Dear Yuri, etc:
We have been using 240-61 cores for KW transformers on 160 meters. So, I
would use something like a one inch core, 61 material for 200 watts or so.
Trifilar winding, with 5 to 7 turns of good enamelled copper wire in
parallel. Top of second winding is 22 ohms, and top of third winding is 50
ohms if all three windings are connected in series. If you need 25 ohms,
not 22 ohms, then remove the top turn on the third winding. Then, for
example with 7 turn windings, the windings ration is 20:14, not 21:14, so
the impedance ratio is the square of the winding turns: 400:196 or 50:24.5.
One can also use Iron Powder core - #2 or #6 material with more turns
(+/- 11) for 80 thru 10 meters. One can also use a ferrite core material
with slightly different permeability for higher frequenciencies.
73 George K8GG
----- Original Message -----
From: "Yury VE3XB" <ve3xb@sympatico.ca>
To: <Amps@contesting.com>
Sent: Sunday, May 25, 2003 11:38 AM
Subject: [Amps] 2:1 Transformer
> I want to build a 2:1 transformer for HF frequencies to match 25 ohm
> impedance. I am wondering if anyone can point me to some info on how to
wind
> such transformer - number of turns, where to tap the coil and what
type/size
> of core should I use, say for 100 watts?
>
> Thanks in advance,
>
> Yuri VE3XB
>
>
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