Show us your square wave

[Wuerstchenhund]

With all the talk of cable and connector quality, what (and where from in UK) would qualify as reasonable up to say 150Mhz, for a BNC to BNC patch?

http://uk.pasternack.com/
http://www.hubersuhner.com/en-gb/

I buy my BNC RG-58 and other RF cables from them.

[tautech]

Rigol DS2202, DG4000:

I hope your DG4000 wasn't set to 50% duty cycle

That was from a Rigol DG4000 series at 40MHz with a rise time less than 2ns?  Must be either a DG4162 or maybe a DG4102.  Either way, impressive.  (I'm betting you had it set to something other than 50% duty cycle.)

If it's other than 50% duty it's a PULSE and EF asked for squarewaves.

Most AWG's have a different spec for pulse as opposed to square wave and to post them is confusing fair comparison.

[Electro Fan]

Anyone have a Tektronix AFG 3000 to show off at 10, 20, or 30 MHz?

[Electro Fan]

Rigol DS2202, DG4000:

I hope your DG4000 wasn't set to 50% duty cycle

That was from a Rigol DG4000 series at 40MHz with a rise time less than 2ns?  Must be either a DG4162 or maybe a DG4102.  Either way, impressive.  (I'm betting you had it set to something other than 50% duty cycle.)

If it's other than 50% duty it's a PULSE and EF asked for squarewaves.

Which is more challenging to produce? A pulse?

[tautech]

Rigol DS2202, DG4000:

I hope your DG4000 wasn't set to 50% duty cycle

That was from a Rigol DG4000 series at 40MHz with a rise time less than 2ns?  Must be either a DG4162 or maybe a DG4102.  Either way, impressive.  (I'm betting you had it set to something other than 50% duty cycle.)

If it's other than 50% duty it's a PULSE and EF asked for squarewaves.

Which is more challenging to produce? A pulse?

IME a clean square wave with a fast risetime

[Yago]

With all the talk of cable and connector quality, what (and where from in UK) would qualify as reasonable up to say 150Mhz, for a BNC to BNC patch?

http://uk.pasternack.com/
http://www.hubersuhner.com/en-gb/

I buy my BNC RG-58 and other RF cables from them.

Thanks Mr hound, may the Walls be with you

[Electro Fan]

As long as we are wandering around the topic a bit, and not to state the obvious, but in case it helps anyone, if you want to compare the effect of cables (different materials, lengths, etc.) an easy way to do it is to attach two alternative cables to a two channel generator and set the channels for tracking - then change frequencies, amplitude, etc. and watch rise times and fall times, etc. on your scope. 

[miguelvp]

DE0-Nano driving an ADV7125 3 channel video DAC capable of 330MHz (8 bits per color)

Not a perfect 50% duty because I was just playing around trying to push it. Not a very clean solution as you can see.

75 Ohm terminated as I recall because it's hooked to a VGA output, and I have a VGA to BNC cable.

12.50MHz (DAC running at 50MHz but needs 4 points for a square wave)


82.51MHz (4 points, low,low,high,high at 330.04 MHz max of what that DAC can do)


The limitation is most likely the FPGA PLL and my coding, the driving clock I believe is derived from the on board 50MHz or it could be 25MHz crystal.

[K6EEP]

OMG I just hooked up my Wun Hung Lo factory signal generator to my Tektronics TDS 2014B 100Mhz scope.  A 1Mhz square wave looked so bad it won't sync to it. The edges have so much ringing on them that it's impossible to see a flat spot.  It just looks like hair in a mullet pattern. I even tried different cables and lower frequencies. No better.
There is a small section on the top of the waveform where a flat spot can be seen.  So that leads me to believe it is in fact a square wave.
Looks like I am going to save up for a new signal generator next. 
I appreciate this thread.  It got me off my bum and made me look. 
Thanks!

[miguelvp]

Like the video DAC.    Show some pictures of the board!

Here you go, board is on the right attached to the inclined FPGA DE0-Nano:



The input clock feeding the PLL is 50MHz, this is from a video converter project that it is dormant at the moment:


Here is a picture of the board from where I bought it, the connector is compatible with the Altera GPIO 40 pin connector:



Not all of the pins from the connector are wired to the top connector btw, which is very strange they didn't do that. I would have loved they did so I could use the unused pins for other things.



Here is where I got it from:
http://www.wayengineer.com/digiasic-fpga-adv7125adv7123-vga-board-p-160.html

[tautech]

OMG I just hooked up my Wun Hung Lo factory signal generator to my Tektronics TDS 2014B 100Mhz scope.  A 1Mhz square wave looked so bad it won't sync to it. The edges have so much ringing on them that it's impossible to see a flat spot.  It just looks like hair in a mullet pattern. I even tried different cables and lower frequencies. No better.
There is a small section on the top of the waveform where a flat spot can be seen.  So that leads me to believe it is in fact a square wave.
Looks like I am going to save up for a new signal generator next. 
I appreciate this thread.  It got me off my bum and made me look. 
Thanks!

