Redundant antennae?

[Hoho]

This must seem like a naive question but I'm wondering what would happen if I attached two or more FM antennae to a receiver or radio? I would think that it would strengthen the signal. It wouldn't cause a short-circuit, would it? Or what if I use a portable table radio with both the attached whip antenna and an external wire antenna?

[Smokey]

Antenna inputs on radio have certain input impedance. Input impedance of 75 ohm is usually attached to antenna such as “T" model (know as dipole or TV antenna). Telescopic antenna input have input impedance of 300 ohm (usually single ended antenna).

Mixing antennas will change antenna impedance thus it create noise rather than signal strength. Although two antennas can be double stacked to have gain in signal strength and direction (antenna have to be same and pointed in the same direction with single feed line), it work best when antenna is outside and not indoor.

Best solution (for indoor) would to optimize a single antenna for single input, and optimize it. If you are going to use an external wire antenna, disconnect the whip antenna.