New Rigol DS1054Z oscilloscope

[jjoonathan]

Rigols have very shallow rolloffs. The DS1102E in the video dedicates 60% of its Nyquist bandwidth to rolloff as opposed to nameplate bandwidth! This cost Rigol dearly -- they had to overclock, dither, and pull all sorts of tricks to get there at their price point -- but it shows in the smooth response that doesn't ring. You aren't just seeing the 5th harmonic, but also the 7th and 9th, and 11th with increasing attenuation. That's why it's smooth, and that's one reason why Rigol comes so heavily recommended. Use a brick-wall filter and you'll get your ringing.

[heatbreak]

Rigols have very shallow rolloffs. The DS1102E in the video dedicates 60% of its Nyquist bandwidth to rolloff as opposed to nameplate bandwidth! This cost Rigol dearly -- they had to overclock, dither, and pull all sorts of tricks to get there at their price point -- but it shows in the smooth response that doesn't ring. You aren't just seeing the 5th harmonic, but also the 7th and 9th, and 11th with increasing attenuation. That's why it's smooth, and that's one reason why Rigol comes so heavily recommended. Use a brick-wall filter and you'll get your ringing.

Surely a Tek, Agilent, GW Instek can match that no?

[Fungus]

Rigols have very shallow rolloffs. The DS1102E in the video dedicates 60% of its Nyquist bandwidth to rolloff as opposed to nameplate bandwidth!

Surely a Tek, Agilent, GW Instek can match that no?

But not OWON?

Even though it's just a single capacitor and a resistor (according to your spice simulation....)

[Fungus]

Just for you: Here's a video that shows Dave Failing to measure a 1kHz square wave as beautifully as a Siglent sales brochure. Using the best setup he can manage - you won't get anywhere near this just by clipping a probe onto a wire.


(on various 'scopes, up to 1GHz).

[jjoonathan]

Rigols have very shallow rolloffs. The DS1102E in the video dedicates 60% of its Nyquist bandwidth to rolloff as opposed to nameplate bandwidth!

Surely a Tek, Agilent, GW Instek can match that no?

But not OWON?

Even though it's just a single capacitor and a resistor (according to your spice simulation....)

All manufacturers should implement revolutionary resistor capacitor technology, get rid of this rubbish:

https://www.eevblog.com/forum/testgear/rigol-mso4000-and-ds4000-tests-bugs-firmware-questions-etc/?action=dlattach;attach=77504

[JPortici]

A 1-pole AFE filter would only make sense if you had plenty of sample rate to burn. Most scopes are more aggressive.

I found a video showing a 10 MHz and 20 MHz on a 100 MHz Rigol scope.  Of course the 10 Mhz looks better, but to me the 20 MHz is doable for home use.  The peak voltage measured are the same and so are the rise/fall times.  4:21 and 4:31 time mark.

it is exactly the same, look at the edges. that's because the square wave is bandlimited so its risetime is < 12ns, according to the datasheet, and it will be like this at all frequencies.
for this units it seems about 6ns judging by eye, probably a bit more
the ds 1102E has a risetime of <3.5ns at the BNC connector.
i think the small ringing is due to the band limited impulse they used and not a reflection.. a bit of ringing would allow higher frequency content (faster edge) but with a sharper rolloff so they don't introduce aliasing and hey chose this one as the compromize
if they measured the TTL output instead it might have been more fun to watch

[rstofer]

Here is an Agilent paper on rise time versus bandwidth:
http://cp.literature.agilent.com/litweb/pdf/5988-8008EN.pdf

[vk6zgo]

According to Agilent the rule of thumb is f(bw) = 5 * f(clk) to get the 5th harmonic.

Nope. 5 * f(clk) is only the second harmonic.

f(clk) is the base frequency

3*f(clk) is the first harmonic

5*f(clk) is the second harmonic

7*f(clk) is the third harmonic

etc.

Sorry,it doesn't work that way.

There is no such thing as a first harmonic.
If there was,it would be the fundamental ----in this case,f(clk)
The 2nd harmonic is  2f(clk)
The 3rd harmonic is  3f(clk)
The 4th harmonic is  4f(clk)
The 5th harmonic is  5f(clk),& so on.

Just because a square wave only has odd harmonics,you don't get to change the designations of harmonics.

Yes,in this case 3f(clk) is the first harmonic you are interested in,but it is still the 3rd harmonic of the fundamental.

heatbreak is correct,as he is using the correct terminology.

