I have an appliation where i need to mount a multiband (VHF/UHF/700/800/900 MHZ) mobile antenna (picture 2) on a tower. The spec sheet for the antenna says it used a 4 foot diameter ground plane for testing. I'm considering using a mobile to base converson kit like the one in the picture with a radial ground plane or counterpoise. My question is on the size I need.
From the way I thought I understand the theory, the radials act as a reflective ground, and should be at least 1/4 wavelenth of the antenna frequency. So is there a situation where the radials would be too long?
I'm thinking I should use radials that are 1/4 wave length of the VHF frequency, and that the extra length when operating at the UHF and higher frequencies would not negitivly impact operation. Is my reasoning correct?
Also, will I need some sort of balun?