Spectrum Analyzer, which one to get?

[amdnra]

Hi. I've been looking to get a Spectrum Analyzer.
The choices at this point are:
Used Anritsu MS2721B
Used Rohde & Schwarz FSEA30 20Hz to 3.5GHz
New Rigol DSA832E-TG
New Siglent SSA3032X
All include the Tracking Generator
Trying to get something with an LCD display and stay around $2500 give or take
Any ideas or advice? Thanks
 

[DaJMasta]

That first one is sticking out like a sore thumb... it's a great unit (I've got one with no TG), but it's in a very different class as a portable SA.  You gain the ability to run off battery and save space on the desk, but you loose sweep speed responsiveness - the minimum sweep speed on the latest firmware is 100ms/sweep.  It's very nice to have the bandwidth too, but it's not well suited to some applications with very short transmissions or looking at very wide spans.  If you're looking for portable SAs, maybe the Rohde & Schwarz FSH series is worth looking at - the 6GHz model (not the current version) should be in that price range.

The others will give you a lot faster sweep speed, even if their DANL isn't all that different, but come at the cost of bandwidth, desk space, and portability.  It's also worth noting that the options packages can be very important for particular applications, so if you're interested in a particular kind of transmission or demodulation capability, that should weigh heavily on your choices.

Worth mentioning that an 3.5GHz FSEA20/30 should not be running you $2500, at least not in the US, and for that money you may be able to strike at the higher 7GHz model (or the FSIQ line).  Could be worth considering the Anritsu/Advantest benchtop models in a more comparable form factor to the FSEA, you'd be getting more performance for your money if the portability isn't important.

The Rigol and Siglent have a nice compromise on desk space, but not the portability, and offer good speed and noise performance.  They've both been pretty well investigated on the forums and have the advantage of being new and having much more reasonably priced options (though perhaps not as comprehensive options as some of the older, larger models).  Good choices, but in terms of raw bandwidth and performance, new instruments rarely compare well to similarly priced used instruments.

[nctnico]

Also look at Advantest and include their 'signal analysers'. Contrary to Agilent Advantest seems to bolt signal analyses onto a regular spectrum analyser so good deals can be had.

[usagi]

My Used spectrum analyzer buyer's guide might be able to help you 

If you want bang for buck it's hard to beat the R&S CMU 200. It's a big rackmount unit though.

I also have some used R&S FSH6 for sale.

[amdnra]

DaJMasta: What's the latest firmware rev for the Anritsu? If you know
So...The Rohde & Schwarz is pretty big and heavy
The Anritsu is not so fast or capable
And from the forums it appears like the Siglent is better than the Rigol (better specs)
The 'winner' seems to be the Siglent. Would you agree?
Thanks for your input

nctnico: Thanks for the tip

usagi:Thanks for pointing out the guide. Informative.
About the R&S CMU200, Is that a Spectrum Analyzer? if so, What's the bandwidth?
Would the FSH6 suffer from the same limitations as the Anritsu (see reply above by DaJMasta)?
How much are they?

[DaJMasta]

Most portable SAs will have that sort of sweep time limitation, not sure if the FSH series has the same lower limit, but I would expect the same ballpark performance (you can probably find videos of them being used to get a general idea).  Firmware is complicated because it gives me four numbers... Package 1.51, OS 3.21, Base 5.71, SPA 5.73 - software updating is easy though, it's got USB ports so you stick in a memory stick with the new one and hit a few buttons (and the download is free from anritsu when registered, if I remember right).  While there is the sweep speed limitation, a portable SA is more likely to have a preamp option, will probably have better input protection, etc.

While portable SAs do definitely have speed limitations, the extra bandwidth is nothing to shake a stick at - you usually pay a pretty big premium for extra bandwidth, so the 7.1GHz it offers is considerably above the other options (and a bit above the R&S 6GHz instruments which may still fit the price point).


I think the FSH6 series should run in the $2000 US ballpark - there was recently a government auction with a few dozen of them, and I'd expect it to be more of a buyer's market on ebay as a result.  I think prices are already down a bit from several months ago, but it still may dip a bit.

[amdnra]

DaJMasta: What's your opinion on the R&S CMU200?
and...
"So...The Rohde & Schwarz is pretty big and heavy
The Anritsu is not so fast or capable
And from the forums it appears like the Siglent is better than the Rigol (better specs)
The 'winner' seems to be the Siglent. Would you agree?"
Comments?

[DaJMasta]

Never used one.  They've been popular for a bit because they tend to be cheaper than many standard SAs while also including some demodulation capability, but I wasn't too concerned with that when I was looking, so i didn't look into them deeply.

