Topband: Common Mode Chokes

[Grant Saviers]

I have built several chokes on FT240-31 cores with RG142 double silver 
shield TFE coax (ok for QRO anywhere at HF) and measured them with my 
VNWA 2.6.  For my 160m top loaded vertical I stacked three cores and 
used 12 turns for >4k ohms resistive.  My results generally agree with 
G3TXQ's and K9YC's charts, although I tend to use a few less turns than 
G3TXQ and more ferrite per K9YC to stay further away from the self 
resonance frequency.  Keeping the windings tight was important.  The 
big  type 31 "clamp ons" are also pretty handy for cables in place or 
with PL259's installed.

Grant  KZ1W

On 6/9/2013 6:57 PM, wb6rse1 at mac.com wrote:
> G3TXQ shows characteristics for common mode chokes:
>
> http://www.karinya.net/g3txq/chokes/
>
> Has anyone built the 17T of RG58 on an FT240-31 choke and verified the performance?
>
> TU - Steve WB6RSE
> All good topband ops know how to put up a beverage at night.
> _________________
> Topband Reflector
>