I started with one of these binocular cores simply because it was already on the bench. It's also enjoyable to get something that has no data to work!
Using the braid from a piece of miniature coax cable as a 1 turn winding, I teased two holes in the closed end so I could wind 3 turns through the inside of the coax braid.
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| 1 turn of braid, 3 turns inside braid |
Good for 80m to 10m. What struck me some time later is the improved frequency response of this conventional style transformer compared to the 9:1 transmission line transformers I tested on the same core. This was contrary to my expectations that transmission line transformers had wider bandwidths. If I have learned anything in recent months it's that measurement beats folklore.
I know that compensating caps are used in conventional transformers so I added 18, 22 and 27pF caps in turn across the 50Ω side.
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| Same transformer with different caps shunting 50Ω winding |
The improvement in return loss is clear. I then repeated this on the 5.55Ω side of the transformer. The capacitors ranged from 220pF to 470pF. But these values appeared too large and I was getting inconclusive results.
It appears a convectional transformer can be wound on these binocular cores. However, I need to do some reading on how to select the compensating capacitor values should they be needed.
73's
Richard
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