[Bicurico]

The R&S CMU200 or R&S CRTU are great devices for amateurs.

They offer a pretty good spectrum analyzer with an incredible fast refresh rate. The freqeuncy range goes all up to 2.7GHz and overall the performance is R&S style.

However, these devices are NOT spectrum analyzers! They were made for the testing of mobile phones and mobile network. The spectrum analyzer and signal generator just happen to coexist with that functionality.

The drawbacks are:

1) The spectrum analyzer functionality is kind of reduced: no modern measurements, no waterfall diagramm (spectrogram), no screen capture to USB, no RJ-45 for remote operation.
2) The signal generator is a signal generator. Great to have, but it is NOT a tracking generator!
3) These devices were popular for their very affordable price, when Nokia (or other) plants closed and people selling them apparently were not aware of the spectrum analyzer/signal generator function. They can still be purchased at great prices - especially in the USA, but the avareage "buy it now" price in Europe is a bit too high, in my opinion.
4) They are USED devices, which means: out of calibration or at least the last calibration was years ago, possible defective components, cosmetic damage
5) They are huge! They occupy 4 slots in a 19" rack. You could line up around 5-6 Siglent SSA3021X behind each other within the same space.

The Siglent SSA3021X is a game changer, when it comes to affordable spectrum analyzers.

They are sold at a very competitive price, can be hacked for full options and increased frequency range (3.2GHz).

The screen is huge, GUI is intuitive and responsive, firmware is pretty decent and it basically just works as expected.

Sure, if you follow all threads in this forum, you will find people complaining about bugs and performance, but in general, the devices ship within specs and are of great quality.

At this price you won't find anything similar. Period.

It is a game changer, because many hobby users are now wondering if it is still reasonable to purchase a second hand device at the same cost as a brand new Siglent SSA3021X, which comes with 2 years of warranty.

I have both: SSA3021X and R&S CRTU. I am an amateur and like to explor the RF for transmissions, test modulators, search for satellite feeds, amateur radio transmissions, etc.

I use both devices:
- I like the CRTU for it's simplicity, responsiveness, fast refresh rate. Also, it seems more robust. You get different RF input connectors, which accept different signal power levels, so it gives me more confidence that I won't damage anything.
- I like the SSA3021X because of it's sheer amount of functionality, waterfall diagram (great for monitoring). Also, Siglents great SCPI implementation allowed me to program my own spectrum analyzer application for this device. My software allows for additional measurements like automatic realtime satellite identification (more info: http://vma-satellite.blogspot.pt/2017/03/vma-simple-spectrum-analyser-for.html).

To sum it up:

- If you want a spectrum analyzer now and the SSA3021X specs are within your needs, that's the device to go for, in my opinion.
- If you want a spectrum analyzer for hobby/amateur/educational purposes you may want the SSA3021X or you may want to search for a good deal on a second hand unit. In this case, I am not sure if the CMU200/CRTU is the right device. Perhaps it is better to look for a "real" spectrum analyzer, but make sure it is modern (TFT screen, don't go for anything with a CRT!) and you are sure it is not broken or specs. See the thread on this forum about purchasing a second hand spectrum analyzer.

Hope this helps.

Regards,
Vitor

[amdnra]

Vitor: Thank you for taking the time for such an excellent reply and content. Really appreciate it. Lost of good information.
Now let me ask you a SA question: If you have a signal sitting at, say, -20db and you add an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. In other words, the addition of attenuation should
show up as lowering the signal on the display by that much. Let me know if this is the case. It sounds reasonable but I'm just not sure.
Please advise.

[nctnico]

With some patience you can get really good deals on Ebay. My current spectrum analyser is an Advantest R3477 which has a TFT touch screen, screencaptures to USB , network connectivity and last but not least: 15GHz bandwidth. It cost me the same as the basic version of the Siglent SSA3021X.

[RoGeorge]

Seems like everybody is in the SA fever these days.
I was looking for an SA last week too. Found some nice equipped R&S CMU200/CMRU units from India then, at a closer look, I was put down by some specs I don't fully understand:

Can anybody please comment this CMU/CMRU specs?
Examples from CMU200 specs http://www.upc.edu/sct/documents_equipament/d_175_id-448.pdf

- pag 7/48, CMU200 Phase noise <-100dBc, 1Hz (SSB f<2.2GHz, la offset 20 KHz to 250 KHz). Is this OK? I don't know the expected performance for GHz range, but a Rigol DG4102 DDS has a Phase noise <-115dBc, 1Hz (SSB f=10MHz, la offset de 10 KHz)

- pag 10/48 DANL <-95...-100dBc. I don't understand why dBc instead of dBm, why 1KHz instead of 1 Hz normalized band of 10-100 Hz?
E.g. the smallest Rigol SA, DSA815, have less than -110 dBm, while an R&S from the FPC1000 series have DANL less than -130...-150dBm, and this outstanding performance is without preamplifier.

