"Thomas & Karen Mitchell" kg7uATolympus.net wrote in message
...
(I realize that a through-the-glass antenna is less than ideal.
Nevertheless, that's what I have to use in my situation.) The one I
have is for 2 meters (NOT dual band), and the label says up to 50
watts. I have an Icom IC-2200H, which has a maximum of 65 watts
output.

What bad things may/could/will happen if I put 65 watts through the
antenna?

Thanks!

Tom Mitchell -- KG7U
Port Angeles, Washington. USA
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Tom Mitchell, Port Angeles, Washington, USA
http://www.olympus.net/personal/kg7u
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Further to my earlier posting and slightly off topic but I have been
browsing through my car manual and note that the manufacturers specifically
forbid the installation of transmitters operating at more than 10 watts
power. Checking up on this reveals that in the event of some of the
electrical earth bonding connections in the car becoming faulty or breaking
two possible disaster scenarios exist. The first is that the computerised
engine management unit might misfunction causing the engine to suddenly stop
or the antilock braking and stability systems to malfunction. The second is
that the pyrotechnic charges in the airbags might be triggered.

Admittedly these two situations are dependent on a chain of faults/failures
occuring and the manufacturers are just trying to cover themselves against
law suits. Vehicles are tested for electromagnetic immunity at far higher
levels than this, but you might want to double check your manual or with the
manufacturer about the maximum permissible transmitter power if the vehicle
is fairly new, fitted with electronic engine management, safety equipment
and airbags.

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

Mike G0ULI

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

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

"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

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.

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.- Hide quoted text -

Exactly... If I were serious about using my capacitor design for the
higher bands I would either redesign the circuit to increase the plate
area or go to borosilicate glass...
My 80 - 160 remote tuners are working like gangbusters, take all the
power I can make, and cost roughly a hundred bucks a pop to build... I
don't operate the other bands much and can make do with simple
dipoles.... Being that I have ADD (antenna deficit disorder) I am
busily working on other ideas now...

denny / k8do

"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