Welcome to my review of Siglent's SDG6000X series arbitrary waveform generator.
This is Siglent's highest end wave generator and it has a 16 bit DAC.
Obviously most people are going to go for the 200MHz model, but what makes this series
interesting is that they have a variant that goes up to 500MHz!
Also, with every variant you can buy an upgrade that lets you generate IQ signals from the
two outputs.
I insisted that Siglent send me the 500MHz version to evaluate because that's a big technical
achievement to pull off, especially when you consider Rigol's closest model goes up to
350MHz and costs a lot more.
It almost sounds too good to be true.
I'm going to test whether this thing can actually deliver on its claims at 500MHz, and I think
it's safe to assume that if it does, then the lower end models will also perform just
fine.
This review is being done under the explicit terms that I can say whatever I want about
the product, good or bad.
Opening up the box, you get the generator, power and USB cables.
There are also two BNC cables made out of 3D-FB coax, which in theory should be a little
better than standard RG-58.
So let's power it up and take a look!
One of the first things I noticed is that there's an annoying beeping sound whenever
you do anything, and fortunately you can disable it.
The screen resolution is 480x272 and it's reasonably bright.
No problems with viewing angles from the top and the sides, but the colors start looking
slightly different when viewed from a sharp angle down below.
It's not a problem, everything is still perfectly readable.
As you can see the user interface is fairly plain, but it's easy to read and it's functional.
Overall the screen is way better than the ones used on Siglent's older models.
The other important thing to note is that it's a touch screen!
Initially I found that I was fat fingering a lot of the button pushes.
After I ran the touch screen calibration routine things worked a lot better, but it still sometimes
feels a little glitchy on the smaller menu options.
So it's not perfect, but it's definitely better than no touch screen, and overall it does
make the product easier to use.
And in case you're wondering there are no problems with fingerprints on this screen.
As for the physical buttons on the instrument, everything seems fine.
The buttons and dial are nice to use, and in general the exterior build quality seems
pretty good.
I will say this though, I feel like Siglent copied a lot of ideas from Agilent/Keysight.
The layout of the controls and ports is very similar.
I'm not sure how Keysight feels about this, but from a user's standpoint, this is a good
thing because I always really liked my Agilent's interface.
(The fan seems slightly quieter than the average piece of lab equipment).
Okay!
Let's start evaluating the performance of the unit.
The first thing to highlight is that although this is marketed as a 500MHz wave generator,
this only refers to the sine wave capabilities of the unit.
It can do 500MHz sine waves, but the square wave capabilities top out at 120MHz.
This is a common thing for manufacturers to do nowadays and if you want to know what it
can do with other waveforms you have to dig into the datasheet.
Also at different frequencies you get different maximum output voltage swings.
For example at 1MHz you can get up to 10Vp-p into a 50 ohm load, at 50MHz it drops down
to 5, and beyond 360MHz it drops down to 640mVp-p.
Okay!
Now let's take a look at the waveform quality.
I've got the unit generating two 500MHz sine waves in antiphase.
I've got my scope inputs set to 50 ohm termination, and as you can see the quality of the sine
waves is surprisingly good at the top end.
There does appear to be about 50ps of lag, but it's hard to say whether this comes from
the generator.
This could be caused by even a few millimeters difference in the signal path length.
When you're working at radio frequencies, this is the kind of stuff you need to think
about.
So the sine waves look great.
But!
Savvy engineers will know this is not a good test.
I'm trying to display a 500MHz sine wave on a scope with only 500MHz bandwidth, and I'm
also running the signals through several feet of coax, so there's going to be a low pass
filtering effect.
The actual waveform may be a lot more jagged and trapezoidal - we just can't see it.
So here's a better test where we view the frequency content of the signal with a spectrum
analyzer.
The setup here is a 12" RG316 cable going into an SMA to type N adapter.
And I'm generating a 0dBm sine wave at 500MHz, which is roughly the maximum you can do.
Now we can actually see the distortion in the sine wave.
Our second harmonic is about -37dB down, and the third harmonic is about -34dB down.
There are a couple of other components but they are relatively insignificant.
Overall, the results are shockingly good.
I played around a little bit, searching for the worst case scenario, and at 400MHz I was
able to find a harmonic at -31.8dBc.
This is several dB better than the datasheet's claim of -28dBc.
And for frequencies around 90MHz we are looking at about -58dBc.
Next, here's a shot of how things look close to the carrier itself with 10Hz resolution
bandwidth.
Excellent - it's sharp and stable.
And here's another shot at a tighter span.
The arb capability is marketed as 2.4GSa/s so I was kind of worried a 500MHz sine wave
would look more like an ugly triangle wave, but that is not the case.
The SDG6000 series spits out very nice sine waves throughout its frequency range.
My test results were even better than the claims of the datasheet.
But!
It's not all sunshine and roses!
While doing these tests with the spectrum analyzer I did find a separate issue.
When I turn the output of the generator off, you can see we get some signal leakage from
the generator at exactly 2.4GHz, which is most likely a clocking signal.
The amplitude is about -65dBm when the output is off, and about -72dBm when the generator
is on.
It's very weird that it's worse when the output is off.