I'm a total RF noob, so I might be totally missreading the specs. Are those just average, or the specs are very good but I don't understand them properly?
For a quarter million USD machine (in its glory days), I am expecting for top notch performance, but does it still is top-notch?

Whoever understand those datasheet numbers, please clarify them for mere mortals.
 

[tmbinc]

(I still owe Bicurico a half-working CRTU; and the primary reason is that they are a mess to ship, especially when disassembled.)

The CRTUs can be really cheap when obtained at an auction. They regularly don't sell or go for $100. But don't be fooled - once you add all the costs (including the stuff you bought because you were already bidding at that auction, but don't really need), you pretty much pay the ebay price...

They don't have stellar RF specs, but they are pretty damn useful for the mentioned reasons. For example, they have the wideband RF power sensor, the RF signal generator, a few basic signal analysis functions (high resolution frequency selective counter) that can be pretty useful.

What they cannot do is more advanced signal analysis. But if you want that, then nothing beats an SDR equipment or a (higher-end) scope connected to the IF output.

Yes, they used to cost a quarter million $, but that was not because of their RF performance, but because of the specialty of the software that they are used with (GSM/WCDMA tests); they are a massive pain to develop with only a few users worldwide. R+S pretty much took whatever RF hardware they had (CMU200) and made a few tweaks, because at $250k (or whatever their price was), it simply doesn't matter if the hardware is not optimized.

Unfortunately that doesn't mean that you got $250k worth of RF equipment...

[amdnra]

Anybody feel like giving this question a shot?
Now let me ask you a SA question: If you have a signal sitting at, say, -20db and you add an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. In other words, the addition of attenuation should
show up as lowering the signal on the display by that much. Let me know if this is the case. It sounds reasonable but I'm just not sure.
Please advise.Thanks

[DaJMasta]

Could depend on the analyzer and whether the attenuator was internal.  For example, if you don't have an internal attenuator or you're using a -25dB attenuator on the input signal, you'll see the -20dB signal at -45dB provided the attenuator is rated at the frequency in question and the SA can see that input level (and I don't know of one that can't).  If you're using an internal attenuator, it probably won't display -45dB, it will display -20dB.  Since it knows what attenuation is switched in, it tells you what the signal is at the input (this is how you get high power input to still be readable on the SA).  In the same vein, if you have an external 20dB amplifier, your -20dB signal (and the noise floor) will be 20dB higher on the SA, but if it's an internal preamp that's being switched in, the SA will display the signal level at the input and correct automatically for the gain of the preamp.

[tautech]

Anybody feel like giving this question a shot?
Now let me ask you a SA question: If you have a signal sitting at, say, -20db and you add an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. In other words, the addition of attenuation should
show up as lowering the signal on the display by that much. Let me know if this is the case. It sounds reasonable but I'm just not sure.
Please advise.Thanks

Exactly this ^ for SSA3000X models to a max attenuation of 51 dB.
Adding external attenuation must be manually deducted from the signal level. 

[usagi]

the R&S CMU200 can safely eat up to +47dbm, one of the reasons I got one. as pointed out the cmu doesn't have a true tracking generator, but the signal generator can be used to (slowly) sweep so you can still do stuff like characterize filters. most of the used ones are loaded to the gills with options for cellphone testing, since they were used by equipment manufacturers and telcos. you are getting what used to cost $300,000 or more for around $1000. the signal generator is really nice, very flexible with many modes and options.

the FSH6 doesn't have the sweep time limitations of the anritsu. per the manual min sweep time is 1ms and it sweeps 600mhz in 20ms. it's a true 6ghz spec analyzer with tracking generator. if you're interested, pm me.

[rf-loop]

Anybody feel like giving this question a shot?
Now let me ask you a SA question: If you have a signal sitting at, say, -20db and you add an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. In other words, the addition of attenuation should
show up as lowering the signal on the display by that much. Let me know if this is the case. It sounds reasonable but I'm just not sure.
Please advise.Thanks

Exactly this ^ for SSA3000X models to a max attenuation of 51 dB.
Adding external attenuation must be manually deducted from the signal level.

