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 <n...@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