[Test-Equipment] HP-606A Calibration question

[John Kolb]

No, there is a unique solution, not multiple possibilities.  This can 
be verified
by using a resonance calculator such as
http://www.daycounter.com/Calculators/LC-Resonance-Calculator.phtml
and entering some different values.

Assume a variable cap/dial has a 350 pf change
between two dial marks.  With 50 pF trimmer and stray C, and 0.633 uH L
the high end of the dial produces 28.3 MHz, and the low end of the dial, 400 pF
total, produces 10.0 MHz.

If the trimmer/stray C is increased to 60 pF, and the L is reduced to 0.527 uH,
the high end of the dial still produces 28.3 MHz, but when the dial 
is set to the
low end, 410 pF total, the output freq is now 10.8 MHz, not 10.0 still.

If the dial was calibrated for a straight line capacitance curve, 
then alternately adjusting
the coil slugs and trimmers will bring the dial into calibration at 
the proper unique
solution, as long as the dial wasn't misaligned so much that the 
trimmer required
a negative value, and the dial would also track across the entire 
range.  If the variable
cap does not have a straight line curve, adjusting the coil and trimmer find a
solution where the change in variable C between dial ends, and the 
trimmer setting and
L value bring the two dial end points to the proper freq, but points 
in the middle of the
variable setting are far from the C required to produce the dial marking freq.

The suggestion to look for the original set screw marks on the shaft 
is a very good idea.

John
KK6IL


At 01:48 PM 5/26/2009, you wrote:

>Something occurred to me about all of this.  Is it possible there is 
>a proper starting position for the trimmer so as to effect the
>final position of the slug?  In other words, there might be almost 
>any number of combinations of L and C that would cause the endpoints
>to be on target, but certain combinations cause the accuracy across 
>the entire dial to be further off than others?
>
>Barry - N4BUQ
>