SIGLENT SSA3032X input related spurious

[TurboTom]

I already thought about doing this as well and I will upon reassembly (don't kow if this will happen today though...). Yet, since the level ratio of the 60MHz spur virtually didn't change at all with the shields removed, it would surprise me a lot if an improperly tightened shield would make all the difference. Even now, there should be some signal reflected back into the circuitry by the metal chassis of the instrument which is located approx. 15mm parallel to the PCB. And for the other spurs, the effect of the shields is more than evident.

Now that it's apart, does anybody want me to take some more measurements? Maybe a more accurate measurement of the observable spurs? Unfortunately, I haven't got any instrument available that would permit me to check for the frequencies of the LOs, at least not for the very high frequency ones.

Cheers,
Thomas

[G0HZU]

Now that it's apart, does anybody want me to take some more measurements?

Yes, but RFDUK may be better placed to do the tests below as he has an xGHz analyser and should be able to repeat the earlier LO leakage tests but this time at CFs of 780 and 3120MHz.

One thing about our current frequency plan estimate is that it puts LO2 (3.120GHz) inside the range of the 3.2GHz analyser. Also, LO3 at 780MHz is inside the range of the analyser. So it would be interesting to see what happens to the frequency plan once the analyser gets tuned at or near to these frequencies. One option would be to shift IF1 up to about 4.17GHz. There may be enough bandwidth in the IF1 filter to allow this. Or maybe they sidestep IF2 slightly.

[Performa01]

Thank you very much, Thomas, for digging so deep into that issue (even though your instrument isn't even affected.
My hat goes off to you! 

I agree with G0HZU, in some circumstances poor shielding can make matters far worse than no shielding at all.

On the other hand, as tempting as the thought about a shielding issue has been, by now I'm inclined to believe it's not the culprit after all. It would still be nice if you can do some more tests with that aluminum block - now that you have torn appart your instrument already...

Thanks again!

[Joel_l]

This got me curious so I looked at mine.

Signal generator - WaveTek 2410, cable - 1M LMR400

SA - HW 07.03.00, Manufactured 02-2017

I also don' get -70dB

I also notice my floor seems a little higher than others.

[G0HZU]

On the other hand, as tempting as the thought about a shielding issue has been, by now I'm inclined to believe it's not the culprit after all. It would still be nice if you can do some more tests with that aluminum block - now that you have torn appart your instrument already...

Yes, I'm almost convinced we can rule out the metalwork.

With the PCB being slightly bowed, obviously take care how you tighten the screws as you don't want to store stress in the centre of the PCB via the pattern you choose to tighten the screws.

[RFDUK]

Now that it's apart, does anybody want me to take some more measurements?

Yes, but RFDUK may be better placed to do the tests below as he has an xGHz analyser and should be able to repeat the earlier LO leakage tests but this time at CFs of 780 and 3120MHz.

One thing about our current frequency plan estimate is that it puts LO2 (3.120GHz) inside the range of the 3.2GHz analyser. Also, LO3 at 780MHz is inside the range of the analyser. So it would be interesting to see what happens to the frequency plan once the analyser gets tuned at or near to these frequencies. One option would be to shift IF1 up to about 4.17GHz. There may be enough bandwidth in the IF1 filter to allow this. Or maybe they sidestep IF2 slightly.

Second instrument returned last week so no SSA3032X here now.

[RFDUK]

Does anyone know what component 'U27' is after the pi pad at the SAW filter input?

Is that just a test node?

[G0HZU]

It would make sense to have a roofing LPF somewhere between the second and third mixers and U27 could therefore be a small SMD LPF. It could also be a thermopad but my guess would be that it's a LPF that helps improve the isolation between mixer 2 and 3 up in the xGHz region.
However, I just spotted that the other SMD LPFs near the first mixer are labelled Z1 and Z2. So maybe this part would be labelled Z3 if it was a SMD LPF? Maybe it's a tiny BPF rather than a simple LPF. But then again it could be something completely different.

[RFDUK]

The photo here is the highest resolution take on that area I could find.

I'm finding Johanson LPF products that fit the size, appearance and 6 connection pin out.

[tautech]

It looks like many peoples have more like audio experience than rf.

So instead of starting to insult 'peoples' Have you as a Siglent dealer, asked Siglent for a reaction on this issue ?

I talk here technical things what are my hobby and profession and what are interesting for me independent of if I some times sell some equipment or not. I'm much more interested about technical things than any kind of business.  Not talking "sales"man.
Also this is good place to talk things what also are sure read by Siglent.  Siglent RF designer engineer can answer here if he/she like.

