URM-127 variable capacitor data
W4KRL at arrl.net
Sat Sep 23 13:04:34 CDT 2006
Frank/Andre & the group,
Frank gave me a URM-127 signal generator with the variable capacitor tuning
last night at the VWS meeting. I'll be able to post a schematic in a few
days. Meanwhile you may be interested in what I found out about the
capacitor. It appears to be a 10 to 540 pF dual-gang unit made in England by
JB. Each gang has circular plates but I've forgotten what that means in
terms of capacitance versus rotation. Each rotor is composed of 17 plates. I
couldn't get an accurate count on the stator but 16 would seem right. The
spacing is VERY small. You could use this unit only at very low power.
Angle of rotation is 180°. There is an antibacklash gear drive connected to
the front dial so that the dial has a larger angle of rotation. The gear is
not part of the capacitor unit.
The capacitance range for dial readings of 20 to 200 goes from 500 pF to 24
pF. I figure it is padded with 29 pF to get the correct 10:1 range. The
frequency range selector switches resistors of 16M, 1.6M, 160k, and 16k for
the X1, X10, X100, and X1k ranges.
73 Karl W4KRL
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