SSA3021x Spur 345 MHz

[AlphaBob]

Hi,

I received a Siglent SSA3021x Spectrum Analyzer about a week ago and its performance has blown me away.  In doing some emission tests, I discovered a rather strong spurious emission that appears to be coming from inside the analyzer itself, as it doesn't go away with a terminated input, nor does it seem to be AC power or position dependent.  The Tracking Generator is turned off.

The 345.0 MHz spur is -72.6 dBm and appears to have some mild sidebands that extend +/- 5 KHz around -92 dBm.above and below that are about -92 dBm.  JPG attached

The unit was received directly from Siglent NA in Ohio and was calibrated in late November 2016.  Firmware is same version 7.07 that Siglent is providing for download on their website.

Has anyone else noticed something similar?

[tautech]

Welcome to the forum.

Can't say I noticed it but I'll put a link to your thread on the SSA3kX thread for better visibility.
https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/

Can you post your FW version please.

[TurboTom]

Yes that spur is definitely there. It's not coupling via the input since it always appears to be approx. 20dB above the noise floor (on my machine @ 300Hz RBW -- and around 33dB @ 10Hz RBW), regardless of attenuator setting or wether the preamplifier is enabled or not. So it may be an internal signal that's directly coupling into one of the IF circuits.

There has been a discussion about these spurs some time ago (there are many more) and the conclusion was that no SA in the world will be completely free of them.

Cheers,
Thomas

[AlphaBob]

Yes that spur is definitely there...the conclusion was that no SA in the world will be completely free of them.

Thanks Thomas -- I can understand that point of view, but feel even better knowing that it isn't just my SA.

[KE5FX]

There has been a discussion about these spurs some time ago (there are many more) and the conclusion was that no SA in the world will be completely free of them.

   Sounds like an exercise in lowered expectations.  The price that Siglent charges for that dubious display of performance would buy you a 35-year-old HP 8568A that has no such issues. 

Of course, in its day, that HP cost about as much as a new Ferrari.  It still consumes more than its share of electricity and gravity, and you will probably need to open it up and fix it at some point, assuming it even survives the tender ministrations of UPS on the way to your house. 

Meanwhile the Siglent is the size of a lunchbox, weighs even less, and can be purchased brand new with factory warranty for the price of a nice lawnmower.  They get points for that in my book... but make no mistake, there's no good excuse for the behavior in that screenshot.

[Bicurico]

Hi,

That is normal.

Here is mine for comparison.

Regards,
Vitor

[TurboTom]

Of course -- I would feel the same if I had this machine just new. You can quite easily distinguish between internal spurs that aren't coupled into the SA via the input and "real" input-related signals by changing the attenuator setting. The relative signal amplitude of the spurs over the noise foor will stay unchanged while the signal will vanish in the noise if the attenuation is increased, or to put it the other way round, the absolute (displayed) input signal will stay constant while the absolute strength of the spurs will change with attenuation setting.

Cheers,
Thomas

[rf-loop]

Previously:

https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg981095/#msg981095

Is it too costly to make a spectrum analyzer with zero spurious response, or is it just impossible by design, based on the topology and build up of the various stages in the spectrum analyzer?

Not only too costly but also impossible.  Just as impossible as doing pure sinewave or ideal rectangle wave - or what ever ideal. School books with nice ideal sine and square are just so out from reality what can. In reality there is no pure sine wave, no exact time, no exact voltage, no ideal mixer, no ideal filter, no ideal amplifier...  you want more. As told previously, all what you see on oscilloscope or spectrum analyzer display are collection of errors mixed with undefined truth.

Too often I quote what Keyshit (former Agilent, former Hewlett-Packard) tell us.
Here from Tektronix.
Why they all talk about spurious, residuals etc. Rohde&Schwarz, Tektronix, Keysight, Anritzu, Advantest, and so on...


From "Fast, Low Level Spurious Search with
Tektronix Real-Time Signal Analyzers"

Considering the Spurious Performance of
Spectrum Analyzers

Measuring low level spurs requires care even when the
spectrum analyzer’s Displayed Average Noise Level has
sufficient margin to perform the required measurements.
All spectrum analyzers create artifacts or spurs that can
appear at low levels. Some spurs are created internally by the
Spectrum Analyzer’s circuitry. Others are generated inside the
instrument as a result of input signal interactions with internal
signals and non-linear circuit behavior. These unwanted
signals, typically related to harmonics of the input signal, are
highly dependent on the maximum signal level present in the
input, even when the large signal lies outside the displayed
span.


