History Lesson...  I bought my AH-4 in year 2002 to tune my 33 ft high home built vertical antenna.  This antenna was like a rigid long wire connected to the ANT terminal on the tuner.  I installed long lengths of counterpoise wire in the rain gutters and eventually to an electrical ground rod.  This set up worked well--- meaning my rig and the AH-4 would tune 160-6 meters 100 percent of the time.  As time went on I discovered the vertical antenna was picking up more of my share of man made noise from my neighborhood.

I changed out the vertical for a 105 ft long dipole fed with ladder line with the center feed point at 33 ft.  Essentially, I turned the rigid vertical into a mast to support the center of the dipole.  The ladder line then connected to the ANT and GND posts on the output of the AH-4.  Why did I do this?  Well, there is an article on the web that shows how one ham has been successful with this set up...

see:  http://home.comcast.net/~hamlakemn/AH-4_General_Information.html

I tried it and it worked well--- meaning that I could tune up 160 to 6 meters 100 percent of the time.  I had less noise receiving at my rig... but there was still a high amount to put up with.  Example:  on 160 meters the least noise I received was S-9... most of the time it was 20dB+S-9.

Recently... I attended a presentation on BALUNS at a my radio club.  After thinking about the functions and importance of using a balun.  Here's why I think baluns, especially CURRENT BALUNS, are important to me and perhaps to whoever reads this blather.

1.  The current balun will equalize the RF current flowing in the balanced feed line.
2.  The current balun will choke RF from flowing down the exterior shield of the coax feed line.
3.  The current balun can/will transform impedances if need be.

Armed with these factoids... I realized that the 35 feet of coax feed line from my rig to the AH-4 was part of my antenna system that radiates RF energy.  I discovered this by installing a 'quickie' home built choke balun at the coax feed line  where it enters the AH-4.  I also added chokes to the control cable where it enters the AH-4 tuner.  After doing this... my noise level on 160 meters dropped significantly from 20dB+S-9 down to S-4.  I could actually hear hams on 160 meters.  Another important discovery was that the AH-4 would no longer tune up on 160 meters.   These two items add up to...

The choke balun has isolated the coax feed line and the control cable from being a 'radiating element' in my antenna system.  The antenna is now RF electrically shorter... and the AH-4 can not achieve a satisfactory tune- - - it was close... but not less than 2:1.

Also, since the choke balun now chokes the RF on the exterior of the coax feed line from the tuner to the rig.. and the coax does not radiate... it also does not receive.  Antennas are reciprocal in nature.  They receive as well as they transmit.  The man made noise from my shack... PC monitors, cable modems, CFLs, etc is being choked off at the choke balun at the base of the AH-4 and not entering the radiating elements of the antenna.

In Fig 9... it is hard to see the two snap on ferrite chokes on the control cable.  The white arrow points to the one of the right.  It is important to use these chokes on the control cable... why risk RF entering your shack via that path?  Just do it.

Another issue with this set up is that the output (antenna) side of the AH-4 is meant to feed an unbalanced wire antenna.  I have my balanced ladder line and dipole antenna connected where the long wire should go.  More theory says that the balanced feed line will not radiate (and therefore not receive) when the currents in each conductor are equal and opposite.  Since the long wire output is not designed to provide a balanced output... the current will not be as I desire.

As an experiment I placed a 9:1 current balun between the ANT and GND lugs of the AH-4 and the ladder line.  The tuner tuned the antenna as before AND my receive noise was noticeably lower sounding to the ear, but not for sure measurably lower with the S meter.

After adding the coax choke balun and the 9:1 current balun... the guys who frequent the 75 meter SSB round table gathering tell me that my signal is the loudest they have ever heard me.  This is encouraging to seemingly have all of my RF energy radiated by the poles of my dipole.

Also... I have experimented with choke baluns made from FT240-43 toroids using RG-58 coax as the conductor.  These work well in the center of a dipole fed with coax cable.  More "big signal" reports from the 75 meter guys.

I wrote an article on some of my experiences with choke baluns as result of some of my local ham club acquaintances asking me questions about how this stuff works.  My article attempts to theorize and simplify the issue.