On 2/24/2018 10:49 AM, Riki, K7NJ wrote:
My main concern with using 600 ohm OWL is the insertion loss for the two 50
to 600 ohm baluns. From what I've read, transformers with 3:1 or 4:1 turns
ratio (for 450 ohm or 800 ohm OWL) have negligible magnetic flux flowing in
the core, which doesn't seem to be true for a 50 to 600 ohm transformer.
Therefore, it appears that a 50 to 600 ohm balun would have more loss than
either a 50 ohm to 450 ohm or a 50 ohm to 800 ohm balun of similar
Comments, and especially information about proven designs for 50
to 600 ohm baluns would be greatly appreciated.
73, Riki, K7NJ
No problem! If you use a 7:2 turns ratio, you get a 12.25:1 impedance
ratio meaning 50 ohms converts to 612.5 ohms, which is only 2% more than
600. Since you're making your own line, you can simply increase the
spacing slightly to get it up to 612.5 ohms.
For ideas on how to make a 7:2 transformer, study 3:2 (2.25 to 1
impedance) transformer designs.
Another possibility is a 11:3 turns ratio, and 672 ohm line. This
lends itself to a balanced autotransformer design because
4+3+4=11. You drive the center 3 turns out of the 11 turns.
This would be similar to my 50 ohm to 450 ohm balanced autotransformer
where I drive the center 3 turns out of the 9 turns. I think
that design would work by simply adding the extra turns.
The line to line spacing has to be increased by a factor of 1.8 to
get to 672 ohms, so that may be an issue for you. With 10 AWG wire,
you would be looking at 13.5 inch spacing, vs 7.5 inch for 600 ohms,
vs 40 inches for 800 ohms.
73
Rick N6RK
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