Welcome to the forum.
Before you do have you read all of this thread?
Termination is very important to inhibit ringing.
Look at miguelvp's setup and see the Tee BNC's terminated with 50 Ohms on his scope inputs.

First try a similar setup before you spend up.

[miguelvp]

Just to point out, that the purple terminators are 75 Ohms (VGA is terminated that way) the green one is 50 Ohms that I connected to the  vertical sync (just because I didn't have more 75 Ohms terminators).

[tautech]

As long as we are wandering around the topic a bit, and not to state the obvious, but in case it helps anyone, if you want to compare the effect of cables (different materials, lengths, etc.) an easy way to do it is to attach two alternative cables to a two channel generator and set the channels for tracking - then change frequencies, amplitude, etc. and watch rise times and fall times, etc. on your scope.

Here's one I set running a for while after Self Cal of both Siglent SDS2304 & SDG1010.
Both AWG channels checked for SAME settings ie.
10 MHz square wave, 3 V p-p, 50 Ohm source

DSO
50 Ohm internal termination
Statistics ON for ~20,000 counts then image saved.
Delay 5ns for ease of reading stats. 

Cables
AWG Ch 1: 1M RG-58C/U as used previously to DSO Ch 1
AWG Ch 2: 500 mm unknown brand/spec/type to DSO Ch2

Seen are some interesting variations in the Mean values recorded.
Risetime in particular between the 2 AWG channels with 0.6ns variation, Channel 2 the slower.
But to be fair Ch 2 is operating at its max 3 V P-P output into 50 Ohms.
Both channels have risetimes nearly twice as fast as the spec'ed 12 ns and as good as the published 7ns Pulse specs.



But what about the unknown spec cable?
Now we have the unknown cable from AWG Ch1 to DSO Ch2.(cables swapped at AWG)
You can see in the stats how the unknown cable risetime is now faster as a result of the greater drive capability of Ch1 of the AWG.



So lets reduce the P-P voltage to a lower level that AWG Ch2 is more capable of driving. (not max'ed out)
The Risetime, V p-p and Std Dev values are now MUCH closer between channels.
AND it seems at 10 MHz this unknown cable has little affect on results. 

[EV]

Rigol DS2202, DG4000:

I hope your DG4000 wasn't set to 50% duty cycle

That was from a Rigol DG4000 series at 40MHz with a rise time less than 2ns?  Must be either a DG4162 or maybe a DG4102.  Either way, impressive.  (I'm betting you had it set to something other than 50% duty cycle.)

Yes it is DG4162 and output is set to 160 sine wave. The scope is connected to sync out connector which gives 40 MHz square wave pulse when output is at 160 MHz sine wave. Rise time is about 1.5 ns measered with DS2202 (BW set to 300 MHz option).

[TMM]

Hah, I was wondering how you managed to get such a nice square wave out of a DG4000.

Here is a DG4062 (mod -> 'DG4202') and DS1054Z (mod -> DS1104Z) using the sync output:


And not cheating (using DAC output):

[Coliban]

Siglent SDG5082 to Siglent1102CML

I soldered 50 Ohm Resistors to the connectors, then it looked better.

[EV]

Hah, I was wondering how you managed to get such a nice square wave out of a DG4000.

Here is a DG4062 (mod -> 'DG4202') and DS1054Z (mod -> DS1104Z) using the sync output:

You have mod DG202. What is the frequency of sync output if you set output to 200 MHz sine? Is it 50 MHz square wave pulse or is it still 40 MHz?

[Rupunzell]

There are a great number of variables at work here. Everything from cables, connectors, overall set-up, instrumentation and more affect the visual results.

If one were to dig into vintage pulse/square wave generators there are often a number of adjustment to get optimized pulse response at the output. Notables would be EH-Research, Datapulse, Hewlett-Packart, Tektronix and others.

There was a time when folks who worked with this stuff really cared about pulse quality to where it was an engineering speciality (aka pulse engineer). This work was part of early digital where the industry was trying to figure what was do-able, what was not and how good pulses had to be to transmit data with reliability and be robust in a system.

This was the age of tunnel diode, snap diode, hot carrier diode clamped and similar devices were used in pulse / step wave form generation. The picosecond race was on.

In time, high speed logic evolved as the industry gained a much better understanding of how to make pulses go fast, be reliable and more. ECL is a good example of fast logic that can offer low noise if implemented properly. The Hewlett Packard 8640 RF signal generator uses a cavity oscillator with a group of ECL dividers and filters to produce a highly stable and low distortion RF sine wave.

Bottom line, newer is not always better. Often times vintage test gear is looked down upon as old. obsolete and in-the-way-boat anchor. When on balance it really depends on what the measurement needs are as the latest and greatest is not always the ideal solution to any given problem. The ideology of smaller is always better should not be the single parameter of desirability.
 

Bernice

Jeez... Some of the low frequency squarewave plots from the modern stuff from Rigol and Siglent are less than impressive.

