DSA-815 Auto RBW help needed - Page 1
Forum section: electronics / testgear

author: Chris Learing
author_rank: Contributor
timestamp: December 01, 2021, 12:52:30 pm
content: I'm trying to get the EMI auto RBW working properly on the above SA. It doesn't make sense to me.On my EMI receiver (not the DSA-815), with it set to auto RBW, it automatically sets the RBW to that required for the band. So for instance a scan from 9KHz to 30MHz will automatically use the "Band A" RBW of 200Hz from 9KHz up to 150KHz, then automatically change from 200Hz RBW to the "Band B" 9KHz RBW for the rest of the scan. This seems logical to me, and exactly what I expect.On the DSA-815 this doesn't happen. What I have discovered is that it only seems to depend upon the frequency span, regardless of the actual centre frequency. A scan with a span of 92KHz always uses 200Hz RBW, regardless whether this is at 10KHz, 500KHz or 500MHz. It makes no difference. A span of 93KHz always uses 9KHz RBW. A span of 92KHz always uses the 200Hz filter. I haven't bothered checking the exact frequency it changes as it doesn't seem relevant to me.To be clear, set the DSA-815 to EMI filter, and "Auto RBW", set the centre frequency to 1.2GHz, span of 92KHz and it uses the 200Hz filter! At 93KHz span it uses the 9KHz filter. At 1.2GHz it should be using a 1MHz filter which it doesn't even have.A typical scan is bands A and B, covering 9KHz to 30MHz in one go. This needs the RBW to change from 200Hz to 9KHz at 150KHz. That doesn't seem to be possible on the DSA-815.Have I missed a setting somewhere or is the DSA-815 just weird/wrong? Maybe I've misunderstood how it's supposed to work?If it's relevant I am using the "infinite time trial" hack, but I'd be surprised if that's in any way connected.

author: egonotto
author_rank: Super Contributor
timestamp: December 02, 2021, 01:41:56 am
content: Hello,I think you misunderstood how it's supposed to work,The RBW should much lower than the span, whatever the center frequency is.Look at the great video from w2aew: ""Best regardsegonotto

author: Chris Learing
author_rank: Contributor
timestamp: December 02, 2021, 11:00:40 am
content: Thanks. When in EMI mode I expected it to set the correct RBW for the band being scanned. Clearly its actual purpose is not related. Again, ta.Edit: Typo.

author: xmo
author_rank: Regular Contributor
timestamp: December 02, 2021, 04:59:03 pm
content: Perhaps in EMI mode the auto RBW is acting like other spectrum analyzers.Take a look at this Keysight document that shows how their auto RBW chooses the setting based on center frequency.

author: paul@yahrprobert.com
author_rank: Regular Contributor
timestamp: December 02, 2021, 05:18:17 pm
content: My experience has been that the number of sweep points, the sweep speed, the RBW, and the detector type are never automatically set to what you want for your task. And don't get me started on the horror known as video bandwidth.

author: Chris Learing
author_rank: Contributor
timestamp: December 03, 2021, 11:59:35 am
content: Thanks all.I was simply misunderstanding the EMI option. I expected it to act more like an EMI receiver (setting the correct RBW for different bands etc) as opposed to a standard spectrum analyzer with a few extra features.