N4EKV Homebrew balanced-L antenna tuner builder's notes -- Nov 25, 2007

Many people have inquired about this project over the years so I thought I'd 
publish an expanded Builder's Notes to help those who are building their own.

1. The B&W coil stock is occasionally available on Ebay and certain catalog 
suppliers.  I never needed more than 30 turns for 160m so there's no need to go 
overboard with turns.  It would be desirable to have a more open coil pitch on 
the first 3-4 turns, i.e. a variable pitch coil.  I think having 2-4 turns per 
inch on the first few turns (at the bottom of the coil) would make it easier to 
tune on 10-20m.

2. The DPDT knife switch is unnecessary for my 50ft EDZ or 270ft doublet 
antennas.  I never used one of the positions (I think it was the lo-z position) 
so if I ever build another one it would be hardwired in the hi-z position.

3. The end caps on the coils are from my local True Value hardware store.  The 
are plugs for holes in counters/desktops.  I found a size that exactly fit into 
the coil stock and simply bored a hole in the black plastic to accommodate my 
wooden dowels.

4. I burned out my balun once running only 100W.  Had to rewind it with new 
RG-58AU coax.  Not sure what to recommend here.

5. The balun is attached to the base with a rubber stopper, also sourced from 
the hardware store.  I simply drilled a pilot hole in the stopper before 
screwing it down with a drywall screw.

6. When sourcing your variable capacitor be sure to get one with a low minimum C 
value.  This will help in tuning 10-12m where my tuner often needs less than 
minimum C from my big chopper.

7. Do use a capacitor knob with a large flange, like my antique vernier knob 
(found on Ebay).  Your eyes will be on your SWR meter and not your tuner while 
you're reaching for/tuning your tuner and you don't want a nasty RF burn.

8. Last and not least, and the source of most of the questions I've recevied: Why
did I use those RF chokes?!  To bleed static from what would otherwise be an ungrounded 
antenna system.  I did not do this proactively.  Rather, one dry and windy day I 
was sitting in my shack when I became aware of an occasionally repeating arcing 
sound.  Every 10-15 seconds it would reoccur.  After a lot hunting in the wrong 
places I finally discovered it was coming from my ladder line-fed rotary EDZ; or 
more accurately, the shack end of its feedline.  The chokes are not an attempt to 
shunt a lightning strike.  The are simply there to bleed off static as it builds up 
when the weather is conducive to such things.  I think I recall reading that a statically-
charged antenna is more attractive to lightning so this mod has two benefits.