Author Topic: RIGOL DSA815-TG @ 10 MHz issue/bug  (Read 39406 times)

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Offline Howardlong

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #25 on: August 08, 2015, 06:18:31 pm »
If you reduce the TG drive level to, say -10dBm or -20dBm, then normalise, the results are much better. -5dBm isn't enough but it's better than 0dBm.

-5dBm:


-10dBm:


-20dBm:
 

Offline mcinque

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #26 on: August 09, 2015, 12:14:06 pm »
Same behavior here.

main board 00.08
radio fpga 00.05
digital fpga 00.05
firmware 01.12
boot 01.04
 

Online cncjerry

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #27 on: August 15, 2015, 05:19:00 am »
Is the bug in the TG or SA?  if you just run a 10Mhz signal in does the glitch show?  I've been thinking about buying this setup with the TG but that bug would drive me crazy.

 

Offline Giorgio

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #28 on: August 17, 2015, 07:22:19 am »
Is the bug in the TG or SA?  if you just run a 10Mhz signal in does the glitch show?  I've been thinking about buying this setup with the TG but that bug would drive me crazy.

The bug is in the SA WHEN TG is activated. When the TG is OFF the SA works flawless.

I did this check to confirm this (I explained in a replay above, to be able to check the bug without having a passband filter on 10 MHz):

- Connected an external signal generator @ 10.000.000 Hz to the SA input.
- Center frequency at 10.000 kHz to have the trace of the external generator .

When I switch the TG ON (without connecting it to the SA input) I get the trace peak position shifting to the right (or left) a few pixels.
If you use a narrow bandwidth it's more evident.

This small shift is the part missing of the trace when measuring a filter response @ 10 MHz

As I said, maybe this bug is repeated at other frequencies I didn't check, maybe someone will find it.

If you use the instrument on the HF portion (as I usually do) you will hit this bug for sure. I often need to build and trim 10 MHz filters and this bug make it impossible to do and for me this is not an instrument and Rigol is not giving any solution. When I met the german Rigol support at Friedrichshafen they gave me no hopes.

Cncjerry, better you buy a used HP/Agilent unit, you will be happier.

I renew here the question:

Is there anyone else who can confirm the Hardware/Firmware pair showing the bug?







 

Offline Howardlong

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #29 on: August 17, 2015, 07:49:52 am »
Do you get any improvement by reducing the TG power to -10dBm or -20dBm and re-normalising? That seemed to largely resolve it in my limited testing.

It's difficult to say what the problem is. At first I thought it was something to do with the frequency scheme either for the SA or TG, in conjunction with mixer non-linearity, but now I don't know: I took a look at the TG output on a sweep triggered to a scope, but although there is a definite smallish blip around 10MHz, I didn't see any difference in behaviour between 0dBm, -10dBm or -20dBm, other than a smaller amplitude across the span. That would point to mixer non-linearity in the SA rather than the TG at higher power levels, but why it's at this spot frequency I can't explain.
 

Offline Giorgio

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #30 on: August 17, 2015, 09:38:16 am »
Do you get any improvement by reducing the TG power to -10dBm or -20dBm and re-normalising? That seemed to largely resolve it in my limited testing.

From the tests I made when I reduce the TG level the distortion get less evident but it's always there and impossible to make measure if the glitch fall exactly where the -3 dB is.
Anyway some filters with a high loss need a higher TG level to get off enough from the noise floor, I find the 0 dBm level already low for a TG for some applications.

I checked the TG output too with another SA to see if there's a frequency hop passing on 10 MHz but to me it seems ok. Of course the level go up and down but there's Normalize for this.
It's the SA that make a frequency hop in the sweep when the TG is activated. It's clearly visible if you make the test I was explaining in the previous replay.

 

Offline Giorgio

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug now really disgusted by Rigol
« Reply #31 on: August 31, 2015, 07:21:07 pm »
Just upgraded to the new FW 1.14 and the problem is still there.

They are really unable to solve this problem
 

Offline mcinque

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #32 on: August 31, 2015, 08:01:17 pm »
I asked Rigol EU about this and they replied telling that there is a beta firmware that moves the issue from 10 to 8MHz as a temporary fix, do you know anything about it?
In 1.14 firmware release notes there is nothing about that issue fix, so why you were expecting to have improvements by installing it?
 

