These mods worked well in my 5200a (2nd gen, no Bessel filters). Thanks for the careful and clear analysis. My CD came with a corrupted visa540_runtime.exe file but I found it easily enough online. The software works but is a bit flaky, and it is possible to hang the device if you drive it too hard at 25 MHz and 20 V, but the waveforms are a lot cleaner than the stock unit was before the mods. The lowest noise free amplitude I could get was 60 mv p-p on one channel, 70 mv p-p on the other - a bit high for my radio alignment work so attenuators will be necessary in my case. Also, I highly recommend you change the heatsink to one as large as you can get between the two relays as it gets quite toasty. Definitely use thermal compound, too, and it might also be a good idea to change to a beefier wall wart P/S to forestall some of the hangs.
These units can go faster than 25MHz using the Arb functions. I can get 40MHz without too much distortion. There is a software interface that works kinda OK with your PC to give access to the Arb functions, sweep generator, and pulse outputs. I haven't figured out how to sync channel 1 & 2 to give synchronous waveforms to measure filter responses. External filters are the way to go :-) As a HAM I'm happy that I can actually get this up to the 10 Meter band. The one problem I still see is that the manual says that the TTL port on the back can be both input and output but there is still no information available for this function. Thanks again for this video!!!
The USB/Software interface shows 2048 samples for each Arb waveform. If you program a single sine wave for all 2048 samples the output freq matches the displayed value. If you program 2 sine waves, each of 1024 samples, then the output will be 2x the displayed Freq. and so on. The output slew rate of the original op-amp is limiting the max Freq. I am going to use the new one you recommenced and see how that works.
Awesome awesome! Thanks for making this follow up video and including your fixes. I just rediscovered the other video, and stumbled across the comments saying the model (and price) had changed. I'd been looking for a decent inexpensive starter generator, and almost bought one of these a while ago, but didn't feel rich enough at the ~$100 price point. Though the original had a lower noise floor, I gotta say I'm pretty tempted to grab one of these cheaper ones now (and the better opamps). Thanks again!
Excellent video. Thanks! I also wish it had a better SEPIC power supply because there is a huge amount of ripple on +/- 13V lines when this thing is driven hard.
Definitely a good unit for the price, I had to solder the bnc connectors. when I would move them, I would lose signal. I also put a brightness adjustment pot on the side for the lcd. Thanks for the vid.
Not too bad for the price.. I use mine for injecting signals into gear I am trying to fix.. since I don't care about damaging this sig gen.. they should be pretty easy to repair too if that happens. I wouldn't want to risk my more expensive sig gens for that type of work.. Love your videos.. keep up the good work!
I wounder how they can make a 12bit R2R ladder that is monotonic. They must use 0.1% resistors, and by implication thin film ones, and those are significant more expensive that 1% or 0.5% thick film ones. As for the output filtering a 7th order Butterworth aligned filter would be practical. A Bessel filter would have no ringing, but the roll-off characteristics is pretty bad (unless you compensate this with pre-emphasis). But a solder blob? Nah! Any kind of low pass filter is preferable. As a end note, I see lots of function generators using elliptical filters. In my honest opinion, that is unneeded and will add too much ringing, even more than a comparable Chebyshev of the same order. Any signal with sharp edges will show lots of ringing.
excellent work, I wish the Chinese had watched your videos, and followed your easy troubleshooting techniques, they would have produced a better product. It seems to me that the op amp AD812 inadequate slew rate never crossed their minds otherwise the would have replaced them with something faster like the one you used the TIS3092. I found the book " RF circuit Design" you used as reference to create your filter very useful. who is the author by the way. again thanks for a job well done
it sucks that the manufacturer eschewed improving their product and simply made the specs look better. you proved that with just a few changes they could have a pretty decent product.
Could they not have added a circuit to switch in or out a low-pass filter? Turn the filter on for sine waves and off for other waves? Is there any way to add a filter to the new model? Great work, by the way. Very thorough!
Your relatively simple and very low cost mods of this model and the previous one which improve the performance greatly makes me wonder about the competence of the engineer(s) who designed these. Anyway, in your "Fixing the MHS-5200A" video, what is the book you show with the bandpass design table in it?
RF Circuit Design by Chris Bowick. A great book all around for RF related design! www.amazon.com/Circuit-Design-Second-Christopher-Bowick/dp/0750685182
It has some kind of amplifier which can drive 1A loads with some connectors it has in the back. I am sure that only works with low frequencies but it's still a very interesting feature.
You have to look at the specifications in the eBay listing. All the ones I saw showed a picture of the old model, but list the newer specifications in the auction description.
Have you noticed any amplitude inaccuracy at the very low-end of frequency capability on this FG or any others? I've got a Rigol 1032Z and at about 10Hz I start seeing amplitude response drop. At 1Hz the amplitude of my sine wave is about 66% of what the instrument is set to. Is this common behavior in FG's? By the way: I've set both the 1032Z's output impedance and my oscilloscope's input inpedance to 1M ohms.
I didn't test the MHS5200's at frequencies that low (only down to 1kHz), but the outputs of my Agilent and Keysight function generators are quite flat down to about 3Hz. At 1Hz, they are at 75-80% of the expected amplitude.
Thanks devttys0: interesting to hear about another AWG's performance in this regard. Technically, I wonder why this amplitude discrepancy occurs. First guess is the LPF isn't optimized for the very low end of the frequency range.
@APVT80 I just measured my HMS at 10hz and I am not seeing any amplitude drop at lower frequencies: i.imgur.com/Y9yESSL.png (1 Mega Ohm termination) MHS is set to the default 5V Vpp, as you can see in the measurements it's just slightly above that.
So basically these are crap and would cost about 50% of their original cost in parts to get them running anywhere near their advertised capacity. Not including labour! Having purchased the first one and being so disappointed with it, I certainly wouldn't buy the new one.