Residuals
Residual Spurious responses are internally generated spurs
that exist in all spectrum analyzers and are independent of
any input signal. These unwanted signal components are
the result of imperfect isolation between the various signal
paths inside the spectrum analyzer and can come from digital
clocks, local oscillators or switching power supplies. Spectrum
analyzers are regularly used to measure spurs far below their
Residual Spurious specifications. One technique to account
for these residual signals is to measure them by taking a spur
sweep with the input terminated. The resulting list of spur
locations and levels can be tabulated and then removed from
the subsequent measurement results. Residual Spurious
are expressed as an absolute power level, specified in dBm.
This means they do not change level with any input. The
specification for the RSA6120B is -90 dBm for frequencies
from 40 MHz to 200MHz, and -95 dBm (-110 dBm Typical)
from 200 MHz to 20 GHz. These signals must be well
understood to ensure they are not mistakenly included in the
results as they may not be from the DUT.


Spurious with Signal
Spurious with Signal Present or signal-related spurs are the
result of unintended interactions between the input signal
and the various internal clocks and local oscillators that are
part of the spectrum analyzer’s circuitry. Most signal-related
spurs are caused by non-linear behavior in the spectrum
analyzer’s circuitry and are highly dependent on the levels
of signals present at the spectrum analyzer input. There are
several types of signal-related spurs which are often specified
separately. They include image rejection, harmonics, third
order intermodulation, second order intermodulation, etc.
The specifications for signal-related spurs are usually in terms
of dB below the input signal level or dBc. Signal related
spurs specifications are especially relevant if a low level spur
search must be made in the presence of a high level signal.
Measuring spurs in a transmitter output, for example, may
require the measurement of spurs at the -120 dBm level as in
our example while the transmitters intended output signal has
a power of several watts. In these cases, it might be required
to filter out the transmitter’s signal (notch filter) to make sure
that its level does not exceed the input level specified in the
analyzer’s spurious specifications.
All spectrum analyzers publish spurious with signal
specifications that vary with acquisition BW and input
frequency at a specified level of input signal. The RSA6120B,
for example, performance varies from -78 dBc to -70 dBc
depending settings with a maximum signal level of -25 dBm
after RF attenuation. The option 51 preamplifier, when used,
would typically achieve similar performance with a maximum
input signal at approximately a 30 dB lower level.

Harmonics
These unwanted signals can appear whenever the analyzer
is tuned to N times the frequency of a signal present at the
input (N is an integer). The most relevant is the 2nd-harmonic
specification (N=2). The RSA6100B Series specifies 80 dBc
harmonics for -25 dBm input signals with no RF attenuation
and preamplifier off. The Option 51 preamplifier, when used,
would typically achieve similar performance with a maximum
input signal at -55 dBm with no RF attenuation.
Predicting the spurious behavior with Input is usually more
difficult than harmonics or residual spurious. A detailed
analysis requires knowledge of the frequency conversion
stages internal to the Spectrum Analyzer (Local Oscillators,
IF frequencies, ADC clocks, etc.) These kinds of spurs will
be present at frequencies related the mixing of internal
frequencies and harmonics of the input. For example, if one of
the local oscillators in a spectrum analyzer is at 9 GHz, then
signals harmonically related to the combination of the input
signal and 9 GHz could show up as spurs.

How to recognize internally generated spurious what are not input related.

It is simple (mostly).

Terminate input and look if it is there.

Thumb rule: If you have signal connected. Change attenuator example 5 or 10dB. If it is your real signal its level do not change or change is minimimal. If it is spur what is there also if there is not input its level change around same amount as you change attenuator. (because this "signal" does not walk through the attenuation)

Type this phrase to Google: spectrum analyzer residual response

....and start reading.

Here SSA3000X most important normal input independent internally generated  "spurs"   and also one internally (input independent) generated spur compared to real input signal and changing attenuator level. There can see how real signal behave and iiis behave when change attenuator.




Correct: recognize

If look example Keysight N9320B ....     well, it reads in specifications and Siglent do not need shame anything.

Of course I and perhaps everyone like if there is less and spurs are more low. But, it is this. And it is not alone in this spur club. 

[KE5FX]

If look example Keysight N9320B ....     well, it reads in specifications and Siglent do not need shame anything.

There are specs, and then there's typical real-world performance.

If you're building a spectrum analyzer, you obviously want to be careful about what you promise.  If I'm wearing the designer's hat, I might specify -80 dBFS SFDR to allow for real-world customer use cases with marginal test environments and practices, but if I personally see a spur anywhere near that level while I'm using my own gear, no further work is going to be done that day (or that week) until I understand where it's coming from.  I certainly won't ship the product until it's understood and resolved.  And if a paying customer was the first to notice something like the spur we're talking about here, I'd look for a nearby bridge to jump off of.

