On Mon, 8 Jul 2002, Jim wrote:

>10 - 20 MHz?
>
>Ouch!
>
>I've got directional couplers that are 'effective'
>as low as 100 MHz - amd as most of my work in
>the past has dealt with this range I've been
>okay.
>
>I've got some on-going work (a filter) in the range
>of .5  to 5 MHz right now.
>
>I am able to measure S21 (Insertion Loss) using a
>spectrum analyzer and signal generator, but shortly
>I've got to measure S11 (Return Loss or 'VSWR')
>as well.
>
>I'm going to use a crude 'bridge' in combination with
>a dual-trace scope or a Vector Voltmeter to accomplish
>this in a round-about fashion (measure complex Z and
>then compute the Return Loss/S11).
>
>http://www.dallas.net/~jvpoll/tech/ph_mag.html

Try to make a bifilar wound directional coupler on a toroid or
snap-together ferrite transformer for 5MHz. It will very likely work for
you. 30 turns at 5MHz would be too much I think. Surely you have a core
like this in the junkbox.

Peter

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