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Topband: front to back?

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Subject: Topband: front to back?
From: k6se at (
Date: Sun May 25 17:16:09 2003
While we're on the subject of Flags, Pennants, Deltas, etc.,  some time
ago I received a few e-mails from hams who tested the xfmr wound on the
Amidon FT140-43 core that I recommended in the July 2000 issue of QST. 
With the high-Z winding of the xfmr terminated with a 900-ohm resistor,
they all measured greater than 3:1 SWR across looking into lo-Z winding. 
W7LR found that this was caused by an inductive reactance and he added a
capacitor in series with the high-Z winding to cancel out the reactance
on 160m and was successful in obtaining a low SWR.  Of course, this made
the xfmr a single band unit.

Then along came Luis, IV3PRK who told me that he wound his xfmr on an
Amidon FT114-77 core and that he checked the SWR at 1:1.  Therefore, I
now recommend using the FT114-77 core and, for 50-ohm coax, suggest using
4 turns for the low-Z winding and 17 turns for the high-Z winding (you
might even reduce this to 3 and 13 turns respectively).

73, de Earl, K6SE
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