All readers can be very sure Siglent are informed of this matter and are working on and watching developments.
They have indicated that they will inform us of their findings.....in what detail and when, only time will tell.

It is my view to leave them to fully investigate why spurs do not meet spec and not press them for fast and short answers.

[RFDUK]

It looks like many peoples have more like audio experience than rf.

So instead of starting to insult 'peoples' Have you as a Siglent dealer, asked Siglent for a reaction on this issue ?

I talk here technical things what are my hobby and profession and what are interesting for me independent of if I some times sell some equipment or not. I'm much more interested about technical things than any kind of business.  Not talking "sales"man.
Also this is good place to talk things what also are sure read by Siglent.  Siglent RF designer engineer can answer here if he/she like.

All readers can be very sure Siglent are informed of this matter and are working on and watching developments.
They have indicated that they will inform us of their findings.....in what detail and when, only time will tell.

It is my view to leave them to fully investigate why spurs do not meet spec and not press them for fast and short answers.

I don't mean to be confrontational I really don't, but your representations are patronising in the extreme and I'm sure unhelpful to the Siglent brand. This is the second input you've made and the first was similarly unhelpful, although I resisted making a point of it.

I ordered the instrument almost 3 months ago. I've had two instruments delivered that fall well short of warranted specification. I've had zero feedback from Siglent or my supplier. I'm still on board with Batronix in the hope the problem will be explained to me, the remedial timescale outlined and an instrument delivered in a reasonable (to me) timeframe.

After nearly 3 months I'm not looking just for 'fast answers', I just want the instrument I paid for, cash drawn down on the day of order.

Coming from a Siglent representative, your views reflect a lack of commercial sensitivity to put it lightly.

I've patiently stuck with it because I believe the SSA3032X to perform well and offer good value.

[tautech]

It looks like many peoples have more like audio experience than rf.

So instead of starting to insult 'peoples' Have you as a Siglent dealer, asked Siglent for a reaction on this issue ?

I talk here technical things what are my hobby and profession and what are interesting for me independent of if I some times sell some equipment or not. I'm much more interested about technical things than any kind of business.  Not talking "sales"man.
Also this is good place to talk things what also are sure read by Siglent.  Siglent RF designer engineer can answer here if he/she like.

All readers can be very sure Siglent are informed of this matter and are working on and watching developments.
They have indicated that they will inform us of their findings.....in what detail and when, only time will tell.

It is my view to leave them to fully investigate why spurs do not meet spec and not press them for fast and short answers.

I don't mean to be confrontational I really don't, but your representations are patronising in the extreme and I'm sure unhelpful to the Siglent brand. This is the second input you've made and the first was similarly unhelpful, although I resisted making a point of it.

I ordered the instrument almost 3 months ago. I've had two instruments delivered that fall well short of warranted specification. I've had zero feedback from Siglent or my supplier. I'm still on board with Batronix in the hope the problem will be explained to me, the remedial timescale outlined and an instrument delivered in a reasonable (to me) timeframe.

After nearly 3 months I'm not looking just for 'fast answers', I just want the instrument I paid for, cash drawn down on the day of order.

Coming from a Siglent representative, your views reflect a lack of commercial sensitivity to put it lightly.

I've patiently stuck with it because I believe the SSA3032X to perform well and offer good value.

On 31 Dec (NZ time) when your 2nd SSA was shown to also not be within spec it was obvious there appeared to be a problem.
Until then it was appropriate that your local dealer deal with this issue and us just watch developments.

Since then, this has been risen up to be placed on Siglent's doorstep since which there has been two weekends lost also.
Unlike some of us enthusiasts, paid staff only work so many hours/week to deliver the answers you and us seek.

So for fear of you taking this the wrong way, this issue to Siglent (as far as we know) is only a few days old.
Please consider this ^.
They need time to explore the cause and report back via rf-loop and/or other Siglent dealers like myself whom are also present on EEVblog.

I'm sorry and understand that 3 months for you is frustrating and I hope we can have answers before this drags out much longer for you.

[RFDUK]

It looks like many peoples have more like audio experience than rf.

So instead of starting to insult 'peoples' Have you as a Siglent dealer, asked Siglent for a reaction on this issue ?

