Re: secondary harmonic suppre

Hi everyone,
            Richard Craven wrote...

> In a standard helical resonator the device is a quarterwave 
> long and can be link or loop coupled (see the ITT databook 
> for a section). The problem is that such a resonator "throws 
> back" at harmonics by which I mean that a band pass filter, 
> for example, will have good out-of-band attenuation except 
> at harmonics of f (2f particularly so in elliptic designs).
> The point is that there is a technique where the top third 
> of a coil is wound in the opposite direction to the first 
> two thirds. It struck me that it might be interesting to 
> wind a TC resonator such that the top third is reversed. 
> Apparently, if you do this, the harmonic response at 2f and 
> 3f is dramatically suppressed and the first significant 
> harmonic occurs at 4f, by which time the amplitude is well 
> down cf. the fundamental.

I'd be keen to try this when time permits. Is this the folded 
resonator concept you mentioned once?