R&S HMO1002 -Why I can't see the FFT graph in slow scans? - Page 1
Forum section: electronics / projects

author: zapta
author_rank: Super Contributor
timestamp: August 07, 2016, 07:00:00 pm
content: This is a Rohde & Schwarz HMO1002 oscilloscope with the latest firmware.If I set the horizontal speed to 50ms or faster and then switch to the FFT view I can see the FFT graph (good). If I set the horizontal speed to slower than 50ms (e.g. 100ms), the FFT graph is not shown even though I can see in the upper view that the signal is captured. I used to have this cutoff at 20ms but it moved this morning to 50ms (better) after I upgraded the firmware.I would expect the oscilloscope to be able to do the FFT analysis as longs as the signal is capturedAm I missing something? Is it a bug?FFT works in 50ms setting:FFT doesn't work in 100ms setting:

author: Stwspoon
author_rank: Newbie
timestamp: August 09, 2016, 03:06:40 pm
content: What is your Roll mode setting? Some scope features are affected by roll mode. Roll mode normally is enabled at 100 ms/div, but is adjustable in the ACQUIRE menu. If Roll mode disables triggering, that could explain why you don't see any data.A general hint. Put the instrument you have a question about in the title of your post.There is a R&S representative who hangs out here by the handle "Cook me some Kai" who may be able to help. I have a HMO1212 I can try to duplicate your problem with tonight.Good luck,Stan

author: zapta
author_rank: Super Contributor
timestamp: August 09, 2016, 04:39:46 pm
content: Quote from: Stwspoon on August 09, 2016, 03:06:40 pmThanks Stan. I updated the thread title. I will check the roll mode when I will get back home.

author: nowlan
author_rank: Frequent Contributor
timestamp: August 10, 2016, 05:01:54 am
content: Can always try their customer service. I found they were quite quick to respond.customer.support@rsa.rohde-schwarz.com

author: Gary350z
author_rank: Regular Contributor
timestamp: August 10, 2016, 05:30:13 am
content: I have a HMO1212. I tested it with your settings.FFT works from 50mS/div down to 1S/div. Did not try any slower.Also at 100mS/div:Record mode:Max Sample Rate: FFT worksAutomatic: FFT worksMax Waveform Rate: FFT does not work.Gary

author: zapta
author_rank: Super Contributor
timestamp: August 10, 2016, 03:28:38 pm
content: Quote from: Gary350z on August 10, 2016, 05:30:13 amBingo! I changed the acquisition mode from Max to Auto and now I can go as slow as 1 sec/div and get the FFT graph (didn't try slower than 1sec/div).I will report it to R&S. If they don't support FFT in certain configurations at least they should have a note on the screen saying it with an hint how to resolve it.Edit: in my case, it doesn't work also on MAX SA RATE, works only in AUTOMATIC.

author: zapta
author_rank: Super Contributor
timestamp: August 10, 2016, 03:56:56 pm
content: Just noticed that changing the acquisition mode to HIGH RESOLUTION = AUTO also doesn't show the FFT graph in slow scans (e.g. 200ms/div). I would expect the higher resolution (16 bit) to actually give more accurate FFT results.The FFT function seems to be flakey in general. For example, in slow scans, when I shift the FFT graph horizontally it sometimes disappears as if it cleared the buffer and need to be recomputed.Edit: shifting the FFT graph display up/down also causes it to disappeared until the next recompute.

author: Gary350z
author_rank: Regular Contributor
timestamp: August 11, 2016, 01:09:27 am
content: Hi Zapta,Some additional info:On my MHO1212, when using the FFT at slower time bases, sometimes the FFT trace is not present. I don't recall exact settings.It's a little frustrating. I don't know if it's having the time base slower than a certain point, or some other settings, or a combination of both.I'm not an expert on FFTs, but using them seems to involve adjusting all the settings until you get a good result, as the settings seem to interact with each other, whereas when using a scope I can adjust each setting and get exactly what I want. Maybe I'm just not experienced enough with FFT use.Additionally, on my MHO1212 the three small knobs, horz position, vert position, and trigger level are quite stiff when rotating them. How are yours.ThanksGary

author: zapta
author_rank: Super Contributor
timestamp: August 11, 2016, 02:15:28 am
content: Quote from: Gary350z on August 11, 2016, 01:09:27 amStiff like hell and small. I replaced them with bigger knobs and it's better now. IIRC, it was a 6mm D type shaft but am not 100% sure. (Away from my desk).

author: Gary350z
author_rank: Regular Contributor
timestamp: August 11, 2016, 03:25:40 am
content: Quote from: zapta on August 11, 2016, 02:15:28 amGreat news.I have been wanting to do that but have not found any good knobs.Could you tell me what knobs you used and where you got them.Thanks in advance,Gary

author: zapta
author_rank: Super Contributor
timestamp: August 11, 2016, 05:31:07 am
content: Quote from: Gary350z on August 11, 2016, 03:25:40 amI am pretty sured I used mouser 450-4667. It has an indicator line with I removed with a xacto knife and a file.IIRC, Dave also had an issue with those knobs in his review video.

author: Stwspoon
author_rank: Newbie
timestamp: August 17, 2016, 12:59:54 am
content: Zapata,Glad you figured it out. My little knobs have started loosening up. I wiggled them around a little and pulled the knobs up just a little to make sure they are not rubbing.Stan

author: zapta
author_rank: Super Contributor
timestamp: August 19, 2016, 04:06:56 pm
content: Quote from: Stwspoon on August 17, 2016, 12:59:54 amYou mean loosening in the good sense, right? Do they feel just right now?If so, I may exercise them a little bit. Will try avoiding the temptation hooking them to my drill.