Ferrite selectivity recordings

jim_kr1s <jkearman@...>

I compared two Hoop Loop matching transformers. One is 5000 uH, wound on an FT114-43 core, with a 100-turn secondary and 6-turn primary (turns ratio = 16.7; tuned inductance = 2350 uH). The other is 6000 uH, wound on an FT140-61 core, with a 200-turn secondary and 12-turn primary (turns ratio = 16.7; tuned inductance = 2550 uH).

The SQT beacon on 257 kHz is in Melbourne, Florida, about 80 miles north; the MTH beacon is on 260 kHz, in Marathon, Florida, about 200 miles south. A line drawn between them passes close to my location, and they both can be heard with the Hoop Loop in the same position. The Hoop Loop was connected to the PL-380 through each transformer in turn. The PL-380 was tuned to 257 kHz and set for 1-kHz selectivity.

Receiver meter readings were 40 25, with slight variations over time, for the -43, and 41 25 for the -61 transformer. With the -43 transformer in place, and the receiver tuned to SQT, MTH can be heard in the background: http://kearman.com/images/dash43.mp3  With the -61 transformer, MTH is only faintly noticeable. http://kearman.com/images/dash61.mp3  The MP3 files are each less than 100 kB.

This is a modest difference. If you're using a PL-360 with fixed 3-kHz DSP selectivity it's probably irrelevant. Given the reported deviations in -43 permeability however, you'd have to measure a transformer wound on a -43 core to confirm it's inductance is as calculated. There is a better chance that you could wind a transformer on a -61 core and end up with an inductance close to the calculated value.

Jim, KR1S

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