DSO question

[Andy43]

Hello all. I'm new to this forum so please treat me gently!
After years of using analogue scopes at work and at home (I'm a radio amateur who likes to build stuff), I decided to replace my ailing Tek 2445 with a shiny new DSO. I think it was the Hantek 5202 (200MHz, 1Gs) and it worked really nicely at audio and low radio frequencies. I was really impressed by the crisp, stable display and prepared myself to enter a new age. Then I tried setting up an AM transmitter (low power, about 0dBm) on 50 MHz. Ooops. The darned thing refused to show me the familiar 'envelope' waveform, it just filled the screen with mush, no matter how I tried to set it up.
I heaved the old faithful Tek back onto the bench and all was sweetness and light again. The Hantek went back and the old Tek just works, despite its many faults. Are they all like this or is it a limitation of the sub £500 market? Is it a memory length thing (the Hantek has only 1M)? Looking around, I see even quite expensive Teks are not over-endowed with memory, but some of the Rigols seem to have plenty.

Many thanks.

 

[estarkey7]

You should have bought a Tek, but I work there so I'm kinda biased .

DSO's have so many settings a conventional scope doesn't have like digital filtering, FFT and triggering options galore, it's possible it was a configuration issue. But one of the issues that occur with these low end scopes is their front end is badly specified, so it may be that it can't handle the signal.

Since it's a DSO, you don't spec it by 3db down at F sub t, but you use Nyquist, which should get you working with signals up to 100Mhz before aliasing errors, but this is an el-cheapo scope you know.

I'm a ham too, but I already told you where I work, no since in telling you where I live too! LOL!

 

[William Gaatjes]

Could be that the dso could not handle it or an configuration error or a limitation of dso scopes.

At my work we made a few years ago a power factor corrector circuit. We wanted to see the envelope of a number of current pulses in a circuit. But with our beloved 1GHz Agilent dso of several thousands of dollars we could not see it. It triggered perfectly on the pulses and could see all detail of every single pulse but we could not get it to show what we wanted to see, the 100 hz half sine envelope of several pulses. We then used an analog scope, turned the timebase up and the intensity and there it was...
Something in the idea of this :

It could be that we did something wrong, but i noticed that although i can hardly imagine measuring without the Agilent DSO, sometimes an old fashioned analog scope is just a quicker way to measure because of the way tube oscilloscopes function.

 

[Andy43]

Thanks for your responses. I took a punt on a Rigol DS2072 and this one displays the AM without problem. I think the critical factor is the display memory - this Rigol has 14 Meg available and does this task without any major fiddling required.
After a bit of reading, it seems that if you set the timebase slow enough to see the audio envelope, there are so many RF cycles that need to be plotted that a lot of memory is required to store the points.
This sounds like the same problem you had, William.
Disclaimer: I have no idea what I'm talking about, having been working in the analogue world all my life!

 

[William Gaatjes]

Thanks for your responses. I took a punt on a Rigol DS2072 and this one displays the AM without problem. I think the critical factor is the display memory - this Rigol has 14 Meg available and does this task without any major fiddling required.
After a bit of reading, it seems that if you set the timebase slow enough to see the audio envelope, there are so many RF cycles that need to be plotted that a lot of memory is required to store the points.
This sounds like the same problem you had, William.
Disclaimer: I have no idea what I'm talking about, having been working in the analogue world all my life!

It could very well be.
The switching frequency was about 60kHz and the envelope is a 100Hz half sine waveform.

The models we have are the Agilent MSO6104A and MSO6054A.
One is a 1GHz model and the other is a 500MHz model. Both have 4 analog channels and both also have a 16 channel logic analyzer.
Both have storage for 8 million memory points.

What i do like about these models is they seem to have some form of adaptive triggering. When i trigger at a specific point, the scope also has a large part of the signal acquired before the trigger point. I can just go forward and backwards in time with these scopes by use of a simple rotary button, scrolling backwards or forwards. I have no idea how they do that but i find it amazing. They are wonderful to work with and are very intuitive in the user interface.

I doubt it wil ever happen but i do would like to have such a model at home for the hobby.