Topband: Beverage Feed Line Choke Installation

[Jim Brown]

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