It is not the case that it's "impossible" to build a spur-free spectrum analyzer.  Fire up the aforementioned HP 8568B and find an internally-generated, non-line related spur that's anywhere near the specified limit.  Go ahead, I'll wait.    Unless there's something wrong with the analyzer, you won't succeed.  That's because HP did something that Siglent evidently didn't bother to do: their firmware anticipates where spurs will appear, and adjusts internal oscillators during the sweep to avoid them.  I don't know if HP patented that idea, but if they did, it expired 20 years ago... so once again, there's no excuse beyond the desire to save a few bucks.

I don't know anything about the N9320B, but I will say that I've been really impressed by the quality and performance of the N9340B portable.  Dave's teardown video of that one was just amazing; it pretty much is a portable 8568.

[AlphaBob]

That's because HP did something that Siglent evidently didn't bother to do: their firmware anticipates where spurs will appear, and adjusts internal oscillators during the sweep to avoid them.

Now that is clever and Siglent should be able to accomplish something similar in their firmware, if they care to.

[Dubbie]

Here is my 345Mhz spur.

[rf-loop]

It is not the case that it's "impossible" to build a spur-free spectrum analyzer.  Fire up the aforementioned HP 8568B and find an internally-generated, non-line related spur that's anywhere near the specified limit.  Go ahead, I'll wait.    Unless there's something wrong with the analyzer, you won't succeed.


I don't know anything about the N9320B, ....

... yes I can see.

I have owned several HP spectrum analyzers previously, and long time. Short time ago last one, 8568B, I throw away. Some tiny function generator tests made with it (using your software) can also find here in forum. Also previously least as good as HP (or bit better) and more heavy R&S..  There is enough difficult to find internal non input related spurs.  This kind of spectrum analyzers  what are in Rigol 800 and Siglent 3000 class are not at all comparable to these nearly State Of Art class old machines. They are not comparable with weight and not with SA performance. 

Siglent have never not even tried or designed to make High End  or State Of Art level SA's. There is no any reason to go this market sector.   

We need cheap oscilloscopes and cheap spectrum analyzers for every asian student and engineer table in new world.  For understand basic things and make basic measurements with scopes and SA's do not really need state of art class equipments. Where one really NEED High End equipments really, these are worldwide available easy with money.

Moreover, the lack of skills can not be replaced by owning expensive High End equipment. Except when absolutely prominent position on the most expensive and the best camera alongside the street, and hopes that all would see.

Travel to nearest CRH station can do using cheap electric scooter or bicycle or tiny Micra or it can do with black RR. There is needs for all.

[DL4RAJ]

Here SSA3000X most important normal input independent internally generated  "spurs"   and also one internally (input independent) generated spur compared to real input signal and changing attenuator level. There can see how real signal behave and iiis behave when change attenuator.

It seems that during production considerable improvements in hardware design have been done without notice.
I have duplicated your settings exactly and made two screenshots for comparison.
The spurs are much weaker on my analyser.
My SSA was purchased around 24th October 2016.
S/N HA3160481
SW1 1.2.8.1
SW2 20160622-2
SW3 000000D1
HW 07.03.00

regards

[tautech]

Here SSA3000X most important normal input independent internally generated  "spurs"   and also one internally (input independent) generated spur compared to real input signal and changing attenuator level. There can see how real signal behave and iiis behave when change attenuator.

It seems that during production considerable improvements in hardware design have been done without notice.
I have duplicated your settings exactly and made two screenshots for comparison.
The spurs are much weaker on my analyser.
My SSA was purchased around 24th October 2016.

regards

Thanks.
Could you list your HW and FW versions please ?
Maybe built date too, xxxxxxx316xxxx is what it might look like in the SN#

Edit
For the sake of neatness, maybe add it to your above post as an edit.

[DL4RAJ]

Could you list your HW and FW versions please ?
Maybe built date too, xxxxxxx316xxxx is what it might look like in the SN#
Edit
For the sake of neatness, maybe add it to your above post as an edit.

Done.

[rf-loop]

Here SSA3000X most important normal input independent internally generated  "spurs"   and also one internally (input independent) generated spur compared to real input signal and changing attenuator level. There can see how real signal behave and iiis behave when change attenuator.

It seems that during production considerable improvements in hardware design have been done without notice.
I have duplicated your settings exactly and made two screenshots for comparison.
The spurs are much weaker on my analyser.
My SSA was purchased around 24th October 2016.
S/N HA3160481
SW1 1.2.8.1
SW2 20160622-2
SW3 000000D1
HW 07.03.00

regards

I have exactly same version as you. Difference only in serial number.

