"DeG" wrote in message hlink.net...
I'm wanting to keep peace within the family.. NO! Extra antennas on the
vehicle..
I want to install a dual band 2m/440 mobile using the AM/FM antenna that is
on the vehicle.. It will be mostly used for receive, BUT....
Other than a duplexer and tuner (s) What is needed to STOP the RF from
damaging the AM/FM radio in case I want to transmit?...
Any help on this??

Just keeping the RF out of the AM/FM radio isn't too difficult, but
you'll have other issues, too. A diplexer (triplexer?) can be made to
do the job of sorting out the RF, with enough attenuation to prevent
burning up the car radio. -50dB from 10W is 0.1milliwatt, for
example, and it's possible to get better than 50dB attenuation of
unwanted bands. I'm not aware of triplexers specifically for
0.5-108MHz/144-148MHz/440-450MHz, but then I'd just design and build
one anyway (assuming I had decided to do it that way).

I assume your car antenna is a cowl-mounted whip, and not an
on-the-glass one which you might destroy by putting power to it. But
even then, the coax used for car antennas is typically high impedance
(low capacitance) to work well on the AM band. You may have some fun
getting 144 and 440MHz power to the antenna through that stuff, and if
you replaced it with RG-58, the AM reception would suffer quite a bit.
Another possibility is a relay at the antenna feedpoint, but typical
car antennas may not make that very easy.

If I was intent on a "stealth" antenna for my car, for 144 and 440,
I'd consider feeding a window frame as a slot-type antenna. If I was
really rabid about it, I'd think of making a slot antenna in the
sheetmetal, filled with dielectric that could be painted to match the
car finish, but that's a bit extreme for me.

The dual-band mag mount sounds like a good idea to me, or if you don't
need coverage, just a rubber duckie on a handheld.

Cheers,
Tom