Link coupled tuner configuration

[stevef]

Presuming I have no need for the series configuration in my situation, what are the pros & cons of these two parallel configurations I commonly see?

In version B I often see additional clip leads on the coil ends to short the coil end across the "unused" turns to the capacitor taps.

[WA4WAX]

Dear Steve:

You want A.  That is what W2DU used.  In his case, the coil was a BC-610 coil; the parallel cap was split stator, with rotor grounded.  In my opinion, you could let the rotor float.  The circuit is inherently balanced.

The circuit in A allows you to resonate the coil and pick out a point where the resistive component is close to your feed line impedance.  With the version in B, the point of resonance will not necessarily coincide with impedance desired.

Here is what you can do:  Make a twin lamp reflectometer with a 6 to 10 inch piece of balanced line.  Next, take a decent length same line (10 feet, say) and terminate with a noninductive resistor corresponding to line impedance Zo.  Next, tape reflectometer to line and apply some power.  You will see something interesting: The lamp closest to the load will go out when  you choose the proper tap point.  The lamp closest to the coupler will remain lit.

In each case, you must adjust the input for 50 + j0.  Make sure  the termination resistor is 1) Truly noninductive, and 2) Big enough.

Have fun!

Matt