AW: [Elecraft] PlugIn Balun for K2/Kat1 ATU

[George, W5YR]

Thanks, Peter.

My experience has been just the opposite using non-resonant 20-meter EDZ
antennas on 80-10 and a large non-resonant loop on 80 - 10, all fed with
ladderline, and using 1:1 current baluns for the transition to unbalanced
tuners. The calculated and measured impedance at the tuners is under 10
ohms on some bands with all three antennas so 4:1 baluns would lead to an
intolerable situation. Hence my use of 1:1 current baluns.

Apart from just matching the antenna and line, tuner losses go up
significantly when the real part of the line impedance falls below about
10-15 ohms. I suspect that the Elecraft tuners are suffering the most loss
when operated with such low impedance loads. In that event, using the balun
as a 1:4 might be better - except . . .

A balun is NOT a transformer. It is, in the words of Jerry Sevick, W2FMI, a
*transmission line transformer* and so its properties are those of a
transmission line and not those of a simple transformer. The actual
"transformation" ratio of the balun can be 4:1 at some frequencies and with
some loads and be far from that under other conditions. So, we cannot
remedy a difficult match situation by merely reversing the balun connection
using the appropriate connectors, as if it were indeed only a transformer.

This is an advantage of the 1:1 current balun: its performance is
independent of the load impedance. Although W1CG disagrees with that
statement, and thus designed his balun to be a 4:1 unit, Lewallen, Maxwell,
Sevick and others do not and are strong proponents of 1:1 current baluns
for line isolation situations.

I really do think that having the 4:1/1:1 switchable capability would make
the unit usable under a wider range of conditions. For QRP, the switch can
be correspondingly "tiny" - perhaps a miniature slide switch could be
worked into the case design.

Again, thank you for sharing your thoughts about this new product. 

73/72/oo, George W5YR - the Yellow Rose of Texas         
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe   
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
QRP-L 1373 NETXQRP 6 SOC 262 COG 8 FPQRP 404 TEN-X 11771 I-LINK 11735
Icom IC-756PRO #02121  Kachina 505 DSP  #91900556  Icom IC-765 #02437


Peter Zenker wrote:
> 
> George,
> the KAT 2 handles abt 8 to 800 Ohm as far as I know. The feed point
> Impedance of a Lambda 1/2 Dipole is abt 72 Ohm, used on the next
> harmonic I assume its higher then 800 Ohm. That�s the reason for me to
> use a step up balun. The impedance transformed to the ATU depends on
> length of the feed line, and frequency. You can bring it up to either
> higher or lower impedances. In my experience, it was very seldom, that
> the impedance at the ATU side was less then 30 Ohm, this happened only
> with extreme short antennas. ( With my ZM-2 I never ever needed the
> extra capacitor at the input side which is needed, if you have extra low
> impedance.)
> 
> BTW,
> If I am outdoor with a twin wire feeder (my normal Antennas :-) I carry
> with me an extra length of 3 Meter feeder line with 2 Banana jacks at
> one side and 2 Banana plugs at the other side. If a given Antenna has a
> "bad" impedance at the ATU end, I add this extra line and, bingo, its
> easy to tune now.
> 
> I will think about adding a switch and will test it. Actually there is
> definitely no place for such a swich, I have to use a bigger enclosure,
> and I am not sure if I get the same excellent results if I use the
> switch.
> But I will try it.