At 07:23 PM 4/15/2005 -0700, you wrote:
>The problem with the stability is that most of these were constructed
>using a Galvinised steel rod to set the tuning correct?
I solved that problem by putting some "slop" into the connection between
the rod and the plunger. It's kind of hard to explain, but I put two nuts
on the threaded rod above the plunger, and two nuts below the plunger. I
then locked each set of nuts so that the plunger had about 1/16" of play on
the threaded rod. This made tuning a little more difficult. If you past
either the notch or the peak, you had to back up and take out the slack
before the tuning went the other way. Once I had it tuned, I turned the
threaded rod one-half the distance that it took to take out the slack. At
this point, the top nuts and bottom nuts are not touching the threaded
rod. Therefore, there was no "thermal pull" on the plunger when the
galvanized rod changed length.
By now, you are probably wondering why I went through all the
trouble! First, 22oMhz duplexers were hard to come by in the
1980's. Second, I'm a very stubborn person and I was going to figure out a
way to keep them stable.
73, Joe, K1ike
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