This is exactly what I've done since moving here in 2006. In NEC, I
tweaked the length of the horizontal top of the Tee to achieve that 50
+jX value at the center of my operating range, computed the series C
value to tune out that jX, then added parallel caps with low values of
series R to hit that value. The same technique would be used for an L.
73, Jim K9YC
On 1/7/2020 11:06 AM, Paul Christensen wrote:
My 160m T is 100 ft high with an 80 ft. flat top. Next season, the flat-top
will increase to 120 ft. where RF current magnitude is uniform across the
entire radiator length with a slight current peak half-way up.
I initially selected an 80 ft top because it made matching super easy. The
base Z is 50+j200 and only requires a series capacitor to achieve a 1:1 SWR.
The series cap will be replaced by a low-pass L network as the R value is
expected to rise up to about 65 ohms. Resonance presently occurs at 1500 kHz
but will shift down to 1400 kHz when the flat-top length increases. Easy to
match with a low-pass L network.
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