[RFI] Where to protect control cables?
Dan Levin
djl at andlev.com
Mon Oct 4 19:22:59 EDT 2004
Well, I went out and bought an MFJ clip-on rf ammeter, and
found that most of my control cables have RF on them. I was
surprised, because my shack is about 70' from the base of
my tower, and the cables run through a 4" conduit that is
"under ground" (actually, laying on top of the 4" conduit
that has my coax's in it in a trench) for that distance. I would have
expected that the proximity to lossy ground would bleed
off any RF on those cables, but apparently not. A pile
of 31 material clip-on ferrites fixed things temporarily,
but a more permanent fix is required. So my questions are:
If I am going to use ferrite to control the problem, should
I put the ferrites on the cables at the base of the tower,
i.e. before the 70' run along the ground to the shack, or
at the wall of the shack?
I assume that the right answer isn't ferrite, but rather
to bypass the cables to ground using caps. Again, if I
am going to do that, should I do it at the tower end,
or the shack end?
I have no lightning issue here in N. CA - this is all
just to keep RF out of the shack and the control boxes.
These cables are for my rotator, 3 SteppIR controllers,
and my 80 meter relay switch box.
Thanks!
***dan, K6IF
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