Fm Band Plan 52.02-53.9 Mhz, Center around 52.96??.......
For 50mhz+ it was recommended to use 475/f instead of 468/f
475/52.96 =107.62 inches
(Not counting the k factor since I don't know what diameter of tubing you are using)
so this is somewhere in the ballpark.
You have the driven element at 107 inches, ok then...
If I Remember correctly it was recommended for the director on a Yagi to be 3-5% shorter
and reflector 3-5% longer than the driven element
so at 107 inches would make the driven element
101.65-103.79 inches... Driven element Length (varies slightly with spacing) so far "within the ballpark"
110.21-112.35 Reflector Length (varies slightly with spacing) May be just a tad long But shouldn't hurt anything.
For a 3 element beam I would probably make the boom a 1/2 wavelength and space the elements equally from the Gamma match (about 111 1/2 inches overall)
I forget how much capacitance per meter was recommended for a typical gamma match........(Listed in old ARRL Antenna Books).
I'm pretty sure somebody around here would have one of the old Antenna Books and be able to dig out the recommended capacitance info, along with gamma Length and spacing etc.
How are you adding capacitance to the gamma match? a piece of some kind of material between the inner/outer tube? or are you using a stub of coax in the end? Are you sure it's properly connected to the antenna?
A cheap trick would be to temporarily mount a variable capacitor in a plastic box on the antenna connected
to the gamma rod. After finding the best adjustment, measure the capacitance and replace the capacitor
with a piece of coax. (outer cover and braid removed, inserted into the gamma rod tube)
with enough length to make up the capacitance (capacitance per foot)
For a 3 element beam I would probably make the boom a 1/2 wavelength and space the elements equally (111.48 inches over all) appx 9 ft 4 in.
67 1/2 inches is pretty short .
Last edited by KD8DEY; 06-27-2012 at 09:41 AM.
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