[Elecraft] MP-1 antenna experiment

[Steve Jackson]

I have a SuperAntennas PW-1 (the precursor to the MP-1 sold by Elecraft) and
also the tripod mount sold for this antenna line

As an experiment, I added two additional ground terminals, for a total of
three.  I did this by drilling and tapping 8-32 holes in the 'hub' piece,
copying what Vern did on the 'factory' ground lug.  The new ground points
are at 120 degree 'points' i.e., 60 degrees offset from each tripod leg.

I then made up 2" lug-to-clip-lead assemblies using a #4 braided wire, a
heavy lug, and a Mueller #27 heavy-duty clip lead.  These components were
chosen to minimize inductance and maximize contact area.

I bought three 3/4" wide, 12' retractable tape measures for $1.99 each at a
discount store.  I extended them to 48" each, and then clipped the metal end
retainer with each of the three ground terminal clips, laying the tape flat
againt the concrete driveway.

For a test, I set the antenna for resonance on 17 meters using an MFJ-207,
and checked it again with an MFJ-259 and also an Autek VA-1 Vector Analyst.
I was going to check for "before-and-after" relative field strength, but it
started to drizzle ... some other time, I guess.

I can now set up the entire antenna in less than 2 minutes, and be on the
air with performance far beyond what I experienced with the ever-tangling
wires I used to use.  Tear-down is even easier: just unclip, hit the retract
button, and my ground radials spool themselves up in seconds.

Some experimentation with the tape measure extension length is still in
order.  Since this conductor is wide and flat, I think it exhibits less
inductance per unit length than a round wire does.  I could be wrong about
that, but it sure seems like I can use a shorter length on the tape than
when I was using a wire.  Also, the coupling to ground from the wide tape is
greater than a similarly placed wire.

The antenna seems to work even better (on some bands) when elevated somewhat
(like on a wooden table).  The K2 ATU now tunes into this antenna with very
little relay chatter; it seems to find a nice match quickly.   At the 5W
level, both CW and SSB contacts reported good signals (NC to Kansas City and
NC to Toronto, 17CW and 20SSB respectively) this afternoon.  I used to
struggle to make contacts in less than optimal propagation conditions with
this setup, but my 'improved' PW-1 seemed to have no trouble now.

I should mention I use two 12" base rods (as opposed to the 'stock' single
one) which seems to yield better performance also.  A 1 1/2" long, 3/8"-24
coupling connects them, and I can still transport the whole kaboodle with
ease ... no piece is longer than 12".

Hope this slightly off-topic commentary helps someone else put together a
more efficient and fun-to-use portable station.

73  Steve KZ1X/4  K2 #771