new poster

Hi all.
I'm new to this list, been following for a few days - lots of great
info. here!
I'm a relatively new coiler, with first one under my belt, and next one

I have two questions:
1)Has anyone experimented much with receiving coils? I have a post
concerning them but it only recommended making one the same frequency.
Isn't it possible to make smaller coils/smaller diameter as long as it's
an harmonic of the original coils frequency? It seems I read this in
Tesla's patents. Couldn't it potentially be a 3rd or 4th harmonic of
the  transmitting frequency? Does it work inversely (1/2,1/4, etc)?

2) Can anyone direct me to a program that includes flat spiral
primaries/secondaries? If not, does anyone have the formulas for
inductance, capacitance, freq, etc. for the same? All the programs I've
tried are for helix spiral secondaries, not flat.

Thanks for any info or direction...

Bob V