With the success testing 4:1 transformers I examined some 9:1 transformers. A trifilar winding, being a bit thicker than a bifilar winding using the same gauge wire, proved difficult with the small cores previously used. I wondered how a single winding through 10 of these cores would perform. I passed a single trifilar winding through 10 turns, arranged them into a U or long binocular shape, and secured them with piece of heatshrink.
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| 1 trifilar turn through 10 cores |
Note the Smith chart response is curving away from the 50Ω origin upwards and to the right. This is the same with a bifilar winding.
Returning to the test results here is the sweep of S11:
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| 1 trifilar turn through 10 cores |
Very useful from 160m to 30m applications and so easy to wind. Just one turn. But it looked a bit cumbersome and not as broad as I had hoped. So I tried two turns through 6 cores. This was better but still didn't improve the upper frequency. So I tried 4 turns through 4 cores.
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| Comparing 1t 10cores v 2t 6cores v 4t 4 cores |
Clearly 4 turns through 4 cores is a better transformer, and would handle the 1W I intend to push through it at 80m. However, not as broadband as I had hoped given the success I had with 50:12.5Ω transfomres using these core.
At present these transformers are destined to be used in the 10W Class AB amplifier for 80m I am planing to drive with the 1W Class A amp I have developed. It will be interesting to see if they handle the power.
Overall, these tiny cores are a useful part. I certainly consider them useful for 4:1 transformers but trifilar windings are more time consuming to wind and solder.
73's
Richard
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