Topband: Air Wound Coil

[Richard (Rick) Karlquist]

On 8/31/2018 6:09 AM, Jim Thomson wrote:

> 
> ##  Are you sure about this ?   I have used  .25 edge wound rollers, 

I am sure that flat conductors result in lower Q than round conductor.
I have done innumerable Q meter measurements to confirm this.
I didn't say that flat conductors don't work at all.

> ##  I have also tried winding  strap coils  flat, like what you used to 
> see for a 10M  tank coil.
> That works superb for LOW amounts of uh.   Then you can also minimize 
> the spacing between
> adjacent turns.   Typ used on 12-10-6m linear amp tank coils..and 

What matters for inductor optimization is the winding PITCH, IE
the center to center distance between adjacent turns.  In a strap
wound inductor, closing up the gap between the turns, at some point
exacerbates proximity effect and lowers Q.  In any event, making
low value inductors is problematical; there is no way to get the same
Q that you would get at higher values, even if you use round conductors. 
  The only workaround AFAIK is to use 2 inductors in parallel,
each with twice the desired value, oriented so as to not
have much mutual inductance.  Or use a single turn loop, over
a ground plane, to reduce inductance.  Of course the ground plane
decreases Q, so nothing is free.

> ##  I have had nothing but grief  with tubing coils used in roller 

Agreed, edge winding is a necessary evil for roller coils.  But you
do pay for it with a Q reduction.  Now that I have an Rig Expert
AA-55, I find that I can measure the antenna impedance and then
model the design with SimSmith, and finally build the
matching network on the bench with fixed inductors, and
then I don't need roller inductors out at the antenna, because
the matching network works the first time I try it.  Just in case,
I can get a moderate amount of adjustability by using self supporting
coils (with the form removed) and then squeezing or spreading the
turns.  Force 12 sells a motorized "Tornado" coil that does this.


> Jim   VE7RF
> 

73
Rick N6RK