6 meter yagi help

[KG4WBB]

I am trying to build a 3 element beam for 6 meters but I have not been able to tune it well into the FM part of the band and my SWR remains high. I'm beginning to think that it has something to do with my measurements for the gamma match since all my elements are right according to the plan that I am using. Element length is as followed : Ref = 113 inches ; DE=107 inches; DI= 101 inches. Spacing: Ref to driven =40 inches;driven to director= 27.5 inches. Gamma tube is at 17 inches and inside tube is about 14 inches. Any help would be appreciated and thanks in advance.
KG4WBB

[K9STH]

You are adjusting the gamma match? That is, it is NOT "fixed".

Glen, K9STH

[K8JD]

Is there an insulating sleeve between the inside and outside sliding adjustments?

[4X1SO]

Are you running the antenna in vertical or horizontal polarization? Vertical is recomended for FM but if you use a conductive mast between the elements it will disturb the pattern and tuning. If you do have the mast between the elements turn the antenna to horizontal and see if it is in tune at the desired frequency. Usually a conductive mast at right angles to the elements of a beam will have minimal effect on the tuning or pattern. If the antenna is in tune horizontally, you need to get the conductive mast out of the radiation pattern of the beam. To keep the polarization vertical you might end mount the antenna, which may be difficult with a 6 meter beam, or you could try a wooden or fibreglas mast.

[W8NSI]

I am trying to build a 3 element beam for 6 meters but I have not been able to tune it well into the FM part of the band and my SWR remains high. I'm beginning to think that it has something to do with my measurements for the gamma match since all my elements are right according to the plan that I am using. Element length is as followed : Ref = 113 inches ; DE=107 inches; DI= 101 inches. Spacing: Ref to driven =40 inches;driven to director= 27.5 inches. Gamma tube is at 17 inches and inside tube is about 14 inches. Any help would be appreciated and thanks in advance.
KG4WBB

Here is a 3 element six meter antenna that looks like it should be a snap to build:

https://sites.google.com/site/wb3bel/3elHex.pdf

[VK4TI]

I am trying to build a 3 element beam for 6 meters but I have not been able to tune it well into the FM part of the band and my SWR remains high. I'm beginning to think that it has something to do with my measurements for the gamma match since all my elements are right according to the plan that I am using. Element length is as followed : Ref = 113 inches ; DE=107 inches; DI= 101 inches. Spacing: Ref to driven =40 inches;driven to director= 27.5 inches. Gamma tube is at 17 inches and inside tube is about 14 inches. Any help would be appreciated and thanks in advance.
KG4WBB

http://www.hamuniverse.com/n2kbk6meterantennas.html offers a guide, remember stand the bean on a chair pointing vertically , slid the shorting bar around looking for a dip and then the outer tube slid until flat , you will an excellent reponse with the unit

[KD8DEY]

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

so
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 .