I have an 8640B in the lab. Bizarre instrument.
David
On 7/13/20 2:57 PM, Richard (Rick) Karlquist wrote:
On 7/13/2020 11:34 AM, jimlux wrote:
There are also "frequency locked" devices that are not "phase locked"
- they essentially discipline an internal oscillator by adjusting its
frequency, but not with any sort of phase locked loop.
The 8640 famously worked (sort of) this way. The cavity
had an extremely limited electronic tuning range, and would
only stay in lock for a few minutes before drifting off.
It would do this even if you left it on 24/7.
The display would then flash, and you had to release the
lock button, retune the frequency using the mechanical
cavity know, and then push the lock button back in. Are
you kidding me?
Definitely in the "gee whiz", "because we can", or "too clever
by half" category. At least they didn't have the chutzpah to
charge $ for this as an optional "feature". The Navy, recognizing
that this was not sailor proof, had the feature/bug omitted from the
military
version. Good for them.
Rick
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