I'm not really into pulse risetime races but I do have some ancient and low spec pulse generators from the 1970s here. eg the bargain basement 10MHz models from HP or Datapulse and they produce nicer square waves at 1MHz and 5MHz. (HP8002A and Datapulse 101) The Datapulse claims a risetime of 5ns and the HP is about 10ns. I paid £5 for each of them about 20yrs ago at a ham surplus sale.

Do people really accept that level of performance from Rigol? Looks woeful compared to basic old school stuff that was designed and built about 40 years ago.

Note: I just noticed that the later plots from the Siglent gear look to be better. So maybe the first plot was poorly set up?

[Rupunzell]

How do you know for fact Bernice is a "he"?
It seems every web forum has their wanna be top dog-know it all types.

Bernice

Bernice thank you for your fresh input, no doubt you have more to offer. 
Can I make the suggestion that you quote before your reply as it makes the post easier to read.
Sort of like how I've amended your last post. 

Save your breath. He's pretty deaf on that ear 

[TMM]

Hah, I was wondering how you managed to get such a nice square wave out of a DG4000.

Here is a DG4062 (mod -> 'DG4202') and DS1054Z (mod -> DS1104Z) using the sync output:

You have mod DG202. What is the frequency of sync output if you set output to 200 MHz sine? Is it 50 MHz square wave pulse or is it still 40 MHz?

Just tried it - 50MHz.

[Rupunzell]

Thermistors don't work that well as the FB stabilizing element. The time constant due it physical size and environmental effects makes a thermistor less than ideal choice.

Photo-resistor coupled with a light bulb or similar was commonly used as a control element in stuff like this from that era. Photo-FETs  devices were also made and used during that time. Other ways would have been to use a FET's channel resistance as the FB control element and control circuit.

What is remarkable, the light bulb works amazingly well and is simple.


Bernice

In the circuit diagram the light bulb is only used as a battery check and there is a thermistor for temperature feedback.  Of course the thermistor might actually be another light bulb -  I've not taken it apart to have a look yet.

[Wuerstchenhund]

The following screenshots show again a 1MHz and a 20MHz square wave from a Rigol DG1062z, but this time the scope (LeCroy WavePro 7300A) was running in 11bit ERES mode which limits the bandwidth to 160MHz (which eliminates some of the noise).

[Electro Fan]

There are a great number of variables at work here. Everything from cables, connectors, overall set-up, instrumentation and more affect the visual results.

If one were to dig into vintage pulse/square wave generators there are often a number of adjustment to get optimized pulse response at the output. Notables would be EH-Research, Datapulse, Hewlett-Packart, Tektronix and others.

There was a time when folks who worked with this stuff really cared about pulse quality to where it was an engineering speciality (aka pulse engineer). This work was part of early digital where the industry was trying to figure what was do-able, what was not and how good pulses had to be to transmit data with reliability and be robust in a system.

This was the age of tunnel diode, snap diode, hot carrier diode clamped and similar devices were used in pulse / step wave form generation. The picosecond race was on.

In time, high speed logic evolved as the industry gained a much better understanding of how to make pulses go fast, be reliable and more. ECL is a good example of fast logic that can offer low noise if implemented properly. The Hewlett Packard 8640 RF signal generator uses a cavity oscillator with a group of ECL dividers and filters to produce a highly stable and low distortion RF sine wave.

Bottom line, newer is not always better. Often times vintage test gear is looked down upon as old. obsolete and in-the-way-boat anchor. When on balance it really depends on what the measurement needs are as the latest and greatest is not always the ideal solution to any given problem. The ideology of smaller is always better should not be the single parameter of desirability.
 

Good post and Good history and Amen  to all that!

There was a time when large companies (providers and/or user organizations) would get together to talk about how to make their private networks talk to one another.  This was when 56kbps and 1.5Mbps were as fast as most data traveled.  The first half of almost every first project meeting was the same thing:  "Are you going to give clock or are we going to give clock?  Who is going to give clock?"  I think if I had to do my career over and could pick something to be really good at in a time when it was definitely needed and valuable I'd like to be one of those specialized "Pulse Engineers", and then if I could move up the chain and broaden out I'd go for "Senior Waveform Engineer"    In an ideal lab you could have some of the best vintage gear (when it's still working) and the best of the new gear. 

[Electro Fan]

The following screenshots show again a 1MHz and a 20MHz square wave from a Rigol DG1062z, but this time the scope (LeCroy WavePro 7300A) was running in 11bit ERES mode which limits the bandwidth to 160MHz (which eliminates some of the noise).

That's pretty cool - kind of like being able to dial-in the signal to noise ratio or the Eb/No

[Rupunzell]

Early on in this discussion mention was made of the Hypress PSP-1000 and PSP-750.

The intent of that note was to see of anyone here had a Hypress PSP-1000 or PSP-750. These are 70 Ghz sampling systems that use super-conducting Josephson junction device based time domain instrumentation, circa late 1980's.

These are the same folks who make really fast digital stuff.
http://www.hypres.com/products/


Bernice