[freebil]

Hello. Can I enter a bnc antenna like this

http://www.ebay.com/itm/1040mm-Telescopic-Antenna-Q9-BNC-Connector-12mm-Dia-Portable-FM-Radio-Scanner-/201507365072?hash=item2eeac660d0:g:OoEAAOSwuAVW1Yv~

in the ds1054z? Thanks

[metrologist]

That antenna will physically connect to the scope as BNC is a standard connector. Not sure what you will see with it, though. I'd expect a lot of line noise.

[Fungus]

heatbreak is correct,as he is using the correct terminology.

Using the correct terminology makes a 50MHz scope able to display a 10MHz square wave perfectly.

Got it! 

[McBryce]

Hello. Can I enter a bnc antenna like this

http://www.ebay.com/itm/1040mm-Telescopic-Antenna-Q9-BNC-Connector-12mm-Dia-Portable-FM-Radio-Scanner-/201507365072?hash=item2eeac660d0:g:OoEAAOSwuAVW1Yv~

in the ds1054z? Thanks

Yes, but what exactly are you expecting to see with it??

McBryce.

[vk6zgo]

heatbreak is correct,as he is using the correct terminology.

Using the correct terminology makes a 50MHz scope able to display a 10MHz square wave perfectly.

Got it! 

No,but making up your own terminology on the spot makes you look like you don't know what you are talking about.

Yes,5 times the fundamental frequency will allow you to display a useable square wave,
It will obviously not be a perfect rendition.

In that part of your argument you are correct.
I was pointing out that heatbreak's quoted "rule of thumb" was correct (as far as it goes),& that your understanding of harmonics seemed to be a bit confused.

I am a bit at odds with the "5f(clk)" rule,as it seems to assume a fairly strange response curve,where the response is still flat at (for the above case) 50MHz.
Many "50 MHz" 'scopes would be 3dB down at that point.

The rule I learnt many years ago was "7 times the fundamental",which would move the 5th harmonic out of the rolloff,with a more accurate (but still not perfect) rendition of the 10MHz square wave.

[freebil]

Maybe some really strong rf signals or not? I have a raspberry which acts as transmitter with https://github.com/F5OEO/rpitx for different frequencies and modulations.

[heatbreak]

heatbreak is correct,as he is using the correct terminology.

Using the correct terminology makes a 50MHz scope able to display a 10MHz square wave perfectly.

Got it! 

No,but making up your own terminology on the spot makes you look like you don't know what you are talking about.

Yes,5 times the fundamental frequency will allow you to display a useable square wave,
It will obviously not be a perfect rendition.

In that part of your argument you are correct.
I was pointing out that heatbreak's quoted "rule of thumb" was correct (as far as it goes),& that your understanding of harmonics seemed to be a bit confused.

I am a bit at odds with the "5f(clk)" rule,as it seems to assume a fairly strange response curve,where the response is still flat at (for the above case) 50MHz.
Many "50 MHz" 'scopes would be 3dB down at that point.

The rule I learnt many years ago was "7 times the fundamental",which would move the 5th harmonic out of the rolloff,with a more accurate (but still not perfect) rendition of the 10MHz square wave.

A square wave will start to look square at the 3rd harmonic.  At the 5th harmonic, it will be very usable (as proven my link to a 100 MHz Rigol displaying a 20 MHz square wave and by my spice simulation).  The bandwidth of the scope is usually defined by the cut-off frequency, ie the -3 dB point.  If a square wave is not usable by the 5th harmonic, then I'd look into probe problem, signal problem, system problem, or crap scope.

[tggzzz]

A square wave will start to look square at the 3rd harmonic.

Of what importance, other than to an artist, is what is "looks like", i.e. its appearance?

What's important is the effect a waveform has on the circuit, or the significance of the measurements that can (and cannot) be made.

In a circuit where the electronics respond to a 1ns event (e.g. reflection transient, crosstalk, ESD, or noise) then who cares what a 1Hz waveform "looks like" on a 10MHz scope.

[borjam]

Maybe some really strong rf signals or not? I have a raspberry which acts as transmitter with https://github.com/F5OEO/rpitx for different frequencies and modulations.

The RF spectrum is really busy and polluted. Radio receivers must do quite a filtering in order to pull a useful signal.

