RadioBanter - View Single Post

September 16th 03, 06:02 AM

(Richard Harrison) wrote in message

The 12-inch rods are capacitance loading used to improve current
distribution in the vertical radiator and to reduce its required length
at resonance.

They do operate that way I suppose, but the makers always used to
advertise them as "static hats". Supposably reduces static buildup and
noise. About the same principal as a round ball. Dunno how well they
actually work, but I think they are a little quieter than one with a
sharp tip. Being the antenna is an appx 5/8 wave in total length, the
difference in current distribution should be pretty small. Max current
is already higher than the halfway point even with a straight
radiator. Seems that max current point would still be the same appx
height from the base, hat or not.
Does make the antenna a foot shorter, probably with very little
reduction in performance. But, I don't think the original designers
had capacitive loading in mind when they stuck those on there. :/ A
full size "all vertical" 5/8 should be better than any loaded one.
Most CB 5/8's are on the shorter end of being a 5/8. This actually
makes sense for an antenna used for mainly ground/space wave. You
usually get a cleaner pattern with less high angle radiation with a
shorter 5/8 rather than a longer one. IE: .60-.62 wave vs .64 wave or
longer. .64 wave is the maximum gain point in theory, but not always
the best length for the real world. Most AM-BC's also prefer a shorter
5/8 for the same reasons, as I'm sure you know . I modeled this once.
I forgot the length for best pattern, but it was .62 wave or slightly
less I think. MK