[Elecraft] Why no doping of torroids in Elecraft kits?

[Don Wilhelm]

John,
Most of the toroids (maybe all) used in the K1 and K2 are in bandpass
filters or as broadband RF transformers, so there is no need to spread or
compress the windings when aligning.  Yes, some designs use toroids in RF
frequency determining circuits which must be peaked for best performance,
but the Elecraft design has avoided that.

Compressing or spreading the turns on a toroid only changes the inductance
by a very small bit - the inductance is mainly a function of the number of
turns for any given core material as long as the turns occupy a large
percentage of the core area (length?) - quite different than a solenoid
coil.  What does change substantially is the self capacitance of the
winding - and if a measuring device uses any kind of resonance condition to
measure inductance it can be fooled into thinking that the inductance has
changed when the turns spacing is changed - inductance meters that use the
time constant principle are better behaved in this regard.

I do recall seeing some tests of different materials used for 'fixing'
toroid coil turns and comparing the resultant Q.  If my memory is correct,
Q-dope and clear fingernail polish had negligible effect as did beeswax, but
the messy stuff like silicone rubber did drop the Q significantly.  Sorry,
but I can't recall the source of this info.

73,
Don Wilhelm  - Wake Forest, NC   W3FPR home page: http://www.qsl.net/w3fpr/
  QRP-L # 485   K2  SN 0020   mailto: w3fpr@arrl.net

----- Original Message -----

> I was wondering if their is a specific purpose that the manuals for some
> kits (including the K1) recommend against applying dope (nail polish, etc)
> to the torroidal inductors and transformers. Sometimes to align a
> transceiver or to acheive its rated RF output, the windings of the coils
> must be spread or compressed. To prevent the windings from returning to
> their previous position, I've always given them a thin coat of clear
> fingernail polish and had never heard of a reason not to do this as the
> coil's inductance reurns to its previous value once the polish dries. Just
> wondering why Elecraft has a different "take" on this?
>