[TowerTalk] Flag Antenna Transformer

Doug Ronald doug at dougronald.com
Wed Feb 1 13:58:06 PST 2012

You are getting these results because you wound a conventional transformer
where a Transmission Line Transformer (TLT) is required. The core is fine,
but twist the primary with the secondary using 12 turns and 3 turns. Here is
a reference to some theory on what you need:


and the author (Chris Trask) has several other TLT articles on his web site
including precise winding tips.

Here is another helpful link to the way your finished transformer should


Hope that helps,

-Doug, AE6SY


> I have a flag antenna which has worked well for several years. I used a
Minicircuits T16-6 transformer to couple the ~800 ohm termination resistance
of the antenna to 50 ohm line. Recently I decided to do some upgrades, so I
followed the recommendations of many (here and elsewhere) and made a
matching transformer using an FT-140-43 core and 34:8 turns, secondary and
primary on opposite sides of the core. I didn't have any #28 wire so I used
#24. I tested this with a miniVNA, terminating the antenna side with an 800
ohm noninductive resistor. The impedance does not look right at all; there
is a lot of inductive reactance and the resistive part starts at 125 ohms
and climbs steeply from 1.7 MHz. No on-the-air results yet.


I'm wondering if this is right or not - measurements indicate the DIY
transformer is much worse than the T16-6 in terms of presenting a good


This would not be the first case of theory saying it won't work but practice
says it will - just looking for a reality check here. Seems to me like the
core material is all wrong...


-Tony, K1KP


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