[HomeBrew] A quick toroid "use" question

[Philip Atchley]

Hi All,
Like most experimenters I've often heard that toroids are "self shielding",
that they are not really susceptible to coupling or pickup from external
sources.  I can't help but believe that there would be at least some coupling
between closely mounted toroid coils in compact construction, such as I show
below with ASCII graphics.

__      __     __
!  !      !  !     !  !         OR    ______     ______
!  !      !  !     !  !                  !______!   !______!
!--!     !--!     !--!

I ask this because I'm building a preamp with a 7 pole (3 toroids) Low Pass
filter in the front end.  I've built many of these LPF's and never thought
about it before, nor do I have a way to measure their "real" rejection.  Space
is at a little bit of a premium, but I don't want to sacrifice performance.

About how far apart should the coils be spaced.


73 de Phil,  KO6BB
http://users.mercednet.com/beaconeer/

DXing from the "Beaconeers Lair".
Where DX begins at the noise floor and 944
different LF beacons have been heard since June/99.
Merced, Central California, 37.3N  120.48W  CM97sh