If you plan on working near that frequency, you should be aware of this as you might mistake
it for a spectrum analyzer spur.
Moving on with performance analysis, Siglent claims rise and fall time edges as fast as
1ns.
I lack the scope bandwidth to properly verify this claim, but that looks about right.
And notice that the edges are fast enough that I'm getting noticeable ringing.
At the RF frequencies this thing can do, you're really limited by the cables and accurate
impedance matching more than the instrument itself.
I already showed you frequency stability on the spectrum analyzer, but in case you're
curious, here's an infinite persistence scope view at 1 million waveforms per second.
I don't see any jitter issues, but again, you'd need scope bandwidth way higher than
1GHz to really capture the limitations of the unit.
Now I want to start talking about features and operating modes.
I found this to be a pleasant surprise - there are a couple of different sweep modes - there's
log and linear, and you can change whether it's sweeping upwards in frequency, downwards,
or back and forth.
I'd imagine audio engineers would have a lot of fun with this.
The other thing that really impressed me was that you can generate a square wave, pulse
width modulate it, then you can change the duty cycle according to pretty much any ramp
function you want!
So within seconds you can create something to test the power stage of a class D amplifier,
or a motor control circuit.
You can do this independently on both channels and I found no problems with keeping things
in phase.
In terms of duty cycle limitations, this depends on the frequency you are using.
At low frequencies you can get way below 1%.
At 3MHz you can just barely get 1-99%.
And by the time you get up to 120MHz you are limited from 40 to 60.
I can't imagine this being a problem for anyone, and overall I am very happy with the PWM and sweeping
capabilities of the unit.
Next let's talk about some of the little extra features that you don't get in most wave generators.
You can artificially add noise to your signal and pick the signal to noise ratio.
You can also add harmonics to a signal.
I've got to say the menu navigation for doing this was pretty awkward, but the onscreen
visualization is extremely helpful.
You can sum waveforms together and pick what you want to get on the channel output.
There's tons more features like this, but I'm not going to waste your time reading things
you can get from the datasheet, the bulk of this review should be testing and verification.
The bottom line is, there's a lot of features.
Next I want to try out some of the modulation options.
We've got a lot of different choices here including phase and frequency shift keying.
I think the most fun way to test modulation would be with actual radios, so here's amplitude
modulation at around 1MHz.
And frequency modulation at 89MHz.
And yes, I am intentionally using poor antennas so I don't annoy my neighbours.
There's plenty of wave generators on the market that can do all this, but this is where things
get interesting.
Can the unit do modulation all the way up to 500MHz?
Well, I can't do exactly 500, because then I'd be deviating above the 500MHz limit.
So let's try 499MHz.
I've got my phone connected to the external modulation input, and as you can hear, it's
working!
Basically, people working in the 433MHz and 440MHz bands could get a lot of use out of
this thing.
Alright, now let's look at the arbitrary waveform generation capabilities.
There are a massive number of built in waveforms.
I checked them out, and in general they seem to be constructed well.
(Hello! Hello! Hello!)
If you want something other than the built in waveforms you can use Siglent's EasyWave
software.
The latest version is a lot better than what Siglent was putting out a few years ago.
There are a bunch of different options for hand drawing waveforms.
You can type out parameters for common waveforms...
And you can manually type out equations.
The software is VISA based and in general I found it to be stable.
But there is one thing that I felt was missing from what is clearly meant to be a high end
product.
You can't copy and paste different waveforms back to back, and chain them after one another.
You'll have to generate the datapoints in excel and import them.
I was hoping to do a demo where I reverse engineer a 433MHz transmitter and clone it,
but it's just not practical.
Overall I would describe Easywave as "simple and functional".
Next let's take a look at what makes this product really interesting for RF work.
For an extra $669 you can get the option to generate I/Q signals.
It's pretty easy to do it right off the unit itself, and there's a ton of options ranging
from 2-ASK to 256-QAM.
I've got a demo set up here with an IQ modulator evaluation board from TI.
I'm going to use it to generate a 1700MHz carrier, and then we're going to modulate
it with the I and Q outputs from the wave generator.
The idea is that you can use the unit to generate test signals for RF equipment that you are
designing.
Here's a shot of 2-ASK at 5Ms/s.
Here's 8-PSK.
Here's 16-QAM at 11Ms/s.
And the unit maxes out at 256-QAM at 18.75Ms/s.
Finally I want to show you that adjusting the DC offset on the I/Q outputs is possible,
but only up to 0.25 volts.
This may not be enough for some modulator ICs.
I also spent some time playing with the EasyIQ software.
It's very simple, it's stable and it gets the job done.
Basically you can think of it as a different interface for changing the IQ settings on
the unit.
Ok, so what's the final verdict?
Overall it's a hell of a waveform generator.
It performed well throughout its frequency range, and it has a very full feature set.
It's marketed as an arbitrary waveform generator, but it can replicate a lot of functionality
you'd get from a dedicated RF signal generator.
The negatives are that the touch screen is occasionally a bit finicky, and there's some
noticeable 2.4GHz leakage which may or may not be an issue depending on what you're doing.
In terms of performance per dollar versus its peers, the SDG6000X series is going to
be pretty hard to beat.