2m 70cm 5/8 and 1/4 Wave Ground Plane Antenna Questions

[Wnocall]

Looking at installing a ground plane antenna on a mast for VHF UHF and have a couple questions.
I see the 5/8 wave antennas have a tapped coil for matching (to 50 ohm?), are clamped to the mast, and have horizontal radials on the coax shield side. Are the radials supposed to supply the entire grounding system, or can/should the mast be clamped to a ground system as well for better performance?
Also, how would a 2m 5/8 wave ground plane antenna perform at 70 cm?
The alternative, of course, would be a 2m 1/4 wave ground plane antenna. I notice they have sloping radials and no matching coil is required. Again, to ground or not to ground the mast? I have also heard that a 2m 1/4 wave antenna can be used at 70 cm, is this true?

 

[nd5y]

The radials only provide an RF ground.
Grounding the mast should not affect VHF or UHF antenna performance.
Depending on your location the mast probably must be grounded to meet electrical and building codes.

The matching network on a 2 m 5/8 wave antenna will prevent it from working properly at 70 cm.
Even if the matching network did happen to be good a 49" antenna at 70 cm is about 2 wavelengths long and the radiation pattern will start to behave like a long wire antenna, which means a few degrees each side of the axis of the antenna or straight up if the antenna runs vertically. That would make it nearly useless.

A 2 m 1/4 wave antenna will have relatively low reflected power on 70 cm but the main lobes of the radiation pattern point about 45° up in the air which is not very good in most cases.