Newsgroups: rec.audio.tech
Subject: Re: Question about antennas
References: 
Nathan Gutman  writes:

> I have a JVC MX-J50. The FM antenna seems to be just a piece a wire. I
> would like to listen to a local FM station on 90.5 MHz. This station
> is hard to receive. When I touch the wire to reposition it the station
> comes in clearly as soon as I let go of the wire it disappears.

When you touch the antenna, your presence there has considerable 
effect on the antenna operation, and when you let go that effect 
dissappears. The effect that you can have to the antenna is 
chage it's tuning by the your capacitance, you acting as extra 
part of antenna picking more signal or you acting as some 
kind of reflector that reflects more signal to antenna..
Dpending your position, reeivign conditions and antenna design 
you touchign the antenna can make th reception consierably 
worse or better. 

> Can someone patiently explain to me all that and how to get to work.
> What kind of indoor antenna can I make or buy to get this station?


The FM dipole antenna is economical and relatively simple to install, 
whilst offering a considerable increase in reception quality compared 
to "just a piece of wire" antennas. You just hang this kind of 
dipole to your wall or window, etc..

The best quality FM radio receiver system for weak stations 
consists of a directional FM antenna, permanently erected externally 
and pointing to the FM station transmitter you want to listen to.
This kind of FM antenna is very much like a VHF television antenna, 
just sligtly different in the constrution (optimized for FM band 
operation instead of TV channel frequencies). 


Some links on the topics:

FM Antennas
http://www.abc.net.au/reception/radio/fm_antenna.htm

FM Dipole for 88-108 MHz
http://www.northcountryradio.com/Articles/fmdip.htm

AXIS 7945 FM Dipole Antenna 
http://electrogalaxy.dtopinc.com/index.html?object=an85001

FM DIPOLE ANTENNA
http://www.ecreso.com/uk/docs/D_DLBFM5_uk.pdf


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/