Offline Giorgio

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #33 on: September 01, 2015, 10:13:16 am »
Yes I already got the beta at the beginning of this year but was of no use, I use the TG mostly on HF region and to have at 8 MHz or at 10 MHz  makes no differences and don't want to switch from a FW to another just to make a new measure.

The fact is that they are not able to find a solution and this is really silly said by a company producing instruments to measure.

Don't you agree?
 

Offline mcinque

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #34 on: September 01, 2015, 11:10:21 am »
I agree. If the unit can't be fixed by the firmware, it MUST be replaced with a different unit with different hardware, in the same way they replaced the DP832. There are no alternatives.
 

Offline ted572

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #35 on: September 01, 2015, 05:01:24 pm »
Hello   Giorgio:
I think that it is very possibly an internal problem with the TG On while using a TG setting of 10MHz at a level greater than -20dBm, and not related to the actual SA Input level.
I suggest trying the following:
1. Set the TG level at -20dBm (default) and add an external 20 to 30dB gain amplifier on the TG Output.  Connect the External amplifier's Output to the SA Input.  You should now have 0dBm to +10dBm for testing a DUT (your 10 MHz Filter, etc.) due to the gain of the external amplifier. 
2. Normalize the system. 
3. Connect your DUT/10MHz Filter between the External TG Amplifier's Output and the SA Input.
4. Does this provide the similar results as 'Howardlong' got with his -20dBm TG level? -> https://www.eevblog.com/forum/testgear/rigol-dsa815-tg-10-mhz-issue/msg726899/#msg726899   But of course you now have a higher TG Level for testing a DUC that has too much loss for testing at -20dBm.
If this helps, the credit should go to 'Howardlong' from the work he did in the referenced link above.  And if it does help, them this may be a useful alternative until this issue is properly addressed by Rigol.
Edit: If your External Amplifier doesn't have a solid 50 ohm output impedance use a 6dB (Min.) to 10dB (preferred) 50 Ohm Attenuator between the Output of your Amplifier and the Input to your DUT.  Of course you will need to Normalized the Spectrum Analyzer (Step 2.) with the 50 Ohm Attenuator on External Amplifier's output.
« Last Edit: September 02, 2015, 05:17:44 pm by ted572 »
 

Online TheSteve

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #36 on: September 01, 2015, 05:17:43 pm »
For building an amplifier this part may be handy - ERA-1sm+ datasheet here - http://www.minicircuits.com/pdfs/ERA-1SM+.pdf
I have considered buying a few myself, it would be as simple as it gets for a nice homebrew amp.
VE7FM
 

Offline Giorgio

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #37 on: September 02, 2015, 04:53:52 pm »
Thank you Ted572 and TheSteve.

I will give a try as soon as I get a nice buffer amp for the TG. I think I have some widebad amps chips in my junk box.

If not I will follow the TheSteve hint.

In the mean time I hope that Rigol comes with a solution to this.



 

Offline ted572

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #38 on: September 02, 2015, 06:03:30 pm »
Thank you Ted572 and TheSteve.
I will give a try as soon as I get a nice buffer amp for the TG. I think I have some widebad amps chips in my junk box.
If not I will follow the TheSteve hint.
In the mean time I hope that Rigol comes with a solution to this.
The Mini-Circuits ERA-1SM+ recommended by 'The Steve' isn't suitable because it doesn't have anywhere near enough gain (also has a minimum order of 20 units).
If I had a DSA815-TG with the 'newer hardware' as yours I would test it myself as I have a RF Amplifier with 20/40 dB of Gain with 50 Ohm I/O impedance.  Hopefully you can come up with approximately 20dB (min.) of gain at 10MHz with a output level of 0dBm (min.).  I guess that this may be a tall order.  So perhaps someone with the newer DSA815-TG that also currently has a 20 - 30 dB gain amplifier will be interested in trying this test for you and everyone else with a newer DSA815-TG.
 

