"There was a little girl,
  Who had a little curl,
   Right in the middle of her forehead.
 When she was good,
  She was very good indeed,
   But when she was bad she was horrid."
   
   	-- Henry Wadsworth Longfellow
	
That sorta sums up how I feel about the Hustler G7-144.	

The repeater group I'm working with has been using one of these
antennas for its primary 2-meter system for about ten years (ever
since a windstorm knocked down and damaged the previous antenna, a
Stationmaster).  It has served quite well - very respectable
performance, especially for the price.

Recently we replaced the old, failing repeater with a new one.  Upon
testing it, we found that the system was suffering from very bad
de-sensitization of the receiver.  An incoming signal which was just
reaching the "full quieting" point, with the transmitter off, would
drop down deep into the noise or would be lost entirely when the
transmitter was switched on.

We started trouble-shooting, and determined that it wasn't a problem
in the repeater itself, or the duplexer cans, or the cabinet feedline
jumpers, or the Heliax going up the tower.  It wasn't a simple
mis-tuning of the antenna, either - reflected power from the antenna
was negligible.  In the end, the only thing which got rid of the
desense (down to barely-detectable levels) was replacing the Hustler
with another antenna (a simple "American Legion" aluminum J-pole).

Down came the Hustler.  Our machine-tools guy tore it apart, and found
several problems: corrosion, corrosion, and corrosion.  

One area of trouble was the sliding (tuning) portions of the
radiators... the aluminum tubing was visibly oxidized, and the steel
hose clamps holding the sections together were no longer enough to
ensure a tight metal-to-metal contact.

The biggest problem, however, was further down, in the matching coil
assembly.  The bolts holding the coil ends and lugs together were
visibly corroded.  Worse yet, the bottom (grounded) end of the coil
tested out as having an extremely high DC resistance to the N
connector at the feedpoint.  Investigation showed that the N connector
was well grounded to the heavy cast-aluminum plate, and that the
matching coil was rivet-grounded to the cylindrical portion of the
antenna base, but that there was poor electrical connectivity between
the cast plate and the aluminum cylinder.  These two parts were
force-fitted together, not welded or screwed.  Ten years up in the
weather had degraded the force-fit junction enough to ruin the
metal-to-metal contact, and the matching coil's grounding was ruined.

All of this corrosion and oxidation was, it seems, enough to cause a
bunch of RF arcing and other nonlinear effects to occur when the
transmitter was keyed up, and some amount of the transmitter power was
being splattered around as broadband noise.  Enough of this noise got
back through the duplexer (a three-can-per-side design) to desense the
receiver.

Fortunately, the problems were all correctable.  Our machine-tools guy
did a major rebuild of the matching-coil assembly:  replaced the
corroded hardware with stainless-steel, replaced one of the N
connector mounting bolts with a longer brass bolt which extends up to
near the base of the matching coil, and soldered the brass bolt
to the connector and to the matching coil.  A new PVC cover was
fabricated to cover the matching coil and bolt (the bolt was in the
way of the original cover).

All of the tuning sections were cleaned down to bright metal and
roughed up a bit with a 3M green scrub pad, coated with a
metal-bearing anti-seize/anti-oxidant goop (something similar to
Penetrox), tuned properly, then drilled and fastened together with
sheet-metal screws and covered with heat-shrink tubing. The
screw-together stud fittings on the phasing coils were cleaned,
roughened with a spring punch, gooped with anti-oxidant, wrenched down
tight, and covered with heat-shrink tubing.

We put the antenna back up, and tested the repeater with a very weak
incoming signal (well down into the noise).  If we listened very hard,
and used our imagination, we could sometimes convince ourselves that
the noise level rose very very slightly when the the transmitter was
turned on, but it was almost imperceptible.  Problem solved.

This sort of problem might not ever be noticed if the antenna were
being used in a standard base-station arrangement (transmit or receive
but not both at the same moment) because the broadband noise products
were probably well below the levels allowed by the FCC rules.
Repeater service is a tougher challenge, though.  If you've got one of
these antennas in duplex service on a repeater, you might want to give
it a checkup.

	Dave Platt AE6EO
	3 March 2005