1/4 wave vs. 5/8 wave ...help choosing

eboe · Post by **eboe** » Mon Sep 06, 2004 5:52 pm

i'm looking at the antenex model #b4503. it's a 5/8 wave +3db with a freq range of 450-470 and an overall height of 13". i operate on frequency pairs such as 451/456, 461/466, 464/469. 467 Mhz also with no repeater. my question is about the tuning. i'm guessing i should tune the antenna to somewhere around 460 Mhz? and would there be any gain on the upper and lower end of the freq range or would i be better off with a 1/4 wave unity for this set of frequencies?

1motoman · Post by **1motoman** » Mon Sep 06, 2004 6:24 pm

It depends on the band width of the antenna.

The antennas are designed to work at any point in the range of frequencies it is made for, the wider the band width, the more frequencies it will work well on.

As you get further away from it resonant frequencie, the worst will be the match and as a result, it will be less effecient .

A 1/4 wave has less gain because you are radiating a lot of the signal up, not out, where it can be used.

nmfire10 · Post by **nmfire10** » Mon Sep 06, 2004 6:29 pm

What kind of terrain are you dealing with? Sometimes a 1/4 wave is actually better at getting up an over steep hills, tall buildings, etc.

450-460 though, a 3dB gain antenna should have no problem covering all of that.

Max-trac · Post by **Max-trac** » Mon Sep 06, 2004 7:00 pm

Hills and dales, 1/4 wave is better;
Parked on top of a hill working a line of site repeater, 1/2 or 5/8 gainer is better....
You can see, it is not that critical.....

eboe · Post by **eboe** » Wed Sep 08, 2004 8:01 am

yeah, i found a VSWR chart for the antenna i was looking at and it looks like they drop off pretty quick once you get off-center of the 'tuned' frequency. unless somebody knows of a nice wide-bandwidth hi-gain antenna, i guess i'll just stick with a 1/4 wave.