Offline N8AUM

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #39 on: September 02, 2015, 07:06:11 pm »
I was fairly happy till I found this thread  :wtf:
As far as I can tell the SA shifts its frequency ever so slightly and its only noticeable when the RBW is fairly narrow. Using my ol Boonton the SA would show a shift in freq of approximately 156Hz. I tried from 100Khz to 1Ghz. Only at 10Mhz do I see the "missing" portion. I suspect this bug might be another reason why they stopped offering the 10Hz RBW feature ???
In my case it made NO difference of the TG output level that was terminated. For shits n giggles I verified the 10Mhz ref clock out and it was AOK.
Made No difference if I used firmware ver 12 or 14
My sa has board ver .08

I think if A LOT of people complain to Rigol than they might come out with a fix within a couple years  :-DD

Another thing I noticed a while back was the 10Mhz bleed thru if your looking at signals below -125dB but hay, what do you want for $1500 ?
 


 

 
 
 

Offline mcinque

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #40 on: September 02, 2015, 07:46:33 pm »
Rigol knows about the problem, probably they are not receiving enough complaints/pressure from clients.

I think that only a video (maybe from Dave, which has an outstanding visibility) exposing publicly this issue can speed up Rigol's solution, as what happened with the DP832's heatsink.
If I would have known about this issue, I wouldn't have purchased this SA, and so many other clients: a popular channel's video about the bug would expose the issue so that many clients would think twice about the purchase of this model.

This IMO would create a quick response from the manufacturer, since many unit would remain on the retailer's shelfs.
 

Offline ted572

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #41 on: September 02, 2015, 08:47:25 pm »
I was fairly happy till I found this thread  :wtf:
As far as I can tell the SA shifts its frequency ever so slightly and its only noticeable when the RBW is fairly narrow. Using my ol Boonton the SA would show a shift in freq of approximately 156Hz. I tried from 100Khz to 1Ghz. Only at 10Mhz do I see the "missing" portion. I suspect this bug might be another reason why they stopped offering the 10Hz RBW feature ???
In my case it made NO difference of the TG output level that was terminated. For shits n giggles I verified the 10Mhz ref clock out and it was AOK.
Made No difference if I used firmware ver 12 or 14
My sa has board ver .08

I think if A LOT of people complain to Rigol than they might come out with a fix within a couple years  :-DD

Another thing I noticed a while back was the 10Mhz bleed thru if your looking at signals below -125dB but hay, what do you want for $1500 ?

They never ever offered 10Hz RBW.  It was in their FW, and for some strange reason they provided it as a Trial on few units in 2012 or 21013 (?), but never planed for it to be released for the DSA815.  Yes, WTF were they thinking!  Give us a teaser and then pull it back.  Sorry, its NOT for you guys (suckers) to buy! They were at the time going to use common code along with the next versions of the DSA800 Series.  Someone here found it lurking in the firmware while looking for a method to activate the offered options, and fortunately we were able to get it on our original DSA815s.  But now its been pulled out (I guess) and we may never be able to get on the newer DSA815 hardware versions (?).  Yet 'To Be Determined' (TBD).  I'm lucky that I have the original version 5 main board in my older unit.

Congratulations:  You made a nice find with the ~156Hz Freq. shift at 10MHz.  The more that is discovered and reported will certainly help in getting Rigol to take action on this.  And a video Rant (as suggested by 'mcinque') would be a real boost to push this along.
« Last Edit: September 02, 2015, 08:50:53 pm by ted572 »
 

Online TheSteve

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #42 on: September 02, 2015, 08:51:18 pm »
I was sure that I read here that Rigol offered the 10 Hz RBW but only for the chinese market.
VE7FM
 

Offline Howardlong

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #43 on: September 02, 2015, 09:32:14 pm »
The weirdness is that the glitch is significantly less apparent at lower TG power levels, assuming re-normalisation after power adjustment. If it were just a synthesiser/frequency chain discontinuity, Imwould (a) expect the discontinuity to be the same in relative terms and (b) fixable in firmware - assuming they use the same reference for generating below 10MHz as they do above. Or maybe that's the problem.
 

