I have a flat-top T transmit antenna as well. I modeled it with EZNEC,
found its feed resistance/reactance, fed these into a L-match program.
I'm another fan of the TLW program. After modeling a "T" design for N4NN
using NEC 4.2, the antenna was constructed and then measured with a vector
network analyzer. We input the measured base Z result into TLW and
instantly had our low-pass L design. I had first opted for a lower loss,
high-pass L, but due to the resulting Z values, only a low-pass version of
the L could be constructed, although we could have just as easily designed a
T or Pi network. Since a targeted phase shift value wasn't required through
the network, the L was adequate.
From the TLW values, we then used a Sencore LC102 impedance analyzer to dial
in the exact L and C network values. The SWR at 1825 kHz was 1:1 and no
experimental tuning was needed. It's great when a plan falls together to
the point where no adjustment is necessary - and TLW was a big part in
making that happen.
Paul, W9AC
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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