[time-nuts] Measuring speed of light or reproducing a metre

[Magnus Danielson]

Hi Jim,

On 06/24/2013 01:03 AM, Jim Palfreyman wrote:
> Hi all,
>
> With a 3325B, a 5370B, and other time-nut miscellany, what's the quickest
> way you can come up with to measure the speed of light OR reproduce the
> metre.
>
> I've got some ideas, but I'd like others' thoughts.

Using a laser that reflects and a detector, create a resonator, such 
that the received signal is amplified and modulated on the laser.
The delay through the circuit needs to be calibrated, but once you have 
done that, you remove it from the measured period of this oscillator, 
and the remaining time will be the flight-time. Using a TIC like the 
5370B you can measure this period with a fairly high resolution, 
averaging and all. Recall that the flight-time will for twice the 
distance. This setup isn't perfect in many senses, but you can do it.
The 3325B might come handy in calibration.

By intentionally insert extra delay (which we assume is stable and 
known) you can reduce the range of frequency and hence phase shift 
variation needed to be calibrated, which can increase the precision to 
some point.

This is a rough method of doing it, but it may serve your needs 
sufficiently good. I could probably hack this up with scraps lying 
around my lab, possibly lacking the optics for the laser.

What is your actual application?

Cheers,
Magnus