what's the formula to build an antenna?

[kc7jty]

I want to build a 3/4 wave ground plane for 444 meg using an so-239 connector.
There seem to be different formulas, meaning a copper wire antenna isn't necessarily the same length as the radio wave in free space, or is it air...ether, or liquid nitrogen?
My back hurts too much to spend hours looking all that crap up.

18.973" & 6.324"?

[N2CHX]

I want to build a 3/4 wave ground plane for 444 meg using an so-239 connector.
There seem to be different formulas, meaning a copper wire antenna isn't necessarily the same length as the radio wave in free space, or is it air...ether, or liquid nitrogen?
My back hurts too much to spend hours looking all that crap up.

18.973" & 6.324"?

The only advantage I can see of using a 3/4 wave antenna at 440 mHz is the fact that you can also use it as a 1/4 wave for 2m. The 1/4 will actually perform better than the 3/4 unless you're in a valley trying to talk to someone high up on a hill (I guess it might work better if you have repeaters at high elevations).

Anyway, yeah, about 19" depending on exactly what freq. Don't even try to calculate it exactly. Build it long and cut it down to size by checking your reflected power as you trim it. All sorts of factors are going to change what the exact length will be, from the ground plane you're using to nearby objects and even the quality and length of your coax.

[kb2vxa]

"The 1/4 will actually perform better than the 3/4 unless you're in a valley trying to talk to someone high up on a hill..."

Isn't it the other way round Kelli? The longer antenna has a lower vertical takeoff angle which gives it somewhat more gain by firing off more signal out to the horizon. As for the coax, measure the SWR at the antenna when pruning so that it's properly resonant, then worry about the coax. Actually the true SWR won't change unless there's a lumped impedance somewhere along the line, pruning it only fools the meter by changing the phase angle as does a tuner. Now do I have to teach engineering to an engineer? (;->)

[KG4CGC]

I always thought it was the thetons present at the angle of incidence in the ground plane.

[kc7jty]

& I thought the longer the radiator the better.

[N2CHX]

"The 1/4 will actually perform better than the 3/4 unless you're in a valley trying to talk to someone high up on a hill..."

Isn't it the other way round Kelli? The longer antenna has a lower vertical takeoff angle which gives it somewhat more gain by firing off more signal out to the horizon. As for the coax, measure the SWR at the antenna when pruning so that it's properly resonant, then worry about the coax. Actually the true SWR won't change unless there's a lumped impedance somewhere along the line, pruning it only fools the meter by changing the phase angle as does a tuner. Now do I have to teach engineering to an engineer? (;->)

Model it. A 3/4 wave antenna actually has a higher angle of radiation than a 1/4 wave at 440 mHz. Much higher.

[kc7jty]

no chit! so much for more wire in the air giving higher gain.
Should I bend the 4 radials down on a 45 degree angle like the 2 meter version of the so-239 connector antenna?

[kc7jty]

This one is going onto the Zed...get the popcorn.

[N5RLR]

...Should I bend the 4 radials down on a 45 degree angle like the 2 meter version of the SO-239 connector antenna?

Yes. With horizontal ground radials it'll present roughly 30? at the feedpoint. Bending them to 45º will raise this to 50?. :geek