[Fungus]

The rule I learnt many years ago was "7 times the fundamental",which would move the 5th harmonic out of the rolloff,with a more accurate (but still not perfect) rendition of the 10MHz square wave.

Is that where 70MHz scopes come from?

70MHz seems a strange number (to me) but many manufacturers do a 70MHz 'scope.

[JPortici]

Maybe some really strong rf signals or not? I have a raspberry which acts as transmitter with https://github.com/F5OEO/rpitx for different frequencies and modulations.

I am using a cheap SDR dongle for that. don't want to trash money on a spectrum analyzer if i only need to check wether the signal is present

[heatbreak]

A square wave will start to look square at the 3rd harmonic.

Of what importance, other than to an artist, is what is "looks like", i.e. its appearance?

What's important is the effect a waveform has on the circuit, or the significance of the measurements that can (and cannot) be made.

In a circuit where the electronics respond to a 1ns event (e.g. reflection transient, crosstalk, ESD, or noise) then who cares what a 1Hz waveform "looks like" on a 10MHz scope.

Yes you're right.  I finally understand what you all meant by it's the rise time that counts.  It's because

riseTime_nSecs = 0.35 / bw_ghz

riseTime_nSecs = 0.35 / 0.05 = 7 nSecs for a 50 MHz scope
riseTime_nSecs = 0.35 / 0.1 = 3.5 nSecs for a 100 MHz scope

So if a signal has a rise time of 3.5 nSecs, then it has the potential to produce frequencies up to 100 MHz and if this signal is picked up by a part of the circuit that acts like a filter that allows, say, 100 Mhz to pass, then you'd have a 100 Mhz signal in your system.  Am I close?  If so, then I see why you'd want as high a bandwidth in your scope as possible.  Thanks for all that replied.  I learned something new.

[tggzzz]

A square wave will start to look square at the 3rd harmonic.

Of what importance, other than to an artist, is what is "looks like", i.e. its appearance?

What's important is the effect a waveform has on the circuit, or the significance of the measurements that can (and cannot) be made.

In a circuit where the electronics respond to a 1ns event (e.g. reflection transient, crosstalk, ESD, or noise) then who cares what a 1Hz waveform "looks like" on a 10MHz scope.

Yes you're right.  I finally understand what you all meant by it's the rise time that counts.  It's because

riseTime_nSecs = 0.35 / bw_ghz

riseTime_nSecs = 0.35 / 0.05 = 7 nSecs for a 50 MHz scope
riseTime_nSecs = 0.35 / 0.1 = 3.5 nSecs for a 100 MHz scope

So if a signal has a rise time of 3.5 nSecs, then it has the potential to produce frequencies up to 100 MHz and if this signal is picked up by a part of the circuit that acts like a filter that allows, say, 100 Mhz to pass, then you'd have a 100 Mhz signal in your system.  Am I close?  If so, then I see why you'd want as high a bandwidth in your scope as possible.  Thanks for all that replied.  I learned something new.

Essentially yes.

Bear in mind the assumptions behind the "0.35" equation, and that it is only a rule of thumb. There are cases where it is inappropriate/irrelevant, but those can wait until you have a deeper understanding.

Never forget that it isn't only "signals" that are of interest. So is noise and interference and, particularly power plane transients and resonances. Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

[metrologist]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

[canibalimao]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

After reading that, I felt like asking if there is such a thing as a standard voltage (or standard ground), kinda like we have a GPS frequency standard and some way of determining absolute power (dBm). But then what you are saying suggests that V is merely relative, like dB. Yet, V seems to be a fundamental component of power.

If such thing was needed, the earth is the absolute 0. But you don't need it for usual power measures and calculations, since it is all based on potential difference. You don't need to know what's the reference absolute voltage, you just need to know the potential difference...

[Fungus]

Forget the concept of "0V" or ground or earth, since they are all fiction that has some use in some limited instances.

If all the electrons and protons match in a lump of matter then surely that's "zero" volts.

If I match up all the protons/electrons in two lumps of matter anywhere in the universe then bring them together there won't be any charge transferred between them. That means there's a universal reference point out there.

[JPortici]

the definition of voltage comes from a potential (which translates into an integral).. in fact voltage is a difference of two potentials between two points in the space. zero is and can only be arbitrary

(choosing the earth as zero would assume the earth is at the same potential - and it has zero resistance - in each point along the surface which is not true. for example, with a lightning or during a short to your home's earth conductor the potential in that area rises, compared to the earth at some meters away)