Rigol DSA1030(A) TG output <10MHz? - Page 1
Forum section: electronics / testgear

author: awallin
author_rank: Frequent Contributor
timestamp: January 23, 2017, 04:06:38 pm
content: I was disappointed to see this TG output from both a DSA1030A and a DSA1030 we have. Only a 50ohm cable direct from TG output to RF input.Seems the TG is only useful well above 10 MHz??https://goo.gl/photos/TMJUeZ231JTZvFUE6(I verified with an external signal generator there doesn't seem to be anything wrong at <<10MHz with the RF input)Can someone else verify this with their DSA1030?Is the Siglent SSA3000 any better?thanks!

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 23, 2017, 04:18:08 pm
content: It says so in the specs:TG Output: Frequency Range 10 MHz to 3 GHz , 9 kHz settable

author: Co6aka
author_rank: Unknown
timestamp: January 23, 2017, 04:42:29 pm
content: "9 kHz settable" Yeah......Chinese have sense of humor!Haven't looked into it, the insides of the DSA that is, but I've hazarded a guess someone goofed on the oscillator design which wasn't discovered until after production, and what company, Chinese or otherwise, wants to pay for a recall/retrofit. The output curve looks like the classic RC highpass of a coupling capacitor. If you feel adventurous, take a look at the tracking generator circuitry and see if anything smells like a Chinatown fish market.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 23, 2017, 06:08:39 pm
content: My Agilent CSA (N1996a) does the same, but at least it's not settable below 10MHz. I think it is not easy to go close to DC with the TG because you have to mix the LO with a frequency very close, and filtering will be problematic, so you probably have to do multi stage mixing which introduces other problems.Having said that, the SSA3000 series are specified from 100KHz up, which could be a good sign but I haven't seen the output.

author: cgroen
author_rank: Unknown
timestamp: January 23, 2017, 06:34:25 pm
content: Quote from: awallin on January 23, 2017, 04:06:38 pmI have a 4 month old DSA1030A-TG, what settings should I use to do the check for you ?

author: TurboTom
author_rank: Super Contributor
timestamp: January 23, 2017, 07:30:02 pm
content: I can only report on the DSA815TG (since my SSA3000X is at home & I'm at work) but this instrument also has some peculiarities regarding the tracking generator at low frequencies. Actually, the TG can be tuned down well into the audio range but the output signal starts to get funny at settings less than about 700kHz, see screenshots below. Above 1MHz the level is fairly flat and the waveform acceptable.

author: pa3bca
author_rank: Regular Contributor
timestamp: January 23, 2017, 08:52:53 pm
content: I also did some tests with my DSA815. Looks (kind of) OK to me. Not usable below 9 KHz as per specifications.Above 9 KHz there are some funny jumps but those shouldn't matter as you would always normalize before the actual measurments. A precise RF generator it is not.> 1 GHz it is a mess. I use 1 mtr coax of unknown origin between the TG and the input. But anyway this can be normalized out.I am a bit puzzled by the screenshots of TurboTom. With my DSA815 the waveform @ 10 KHz is not so nice, but from 20 KHz and up it is quite acceptable. (and even so the harmonics from the TG don't matter much, as the SA will only look at the set frequency when tracking).I see you used the 1054. Did you use a 50 Ohm terminator at the scope (especially relevant if the coax between the TG and the input is not very short).My screenshots below:

author: TheSteve
author_rank: Unknown
timestamp: January 23, 2017, 08:55:58 pm
content: Quote from: PA0PBZ on January 23, 2017, 06:08:39 pmTrue, but with the N1996A a small tweak has the tracking gen starting at 1 MHz where it will normalize and still measure return loss etc just fine.

author: TurboTom
author_rank: Super Contributor
timestamp: January 23, 2017, 10:26:52 pm
content: Quote from: pa3bca on January 23, 2017, 08:52:53 pmYes I terminated the line at the scope's input with a BNC "T" and a 50 Ohms terminator on the other side. What's quite interesting with your TG's performance is the shape of the spectrum at full span. What kind of cable / adapters did you use to connect the TG output to the SA input? And what hardware revision is your DSA815TG? Mine is 00.08 (digital) and 00.05 (RF/FPGA). Please see below the TG spectrum that I recorded. I used two N->SMA adapters and a short (25cm) SMA cable to connect TG output to SA input. For better comparison, I scaled one of the screenshots to the same size as yours. I didn't use normalisation. Strange, isn't it?Cheers,Thomas

author: cgroen
author_rank: Unknown
timestamp: January 24, 2017, 08:37:04 am
content: I did some testing on my DSA1030A-TG, both sweep and zerospan (with a MSOX3024T).Funny things happen at 1 MHz and below...Sweep is done with 0.5 meter RG142 between in and out of the analyser.Zerospan measurements are done with 0.7 meter RG58/BNC between analyser and MSOX3024T (set to 50 ohm).

author: pa3bca
author_rank: Regular Contributor
timestamp: January 24, 2017, 09:07:45 am
content: Quote from: TurboTom on January 23, 2017, 10:26:52 pmHere main board 00.04, RF 00.05, Digital FPGA 00.05, boot 00.01.03 and FW 00.01.15. Device is now exactly 3 years old.See attached screenshot of the TG from 0-1.5 GHz. I replaced the iffy coax with the same setup as you: two N-SMA adapters and 25 cm good quality SMA cable. This looks much better (the influence of unspecified coax+bnc connectors never ceases to amaze me)My scan is more jumpy than yours with a few funny bumps, but for a TG quite useable (plm 1 dB variations, easy to normalize out).The scans from 1030's are a lot worse it seems, especially below 100 KHz. The 815 is ok-ish above 9 KHz..

author: rf-loop
author_rank: Super Contributor
timestamp: January 24, 2017, 09:51:28 am
content: Quote from: awallin on January 23, 2017, 04:06:38 pmSSA3021XTG out = SA in (20cm 50 ohm)SA In 50 ohmPeak detect0-1MHz RBW=VBW=1lKz0-200kHz RBW=VBW=300HzTG Normalization OFF0-1MHzA TG 0dBmB TG -10dBmD TG -20dBm0-200kHzC TG 0dBm

author: Co6aka
author_rank: Unknown
timestamp: January 24, 2017, 02:57:15 pm
content: Quote from: cgroen on January 24, 2017, 08:37:04 amYour 1MHz and below traces look like fast edges ("square waves") that have passed through a small coupling capacitor.Thinking about it some more... I'm suspecting they've done something so lame as implementing the tracking gen with a square wave source. Prolly there's a output buffer amp that's RC filtered to "synthesize" a sine wave, and a tiny coupling cap before it that's letting only the fast edges of the low frequencies through. If you have another spectrum analyzer, set the Rigol to zero span and see if the TG output is rich in harmonics.A component change or two might be in order.

author: cgroen
author_rank: Unknown
timestamp: January 24, 2017, 03:00:01 pm
content: Quote from: Co6aka on January 24, 2017, 02:57:15 pmAgreed, it seems that the "9 KHz" is to be taken not too seriously with regards to the tracking generator