Solarcon 99 or 2000 ?

[JAF0]

isolating the 500 (with it's ground elements) from the metal mast and then grounding it by the braid of the coax shield negates most any (possible) benefit of isolating it from ground/mast .... i'd connect straight to the pipe and put the pipe a few feet in the ground or bolt heavy gauge wire to the bottom of the pipe going to a ground rod for max ground effect . the 500 has a proper ground plane and isn't typically prone to creating CMC's like 99/2000's can .

if you're not comfortable soldering 259's onto coax use what ever length you have that's long enough and make the slack into a bow-tie . if you are comfortable soldering and like splitting hairs use a multiple of the electrical wavelength of what ever coax you're using for your center frequency .

Booty I was referring to RF isolation, not DC isolation.

You want DC grounding, coax shield to real Earth ground for a static bleed-off path, and to help your radio's noise blanker & ANL work it's best, but you want total RF isolation if possible, at the antenna in order to maintain the best pattern & least RFI.

The 5T x 4.25" choke wound right below the 5/8's radials & coax connector, and around the fiberglass "mast top", will isolate any RF coupling on the shield from propagating down the coax, though DC grounding will still occur all the way up to the radials from Earth ground.