Topband: Optimum Choke at N0FP

[Ford Peterson]

I have built dozens of baluns and measured their choking effectiveness on
160 (the toughest band to get choking action).  I have been interested in
power handling and choking action.  The best choke I have been able to
construct for 160 looks like this...

4 type 43 beads (1" long beads w/1/2" hole).

50 ohm 4 line conductor made of teflon coated wire (14 awg see below)

3 turns through all four beads

I have run about 1000W through this balun and it barely got warmer than room
temp.  The choking action is quite good.  I use it at the shunt feed of my
tower.

Sevick describes part of the balun problem as one of controlling the
characteristic impedance of the line used to construct the balun.  Making a
50 ohm line with anything other than coax is impossible with two wire line.
Quite practical with 4 wire line.

I wrote an Excel spreadsheet that computes the characteristic impedance of
lines.  Two wire, four wire, and coax, using various common dimensions.
What I found is that the 50 ohm two wire line is impossible to construct.
The four wire line is quite practical with the right choice of insulated
wire.

I found some really trick wire used by Carrier (the air conditioning
people) that has excellent temperature stability and voltage rating.  The
insulation was just the right thickness to allow a four wire line at 50
ohms.  The balun constructed with 4 wires, held together with heat shrink
tubing, is my best performer to date.

If anybody is interested in looking at the spreadsheet, I'd be happy to zip
it up and send it to them.  The technical references are listed on the
tables computed.

Ford-N0FP


--
FAQ on WWW:               http://www.contesting.com/FAQ/topband
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Problems:                 owner-topband@contesting.com