[Elecraft] KAT-500 (was: K3-Twin with Remoterig)

[Ron D'Eau Claire]

In the 1960's one very popular and cheap H.F. antenna was the folded dipole.
Often they were made from the ubiquitous 300 ohm "twin lead" used on TV
antennas and fed with the same twin lead since the impedance of a folded
dipole is close to 300 ohms. The first time I saw 4:1 baluns being sold to
Hams was to make it easy to connect the 300 ohm feeder to such a folded
dipole to the output of a rig designed to feed 50 ohms. 

As Hams migrated away from rigs with tunable output networks to rigs with
fixed tuned outputs, MFJ and others produced a line of antenna tuners
specifically designed to correct feed line mismatches since that could no
longer be done at the rig. They included the popular 4:1 balun for those who
were feeding various open wire lines (typically 300 to 600 ohms but which
may have significant SWR - so the impedance might vary much more). 

It seems that many Hams considered the 4:1 ratio some sort of magic number,
when all it was intended to do was provide a good transfer between 300 ohms
and 50 ohms.


Ron AC7AC


-----Original Message-----

I can attest to what Vic says. I have an 88-foot long doublet, hung about 45
feet up, fed with 85 feet of 600-ohm ladder line. At the shack end I have a
1:1 balun, and then about six feet of RG/8X running to the K3. The K3's
tuner likes the combination. I tried replacing the 1:1 balun with a 4:1 from
the same manufacturer. The K3 was quite unhappy with the change in
components. The 4:1 went back on the shelf, the 1:1 went back inline. YMMV

Jim / W6JHB

On   Thursday, Dec 8, 2011, at  Thursday, 9:14 AM, Vic K2VCO wrote:

> It is a common misconception that a 4:1 balun is the best choice to feed a
tuned balanced 
> line. The assumption is often made that this is appropriate because the
characteristic 
> impedance of ladder line or open-wire line is higher than the 50-ohm coax
that's connected 
> to the balun's input.
> 
> Actually, since the tuned line is being operated at a high SWR, the
impedance seen by the 
> balun will vary all over the map. It may be very high or very low. This is
a very tough 
> job for the balun, and in some circumstances it can be quite lossy. This
is why a real 
> balanced tuner is better than an unbalanced tuner followed by a balun.
> 
> A 1:1 balun is likely to have lower losses in this application, although
there might be 
> combinations of frequency and line length where a 4:1 is better. I hope
that Elecraft is 
> planning to make their balun either 1:1 or switchable.

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