[time-nuts] 5061A S/N ratio, EM voltage questions
wje at quackers.net
Fri Jul 25 13:28:19 EDT 2008
Can someone provide a sanity check on my S/N and FOM measurements? I've
used the procedure in my manual, but there is one rather vague
calculation involving 2.3 e 13 x V403b. I assume this is actually 2.3 e
-13 x (noise voltage in mv), because otherwise the other calculations
result in absurd values.
I have a high-output tube and got the following measurements:
Vpeak -278 mv
Vvalley -81 mv
Vbase -65 mv
which gives a 'flop' of 3.03.
Using the more advanced measurements for the high-output tube, I get:
Isig 1.97 e -9
Inoise 6.44 e-13 (assuming my comment abut the V403b calculation is
correct; I measured a noise voltage of 2.8 mv rms).
which gives an S/N ratio of 3059 (!) and a FOM of 7.89.
This is all from a 25-year-old CBT, so I'm a bit suspicious. It does
lock and stay locked, even in low-flux mode, though.
As for the EM voltage, I measured a peak beam current of 3.6 e -9 amps;
HP says the acceptable low bound is 8 e -9. This current makes sense,
since the tube is so old.
So, would it be useful to increase the EM voltage from 1700 (as marked
on the CBT and verified) to increase the beam current?
I assume doing so would accelerate the deterioration of the EM, though,
so maybe I should leave well enough alone.
BTW, I had to make up a precision 100 meg probe to do the Vp, Vv, and Vb
measurements; my voltmeter has a 1 e 13 ohm input resistance, which
makes the technique in the manual useless. (a Solartron 7081 8.5 digit
They said 'Windows or better'
so I used Linux.
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