1/4 wave ground plane

[brizzotheizzo]

I'm building a 1/4 wave ground plane centered on 120mhz. All of the antenna calculators that I have used do not take into account velocity factor of feed cable. I'm using 15 foot of feet cable with the velocity factor of 80%. Should I go ahead and shorten my 1/4 wave results from my calculator by 20% to account for vf ?

 

[mmckenna]

No. If you construct your antenna correctly, the feed line has nothing to do with the resonance of the antenna.

 

[brizzotheizzo]

I guess I was confusing factoring velocity factor for a collinear antenna made of coax last with with my current project of the 1/4 wave ground plane. Thanks.

I understand that the feed line will no be an issue in terms of vF and antenna wavelength, but what about the copper wire actually used in the antenna? Bare copper wire has a velocity factor of 96%. This makes about an inch for 1/4 wave length at 120mhz. Should I cut an inch off the antenna length?

 

[NC1]

I agree with mmckenna. Make the antenna using the formulas and there should be no problem at all.

If you really want a little more explanation, read through the below link. Mostly it's about antenna length but further down it does touch on the topic of velocity factor.

united states - Calculating Antenna Length on the FCC Exam vs. in Reality - Amateur Radio Stack Exchange

Good luck.

 

[wyShack]

The common formula for a 1/4 wave of 234/(frequency in MHZ=length in feet actually includes a velocity factor of 95%-close enough to most materials used for antenna building. After you build a few, you quickly find that the effect of nearby objects and other factors make the formula a starting point -a little trimming (and checking with an analyzer) is the finial step.