I talk here technical things what are my hobby and profession and what are interesting for me independent of if I some times sell some equipment or not. I'm much more interested about technical things than any kind of business.  Not talking "sales"man.
Also this is good place to talk things what also are sure read by Siglent.  Siglent RF designer engineer can answer here if he/she like.

All readers can be very sure Siglent are informed of this matter and are working on and watching developments.
They have indicated that they will inform us of their findings.....in what detail and when, only time will tell.

It is my view to leave them to fully investigate why spurs do not meet spec and not press them for fast and short answers.

I don't mean to be confrontational I really don't, but your representations are patronising in the extreme and I'm sure unhelpful to the Siglent brand. This is the second input you've made and the first was similarly unhelpful, although I resisted making a point of it.

I ordered the instrument almost 3 months ago. I've had two instruments delivered that fall well short of warranted specification. I've had zero feedback from Siglent or my supplier. I'm still on board with Batronix in the hope the problem will be explained to me, the remedial timescale outlined and an instrument delivered in a reasonable (to me) timeframe.

After nearly 3 months I'm not looking just for 'fast answers', I just want the instrument I paid for, cash drawn down on the day of order.

Coming from a Siglent representative, your views reflect a lack of commercial sensitivity to put it lightly.

I've patiently stuck with it because I believe the SSA3032X to perform well and offer good value.

On 31 Dec (NZ time) when your 2nd SSA was shown to also not be within spec it was obvious there appeared to be a problem.
Until then it was appropriate that your local dealer deal with this issue and us just watch developments.

Since then, this has been risen up to be placed on Siglent's doorstep since which there has been two weekends lost also.
Unlike some of us enthusiasts, paid staff only work so many hours/week to deliver the answers you and us seek.

So for fear of you taking this the wrong way, this issue to Siglent (as far as we know) is only a few days old.
Please consider this ^.
They need time to explore the cause and report back via rf-loop and/or other Siglent dealers like myself whom are also present on EEVblog.

I'm sorry and understand that 3 months for you is frustrating and I hope we can have answers before this drags out much longer for you.

I have a suggestion to help Siglent ...... Siglent 'distributors' do one of two things ...
a) don't identify themselves as such on forums if they wish to constructively contribute to 'in-house' issues similar to this, or
b) refrain totally from involvement with 'in-house' related threads of this nature.

Nothing personal, but your input in this thread has raised more questions for me about just what I've invested my cash in than otherwise would have been the case.

[TurboTom]

My SSA has undergone some more testing and I have to admit that -- at least partially -- I was wrong with my assumptions, so here we go:

First, before attempting anyting else, I took several screenshots in 50MHz span intervals and 10kHz resolution bandwidth in completely unshielded configuration. Input of the SSA was left open. Since probably not too many readers may be interested in this bunch of screenshots, I packed them all up in a single ZIP file.

After that, reassembly of my SSA commenced. Initially, I only sandwiched the RF board between the shields and put in the long screws, labeled "1" but didn't tighten them at all.  The whole assembly was rattling like a can filled half-way with dry beans...

The full span spectrum shows a whole forest of spurs, apparently even stronger than without any shields at all. The 60MHz spur is also much stronger than it was initially and also stronger than without the shields, averaging in at approx. 64dBc. Yet, this figure alone is almost within spec (65dBc) but far off compared to a good instrument (>70dBc). But with only about 25% of the screws and none of them tightened at all, that's probably no surprise. There was approx. 1mm play in the screws until they were seated.

Next step was tightening the long screws but still leaving out the short ones. In that configuration, I unfortunately made a mistake with the SSA settings -- sorry gals and guys -- I left the attenuator at -20dB so it doesn't tell that much about the SSA's performance. The 60MHz spur at least doesn't emerge from the noise floor. Apparently, the SSA performs within specs in this configuration.

In the final run, I had some cans of spinach  (...Popeye...) and inserted and tightened all the screws and took one more screen shot of the 60MHz spur. I guess 72dBc is as good as it will get on my machine...

So my conclusion is -- yes, the shields may have some effect but unless they are machined completely inaccurately or not properly seated at all, they shouldn't push the SSA's performance out of spec. So there has to be something else wrong with the (more recently manufactured) machines that don't meet the specs.

By the way, the shields of my SSA are pretty accurately made and each has got two alignment pins that fit into bores of the RF PCB so the assembly position of the shields is accurate to within approx. one tenth of a millimetre. Not shabby at all I'ld say...

I hope I could shed some light on the shielding situation of the Siglent SSA and its influence of the instrument's performance.

