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FeelTech FY6600 60MHz 2-Ch VCO Function Arbitrary Waveform Signal Generator

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rhb:

--- Quote from: maxwell3e10 on August 23, 2019, 03:01:11 pm ---rhb, in all your work in the oil business, have you ever worked out solutions to Maxwell's equations in a cylindrical waveguide with a center conductor?


--- End quote ---

Just for the record, the last time I solved that was 40 years ago when I went back to school to get an MS in geology after taking a BA in English lit.

The class average on the Physics II (EM) final was 45.  I had the highest score, 89.  I derived the solution to a complex capacitor problem from first principles during the exam.

That's the only grade I ever got I truly cared about.  And that was because some twit sitting next to me in class, after hearing I had a BA in English lit,  remarked I'd never pass because  "This is where they weed out the engineers."   

maxwell3e10:

--- Quote from: rhb on August 23, 2019, 03:18:46 pm ---I suggest you find a good primer on the use of oscilloscopes and read it.  In particular the section on input impedance and bandwidth.

--- End quote ---
Good for you. But people who have PhD like to understand things at a deeper level than an instruction manual.

rhb:

--- Quote from: maxwell3e10 on August 23, 2019, 05:26:38 pm ---
--- Quote from: rhb on August 23, 2019, 03:18:46 pm ---I suggest you find a good primer on the use of oscilloscopes and read it.  In particular the section on input impedance and bandwidth.

--- End quote ---
Good for you. But people who have PhD like to understand things at a deeper level than an instruction manual.

--- End quote ---

ROFL!!!!  I was merely suggesting you learn to crawl before you try to walk.

I was paid to sit as judge and jury on Stanford professors and their students for several years.  I worked as a contract consultant and my client paid around $35K/yr for consortium membership.  I was sent to the annual meetings to make sure the work they did was worth the money.  There were others, but you probably have not heard of Mines or the others.

Clearly not a world you're familiar with.   I know you have a BS, but it's obviously not a Bachelor of Science degree, even allowing for the horrible degradation of academic standards.

Attached are photos taken of the same 36 ps rise time pulser on a Tek 485.  It needs a full cal run, but it's still very good, especially compared to the horrible step responses of DSOs such as the Keysight MSOX3104T I returned  or the R&S RTM3104 I had on demo. It just isn't up to my (or Tek's) rather stiff demands for a proper scope step response.  A full cal on one of these is a full day's work which is why it's not in full cal.  Adjusting the front end attenuators takes a couple of hours.

For the benefit of the youngsters, the 485 was *the* premier portable analog scope for many years and has a 350 MHz BW.  It also has both 50 and 1 M ohm input selectable by switch.  The sweep is set at 2 ns/div for both photos.

Rather than spoil the fun, I shall allow our "PhD" friend here to explain which is 50 ohm and which is 1 M ohm and why the 36 ps rise time square wave looks so different.  In this case, aside from gain adjustments, the only change is the input impedance setting.  My apologies to the old guys who realize I botched the gain settings relative to the 0% & 100% lines.

BTW  For the benefit of the more intelligent readers of this farce, Leo Bodnar supplies with each of his pulsers a plot from a CSA803A with either an SD-30 or SD-32 head.  The SD-30 is a 40 GHz,  8.75 ps rise time head.  The SD-32 is a 50 GHz, 7 ps rise time head.  I'm not sure which he used for my plot.  Leo only claims < 40 ps in his listings to allow for individual unit variations.  The laser driver he uses has a 21-23 ps rise time IIRC, so he also offers 3.5 mm and 2.48 mm versions with faster rise times, albeit at higher cost as the connectors are *much* more expensive.  A 1 MHz square wave version of his BNC pulser will give exceptional TDR capability for very low cost with whatever scope you have.  Leo very graciously will provide that instead of 10 MHz if you ask. I have 1 MHz & 10 MHz square wave units and a 100 ps impulse unit.  They are fantastic!



BU508A:

--- Quote from: maxwell3e10 on August 23, 2019, 05:26:38 pm ---
--- Quote from: rhb on August 23, 2019, 03:18:46 pm ---I suggest you find a good primer on the use of oscilloscopes and read it.  In particular the section on input impedance and bandwidth.

--- End quote ---
Good for you. But people who have PhD like to understand things at a deeper level than an instruction manual.

--- End quote ---

Arrogance will not help you understanding why proper termination is necessary.
But maybe if you will have a look at this, then perhaps you will understand.
And if you want to discuss this topic with someone on your level, I can recommend Shariar from The Signal Path.
He is a RF expert and has a PhD.

First: introducing s-parameters, the basics:
https://www.edn.com/design/test-and-measurement/4437010/S-parameters-basics

A paper from CERN:
https://cds.cern.ch/record/1415639/files/p67.pdf

a more general article from Wikipedia:
https://en.wikipedia.org/wiki/Transmission_line

a nice usecase of not correctly terminated transmission lines, example by Rohde & Schwarz
https://www.rohde-schwarz.com/de/file/Distance-to-Fault_Measurements.pdf

And here is the link to The Signal Path if you want to discuss this topic with a PhD and not some mediocre EEs.
http://thesignalpath.com/blogs

And just a last remark:
Every, really every transmission line MUST have a proper termination, otherwise it will fail.
This is more true, the higher the frequencies are. High frequencies means: fast square signals.
All the high frequencies are in the edges covered. The related topic is "Fourier-Analysis", explained here:
https://en.wikipedia.org/wiki/Fourier_analysis

HTH,

BU508A



maxwell3e10:
No one argues that a transmission line needs termination. The question is what constitutes a transmission line. The general rule is that the length of the line needs to be comparable to the wavelength of the signal transmitted. That is why impedance matching only becomes an issue at higher frequencies (shorter wavelength).

I perfectly stand by the original statement:

--- Quote from: maxwell3e10 on August 22, 2019, 03:07:05 pm ---All of this transmission-line considerations of cable impedance and load impedance matching apply only if the cable is long enough to be a transmission line, which means its length is comparable to the wavelength of the wave. With light speed on the order of 1 ft/nsec one doesn't need to worry about impedance matching for a 3-ft cable and 100 nsec pulses.

--- End quote ---
It has already been shown by radiolistener that changing impedance matching only affects the ringing on pulse transitions (which necessarily have much higher frequencies or shorter wavelengths), it does not affect the DC value of 100 nsec -long steps (apart from trivial factor of 2 attenuation). So if one only cares about those 100 nsec flat steps, there is no need for termination. 

Now as for rhb tests, it doesn't even involve a cable, just a direct signal connection as far as I understand. As was discussed on another thread (https://www.eevblog.com/forum/testgear/oscilloscope-input-noise-comparison/), oscilloscopes often have different input circuits for 1 MΩ and 50 Ω signal paths, so the rise time difference is not surprising at all. I don't know about the details of Tek 485 input, only that the bandwidth is quoted as 350 MHz (50 Ω) / 250 MHz (1 MΩ) at http://w140.com/tekwiki/wiki/485.

I am sorry for tweaking rhb, he just likes to brag about his credentials so much that I couldn't resist.

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