This works for me: 1. 10 Mhz to be measured input to vertical channel 2. Standard input to ext trig. 3. Set scope for 10 ns per div. (1 cycle of 10 Mhz will fill up whole screen) 4 Time the time it takes for trace to move 1 div. (not the whole cycle - just one of its sides.) 5. Divide these seconds into 1x10-8 using your calculator. ( I set 1x10-8 into one of the memories) 6. The answer will give you your offset. 7. Example: If it takes 20 seconds for one of the sides of the cycle to move, your offset is 5x10-10. It does not take all day to get a reading,
73 Bill, WA2DVU Cape May -----Original Message----- From: time-nuts <[email protected]> On Behalf Of Tom Van Baak Sent: Thursday, September 27, 2018 2:18 PM To: Discussion of precise time and frequency measurement <[email protected]> Subject: Re: [time-nuts] A silly question ... > "I think", that if for example, it takes 1 second to drift one cycle, > that works out at 0.1 ppm. If it takes 2 seconds, it's 0.05 ppm, if it > takes 5 seconds, it's 0.02 ppm etc. Is that correct? Yes. At 10 MHz one full cycle is 100 ns. So if the cycles are drifting by 100 ns per second that's 100e-9 s / 1 s = 1e-7 = 0.1 ppm. At these levels of frequency accuracy, using a 'scope is plenty good enough. In fact, it's more educational and somehow more enjoyable to watch analog sinewaves drift past each other than it is to see the digital display of boring frequency counter. Where the 'scope method starts to break down is when the frequency error gets down to the ppb level. At 1e-9 it will take 100 s for the waveforms to drift by one cycle. And at 1e-12 you would have to wait an entire day (100 ns / 86400 s = 1.157e-12). On the other hand, with frequency offsets this low you don't have to sit there the whole time. One trick would be to take a photo of the 'scope once an hour, or, say, once every 1000 s. If you played that back at 1 fps you'd have a 1000x "time magnifier". /tvb _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
