Dan,
Here's another idea. Use a short length of coax like 1' or less of RG-58
or better RG-174, and put some ferrite beads around the coax to make a 1:1
balun. On the antenna side it is balanced, so solder this to the ladder
line. I hope you are at least using the small 300 ohm ladder line for 5
watts. If the feedline is small enough; #22 or smaller twisted pair, you
can use the beads right over the feedline as a 1:1 balun. I have made up
some feedline using #28 teflon insulated solid wire wrap wire held together
with heat shrink tubing. The characteristic impedance is not important and
it is low loss. I measured some #26 twisted pair once and it's impedance
is about 180 ohms.
In this application, a 1:1 balun works as well as a 4:1 balun. A 1:1 balun
can be made up using a pair of #28 magnetic wire and a F-50-43 1/2" ferrite
tordal core. Wind 10 turn of the wire pair on the core and secure both
ends with wire wrap ties. Alternatively, you can use RG-174 instead of the
wire. It usually takes a somewhat larger core, like a F-82-43 .825" core
in order to get enough turns to work well on 40; or use a F-50B-43 core and
fewer turns. I have made lots of these small 1:1 baluns and my favorite is
one using a F-82-43 core and as many turns of RG174 as you can get on it.
On my KX1, I use a 8' length of RG-58 soldered directly to one side of a
42' antenna and a 8' counterpoise soldered to the coax shield for a
portable antenna. The other end has a BNC plug for the KX1. Works well
for a portable. Doesn't beat an inverted V at 30' though, so you are on
the right track.
At 09:08 PM 9/9/2005, Dan Romanchik wrote:
Hi again--
Last night, I worked a guy who also is a KX1 owner, and we got to talking
about antennas. I mentioned that while the antenna suggested in the
antenna tuner manual (24-28-ft. driven element with a 16-ft. counterpoise)
tunes up OK, I was kind of disappointed in the performance. The other guy
mentioned that he uses a 40-meter doublet, usually in an inverted vee
configuration, fed with ladder line, and that it tunes up well on all
three bands.
I asked him whether or not he used a balun, and he said no, he just fed it
directly into the radio. I suppose his antenna could be fairly
well-balanced or that the KX1 is able to tolerate a fair amount of imbalance.
Whatever the case, I was thinking that it shouldn't be too difficult to
build a small balun--and it really could be a small one since the maximum
power level it needs to handle is just 5W--into a small plastic project
box. On one end, the box would have two binding posts to connect the
ladder line, and a panel-mount male BNC (if they make such a thing) on the
other.
Does this seem reasonable to do or is it overkill?
73!
Dan KB6NU
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