Hi George,
I would recommend a transmission line transformer from the equal delay family
which exhibits the best wideband response.
A pair of coax cables with 100 (93 close enough for ham work) ohm impedance
wound on a convenient size to wind ferrite cores of u125. Any core that has
space for the turns will be fine for your power level.
The input is connected to the parallel connection of one end of the cables.
The other end of the cables are series connected: One line's shield to the
other's center conductor. The output is taken between the remaining free
center & shield.
Wind enough turns to produce >= 1000 ohms impedance (on the shield) at the
lowest frequency of interest.
It is not necessary to wind the line with its shield at ground potential on
both ends on a core if the impedances are all correct. If it is wound on a
core, then 50 ohm coax may be used in a pinch.
73 & Good morning,
Marv WC6W
-- gdaught6@stanford.edu wrote:
Hi all,
I'm trying to build a 50:200 ohm broadband transformer for the input
of a tetrode amplifier. Sevick's book and Measures' website give
instructions for such a 2.4 inch unun. Sevick says it can handle
over a kW: I only need a 100W job. The ARRL handbook says a 1.5 inch
version will handle over 100W. Does anyone have a "recipe" I could
follow to make such a thing? Requirements are:
a) 50 Ohms to 200 Ohms
b) 3-30MHz
c) low loss (I don't want it heating up and self-destructing)
What core material and what size should I use? What is the best
place to get one (or two) of the cores? What wire and how many turns
should I use?
I readily confess that I'm woefully knowledge-and-understanding-
deprived in this area!
Thanks in advance for any help!
73,George T. Daughters, K6GT
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