At 01:58 PM 7/25/2007, n7ka@comcast.net wrote:
>Getting ready to install another 6M yagi here and building another
>for a friend. Want to use a choke on the feed line which will be
>either RG-213 (MIL-C-17 compliant) or on LMR-400UF (super flex). In
>all cases I want the capability for 1500W. I do not like the idea
>of additional connectors so my plan is to but the beads on the line
>at feedpoint of the cable that goes down to the hardline just below
>the top of the tower. Would Fair-Rite 2643102002 be the correct
>choice? The id at 0.505 inch is large enough to fit over the
>RG-213/LMR-400. Or do I need another mix and how many beads.
You can also use a larger diameter toroid and run multiple turns of
your coax through it. The inductance of the choke goes as the square
of the number of turns, so 5 turns through one core is like 25 cores
in a row (in an ideal world... there's capacitance and leakage L...
but still... )
Jim Brown's website http://www.audiosystemsgroup.com/ has a paper on
various ways to make RF chokes for feedlines (among other things)
with measured data over a wide range of frequencies. It's that
RFI-Ham pdf file referenced in recent posts. 5 turns on a #31 2.4
inch core looks like around 1Kohm Z.. (see page 12) page 28 has a
photo of a mondo choke. I use one very similar to this for
connecting a network analyzer to antennas (except I use smaller coax).
Jim, W6RMK
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