Tuning a folded Dipole?
 

Hi.
Well sort of - its a 5 element yagi with the driven element being a folded
dipole.
I have two questions, one, I need to tune it higher in the (2m) band and as
I have never used a folded dipole before, I am not sure how to go about
tuning it, but I would think I just need to shorten the dipole a fraction?
(untill I get the best swr)
Second question - how do I optimise the length of the feedline ?(quarter or
half wavelengths) as it seems to have a marked affect on the swr of the
antenna.
I am inclined to replace it with a halfwave dipole and just feed it with a
gamma match.
Thanks for any help
73
Mark - ZL3VML

Well sort of - its a 5 element yagi with the driven element being a folded
dipole.
I have two questions, one, I need to tune it higher in the (2m) band and
as
I have never used a folded dipole before, I am not sure how to go about
tuning it, but I would think I just need to shorten the dipole a fraction?
(untill I get the best swr)
Second question - how do I optimise the length of the feedline ?(quarter
or
half wavelengths) as it seems to have a marked affect on the swr of the
antenna.

If the antenna was designed for the lower portion of the band and you are
moving it higher, you will need to adjust the lengths of all the elements.
Not so much as for swr but for the gain and patern.
YOu adjust the dipole by shorten it. If the swr changes due to the
feedline length the antenna needs adjusting. As well known the swr at the
antenna is the same but the length of feedline will have some effect. To
get the impedance to match at the antenna use a 1/2 wave length of feed line
betweent the antenna and the swr meter.