R7000 question
 

I disassembled my CT-3 trap (20/30 meters) and found absolutely nothing
wrong with it, no carbon, no wetness, no burns and electrically
connected wires. However, is there supposed to be a capacitor in
there, (this is the older one), just the plastic coil forms with the
two rods and properly riveted wire ends. Is the capacitor formed by
the spacing of the two inner tubes. I replaced the trap with the newer
version (I think - no center dimples, but black screws in the center).
Cushcraft tech support states the traps were redesigned and are not
interchangable unless you change CT-2 also, and change the spacing
between the traps. (so why didn't they rename them (CT-3R), so now that
I put the new trap in place, I still cannot transmit on 20, 30, or 40
meters (infinite SWR on built in tuner. Of coursec the spacing between
the traps changed, due to the redesign, so I guess I'll have to lower
the antenna down again and reinstall the original trap. If not the
trap, then is there anything band specific in the matching network?

"M.M." wrote:

wrote:
I disassembled my CT-3 trap (20/30 meters) and found absolutely nothing
wrong with it ... is there supposed to be a capacitor in
there, ...

I believe the capacitor is the capacitance between the inner tube(s) and
the outer tube. I found on mine that the connections at the ends of the
coils in the traps corrode and then make a poor connection to the tubes.
IIRC, they're riveted so I drilled out the rivets and replaced them with
sheet metal screws. I also applied some anti oxidation paste meant for
aluminum wiring...I got it at Lowe's. That seemed to help. You might
check all aluminum-to-aluminum joints and and connections and clean them
and apply the paste. It seems to help mine to do that periodically. You
might also check inside the box. A close lightning strike a few years
back wrought havoc on the matching box on mine.

The R7000 is definitely not Cushcraft's best piece of work. It has been
a PITA ever since I bought it several years ago from the estate of a SK
who belonged to our club. The 14AVQ I bought 35 years ago was a lot
better antenna, as was the Butternut I had before the 7000.

You wouldn't happen to be the guy who bought the trap from K0FL, are
you? I bought the box & other two traps...

73... Mark AA7TA

Yes -- the capacitance between the inner rod and the outer form a variable
(or at least adjustable) cap, just like a 'piston trimmer'. This is used
to bring the trap to resonance. Before you spend
a lot make sure the connections at the end of the coils, as Mark suggested,
are good. This is a simple fix and will save a lot of money and grief.
--
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Beating it with diet and exercise!
297/215/210 (to be revised lower)
58"/43"(!)/44" (already lower too!)
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--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

Yes, I did buy the CT-3 trap from him. I would assume its the newer
model (I have no way of knowing, except that it had black screws in
the center of the trap instead of the dimples). Mine didn't come with
the protective boot, but I had one from by 80 meter add-on I'll never
install. Replaced the CT-3 and still have infinite SWR on 20/30 and 40
meters. Maybe its a problem with the auto-antenna tuner in the rig
(Kenwood 570D) and not the antenna. There is different spacing when
using the new traps 6" and 18" between CT-1 and 2 and CT-2 and 3, from
the original 16" and 16" spacing. As mentioned, old trap was
completely dry with no burn marks, loose connections or carbon buildup.
Everybody mentionms drilling out the dimples, I just tapped the trap
on the stoop pushing the forms inward, and just pulled them out.
reinstalling them would probably require an awl is hard nail to exactly
line up the endpoints.
According to the criptic Email from Cushcraft tech support, the traps
are proabably not interchangable, unless a tuner is used? They were
willing to sell me their R7000TFK for $112+ which proably contains a
new CT-2 and new CT-3 and some tubing.