[Elecraft] Thanks! OT: Vertical doublets / baluns / tuners

[Darrell Bellerive]

Joe,

You do not need a 4:1 balun. The impedance conversion of a balun is only
effective for a resistive load. As the reactance increases away from
resonance the impedance transfer ratio degrades.

Your KAT100 tuner is what is doing the matching anyways. The only thing
you would need is to convert from the unbalanced tuner to the balanced
feedline with a choke or current balun. Your ferrite bead covered coax
stub is a choke balun. Five beads may not be sufficiant. M. Walter
Maxwell in his book Reflections recommends 50 #73 beads on a 12 inch
piece of RG-303 coax for operation from 1.8 to 30 MHz. You might be able
to get by with a few less beads if you limit operation to 7 MHz or
greater.

Zip cord can be used as a transmission line. It has a characteristic
impedance of about 100 ohms through HF frequencies. It is rather lossy
though. Losses at 7 Mhz for 28 feet are about 0.5 dB, but increase to
about 2 dB at 28 MHz.

Darrell VE7CLA K2 #1973


On Wed, 2004-03-24 at 17:31, Joe - aa4nn wrote:
> Hi 'Crafters, I  have an experiment here with a doublet.
> 
> Take 50ft of zip cord.  Split apart 22 ft to make the overall horizontal
> length be 44 ft.  The remaining unsplit 28 feet is the vertical parallel
> feedline to the shack.  Center height is 17 feet, two ends are at 10 feet,
> inverted "V".  I have a 12 inch stub of RG8X with 5 ferrite beads on it.
> PL259 on one end of the stub and alligator clips on the other end.  I use
> the alligator clips to connect to the zip cord feedline and I attach the
> PL259 to the KAT100 tuner.
> 
> Now this KAT100 tries its best to tune, and on 10m through 40m it is not
> bad.  But am I not missing something.  Wouldn't some kind of maybe a 4:1
> balun be needed to go between the balanced parallel feedline and the
> unbalanced tuner output.  ??
> 
> I'm looking for a simple K2 Field Day setup.  Thanks.
> 
> de Joe, aa4nn