On Mon, 01 Jun 2009 08:48:14 -0400, Bill Tippett wrote:
> I doubt it. I believe the choke needs to be as close to
>the feedpoint as possible. Carlos N4IS is very knowledgeable about
>flags and uses 14 turns of RG-58 on a FT 244-77 toroid (or 14 turns
>of RG-174 on FT 140-77) on his Waller Flags (two chokes).
Very interesting. Thanks for contributing this. Carlos's chokes are
essentially the same as mine on 160M.
See measured data on pages 43-44 of
http://audiosystemsgroup.com/RFI-Ham.pdf
and compare to the same number of turns on #43 or #31. While the
measured on pages 43-44 are for small wire, the primary difference
to one wound with coax is inter-winding capacitance due to the
larger conductor, which moves the resonance down a bit. All of these
chokes have Z on the order of 5K ohms at 2 MHz.
Then compare these chokes with W2DU's original choke using 50 #73
beads (Fig 34 on page 25), which have Z on the order of 600 ohms at
2 MHz. The difference is nearly an order of magnitude!
So Carlos is using two 5 KOhm chokes with the DXE circuit (that is,
two ground rods). That's a two-stage filter, which is an order of
magnitude greater than what I'm using, and mine is an order of
magnitude better than the 50-bead choke. I'd be interested to know
if the second choke makes a difference.
I haven't seen the DXE choke in question, so have no idea of its
performance.
73,
Jim K9YC
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