Thanks Tam, for the reply.
I am using a T-match, with the driven element NOT insulated at the
center, similar to the T-match used on the M-squared yagis for VHF. I
cannot get a match no matter how much I move the shorting straps on the
T-bars.
Steve

Tarmo Tammaru wrote:
Steve,

Are you doing a T match or a Beta match? I looked at a Hygain 6 m beam, and
the shorting bars are set to 9-1/2 inches from the center. The driven
element is insulated at the center, and the beta rod is connected to the
boom at the center. The coax is connected to the driven element. As I
understand it, in a real T match the coax is connected to the T rod, but it
supposedly does not have as good an adjustment.

Tam/WB2TT
"Steve B." wrote in message
...

I have a 6 meter beam with "plumbers delight" construction. I have not
been successful in making a 1/2 wave coax balun (T-match) get a proper
impedance match at 50.125 MHz center frequency. The driven element is
0.625" Outside diameter. The T-bars have adjustable shorting straps for
a max length of 14", with 3" spacing below the driven element.

The balun is made of RG-142 Teflon-coax, and is 81 inches long. The
velocity factor is 0.695, so the length is:

1/2 WaveLength (meters) = (150 * V)/F where F is in MHz.

Thus, the half-wave coax would be (150*0.695)/50.125 in meters.
Multiply by 39.37 inches per meter to get 81.8 inches for the coax length.

Any ideas why this did not do the job? I checked the coax for
opens/shorts and moved the T-bar shorting straps to no avail. The best
SWR was no better than about 3:1, even after adjusting the length of the
driven element.

I tested the driven element (both by itself and installed on the beam)
mounted on a temporary mast at about 10 feet to avoid most of the ground
effect.

Thanks,
Steve Bell KJ7OG