[TowerTalk] Solenoid or Binocular configuration?

[K8RI]

On 10/21/2012 6:09 PM, Jim Brown wrote:
> On 10/20/2012 7:23 PM, K8RI wrote:
>> My question is about the difference between the 6 cores stacked or two
>> stacks side by side.
>
> For a ferrite choke with close-spaced turns, it does not matter if he
> cores are together or separated. What matters is the number of turns and
> the number of cores.  The inductance increases with the square of the
> number of turns, and in proportion to the number of cores. The
> capacitance increases with the number of turns and with close spacing.
> What you want is the lowest practical resonant frequency, and you can
> use the measured data in my RFI tutorial as a guide.  So for the lowest
> possible resonant frequency you want more turns and more cores, tightly
> spaced.

Thanks Jim,

It's pretty much what I figured. I actually super glue the cores into a 
stack. Just 4 tiny dots of glue and then pressure for about a minute.
 From the tutorial I figured 6 cores in a stack with about 9 or 10 turns 
of RG-400 although I can close space it all the way around the inside, 
tack each turn in place with a dab of epoxy and let the outside take 
care of itself.  That results in a coil about 3 to 4 inches longer than 
the stack but with the RG-400 flush against the core on the inside and 
close to that on the outside.  Stacks this long start making 7 turns of 
the larger cable a lot of work.

If find a need to use the larger cable (run out of RG-400) I'd go to the 
binocular format as I can wind a coil with 7, or possibly 8 turns in a 
single plane that takes up less than half the volume of one wound on a 
solenoid stack. It also makes for a nice, tight, and neat close wound 
coil that will fit in a 6 X 6 X 4" or 8 X 8 X 4" PVC box under the boom. 
  I think I'll have enough RG-400 to build these though.

I'd have to go back and look at the tutorial again, but IIRC 4 or 5 
cores will be enough for the tri-bander and much more effective than the 
original "cores over the coax" used.

73

Roger (K8RI)


>
> 73, Jim K9YC
>
>
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