[Elecraft] PlugIn Balun for K2/Kat1 ATU

[George, W5YR]

Balun placement before or after an unbalanced tuner connected to a balanced
line has been covered extensively on the rec.radio amateur.antenna
newsgroup. Roy Lewallen, W7EL, has shown that there is no advantage to
placing the balun at the tuner input insofar as line balance is concerned.
Theoretically, the effect of the balun is the same in either location, but
practically it may work better to balance the line currents when placed on
the output of the tuner.

I have the text of one of his r.r.a.a postings which I can send, Stuart, if
you are interested.

While there seems to be merit in having the balun working totally within a
50-ohm environment, it turns out that the balun does the same job in the
same way plced in either location. For this and probably a lot of other
reasons, most commercial tuners place the balun on the output side.

Those considered to be the authorities on balun operation, etc. are
unanimous in choosing the 1:1 current balun for coupling a balanced
transmission line to coax or to an unbalanced tuner.

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


Stuart Rohre wrote:
> 
> Use of a 1:1 balun or cable choke on the input side of a floating transmatch
> would seem to be the better thing to implement in tight spaces of a K2.
> 
> The advantages of input side balance device such as the cable coax choke, is
> that both sides see 50 ohms at all times when the transmatch is in
> adjustment.  Voltages are lower than output baluns of the 4:1 type.  With
> high current, low impedance, you might not couple into the case or nearby
> conductors as much as a high step up balun.  Losses of a 1:1 device are
> purported to be lower, and certainly minimal using a cable choke.
> 
> Most autotuners are unbalanced circuits I believe, what effective unbalance
> amount this would be to balanced feeders and antennas has not been covered
> in the literature to any well known degree.  I think there are some web
> postings on antenna web sites about percentage imbalance seen when feeding
> parallel line to such antennas as the end feed Zepp, but effects of L net or
> pi net auto tuners have not been covered that I could find.
> 
> Anyone have any data on that balancing means?
> 72,
> Stuart K5KVH