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QMX+ T507 winding direction?

 

In the QMX+ does the polarity of the 10-turn windings on T507 (part of the Fwd/Ref power detector) matter? In the assembly manual the photo looks like they're wound to be mirror images of each other. I wound mine so the turns advance clockwise on both sides.
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Will this cause a problem with RF power measurement? Or worse yet, cause a serious impedance mismatch for the lowpass filters and finals?
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It won’t make any difference. I tested one wound in the same sense and again in the opposite sense and no difference. These are two independent windings. As long as you put the wires in the circuit board hole on the same side of the core where the wire exits, it will work. If you cross the wire under the core and connect to the board hole near the other end of the core you will have problems.?

Ron

On Tue, Apr 8, 2025 at 16:23 Dave WD8CIV via <dhinerman=[email protected]> wrote:
In the QMX+ does the polarity of the 10-turn windings on T507 (part of the Fwd/Ref power detector) matter? In the assembly manual the photo looks like they're wound to be mirror images of each other. I wound mine so the turns advance clockwise on both sides.
?
Will this cause a problem with RF power measurement? Or worse yet, cause a serious impedance mismatch for the lowpass filters and finals?
?
 

Thank you. I wasn't sure if there was interaction in the core between the two windings.
 

There is some small interaction between the two windings on a binocular core which ultimately limits the directivity of the coupler, but it is not at all an issue for the QMX.

I would usually include a URL to Owen Duffy's website at this juncture, but sadly, it was shut down ?

72 de Russ, va3rr
 

Thanks Russ! Fortunately the Internet Archive's "Wayback Machine" has an archive of that page:
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Looks like a handy circuit. I may start using this in other projects.
?
 

On Wed, Apr 9, 2025 at 09:15 AM, va3rr wrote:
There is some small interaction between the two windings on a binocular core which ultimately limits the directivity of the coupler, but it is not at all an issue for the QMX.
I believe that the largest contribution to imperfect directivity is capacitive coupling between the thru and coupled windings, causing VSWR readings to increase at higher frequencies despite having a good termination.
On my list is to find a small-enough miniature coaxial cable and replace the plain wire thru winding with an electrostatically-shielded one.? This should flatten out the VSWR readings be eliminating the capacitive leakage.? IIRC this has been done and reported on this forum.
73, Don N2VGU
 

If you use a binocular toroid isn't there also coupling between the two transformers?

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