Axiom Home Page Forums General Discussion Technical Questions FM Antenna

I have been playing with my receiver lately and last night was setting all the FM presets. I have a question about the antenna. The receiver is a Yamaha and the FM Antenna is just a wire about 3 ft long that plugs into the back. Question is - if I took some copper wire of the same gauge and spliced it to the end of the wire to lengthen would that work or have any positive affect? My set up is in the bonus room over the garage with a small storage/crawl space directly behind. I figured I could run the wire through the wall and into the crawl space and create a crossing pattern inside the crawl space in an attempt to tune stations better. Is this a waste of time/overkill?.......Rob

Hi Argon,

Rather than the fairly primitive length of wire, you might want to consider making a T-shaped dipole antenna, which will give you a bit more selectivity if you are able to position it so it rejects stations you don't want and receives stations that you do want. (A dipole FM antenna rejects signals in two directions and favors signals in the other two directions.) Also, running bare wire into your wall may pick up hum and interference from the AC wiring in your walls.

An alternative is a variation on the old TV "rabbit ears" type of antenna, which you can easily rotate to or shorten or lengthen the telescoping arms to favor one station over another. It is also a dipole but it's less cumbersome than the T-shaped piece of wire.

Dipole antennas are really only effective for strong local FM reception--about 15 miles or less from the transmitter. Anything beyond 20 miles, you're into "fringe" reception, and you'd need to consider some type of RV antenna or FM yagi in the attic of your house or on your roof.

Check out Radio Shack and other souces for various types. There are some small, rotatable attractive dipole-type antennas made by Terk, meant to sit on a shelf, although in my experience, they are only effective for fairly strong local urban reception.

Regards,

Alan

The length of the antenna serves to make it couple more readily with a specific electromagnetic frequency. Making an antenna longer will effectively "tune" it to a lower frequency, and thus lower its efficiency of selecting the FM band out of the air.

The ideal length of an antenna is for it to be a multiple of the wavelength which you are trying to receive. The wavelength can be found by dividing the speed of light by the frequency. The center of the FM band is 98 MHz, so C / 98 MHz ~= 3m.

Thanks, guys. I knew someone would know more than me on the topic........Rob

I believe Monster sells a snake oil antenna at $100 a foot, might want to check that out

Rob, as Chris pointed out, the length of an FM antenna should be a multiple of the FM wavelength. The wavelength at the middle of the FM band is about 10 feet. For a single wire antenna to work best(but still not all that great)a half-wavelength length, i.e., about 5 feet, is usually suggested. So if you happen to have some copper wire around, you might twist a couple more feet on to the end of the present wire to see if it makes any difference.

But so much for theory. For the real world you have to study this survey from the Berkeley boys.

Jesus mount? Leave it to the Berkeley boys...

Ok....I'm convinced. I will just buy and IPOD dock. I hate to miss out on all the commercials though.....

There are many ways to build a better antenna and scale it to an indoor verses outdoor model. Here is a decent article on a very simplified design. Pictures are crappy but hopefully effective. There are probably better write ups but I built a successful one with these notes and a bit of searching to find the correct ratio already explained in the posts above.

DIY antenna

Like audio, you can get overly complex depending on what you want the end product to look like.

Thanks, Murph. A quick scan of the article tells me that the antenna that I was imagining isn't that far off from ones that are listed. I will read it more closely when I get home.......Argon