cycle)

But then, you have done your RF safety analysis, right? (Even though
there's a categorical exemption from the requirement for routine
evaluations for amateur mobile and portable operations, that doesn't
relieve you from the requirement for safety).


In comparison, you're not going to be driving somewhere the field
exceeds the limits, because they'll have a big fence keeping you beyond
the distance for uncontrolled exposure limits.


As far as the original question about through glass...

Glass isn't the lowest loss dielectric to make a capacitor of (heck,
even at the 100kHz used in tesla coils, it's lossy enough to crack from
the thermal stresses). The glass is the dominant source of loss in using
FR-4/G-10 PC boards at microwave frequencies, for instance. However,
even a spectacularly bad loss tangent of 0.01 is only going to result in
a 1% loss. (wood has a loss tangent of 0.03 or thereabouts at 100MHz,
depending on moisture level)

A bigger issue would be wires/conductive films for defogging.

Jim

Jeff wrote:
"Denny" wrote in message
ps.com...

In my search for knowledge I recently went through a big thrash with
antenna tuners... Because of cost I built my own variable caps... To
keep the size down I experimented with various insulators between the
plates, from air up to glass...

Being that the tuners on 40 and 20 were end matching a half wave
antenna element the circulating tank current was considerable... On
20 meters where the capacitor plates are 1.5" square for resonance the
glass would simply shatter at about 800W for 5 seconds... Plexiglass
would boil internally in roughly 20 seconds leaving this interesting
rippled piece with 'steam' bubbles in the center of the plexi...
Ceramic tiles seemed to work OK, but I didn't find any thin ones
locally and the thick pieces resulted in plates being awkwardly
large...

On 80 meters the glass plates are 4" X 6" and the glass runs barely
above ambient at 2KW...

denny / k8do



An very odd result considering that glass dielectric capacitors are sold
specifically for high rf current use by people such as AVX and the like. I
guess it depends on what type of glass you used. You shouldn't have used
your old lead crystal glasses (;-))



Lots of kinds of "glass" out there.

fused silica is pretty low loss
borosilicate glass (e.g. Pyrex, Kimax, etc.) is medium
windowglass (soda lime) is all over the place.

John Smith I wrote:
Thomas & Karen Mitchell wrote:

...

So: I'll stay at 25 when in the car.

-- KG7U
--------------------------------------------------------------------------

Tom Mitchell, Port Angeles, Washington, USA
http://www.olympus.net/personal/kg7u
--------------------------------------------------------------------------



Every engineer, worth his pay, which I know, allow at least a 20% excess
on ratings.

50 X 20% = 10 watts

50 + 10 = 60 watts

I'd run the 65 and examine the glass mount now and then. You'll see if
damage begins and switch lower power.

Warm regards,
JS

Obviously the engineers who established the maximum power
specification would not advocate using greater than 50 watts.

ac6xg

Jim Kelley wrote:

...
Obviously the engineers who established the maximum power specification
would not advocate using greater than 50 watts.

ac6xg

1) No engineer would advocate over-clocking computers the way I do.
2) No engineer would advocate pushing rigs and liners (power amps) to
the limits I do.
3) No engineer would advocate doing the mods to equipment I do.
4) No engineer would advocate the antenna experiments I carry out.
6) No engineer would advocate the engine mods to my vette which I have done.
7) No engineer would advocate the levels of exposure to RF I expose
myself too.
8) ...

That's what makes it fun, now doesn't it?

JS

John Smith I wrote:


1) No engineer would advocate over-clocking computers the way I do.
2) No engineer would advocate pushing rigs and liners (power amps) to
the limits I do.
3) No engineer would advocate doing the mods to equipment I do.
4) No engineer would advocate the antenna experiments I carry out.
6) No engineer would advocate the engine mods to my vette which I have
done.
7) No engineer would advocate the levels of exposure to RF I expose
myself too.
8) ...

That's what makes it fun, now doesn't it?

It's unquestionably something which separates fools and their money.

ac6xg

Jim Kelley wrote:

...
It's unquestionably something which separates fools and their money.

ac6xg



Yes, well, I am still working on a way to take to the grave with me ...
so far, NO PROGRESS!

I wish you better luck ... however, I guess others who will benefit from
the money will be more than grateful ... granting that I will be
unsuccessful in finding a way.

JS