"Homebrew FM tap" for the mobile ?
 

Hi all Any of you guys experimented building a "FM tap" for the mobile ?
I want to use a Fender mounted CB antenna for the car's AM/FM radio also

A center loaded mobile antenna directly threads on to my Blazers AM/FM+
RG-58 hardware
( just added PL259 plus devise a safe way of shunting the RF on transmit.

1.7:1 SWR confirmed
Now I need to make a tap perhaps:
68pf + 10K resistor to 2 detector diodes back to
back + 10:1 for 50mv shunt ?

-Joe (NOSPAM in effect)

Some time ago I obtained a roll of 6 mil thick 10 inch wide aluminum sheet
at a bargain. I intended to use it for an antenna in my attic. I would use
plastic clothes hangers as supports stapled to the rafters.

When I mentioned I was finally going to get it installed, a friend told me
that the sheet won't make a good antenna. There is plenty of room for a
bent dipole so I ask why he thought it wouldn't work. His answer was that
the thin edges would have a corona discharge and might set fire to the
house. I considered it nonsense, but I wonder -- Running only 100 Watts.

Is there any reason that a thin sheet of the proper length would be
unsuitable as an antenna for "indoor" use?

Thanks for you insightful comments.

K7DUP

On Tue, 13 Jan 2004 22:42:36 GMT, "Roger Gt"
wrote:
thin edges would have a corona discharge and might set fire to the
house. I considered it nonsense, but I wonder -- Running only 100 Watts.

Hi Roger,

Same thing "might" happen with wire too (it is just as thin and pointy
at the edges and the ends). That is why you use standoff insulators.

"Only 100W" has nothing to do with it, except making it happen faster.
Why, where, or when is strictly a matter of Geometry and wavelength.

Aside from being a thick wire (at least in one dimension); there is
nothing novel that couldn't be accomplished with simple wire. You may
enjoy wider bandwidth at a shorter dimension.

73's
Richard Clark, KB7QHC

No to your question, but why? Wire would work every bit as well..

"Roger Gt" wrote in message
om...
Some time ago I obtained a roll of 6 mil thick 10 inch wide aluminum sheet
at a bargain. I intended to use it for an antenna in my attic. I would
use
plastic clothes hangers as supports stapled to the rafters.

When I mentioned I was finally going to get it installed, a friend told me
that the sheet won't make a good antenna. There is plenty of room for a
bent dipole so I ask why he thought it wouldn't work. His answer was that
the thin edges would have a corona discharge and might set fire to the
house. I considered it nonsense, but I wonder -- Running only 100 Watts.

Is there any reason that a thin sheet of the proper length would be
unsuitable as an antenna for "indoor" use?

Thanks for you insightful comments.

K7DUP

Some time ago I obtained a roll of 6 mil thick 10 inch wide aluminum sheet
at a bargain. I intended to use it for an antenna in my attic.

Hi,
it might be interesting to make a magnetic loop from the sheet. It
should behave like a 5 inch dia aluminum tube according to theory, so
good efficiency can be expected.

73 Ivan OK1SIP

Install it with end insulators, for some applications a small piece of
dowel with the aluminum wrapped on it will make a suitable insulator.
Then tie off the dowel in the attic with 30 pound monofiliment fishing line.

The 10 inch width will give a wider resonance than a wire, assuming you
will be using it at 20 meters or lower wavelengths.

For an attic installation use nuts/bolts/washers to fasten the
transmission line to the antenna. Soldering to Aluminum requires much
more than simple solder.

Deacon Dave, W1MCE

Roger Gt wrote:
Some time ago I obtained a roll of 6 mil thick 10 inch wide aluminum sheet
at a bargain. I intended to use it for an antenna in my attic. I would use
plastic clothes hangers as supports stapled to the rafters.

When I mentioned I was finally going to get it installed, a friend told me
that the sheet won't make a good antenna. There is plenty of room for a
bent dipole so I ask why he thought it wouldn't work. His answer was that
the thin edges would have a corona discharge and might set fire to the
house. I considered it nonsense, but I wonder -- Running only 100 Watts.

Is there any reason that a thin sheet of the proper length would be
unsuitable as an antenna for "indoor" use?

Thanks for you insightful comments.

K7DUP

Roger wrote:
"---Running only 100 Watts?"

At resonance, you should have 85 volts at the dipole drivepoint. If
there were no radiation from the antenna, voltage at its tips would rise
to 170 volts from the Ferranti effect, that is the voltage doubling from
collapse of the magnetic field caused by current interruption at the
conductor`s end.

It`s possible to build a Tesla coil with inductive loading of an
antenna, but if you don`t do that, there`s not much chance of generating
enough voltage to make a corona with 100 watts. At a kilowatt you only
have 3.16 X the volts at 100 watts. It takes several thousand volts to
generate a corona at normal atmospheric pressure.

Install a fire detector and be comfortable.

Best regards, Richard Harrison, KB5WZI