Author Topic: Max input freq on ds1000z And ds2000a series. .  (Read 2235 times)

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Offline Emi

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Max input freq on ds1000z And ds2000a series. .
« on: February 11, 2016, 05:38:39 PM »
Hi :)
I've seen a test where an hacked ds1102e can reach 500 mhz! 
Do you ever tried to stretch ds1000z or ds2072a ( hacked too...),finding its max admissible freq ?
...  https://hackaday.io/project/4327-stretching-the-limits-of-a-rigol-ds-1102e-scope

« Last Edit: February 11, 2016, 06:11:19 PM by Emi »
 

Offline awallin

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #1 on: February 12, 2016, 04:15:24 AM »
A series of screeshots is quite a lousy way to communicate a frequency-response...
Here's my plot of the original and liberated DS2072A response.

A more interesting question IMO would be to compare Rigol frequency responses to brand name (Tek, Keysight, LeCroy) scopes with similar bandwidth.

 

Online Fungus

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #2 on: February 12, 2016, 04:40:21 AM »
Hi :)
I've seen a test where an hacked ds1102e can reach 500 mhz!

Signals don't suddenly vanish the moment they go past a 'scopes rated bandwidth, they get attenuated (progressively smaller).

The number printed on the front of a 'scope is simply the frequency when an input sine wave is reduced by 3 decibels (ie. it's you don't see the true amplitude of the signal even at the scope's "bandwidth" frequency).

IIRC the true, measured, bandwidth (ie. the -3dB point) of a hacked DS1054Z turns out to be somewhere between 130MHz and 160MHz, depending on the individual 'scope.

There's a thread on here somewhere with people measuring that number and comparing their results.
« Last Edit: February 12, 2016, 04:45:31 AM by Fungus »
 

Offline Mechatrommer

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #3 on: February 12, 2016, 11:48:22 AM »
poor this guy tabulated the data using 10X probe, i wish he can redo with 50 ohm terminated coax..
http://www.natureandtech.com/?page_id=8149
« Last Edit: February 12, 2016, 11:51:05 AM by Mechatrommer »
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Offline uncle_bob

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #4 on: February 12, 2016, 12:07:57 PM »
Hi

Ok, so I'll try this again. Last time I tried it broke the server :)

With an analog scope, you can keep driving signals in for a *long* ways past the rated bandwidth and still see *something* as a smear on the screen. It depends a lot more on what you have for amps than anything else. The issue on the old analog beasts was always "how fast will they trigger". Once it turned into a smear it was useless.

With a digital scope, you have both the channel bandwidth and the sample rate. These scopes pretty much all share the sampling between the channels. You get 1GS/s on one and 250 MS/s if you run 4 channels. Nyquist says that anything past 1/2 the sample rate is ambiguous. With 4 channels on a 1000Z, that is 125 MHz. With two channels on a 2000A, that is 500 MHz. With only two samples on a waveform, your ability to know what it is ... not so good. A more practical limit is 1/4 the sample rate (4 points per cycle). That gets you to 250 MHz on a 2 channel 2000A or (gulp) 67.5 MHz on a 4 channel 1000Z. With only one channel on each, you could get 500 MHz and 250 MHz.

Next up is the wonder full world of probes. If everything is simple (single pole) bandwidth goes down as you add a probe. Back in the "good old days" they figured out a way around this. Stick another pole in the response and peak it at some frequency. You could do it with the probe or without. If you did it with the probe, things could get a bit odd when the probe was not there. Works great for sine waves. If you have a square wave, it messes with the phase of the harmonics. At some frequencies it distorts the waveform a bit. Taken to far (and some did that) it distorts the waveform quite a bit.

What does this all mean? If a 1000Z had a bandwidth of > 250 MHz it would be pretty useless. This is not a guess, I've used scopes like that. In fact, with a simple roll off (good for square waves) you really don't want to even get that high. Something needs to take care of the alias products. With a more complex filter, you can indeed "do better".

On the 2000A, 300 MHz is pushing a bit hard in the two channel mode. It is arguable that going further is actually a bad thing.

Lots of tradeoffs in this. With digital, uber bandwidth and slow sampling make for a real mess.

Bob

 

Offline Emi

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #5 on: February 12, 2016, 08:54:29 PM »
Thanks a lot for your clarifyng answer. .
That graph speaks great! !!
So You think a 2072a would  be right enough to monitor (with decent precision )Vhf/uhf signals?
 I dont care almost anything over 500 mhz  ;D
« Last Edit: February 12, 2016, 09:08:49 PM by Emi »
 

Online Fungus

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #6 on: February 12, 2016, 09:20:09 PM »
Thanks a lot for your clarifyng answer. .
That graph speaks great! !!
So You think a 2072a would  be right enough to monitor (with decent precision )Vhf/uhf signals?
 I dont care almost anything over 500 mhz  ;D

An unlocked DS2072A with good probes will certainly show a 500MHz signal (it's rated bandwidth is 300MHz).

The rest depends on your definition of "monitor" and "decent precision".

You're probably better off with a spectrum analyzer if what you want is to see if signals are there (and at what frequencies).
 

Offline Emi

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #7 on: February 12, 2016, 10:06:24 PM »
Oolpps..I used a wrong expression :-[ My only intents are  verify if there is signal in various sections of rf circuits. .
I suppose 500mhz is the extreme freq i Will operate. .
Ham radios uhf 470 mhz to be precise. ...
 :-+
But if i could also observe some kinda " modulations" on a so high carrier ..well. .It will be awesome! !    :popcorn:
« Last Edit: February 12, 2016, 10:14:52 PM by Emi »
 

Offline alsetalokin4017

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Re: Max input freq on ds1000z And ds2000a series. .
« Reply #8 on: February 13, 2016, 02:29:09 AM »
By a strange coincidence I've been trying to verify the RF output of a 300MHz garage-door-opener transmitter with my unlocked 1054z. I sort of think I can see the RF signal in there but I'm still not really sure. I can see the much slower pulse codes being sent to the RF output transistor, no problem there, but I still don't quite know if the thing is actually transmitting them.
« Last Edit: February 13, 2016, 02:31:12 AM by alsetalokin4017 »
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