Yes, but then also:
Just use SSA level offset setting for correct external attenuator. Only disadvantage is that unlike internal step attenuator every step, external attenuator do not have flatness and level calibration data table inside SSA for automatic correction. But if user can trust external 20dB attenuator is enough flat over frequency band then user can set this offset. (if external attenuator frequency response is not enough flat but known, then user can make correction table and enter this table to SSA so that it can do also wanted flatness corrections for this individual external attenuator or other circuit as external amplifier etc..

[amdnra]

To clarify: I originally should have said "Internal Attenuation Level" (as opposed to it being external).

Could depend on the analyzer and whether the attenuator was internal.  For example, if you don't have an internal attenuator or you're using a -25dB attenuator on the input signal, you'll see the -20dB signal at -45dB provided the attenuator is rated at the frequency in question and the SA can see that input level (and I don't know of one that can't).

If the attenuator in question is Not internal, How's the SA going to 'know' and compensate for the measurement and show -45db?

If you're using an internal attenuator, it probably won't display -45dB, it will display -20dB.

So, is the operator supposed to keep track of what attenuation level is set on and mentally compute for the true input signal strength? I would have thought the SA automatically scales the display for the internal attenuation factor.

 

Since it knows what attenuation is switched in, it tells you what the signal is at the input (this is how you get high power input to still be readable on the SA).

How is the SA going to 'tell' me what the signal is at the input? By displaying a number off to the side OR by displaying a graph showing the signal at the proper level?

[nctnico]

So, is the operator supposed to keep track of what attenuation level is set on and mentally compute for the true input signal strength? I would have thought the SA automatically scales the display for the internal attenuation factor.

No, the SA will compensate the display for whatever internal attenuation or gain it uses.

[amdnra]

If you're using an internal attenuator, it probably won't display -45dB, it will display -20dB.

Therefore his statement above that I quoted is incorrect? That is what I thought...

[nctnico]

If you're using an internal attenuator, it probably won't display -45dB, it will display -20dB.

Therefore his statement above that I quoted is incorrect? That is what I thought...

It is written in a confusing way. If you apply a +20dBm signal to a spectrum analyser it will display this as a +20dBm signal no matter what internal attenuation or gain it uses. The spectrum analyser knows it's internal attenuation and gain settings so it compensates the numbers on the display so you don't have to worry about that.

[amdnra]

It is confusing alright ! 
I was playing with an Anritsu MS2721B Spectrum Analyzer at work and it has an Internal Attenuation Level control.
I fed it a signal of -25db.
Then I changed the Int Att Level to 10db, 20db and then to 0db but it did not affect the graph or apparent signal strength...It remained at -25db
Then of what use is this internal Att Level control? Or is the unit not working properly (I wouldn't be surprised if that was the case)?

[CJay]

Same with all 'problems', define your requirements and then match the specs.

You can get a *lot* of SA second hand for your budget but, for my needs and if I had the budget, I'd definitely be paying the Siglent a lot of attention (and have done, there may be a sell off of 'stuff' to fund the purchase of one).

Bear in mind that service info and even software/firmware for a lot of recent SA's and indeed lots of other test gear is just not available to anything other than 'replace this board', return to base level so buying second hand without a warranty might become a very expensive lesson.


I've been extremely lucky and got great bargains but always with the worry that they'd be scrap, I have now got two CMU200s and find them excellent for my current needs but they lack a proper tracking generator (there is a seller on eBay who has designed a TG for them) and are only good down to 10MHz and up to 2.7GHz which may or may not become a problem for me soon.

[nctnico]

It is confusing alright ! 
I was playing with an Anritsu MS2721B Spectrum Analyzer at work and it has an Internal Attenuation Level control.
I fed it a signal of -25db.
Then I changed the Int Att Level to 10db, 20db and then to 0db but it did not affect the graph or apparent signal strength...It remained at -25db
Then of what use is this internal Att Level control? Or is the unit not working properly (I wouldn't be surprised if that was the case)?

The attenuation level is usefull when dealing with the noise floor of a spectrum analyser. If you attenuate a small signal too much it may dissapear under the noise floor. If you can see the attenuator is on, you can switch it off or (if available) enable a pre-amplifier. Most spectrum analysers set the attenuator to 10dB by default to have some input protection.

[Bicurico]

May I add the following:

The Spectrum Analyser can only handle a certain signal power level. If it is too high, you risk damaging the input stage. This is written next to the input connector! i.e. "MAX +10dBm"

The attenuator allows to lower the signal power level, so that the remaining signal is "safe".

As ntnico said, if you attenuate the signal too much, you won't distinguish the signal from the noise. Hence why you need a configurable attenuation.

