In the last two weeks, I’ve received e-mails from two readers of The No-Nonsense General-Class License Study Guide. Both questioned my explanation of how transformers transform impedance. I wrote:
Transformers are also used to transform impedances. The impedance ratio is also related to the turns ratio, but the transformation is equal to the square of the turns ratio. The turns ratio of a transformer used to match an audio amplifier having a 600-ohm output impedance to a speaker having a 4-ohm impedance is 12.2 to 1. (G5C07)
Doug wrote, “The only way I can reproduce the calculation is by taking the square root of the turns ratio.” His comment made me see where my explanation could be a bit misleading. I wrote back:
Think about it this way. An impedance transformation can go either way. When transforming from a higher impedance to a lower impedance, you divide by the square root of the turns ratio. When transforming a lower impedance to a higher impedance, you multiply by the square of the turns ratio. In either case, the impedance ratio is “related” to the square of the turns ratio.
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Dan, what is a G5C07??? I really enjoy your daily email, read everyone of them and save many to my KB6NU mailbox for future reference! You do a great service to the ham radio community!!! Keep up the great work! cu es 72/73 Bart W0IIT
Thanks for the kind words, Bart. G5C07 is the question designator for this particular question.
this one had be baffled until I realized that it wasn’t 600 that I needed to find the square root of. I needed to divide 600 by 4 to come up with 150 and find the square root of that. then you do come up with the 12 to 1 ratio