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Re: LF: Loop (was Re: IGBT in 136 KHz TX?)

To: [email protected]
Subject: Re: LF: Loop (was Re: IGBT in 136 KHz TX?)
From: John Andrews <[email protected]>
Date: Tue, 21 Jul 2009 20:41:40 -0400
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Ha-Jo,

That's one way to look at it, and a valid approach. But consider another example:
Suppose you have a single-turn loop that has an (arbitrary) impedance of
0.1 +j10 ohms at a frequency of interest, and you desire to make it look
like a 10-turn tuned loop. A 1:10 transformer will provide the same
voltage step-up as a 10-turn loop, and will ideally step the impedance
up by 10^2 = 100, giving you 10 +j1000 ohms. You would then have an
option of series or parallel tuning the loop on either side of the
transformer. The secondary side is much nicer for our use than the
primary side. Parallel tuning would be a good choice into a hi-z input
preamp. Series tuning would leave you with the 10 ohm resistance, which
you could then step up to the characteristic impedance of your line, or
leave at a lower value if BW were an issue.
In the above case, I'd suggest a primary inductance on the transformer
of 5X the magnitude of the loop impedance, but your 4X would probably
do. Leakage reactance is pretty much inevitable, and will throw things
off a bit.
There's all sorts of ways to approach this, depending on your desire for
tuning, etc. But I just wanted to point out that the much simpler single
turn construction can work just as well as multi-turn.
John, W1TAG


[email protected] wrote:
Dear John, LF,

I would like especially to comment on using a one winding loop combined
with a step-up transformer:

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