[TowerTalk] Quad question

[John King]

I am about to install a two element "pretuned" commercially manufactured  2 element cubical quad on a fixed tower and would like to know it is tuned before it goes up the tower. I am dubious about "pretuned" quads. 

I plan to use my antenna analyzer to check resonant freq and SWR while it is near the ground.

Anyone have an idea how much the resonant freq will change from ground level to final height of 72 feet?

Also if the SWR is low enough to be acceptable will that mean that the reflector on 8 foot boom is also in the ballpark for front to back? I realize that the maximum forward gain and maximum front to back does not occur at the same setting. However there is an adjustment that will give close on both measurements. Will the SWR be an indicator of the best ballpark setting? 

Please share information based upon experience with quad antennas if you have had such experience. Thanks and 73, John, K5PGW