Balun for KX1 - doublet combo?

[Frank R. Oppedijk]

Hi,

I've been lurking on this list for about a month now, so I guess this is my
official "hello" to the group. (Great group, BTW; excellent posts; am
learning a lot here!)

In the meantime I've bought and assembled a KX1 and am now thinking about
which antenne should accompany it on my upcoming holiday to the Alps... I'm
considering buying one of those DK9SQ telescopic masts (as soon as I've got
a definitive answer about the mast being RF absorbent or not; I want to be
able to use it to put up a vertical too) so I can put up a doublet antenna
in inverted vee mode. I don't like the 3 dB loss from 10 meters (that's 33'
for you non-metric people out there) of lightweight RG174 coax, so I'm
contemplating feeding with open wire.

Now the big question: how to connect the symmetric open wire feeders to the
KX1?
a) Don't bother; just plug one wire into the hot side and connect the other
side to the case
b) Use a balun
c) Something else.

If b), then what configuration would you use? How small a toroid would keep
up with the torturing that it might get in such a high SWR environment?...

Thanks in advance for all the help!

Cheers,

Frank
PA4N (ex-PA3FLV)
KX1 #1166
K2 coming up in a couple of months...

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[Ron D'Eau Claire-2]

Frank, PA4N asked:

In the meantime I've bought and assembled a KX1 and am now thinking about
which antenne should accompany it on my upcoming holiday to the Alps... I'm
considering buying one of those DK9SQ telescopic masts (as soon as I've got
a definitive answer about the mast being RF absorbent or not; I want to be
able to use it to put up a vertical too) so I can put up a doublet antenna
in inverted vee mode. I don't like the 3 dB loss from 10 meters (that's 33'
for you non-metric people out there) of lightweight RG174 coax, so I'm
contemplating feeding with open wire.

Now the big question: how to connect the symmetric open wire feeders to the
KX1?
a) Don't bother; just plug one wire into the hot side and connect the other
side to the case
b) Use a balun
c) Something else.

If b), then what configuration would you use? How small a toroid would keep
up with the torturing that it might get in such a high SWR environment?...

---------------------------------

Welcome to the gang Frank!

I'd use choice a.

If you use a balun, the size of the toroid isn't the issue. It's how many of
those 2 to 4 watts from your KX1 you want to throw away as heat. The smaller
the core, the more obvious the losses because it'll get hot to the touch,
but the losses are still there even with a big core.

Of course, on some bands the balun may be okay.

A couple of options you might consider. Use RG58 coax (or even RG174 if you
absolutely, definitely must have the small stuff) and feed a double-dipole
cut to length. You can make it out of 300 ohm TV "twin lead", some rotator
cable or even zip cord. You make one half of the cord 66 feet long and the
other half 33 feet long. That covers 40 and 20 meters. On the shorter
length, let the last couple of feed dangle down to provide good RF
insulation and decoupling from the ends and the longer radiator. If you must
include 30 meters, consider a 1/4 wave "radial" on the ground and tie the
feeder together and load it as a vertical on that band with the dipole
acting as a "top loading".

Ron AC7AC


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[Charles Greene-2]

Frank,

Order a F-50-43 core.  Take two #26 enamel insulated wires about 2'
long.  Clamp the start for the pair with about 2" from the end, to the core
with a cable tie.  Wind the pairs through the center.  Every time it passes
the outside, run the pair through a piece of heat shrink tubing, as small
as will take the pair and hit it with a heat gun.  Alternative, twist the
wires together, not too tightly.  You can't tell the difference in
performance.  Continue winding until you can't get any more turns
on.  Clamp the end of the pair to the core with a cable tie with about 2"
of pigtail.  Solder one pair to a BNC  male connector and put alligator
clips on the other ends.  Guaranteed to be a good balun for the KX1.  You
might check Tom Hammond N0SS's web site for some variations, mostly
larger.  Last time looked, they were still there.  For the feed line, try a
twisted pair of #22  stranded, insulated wire.  Not too tight on the twists
or you will spend all day at it and it doesn't need it.  If you can find
some teflon insulated silver plated stranded wire, so much the
better.  It's not worth the difference which is mostly mechanical if you
buy it new, but if you can guy some cheap like on eBay, go for it.  You can
buy 300 ohm ladder line, but that takes the fun out of it.

For the K2 or K2/100, you should use a F-114-43 core and 15 turns.  That is
good from 160 meters through 6 meters.

73,  Chas W1CG

At 02:39 PM 6/15/2005, Frank R. Oppedijk wrote:

>Hi,
>
>I've been lurking on this list for about a month now, so I guess this is
>my official "hello" to the group. (Great group, BTW; excellent posts; am
>learning a lot here!)
>
>In the meantime I've bought and assembled a KX1 and am now thinking about
>which antenne should accompany it on my upcoming holiday to the Alps...
>I'm considering buying one of those DK9SQ telescopic masts (as soon as
>I've got a definitive answer about the mast being RF absorbent or not; I
>want to be able to use it to put up a vertical too) so I can put up a
>doublet antenna in inverted vee mode. I don't like the 3 dB loss from 10
>meters (that's 33' for you non-metric people out there) of lightweight
>RG174 coax, so I'm contemplating feeding with open wire.
>
>Now the big question: how to connect the symmetric open wire feeders to
>the KX1?
>a) Don't bother; just plug one wire into the hot side and connect the
>other side to the case
>b) Use a balun
>c) Something else.
>
>If b), then what configuration would you use? How small a toroid would
>keep up with the torturing that it might get in such a high SWR environment?...
>
>Thanks in advance for all the help!
>
>Cheers,
>
>Frank

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