[R-390] Theory Question - RF Transformer Alignment

[Barry]

> Collins coils are wound in a nonlinear fashion (Variable-Pitch
> Progressive),such that the resonant frequency is linear - exactly proportional
> to core position.  (In tuning caps, this plate profile is called
> Straight Line Frequency.)  Therefore, when you adjust a slug, the
> entire band is shifted without changing its shape.  (This permits
> use of spiral-cut cams; easy to manufacture, and a small error in
> cam angle can be trimmed out by adjusting the core.)
<snip> 
> Dave Wise

That demystifies those cams just a bit, at least for me.  I didn't realize they were spiral.  It makes sense, though, as the PTO is probably wound the same way and its slug position is controlled by a linear movement of PTO's lead-screw.

Thanks,

Barry - N4BUQ