What does 5/8 wave mean? Should I get a new base antenna?

[Jhernan488]

So currently I have a dual band 2m 3/8 wave and 70cm 1/4 + 5/8 wave. What do
I need to know about this? What are the differences in the wave?

I currently mount that antenna out side with a mag mount on my window ac unit. (Due to owners not wanting any antenna mounted on the roof) I do currently get a great SWR 1.1 to about 2.0 reading with that antenna on the ac unit. The current antenna is about 20 inches long. I was thinking of getting another tram 1180 5/8 wave with a NMO mag mount. The same antenna I have on my car.

 

[a417]

5/8 means the antenna will be 5/8ths of the wavelength in length. The lower the frequency, the faster they get longer and longer. As you change the wavelength that the antenna is tuned for, you will also change the emission lobe shape and affect gain towards the horizon.

I think your biggest limitation right now is the mag-mount actually being on an AC unit. Big ol' hunk of ferrous metal and spinning magnets I think would effect your efficiency...

 

[W5lz]

a417 pretty well explained it. Antennas can be classified by their length, which is a fraction of the full wave length of the frequency of use. The various 'sizes' of antennas have different radiation patterns, some more desirable than others depending on the circumstances. That 1/4 wave should be usable for you with no problems. That means you have to provide the metal the magnet sticks to, as in that A/C, a car, whatever. Naturally, if that antenna and A/C was 40 feet higher the antenna would 'hear' more. (Don't know about moving the A/C though.) A 5/8 wave antenna -may- hear more than the 1/4 wave if it's mounted in the same place, maybe. If you want to try it and see, why not? Don't expect huge differences though.

 

[jaspence]

Also don't expect much if you are using a repeater. The 5/8 will give you a little gain in simplex operation but will do nothing better if you can already get full quieting from the repeater. If you are trying to hit repeaters farther away, the 5/8 can help, but your height disadvantage and mounting limits the ability to do much better. I use a quarter wave dual band mag mount running 10 watts on 2 meters on a wire rack in a closet and get full quieting using 3 repeaters that are about 4-5 miles away.

 

[KK4JUG]

Also don't expect much if you are using a repeater. The 5/8 will give you a little gain in simplex operation but will do nothing better if you can already get full quieting from the repeater. If you are trying to hit repeaters farther away, the 5/8 can help, but your height disadvantage and mounting limits the ability to do much better. I use a quarter wave dual band mag mount running 10 watts on 2 meters on a wire rack in a closet and get full quieting using 3 repeaters that are about 4-5 miles away.

Is the antenna sitting on the wire rack or are you using the wire rack as an antenna? ☺

 

[jaspence]

The wire rack is used for the same purpose as the roof of a car would serve. I also have an Ed Fong dual band antenna on a flag pole (no towers allowed in the plat) in the back of my house for my shack in the basement. It works very well and I have an all mode 2 meter Icom and a dual band Yaesu hooked up to it. Ed's Antennas