Rigol DHO802 Oscilloscope - Bandwidth better than advertised !

I purchased the low-end of the new Rigol DHO800 series scope line, hoping the bandwidth might be a bit better than advertised, based on previous experience I had with some Keysight scopes. It is ! (Your mileage may vary.)

[@electronics.unmessed]

Great! Just bought exactly that model. Thx for your hints.

[@itluis2009]

Me too

[@Tokyo1991.JL1AJE]

Have you played around with the FFT on this? I couldn’t find details on the RBW setting range in the info available online and am wondering if this scope can work as a spectrum analyzer for HF/6m.

[@MegawattKS]

Yes - it works pretty well, for a scope. But it's not going to be anywhere near as good as a real spectrum analyzer, since it has no analog filtering to address intermods and other distortion products. Have you considered one of the low-cost "TinySA" instruments? I'm actually amazed at how well they work, especially given the US $60 cost 🙂 As for the scope, the controls aren't great, but you can set the basics, like Start/Stop frequency. You have full control over attenuators, RBW, etc on the TinySA, but none of that on the scope. That said, I was impressed when I used it to look at the FM Broadcast band (88 to 108 MHz in the US). Here's a video where that's done so you can see the screen: kzbin.info/www/bejne/Y6HQZnR6f9d-ipY I keyed it up to start at that point in the video. Note that there are signals below 88 MHz, and I'm pretty sure these are distortion products in the scope/ADC and not real. Hope that helps. 73's

[@Tokyo1991.JL1AJE]

The TinySA Ultra is a no brainer for the price for sure. Just wondering what this scope offers or how close it comes to ‘usable’ in that regard. There are some nice multi domain scopes out there for about $900 but sadly not 12bit and unfortunately the TinySA Ultra doesn’t offer the RBW required for the local Japanese ‘FCC’ registration criteria when submitting for a permit to operate an imported or home brew rig. Background info - every single piece of kit that either generates or amplifies RF has to be approved and registered (tied to your station permit & callsign) over here. Real PITA 73 John

[@Tokyo1991.JL1AJE]

Just watched the video. Saw the RBW was 100KHz. It must go smaller no? Btw - who’s going to offer a 20KHz LPF option on a scope with a 125-150MHz front end 😅 I’ve always knocked up my own test gear/adapters etc to get the job done. It’s all part of the fun 👍🏻

[@MegawattKS]

Sorry for the delay in replying. Yes - I just tried some things today and it can definitely go lower. But the trick is to work with the number of points used (memory depth) and the sweep speed. I can't just tell it what RBW I want. But it might be doable by varying those. I tried a 51 MHz CW signal at -20 dBm and was able to get a phase-noise spectrum display pretty well. I used 51 MHz center and 100 kHz span settings with the memory depth set to 1M (the max for the FFT on the 800 series), and a timebase of 500us/div. That gives a sample rate of 156.25 MS/s, so there's no aliasing. The RBW reads out as 100 Hz. Not sure why it says 100 Hz, since the total time window is 5ms, which would imply a 200 Hz FFT bin size. Hmm... Anyway, the spectrum looks pretty decent, and I can even pick out the PLL loop bandwidth from it. I think its a bug. If I turn on the horz vernier and change the timebase to 490us/div, it then says RBW=199.9 Hz. There are also possibly some spurs, but overall, I'm impressed with the digitizer and FFT the more I play with it :-)

[@MegawattKS]

To be fair, on the 20 kHz LPF thing (in the other video), it's needed of course to see low level signals. Bandwidth is great, but unnecessary BW for the signals of interest leads to excessive noise :-)

[@johnwest7993]

What does it do with 100 MHz sine waves?

[@MegawattKS]

I made some tests with up to 300 MHz sinewaves and it had the expected rolloff in amplitude for a 125 or 150'ish MHz 3dB corner. And it even triggered up to at least 300 MHz sinewaves with no ill effects. One thing I did notice was that at the higher frequencies (> 70 or 100 MHz), it won't display a sinewave to full plus and minus 4 vertical units. My guess is it has a slew-rate limit in the vertical amps - producing the "full power bandwidth" limitation that opamps suffer from. Knowing this, I will just keep my displayed waveforms to maybe 4 vertical units peak to peak or less to avoid waveshape distortions when pushing the frequency range ...

[@johnwest7993]

@@MegawattKS, thank you. I'm subscribed to your channel because you actually understand your subject. It's refreshing to watch a technical channel created by a university prof who knows exactly what he's talking about, instead of a HS kid who doesn't know a dBi from a dBd, or an amp builder who speaks in terms of 'Birds' and 'pills', like a couple of channels I've had the misfortune to stumble on. BTW, my DJ name on the college radio station was , 'Meager-milliwatts'.

[@MegawattKS]

Cool! I'm guessing the college station was more than milliwatts though? I went to our college station's tower once to try to track down some intermod issues with a co-sited ham radio repeater. I think they said it was 5 kW when we worked with the station operator to switch the FM transmitter's final off briefly to see if it was contributing (they actually just brought it down to the couple hundred watt level, which was enough for us to confirm it was part of the issue).

[@robertdixon8238]

I assume that the same hardware is used for a range of bandwidths, and software sets the available BW. Why would a 70MHz scope use 1.25GS/s ADC. 125MHz x 10 = 1.25GS/s. Sounds like the software is unlocked, and you have the native BW.

[@MegawattKS]

It's fresh out of the box, so not unlocked. So this is apparently just how its made. Agreed that they likely use the same hardware for the 4 models in the series - except of coarse they don't populate the second ADC or third and fourth vertical amp sections for the 2-channel ones. The same sample rate is used for all. It helps avoid aliasing I guess. The EEVblog channel has some excellent teardown videos that show and discuss the internals. A speculation is that the same custom vertical channel amp ICs are used for all models - so I was curious if it's really significantly dialed back in bandwidth somehow. Unfortunately I don't have the 812 or 814 model units, so I couldn't compare and see if they also go much higher than their specs. Maybe someone with a NanoVNA (which has up to 300 MHz squarewave outputs) and one of those models can check :-)

[@user-vl5hu1mt8m]

This is cose 12bit!