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Adding an external antenna to radio for EAS reception

R

radiofish

I have a very decent digtal tuning FM receiver that I want to use as an LP1FM receiver. However, the unit needs to be placed inside a steel reinforced concrete building with two FM transmitters. It is nearly impossible to get reception of the LP1FM inside. I would like to place a yagi or whip antenna on the roof of the building and run coax into the building. However, the radio doesn't have an input for an external antenna, just the built-in telescoping antenna.

Can such a telescoping antenna be disconnected so that a coaxial line can provide signal into the radio? would this be 75 or 300 ohms, or does this matter?
 
> Can such a telescoping antenna be disconnected so that a
> coaxial line can provide signal into the radio? would this
> be 75 or 300 ohms, or does this matter?
>
Yes, with varying results. There is probably a little screw that you can tap into that holds the whip antenna in place. Or just use a clip lead.

Hard telling what impedance it is, but use 75 ohm cable in from the antenna.
 
> Can such a telescoping antenna be disconnected so that a
> coaxial line can provide signal into the radio? would this
> be 75 or 300 ohms, or does this matter?

The wire going to the telescopic antenna is connected to the coax center conductor. The shield goes to the ground plane inside the radio (probably connects to battery negative as well).
 
You may want to consider a high end unit with a preselector front-end in the receiver. Even if you mod this portable unit, the receiver will probably be completly overloaded by the 2 FM's at the site. Interference from any 2-way radio or paging at the site will also potentially hammer that radio.

http://www.fanfare.com/ft1ap-sht.html

These receivers work well in harsh environments.

Even with a decent unit, you may still need to notch out the local transmitters.
Deep single freq notches are available from Microwave Filter Company,
http://www.microwavefilter.com/specialtraps.htm
They make the "5KFM" that you order to notch the specific freq(s) in question.

Good luck,

fmnostatic


> I have a very decent digtal tuning FM receiver that I want
> to use as an LP1FM receiver. However, the unit needs to be
> placed inside a steel reinforced concrete building with two
> FM transmitters. It is nearly impossible to get reception
> of the LP1FM inside. I would like to place a yagi or whip
> antenna on the roof of the building and run coax into the
> building. However, the radio doesn't have an input for an
> external antenna, just the built-in telescoping antenna.
>
> Can such a telescoping antenna be disconnected so that a
> coaxial line can provide signal into the radio? would this
> be 75 or 300 ohms, or does this matter?
>
 
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