Problem lampoly SNF 2008-08-12 17:01:04: High Reflective Power

shott at snf.stanford.edu shott at snf.stanford.edu
Wed Aug 27 19:45:41 PDT 2008


Cesar replaced the tuning cap with a new Jennings 3-30 pf variable cap.  This cap takes 18 turns to tune from 3-30 pf .... but the Lampoly can only mechanically tune over about 6 turns.  So, we need to "preset" at about the proper range so that it can properly lock in.  This was accomplished with the help of Jim McVittie and his magical HP 4815A RF Vector Impedance Voltmeter.  Many would call it a museum piece .... but it saved our bacon.
Basically, we were able to use it to find the tune point (zero phase angle and maximum impedance).  This is very sensitive ? 1/8 turn offsets the tuning by about ? 45 degrees.  Once we found the center point, Jim recommended that we tune just to one side.  So, we arbitrarily pre-tuned to +30 degrees.
Tuning seem to be behaving well.  Cesar has tried a variety of recipes and, thus far at least, all of them seem to be tuning properly.
Happy etching,
John




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