At 03:27 PM 2/10/1999 +0000, Mike Lamb wrote:
>Hello Pete,
>
>Yes, you are quite right if you are operating only on one band. I use my
coax
>for feeding a triband stack and it needs to be flat across that portion of
the
>spectrum. Parenthetically, I had a devil of a time getting a respectable SWR
>with my stack last summer after 3 years of no maintenance. I finally had to
>just make everything flat to 50 ohms with UNUNs, etc. and it finally started
>behaving. Before, I just went direct from 50 to 75 ohms and vice versa.
That
>introduced all kinds of strange impedances back in the shack at different
>frequencies.
Well, a 6-high tribander stack isn't THAT common ;^}
There is no reason I know of why a stack shouldn't behave just fine on the
end of a half-wave multiple of 75-ohm. It would be interesting to work
through the transformations that actually happen when the terminating
impedance is reactive to the extent that a stack might be. I just know
that in my case, I'm feeding everything through a length of 75-ohm
carefully pruned to be a half-wave multiple at 28100 kHz -- including an
80-meter array, a 2-element 40, and a C-3. The SWR curves are essentially
the same in my shack as they are at the antenna switch at the bottom of the
tower, where the 50-ohm feedlines start.
73, Pete N4ZR
Loud is good
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