S/N SSA3XHA216xxxx   (as we know after last digits 6000 (or was it 6100)  there was TG hardware some improvements)
SW1 1.2.8.1
SW2 20160622-2
SW3 000000D1
HW 07.03.00

As can see some spurs in your equipment are more low and some more high.
But then over whole frequency span your equipment base noise is  higher.

I have tested more than just one SSA and I can say there are some  differences  between individual units, as is particularly natural.
This is why every spectrum also have individual calibration tables (and it is example for every 51 attenuator positions and over whole frequency span) Base noise level is "where ever" after cal factors  and as long as base noise level meets equipment specifications, it is ok.
Every amplifier, every mixer, every filter, every attenuator - everything have own variations between some tolerances. Finally after summing all together result is "random" but inside some rough limits. It is even possible that some small fraction from manufacture lot do not meet specifications at all but perhaps meet other model specs.  All peoples whoi have been in any electronic equipments manufactuuring know this.
But as we know. There is also interesting model table. SSA3010X, SSA3015X, SSA3018X, SSA3021X, SSA3030X, SSA3032X...   it is well possible that if example some unit do not meet  all SSA3032X specs it can still be ok for SDS3010.  (just same as example some oscillosscopes analog front ends etc)

 Sidenote (not big difference in result)
You told you have used same settings. No you have not. Look your image about 1540MHz. There read FFT !   In my image, there do not read FFT.  Of course if user keep "All Auto" mode spectrum set as default FFT if it can. But it is also good to know that sometimes sweep mode is good even when it is much more slow.

[DL4RAJ]

Sidenote (not big difference in result)
You told you have used same settings. No you have not. Look your image about 1540MHz. There read FFT !   In my image, there do not read FFT.  Of course if user keep "All Auto" mode spectrum set as default FFT if it can. But it is also good to know that sometimes sweep mode is good even when it is much more slow.

Here is the same screenshot without FFT.
Spurs are now about 2dB stronger than in my last screenshot with FFT but still 10dB weaker than in in your screenshot.

regards

[bozidarms]

Hi to the group,
Here is the same screenshot from my SSA:

S/N   SSA3XHA3160xxx
SW1 1.2.8.1
SW2 20160622-2
SW3 000000D1
HW 07.03.00

Seems that mine have a little bit lower noise, more regular shape, and almost no 345 MHz spur (but have others).
Both traces without any averaging.

[pascal_sweden]

Why doesn't Siglent implement some kind of calibration feature in software, where the user has to ensure that there is no input signal connected to the front-end, and the spectrum analyzer would sweep the full spectrum and equalize out the internal spurs?

In the current implementation, you would almost have to order 4 units at the same time, try out all of them, keep the best unit, and send back the other 3 units within the available return time of the distributor

[rf-loop]

Why doesn't Siglent implement some kind of calibration feature in software, where the user has to ensure that there is no input signal connected to the front-end, and the spectrum analyzer would sweep the full spectrum and equalize out the internal spurs?

In the current implementation, you would almost have to order 4 units at the same time, try out all of them, keep the best unit, and send back the other 3 units within the available return time of the distributor

This same can do with Keysight, Tektronix, Rohde&Scwartz, Anrizu, Advantest, SignalHound, GoodWill, Rigol .... and so on.

For @pascal_sweden


......, all can do. Are you now happy?  1540 and 1904MHz spurs are nearly gone...

Attached image is untouched original png from "tweaked" SSA.
Input teminated, full span, RBW=VBW=1kHz. Atten 0. Detector Pos Peak.

When I did this tweak I use chinese  bamboo (material is important)  chopsticks and  glass  tea cup (it need be glaass, not porcelain)  and dry genuine rice paper (mandatory). No need solder anything and no need hammer or screw driver.

[DL4RAJ]

When I did this tweak I use chinese  bamboo (material is important)  chopsticks and  glass  tea cup (it need be glaass, not porcelain)  and dry genuine rice paper (mandatory). No need solder anything and no need hammer or screw driver.

I've used German Bratwurst and Sauerkraut for my tweak. _.)
Seems to work even a bit better.

[rf-loop]

When I did this tweak I use chinese  bamboo (material is important)  chopsticks and  glass  tea cup (it need be glaass, not porcelain)  and dry genuine rice paper (mandatory). No need solder anything and no need hammer or screw driver.

I've used German Bratwurst and Sauerkraut for my tweak. _.)
Seems to work even a bit better.

Of course  this more advanced method  "I've used German Bratwurst..."   helps lot of...