Topband: Feeding Pennants and Flags

[Earl W Cunningham]

In my last post I forgot to include the information on match a 50- or
75-ohm coax feedline to the antenna.  It is mandatory to properly match
the antenna to the feedline, else results will be disappointing.

To match the 900-ohm feedpoint impedance of the Pennant or Flag to 50- or
75-ohm coax, a transformer may be wound using an Amidon FT140-43 toroid
core.  Two windings on the core are required.  Let's call the winding
that goes to the coax the "primary" and the winding that goes to the
antenna the "secondary".

The primary should be 9 close-spaced turns for either 50- or 75-ohm
feedline.  If you use 50-ohm line, make the secondary 38 close-spaced
turns.  For 75-ohm line the secondary should be 31 close-spaced turns.

To minimize common mode currents, the primary and secondary windings
should be spaced as far from each other as possible, i.e., 180 degrees
from each other on the toroid core.

73, de Earl, K6SE





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