Topband: Homebrew Hairpin

[Paul Christensen]

> 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