1/4 wave unity antenna

[_Jerry_]

I don't know a lot of antenna terms like 1/4 wave and unity. But would this be a good scanner antenna from vhf-800mhz?

http://www.antenex.com/index051206.htm

 

[gcgrotz]

An antenna that is 1/4 wave is resonant on a single narrow frequency range, typically +/- 3 Mhz at VHF 155 MHz, it requires a ground plane, or "image" under it to work properly - like your car's roof. Unity means it has no gain relative to some other type antenna; typically a 1/4 wave or sometimes it is referenced to a theoretical antenna that radiates equally in all directions like a sphere. In that case a 1/4 wave does have gain.

Any antenna outside your vehicle will work better than the one on the scanner, but a better choice would be something designed for scanners. Do a lot of reading here in the antenna pages, and read through the wiki here. You will find that everybody has a favorite. Multi-band Ham antennas work well, and I have used old 800 MHz cellular magnet mounts quite successfully.

Just keep reading all you can find. There is a lot of free info on antennas.

 

[NAVCAN]

Unity gain antennas have 0 gain, or amplification, and are usually omni-directional. In other words, it is going to be sensitive to signals in the same way in all directions.

1/4 wave simply means that the antenna is electrically 1/4 of the length of 1 full, 360 degree sine wave at whichever frequency.

Basic math shows that at 1/4 of a wavelength, the engergy (voltage) is at it's peak, and the antenna will output the most signal.