How did you turn the CB antenna into a 2m whip? Ive got an old mobile CB antenna thats not being used. Did you just put it on and SWR it or what? Id love to know more, it would be brilliant if i could turn the CB into a 2m whip for the bike.
Many of the base-loaded CB antennas are about 1 metre long (often a 36" radiator
on top of a housing with a base loading coil inside.) This makes an excellent half
wave antenna for 2m. Conversion depends on the exact details of the antenna
base - it works best to have some extra room to install components.
The loading coil is often 20 to 30 turns of wire between the antenna and ground,
with the coax feed tapped up perhaps 5 turns of the coil above ground. I removed
the coil from the housing and rewound it to have only 4 or 5 turns total, with the
coax tapped about 1/2 or 3/4 turn up from ground. Then connect a trimmer
capacitor across the coil and tune it for minimum SWR. If it isn't low enough,
move the coax tap by a fraction of a turn and try again. If there isn't room inside
the housing at the antenna base to mount the variable capacitor, you may need
to use a different housing with the whip portion bolted to it. The exact details
are highly dependent on the specific antenna you have to start with, but if the
whip is a bit shorter than 1 metre you should be able to use it as a half wave
antenna with a suitable matching network at the base.