Pete,
You're correct on the turns ratio: the impedance ratio is the square of the
turns ratio. I'm wondering whether you are considering that one turn on a
binocular core is actually one pass through both holes. There's a photo
clearly showing this at
http://www.w0btu.com/Beverage_antennas.html#Beverage_Antenna_Transformerson
the right side of that page.
For a 4:1 transformer, I use two turns (four passes) for the 75 ohm winding
and four turns (8 passes) for the 300 ohm winding.
You can download a PDF (http://www.w0btu.com/Binocular_core_turns_ratios.pdf)
of the turns ratios I use from
http://www.w0btu.com/buy_beverage_antennas.html . I think if you try and
download the PDF directly from here, you'll get an error.
I assume you are using a BN-73-202 core?
73, Mike
www.w0btu.com
On Sun, Mar 24, 2013 at 2:48 PM, Pete Smith N4ZR <n4zr@contesting.com>wrote:
>
> I'm trying to wind a binoocular core matching transformer for 75-ohm coax
> to a BOG with (for a start) 270 ohms of terminating resistance. I figure
> that is a 4:1 stepdown, which should require a turns ratio of 2:1.
> Initially I wound a #73 core with identical windings, 3 passes each.
>
> I put this on the output of my MFJ-259 with a 270-ohm resistance on the
> secondary. To my surprise the MFJ read 135 ohms, not 270 as I would have
> expected. Is this not appropriate as a way of measuring the transformer?
> Should I just go ahead and wind 2:1, and if so, how many turns/passes are
> appropriate for 160M?
>
All good topband ops know fine whiskey is a daylight beverage.
_________________
Topband Reflector
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