[Elecraft] antenna question

[N2EY@aol.com]

In a message dated 5/24/02 6:47:11 PM Eastern Daylight Time, 
w3fpr@peoplepc.com writes:

(some good stuff about dipoles snipped to save space)

>  Remember that if a 'leg length' is close to a half wave will be hard to 
feed
>  with all but a parallel tank circuit type balanced tuner (we can't hardly
>  buy these now-a-days).  

Yes, but we can build them!

>  The leg length that I am referring to is the length
>  of half the flattop plus the electrical length of the feedline (this is
>  length/0.95 for window line).  You did measure your feedline didn't you???
>  It helps in figuring what the matter may be.

The following website has some simple but useful freeware:

http://www.g4fgq.com

Program DIPOLE3 lets you describe any dipole/feedline combination, and will
tell you the expected efficiency, SWR and feedpoint impedance. (It won't tell
you the pattern, though). 

Program ENDFEED does the same for end-fed wires.

Lots of other neat stuff. These are simple DOS-based programs. They are 
small, run on almost any computer and the instructions are built-in.

You may have to convert to metric units but that's no big deal. 

Many hams use unbalanced tuners and wound-core baluns to feed balanced 
lines. This method works OK if the feedpoint Z is close to the impedance that 
the balun is designed to see. It can work very poorly otherwise, causing all 
sorts of odd effects. The obvious answer is a balanced tuner. 

This problem, and an easy solution,  was described in QST back in February, 
1990, by AG6K. A recent QST article also dealt with it. Online, see:

http://www.vcnet.com/measures/bbat.html

Although he uses ganged roller coils, there's no reason
switched coils couldn't be used instead. Note that this
design works for balanced or unbalanced loads.

Standard disclaimer: I have no connection to either of these hams
except agreement with and admiration of what they have written.

The KAT1 and KAT2 are unbalanced tuners. Feeding
 their unbalanced output to a balun and balanced line 
is an iffy setup. Elecraft could lead the way (hint hint)
by producing a true automatic balanced tuner, using
switched coils instead of the ganged roller inductors
used in the above article. Only downside would be
that twice as many toroids would be needed....

73 de Jim, N2EY