Topband: Binocular Xfrmr

kurt-erich.finger at kurt-erich.finger at
Fri Oct 19 02:57:49 EDT 2007

Hello Mike,

for my K9AY I used the version I found in Devoldere's "Low-band DXing" (a recommendation from W8Ji).
I glued 3 BN73-202 together,  and  used 3 turns primary and 1turn secondary ( 500Ohm:50Ohm)
For 500:75 it should be 2.5 turns:1 turn.

For the insulation I didn't used the trick with the straw, but heated a heat shrink tube that was a little to wide until it fit into the holes.

For me the transformer worked fine.

For a comparison of different transformer I also found Mark Conelly's (WA1ION) article "Broadband receiver antenna matching" (2003)  also very usefull. J. Briant's, B.Bowers, N Hall-Patch's "Impedance matching transformer for receiving antennas at mediaum ans lower shortwave frequencies" (2003) also contains a wealth of information.

Good luck


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