Cheers,
Thomas

[G0HZU]

Thanks again for doing these tests. It does look fairly benign even with loose screws. It doesn't leave much else to play with unless they changed something to do with the SAW filters themselves. Maybe a different supplier or a batch issue. Or maybe something changed in the PCB/mechanical layout in the later units.

I don't have any experience of directly cascading two SAW filters without also having some degree of resistive loss or active isolation between them so I can't say what the risks (to stopband performance) are if the filters are connected directly like this. I suppose in theory it might be possible to get a spiky stopband resonance if there was a conjugate match (with a low resistive loss) at the image frequency. But that would be a bit unlucky. Maybe adding a small amount of ESR in the form of a tiny series SMD resistor (of just a few ohms?) between the two filters would damp a stopband resonance. But I'm just guessing again. I've never tried this with SAW filters.

[G0HZU]

In case anyone hasn't seen the SAW filter datasheet, here's a typical response plot for a single NDF8027. I assume this is the correct datasheet and it shows over 50dB rejection at 750MHz with a single SAW filter. At work, we generally use two SAW filters but with something in between them and it's usually possible to get very good overall stopband performance. Something has to be very wrong if some units are only getting 51dB rejection if we assume they are still trying to use a pair of similar SAW filters in the Siglent analyser.

[Orange]

Perhaps Siglent used a different SAW filter, which has lesser specs. It would also explain the raised noise level that has been observed with these new analysers.

If the new type SAW filter has more pass-band attenuation, the dynamic range of the whole RF chain will suffer. Simply replacing the SAW filter will give you an un-calibrated instrument......
Again this is pure speculation.

Looking forward to see a reaction from Siglent to see what the real reason is of this deficiency in the analyser.

[RFDUK]

I've had no information back from Siglent or my distributor. So still no acknowledgement there is an issue and no timeframe outlined for a replacement.

It remains interesting to know if any other owners of 2017 manufactured SSA3000 series instruments could post -dBC performance numbers on the input related spurious that appears approximately 60MHz below the wanted input signal. Please refer to the plots at the start of this thread for examples of instrument setup.

[rfspezi]

I just did the test with my brand new ssa.
Got a delta of 55,4 dB. 
By the way... did your units come with a screen protector foil or not?

[RFDUK]

I just did the test with my brand new ssa.
Got a delta of 55,4 dB. 
By the way... did your units come with a screen protector foil or not?

Thanks for posting and very sorry to hear that.

I've had two (faulty) instruments in the last several weeks, neither had a screen protector.
I figured that's normal now, I noticed in a teardown video of an older instrument the screen protector was fitted new and wondered about that too.

[tautech]

By the way... did your units come with a screen protector foil or not?

It's quite unusual if units come with screen protection now.
The vast bulk of the Siglent range are no longer shipped with them.
The only exception was a SDG2042X (AWG) that I got in December and that range also being touch screen might be some reason why protection is still included. These still are quite usable with the overlay.
Maybe it was just older factory stock. 

I have occasionally had problems with older demo units and the overlay has not peeled cleanly leaving behind a gel like substance but this can be easily rubbed off with a cloth.
This toughened non-reflective glass is pretty tough stuff and arguably doesn't need an overlay for protection.

[rfspezi]

I've had two (faulty) instruments in the last several weeks, neither had a screen protector.

Do you have a correctly working unit in the meantime?

By the way, i am just playing around with the spurious.
Feeding in a 100 MHz AM-modulated (50%, 1MHz) signal gives me peaks at 40 MHz (=carrier), 49 and 51 MHz (=sidebands).
Feeding in a 110 MHz AM-modulated (50%, 1MHz) signal gives me peaks at 50 MHz (=carrier), 39 and 41 MHz (=sidebands).

The difference between the real sideband signals and the spurious are only 40 dB. 
Hmm... not sure what to think now...

[EDIT]
Find attached the screenshot of the 100 MHz signal mentioned above.

[RFDUK]

I've had two (faulty) instruments in the last several weeks, neither had a screen protector.

Do you have a correctly working unit in the meantime?

No I don't have an instrument here, I'm in dialogue with Batronix.

[RFDUK]

Thanks for the plot rfspezi, applying AM mod was an interesting thing to do as it turns out.

This is looking like the performance of a very poorly analyser.

[rfspezi]

This is looking like the performance of a very poorly analyser.

Just my thoughts...
I would love to see a fix for that since otherwise i really like that spectrum analyzer.