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Old 18th November 2021, 06:26 AM   #61
NickKUK is online now NickKUK  United Kingdom
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Originally Posted by 1audio View Post
The smart move is to use a soundcard and some software which can create a narrow band filter. You still need to verify the measurement but with 20+ bits and a big FFT you can measure down pretty deep, but only of the signal does not drift. otherwise its more complicated but i'm sure someone has a solution.
Phase correlation doesn’t care about where the location is. The input parameter can be as wide as the image itself, so you could create a either a narrow pattern or a wider pattern with harmonics. The down side of the wide pattern is constant however that same system allows deconvolution (discovery of fundamentals) plus could (inversely) also detect odd behaviour.

If the signals drift then it depends if it’s a constant vector, a cycle pattern or random distribution. The first two are relatively straight forward but a random perhaps searching for a Gaussian distribution (make a Gaussian input then correlate on the result of the initial search) is a little more difficult. Assuming constant linear signals (and phase shift as a linear function).
Non linear - that’s where it becomes complex. You can use the signal over time and search for patterns but I suspect there’s ideas and concepts that can be applied from radar and machine learning.

I forgot to say - the phase correlation is highly resistant to noise.
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Last edited by NickKUK; 18th November 2021 at 06:42 AM.
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Old 18th November 2021, 06:30 AM   #62
1audio is offline 1audio  United States
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oscilloscope-Analog or digital
I should have thought of this. A lock in amp is the right instrument for unstable sources. I even have one.
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Old 18th November 2021, 06:46 AM   #63
NickKUK is online now NickKUK  United Kingdom
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Originally Posted by 1audio View Post
I should have thought of this. A lock in amp is the right instrument for unstable sources. I even have one.
Nice

In a digital context you can even hunt for known injected signals (of sweep even), correlate to create a distortion map and then supplement by simply multiplying in too. A rough calibration.

I used the stars in the CCD image as point spread functions, detect the distortion of the lense and also the distortion of the earths atmosphere (small angle of the sky which helps).

A further technique would be super resolution. If you shifted the signal both in voltage level and time base over the ADC, then use the correlation to align the samples interpolated on a 10:1 up sampled grid, you can retrieve data from the signal thus increasing resolution. I use this for detecting objects that my scope and camera could not normally see.
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V2 - pure digital tube HPA, RF-tube DSD512 modulation with mosfet output stage. (initial design)

Last edited by NickKUK; 18th November 2021 at 06:53 AM.
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Old 25th November 2021, 11:54 AM   #64
nigelwright7557 is offline nigelwright7557  United Kingdom
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Be careful of exaggerated claims for scopes bandwidth wise.
Take max samples/second and divide by 20 to 30 to get real bandwidth.
It takes about 25 samples to get a half decent picture on the screen.
Some claim 2 dots is enough ! which is rubbish.
It can maybe extrapolated into a sine but is pretty useless.
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Old Yesterday, 12:03 PM   #65
NickKUK is online now NickKUK  United Kingdom
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Originally Posted by nigelwright7557 View Post
Be careful of exaggerated claims for scopes bandwidth wise.
Take max samples/second and divide by 20 to 30 to get real bandwidth.
It takes about 25 samples to get a half decent picture on the screen.
Some claim 2 dots is enough ! which is rubbish.
It can maybe extrapolated into a sine but is pretty useless.
10:1 based on previous measurement experience (ie arc second rotation for telescopes). Think three 10p (cent) side by side at over a km away precision and repeatable pointing/tracking accuracy.

I know that 5x is a minimum and for a 24MHz square wave signal. that you're going to need quite a bit of BW. From the reviews and testing the 1104X-E bandwidth is at least 250MHz+. In terms of samples - 1GS/s that's 250MS/sec for a 1:4 so for a 24MHz wave that's ~10 per wave which is good enough, however also the question is - how does the ADC see a dB attenuation at a higher frequency? 8Bit means you're going to quickly find resolution problems between a 0dB signal and an attenuated higher frequency signal when the frontend amp starts being non-linear.

Some of the cheaper '100Mhz' measure way lower. Always best to see at least three reviews where the bandwidth is measured to exhaustion.
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Last edited by NickKUK; Yesterday at 12:10 PM.
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Old Yesterday, 12:18 PM   #66
nigelwright7557 is offline nigelwright7557  United Kingdom
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Its very hard to see 10 pixels on a 2k wide screen.
On my USB scope design I also added a zoom function where you could zoom in on the screen 1:1 2:1 3:1 and 4:1 this made it much easier see but did add steps in the waveform as wide as the zoom value.
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Old Today, 11:02 AM   #67
Roog is offline Roog
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Having made do with an ex university Tektronix 502a with 2 no. differential inputs for 30 years, (and only 1MHz bandwidth!) which in the time honoured fashion had a control for every parameter,Click the image to open in full size. I recently treated myself to a popular Rigol 4 channel digital scope.

On one side the new one uses less power, takes up much less space, makes less noise and is portable (not trolley bound) but I don’t like it. Sure it has better bandwidth and I am beginning to appreciate the one button auto function, but I don’t like the general usability what with all of the twist and press controls that somehow jog on to the next setting requiring you to repeat the action and button presses which lead to sub menus and more button presses, argh!

I am currently on the look out for a nice example of a late tektronix analogue scope, 100 or 60MHz or a Japanese scope of similar era and spec. I have fond memories of our firms’ lab scopes of this type, easy to operate, good quality with a sharp trace. I recall a really nice mains/battery operated Hitachi 20MHz model too, not the last word in sophistication,but nice to use and really handy.

A case of Rose tinted glasses? perhaps and maybe it’s because that’s what ‘I grew up with’ but sometimes you just click with a particular instrument.

Last edited by Roog; Today at 11:23 AM.
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