Review of Tektronix Mixed Domain Oscilloscopes MDO4014-3

great review!

Hi Alex,

Forget about testing anything for me, spend your time with your bride to be.

Nothing impresses a woman more than telling her that you stopped playing with your technical toys to have more time for her.

Trust me, I have been happily married to an artist for 26 years.

It will also encourage them to see what you are doing.

Good luck with the wedding,

DAB

i might be able to rig something up...i don't have a pair of signal generators...but i have an idea that i'll try...and hopefully it will work out well....do you want the two 800 Hz signals driven into one input or into two?...i just have to pick up from jack adapters

I am getting married on the 20th, so i am getting busier and busier, but i'll keep working on the review...i'll post what i have before the wedding...and worst case i can keep working and keep posting after my honeymoon...feel free to message me anytime with any updates or questions and i'll try to get them answered as soon as i can!

Wish me good luck!

-Alex

Hi Alex,

Yes, I plan to use an analog microphone to drive an A/D into a microcontroller or DSP.

As for the delta F, that is the question I am trying to answer.

If my theory is correct, they could be huge or a lot of small subtle changes.  The 800 Hz is my starting point based upon my initial calculations of how much air expansion I should see from a nominal lightning bolt vaporizing the moisture along the conductive path.

The sound waves could last for about ten seconds or so.  It depends upon the length of the strike path and the distance from the sensor.

I am not sure of the needed sample rate.  My initial sensor test should generate some good first cut data.

If you have the equipment, you might setup two 800Hz signal generators and set them up with a delay trigger from 1 microsecond to 1 millisecond.

I want to see how much sampling resolution would be needed to find the two sources.

I am also planning to deploy a MSP Launchpad with a three axis accelerometer to see if I can measure the air pressure waves during these events.

As for the infrasound, I am again using some initial calculations on the speed of the charge packets I estimate are moving with the storm front.

I hope to get my initial sensor ready for the coming spring storm season.  If I can get it up and running, it should give me some good first test data.

Anyway, thanks for your efforts.  Your tests should help me with the initial settings.

DAB

"Time-Correlated Multi-Domain display":

Wow, That sounds like a very neat application DAB!

For 800Hz: I'm trying to imagine your setup...am i correct that you would be using an analog mic as your signal source....essentially using the input as an ultra-fast sound card for audio capture? (recording at 5 GSamples/Sec definitely beats the ~194-320 KSamples/Sec of a PC sound card)...then exporting the data and doing post-processing on the PC?...did you plan to record the source voltage-vs-time via a channel of the Scope, record the frequency-vs-time via the spectrum analyser, or both? Remember internally there is only 20Megapoints of internal memory (see below: note #1)....how high of a sampling rate do you intend to use (or to phrase it inversely, how long is your "event")...

i think based on your application, you may prefer using both...it's referred to in the manual as the "Time-Correlated Multi-Domain display". (see image) and starts on page 150 of the manual....although for the 20Hz signal the spectrum analyser is not an option as it has a minimum input frequency of 50KHz

perhaps the most informative demo i could present to you (800 Hz application) and vary it with slightly with time. (how much of a Delta-F do you expect)...given what i have laying around the house, i think the only practical way i can do this is to use a PC to generate the signal...

Any thoughts?

Cheers!

Alex

NOTE #1-------------------------------------------------------------------------

I'm still not sure about the maximum recording length via a pc with software (called "TEK VISA")...but my understanding is that when using the scope stand-alone; it is limited to the 10 MegaPoints, even you have a Flash drive or HDD. I have not figured out how to directly save to external memory, it seems you still have to manually tell it to save the waveform to the USB (there is no way to plug in an 8 gb flash drive and say "fill-er-up!")

...i've been thinking about this and the limitation should be because of the following:

5 Gsa/sec (up to 2 inputs, or 2.5 Gsa/sec on all 4) generates up to 10 GigaValues/sec ...the 20 Megasamples of total internal memory can be filled by this unit in only 2 milliseconds...I cannot remember the precision of the data points (i think values are "double-precision floating-point" = 8 bytes/value)...which would mean that at 10GigaValues/sec we are in the ballpark of 37 GBps of data generation...whereas USB 2.0 is limited to 480Mbps (but most drives are much slower)...it would be a nice feature to add though: if data generation is low enough, allow direct saving to external memory, but i suspect that this would pose a miriad of very difficult design considerations for TEK (ex: having to test each storage device to determine max data transfer rate, and files could grow to ridiculous sizes and bog down scope performance, etc)...

Hi Alex,

I have two research projects I am working on.  For the 800Hz, I am interested in recording the sound of thunder after a lightning strike where I can establish the very first wave of sound, determine the root frequency and then look at each succesive wave to calculate its doppler shift around the base frequency.  Strange I know, but I have a new theory that I am trying to resolve on how the charge propagates through the atmosphere and the directions each section takes as it goes up or down.

The sub 20Hz measurements are needed to analyze the movement of cloud charge as the weather front moves over the ground.  In coordination with my other measurements, the movement of charge should also be possible and contribute to my theory.

What I would like the scope to do is be able to record data and then enable the user to process the stored data to pull out the frequency spectrum over time to show how the frequencies shift as the pressure front moves to the ground after the lighning strike.

The infrasonic frequencies will shift over time and space, so I might want to collect several sensors at the same time to see if the movement is localized.

Overall, it sounds like this scope has some tremendous features.  As I assess your review, I can better establish the features I will need for my project.

Thanks

DAB

DAB,

I have tested the unit at work which in my case deals with very short pulses for radar applications. But i'd be happy to rig up a sample around 800Hz, and i'm sure i can find a source to put out sub-20Hz...

The scope has a recording length of 20MegaSamples, what kind of sampling rate do you need for your signals? When you talk about compressing the time domain, i believe the feature that you are looking for is the "waveform inspector"...it is one of my favorite features...If you set the scope to view the entire time domain, you can use the waveform inspector to zoom in and search through the recorded time...if you are looking at a wide period of time and have a low sampling rate, this will not increase the "resolution", but it is still very very very handy...and if your time domain is too large it will start "scrolling" through time...in which case you can either set the trigger, or switching from "Run" to "Stop", or use the "Single" to update your time domain...i have actually just recorded a demo of the waveform inspector, becuase i didn't think that it was very well documented, i have a few other features to show off before i post my update (for instance i want to include that mid-audio-spectrum sampling for you)

i'm starting to get into the bundled software...if the scope by itself cannot resolve a long enough sample, then perhaps the software could compensate

Best regards

Alex

Hi Alex,

Have you put together an overall test plan?

I would like to see some testing on mid audio spectrum at about 800 Hz and I would also like to see some infrasonic down below 20 hz.

If possible, I would like to see if the scope could resolve those low frequencies over at long sampling time.

Does the scope enable you compress the time domain to see the whole collection time?  That feature would be useful for my research.

Thanks

DAB

Certainly Michael,

I had planned on filling the frame with the unit in my next review...this first half was really more of an unboxing/initial thoughts...i've been making notes and working on more content...i'll hopefully get a change to draft it up this weekend.

Are there any specific features that i could demonstrate for you? This unit has so much it can do, it would be helpful if i had an idea of what specifically you are looking for in comparison to rogol or hameg units.

Thanks!

Alex