Offline N8AUM

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #44 on: September 02, 2015, 10:11:08 pm »
I noticed absolutely NO change regardless of the TG's level with my toy.
It would be nice if Dave or Shahriar could find some time and investigate this "bug".
Since I dont plan on launching any deep space probes any time soon I can live with all the little Bugs. It's good to know about all of them so you can hopefully find a work around? Thanks to Giorgio for bringing this Bug to everyone's attention.
Anyways, I am not going to hold my breath for Rigol to come up with a fix just to satisfy 10 or 20 customers.
Here's another thing that I noticed with my toy, when I do a screen dump using the LAN connection the speed is super slow, about 30KB/s.  :wtf:
 
 

Offline ted572

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #45 on: September 02, 2015, 10:33:29 pm »
The weirdness is that the glitch is significantly less apparent at lower TG power levels, assuming re-normalisation after power adjustment. If it were just a synthesiser/frequency chain discontinuity, Imwould (a) expect the discontinuity to be the same in relative terms and (b) fixable in firmware - assuming they use the same reference for generating below 10MHz as they do above. Or maybe that's the problem.
I think it is due to some internal coupling at the higher TG levels, and unrelated to the SA Input Level.  That is why I suggest running the TG at the lowest level and externally amplifying it back up to see if this could be a possible workaround.  Or at least help us understand it more than we do now.
 

Offline N8AUM

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #46 on: September 03, 2015, 04:26:47 am »
I hooked up the 300Mhz cal source from my HP SA and did some more poking around. Other than the slight shift in frequency when the tracking gen is on the wave looked normal REGARDLESS of the SA  power output. I decided to try it with the power sweep on and got some strange results.
I just picked 3 power ranges 3, 9 and 20dB
 

Offline Giorgio

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #47 on: September 03, 2015, 04:01:26 pm »
Hi Gents,

I am sorry if I made unhappy lot of you opening this thread. You were thinking the 815-TG was nice and precise (for it's price) but by my side I am happy that now you know that it has a problem and maybe, as said here, with a lot of requests to Rigol we could have a solution.

As far as I know I was the only one who opened a ticket about this problem 1 year ago with Rigol and now maybe there's more unhappy customer opening their ticket to force Rigol to do something about it.

I didn't wrote here or anywhere else just because I was trusty with Rigol support finding a solution but after many months without solution I decided that this had to be public.

In April I wrote to Dave asking if he could analize the problem but he replied it was too busy for that and said to post here in the forum.

Now I hope Dave will make a video of this so more people will know what they will get if they buy the 815-TG at this time.

About the shift in the frequency sweep at 10 MHz when the TG is activated: that hop is the missing part of the trace when you analize the response of a filter.

 

Offline mcinque

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #48 on: September 03, 2015, 09:20:22 pm »
Totally agree with you Giorgio.

 

Offline Howardlong

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Re: RIGOL DSA815-TG @ 10 MHz issue/bug
« Reply #49 on: September 03, 2015, 09:59:55 pm »
I did a couple more tests, but the results are not what I expected.

First, I set the TG to sweep 9.999MHz to 10.001MHz with a sweep time of about 4s, 100Hz RBW & VBW, TG at 0dBm, and listened to the result on a communications receiver on upper sideband (have to be careful about using "USB" on here, could easily mean different things to differnent people!) There was no discontinuity that I'd expect if there was a jump in the TG. I also tried it at different TG power levels, down to -20dBm, and again no audible frequency jump, it was a clean sweep. Not a very scientific test, but I can be very sure I'd be able to hear a 150Hz frequency jump if there was one coming from the TG.

Without any normalisation, there is a definite bump down of 0.73dB at 10MHz with 0dBm TG. An external 20dB attenuator brings the bump to 0.78dB.

Back to direct TG to SA connection with no external attenuator, dropping the TG power to -5dBm gives a bump down of 0.50dB at 10MHz. -10dBm TG gives a 0.53dB bump. -20dBm TG gives a 0.32dB bump. -30dBm TG gives a 0.32dB bump also. Again, this is without normalisation.

Now, a new test.

Setup an external RF sig gen to 9.9999MHz unmodulated carrier, -30dBm and plug it into the SA. Nothing's connected to the TG output.

Preset the SA to default settings. Set the centre freq to 10MHz and the span to 1kHz. You should see a nice bell curve. The carrier is deliberately offset from the SA centre freq to get the curve slope rather than the peak on 10MHz.

Now switch on the TG (still without it connected to anything). You'll see (a) there's a big discontinuity appears and (b) the curve moves.

Weird!

Here's a quick video of it. Sorry it's a bit shaky.




 


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