If you use the internal attenuator, the spectrum analyzer will automatically do the math plus the attenuation has been calibrated (it is never perfectly flat across the frequency range).

If you use an external attenuator, then you need to subtract its attenuation from the displayed values, as the spectrum analyser obviously just measures the input signal, not knowing what you have done with it outside the spectrum analyser.

For example, if you are dealing with antennas and/or transmitters, it is easy to exceed the maximum input rating. Doing so will quickly break the spectrum analyser. What I do is to connect a switchable external attenuator, that has a range up to -60dB (if I am not mistaken). I start with the biggest attenuation and lower it, always keeping an eye if the input signal is under the spectrum analyser's rating (written on the Input connector). Ideally, the signal does not need any external attenuation - but I like to be on the safe side.

In order to get you as paranoid as myself: if you are using i.e. a cheap Baofeng radio transmitting 5W and hold the antenna close enough to the spectrum analyser's input connector, you may break it, as 5W are roughtly 37dBm!

Spectrum analysers are sensitive equipments.

Why don't you consider buying yourself a cheap "SMA Simple Spectrum Analyser" device for aruond 50 Eurio from Chinese eBay? It can do 35MHz up to 4GHz and you can run it with my software (http://vma-satellite.blogspot.pt/2016/12/vma-simple-spectrum-analyser-download.html). This gives you a cheap introduction to spectrum analysis with little risks.

Also, do read the manuals of spectrum analysers! You will learn a lot without spending any money.

Regards,
Vitor

[rf-loop]

It is confusing alright ! 
I was playing with an Anritsu MS2721B Spectrum Analyzer at work and it has an Internal Attenuation Level control.
I fed it a signal of -25db.
Then I changed the Int Att Level to 10db, 20db and then to 0db but it did not affect the graph or apparent signal strength...It remained at -25db

If it do not work like this, it need repair or set for recycling of electronic waste!

It is designed to show signal level in input connector! Your signal is -25dBm so what ever internal attenuator you set it need show your signal level. Of course it remain -25dB on the screen becvause your signal IS -25dBm.  If you add EXTERNAL attenuator, say example 10dB, then your signal is after attenuator (in SA input connector) -35dBm and your SA show this level, because tjhis is signal level in SA input connector.   If you change SA internal attenuator, your signal level in input connector do not change and it display it just right.
 

All SA's what I know over tens of years, and I know many, are designed for display correct signal level what is connected to SA input connector independent of what is internal attenuator level as long as signal is still well over base noise level..

[TurboTom]

The internal attenuator of an SA is less useful for input protection but rather to keep the signal level entering the active circuitry of the SA fronend within the linear range. Too strong an input signal produces harmonics and intermodulation products long before dangerously high levels are approached. The Siglent SSA specifies a damage threshold of +30dBm (IIRC) but will provide half-way decent input characteristics at 0dB attenuation at signal levels lower than -10dBm. These signal levels refer to the strongest signal present at the input, not just what´s visible within the selected frequency/span. So, to identify the strongest individual signal (if performing measurements of unknown signals), it´s always a good idea to start with full span / wide bandwidth, the select input attenuation to keep the strongest peaks attenuated to -10dBm at least (i.e. if you see peaks up to +10dBm, you should select an internal attenuation of at least 20dB) and only then narrow down frequency/span/RBW parameters. If you just "play along" and keep input levels within the SAFE range, you can also decrease attenuation and observe how too strong signals at the active input circuitry will affect the spectrum. Eventually, the SSA will start "buzzing" at you to notify that the input signal is too strong. But this all happens long before dangerously high levels are reached.

Cheers,
Thomas

[Bicurico]

 @TurboTom:

Thank you for your excellent explanation - this is why I love this forum. Again I learned and consolidated knowledge.

@amdnra:

Not breaking the spectrum analyser is something you need to consider.

This is a famous Youtube video:https://www.youtube.com/watch?v=E6P-R0C9ro0&t=261s

Regards,
Vitor

[rf-loop]

The internal attenuator of an SA is less useful for input protection but rather to keep the signal level entering the active circuitry of the SA fronend within the linear range. Too strong an input signal produces harmonics and intermodulation products long before dangerously high levels are approached. The Siglent SSA specifies a damage threshold of +30dBm (IIRC) but will provide half-way decent input characteristics at 0dB attenuation at signal levels lower than -10dBm. These signal levels refer to the strongest signal present at the input, not just what´s visible within the selected frequency/span. So, to identify the strongest individual signal (if performing measurements of unknown signals), it´s always a good idea to start with full span / wide bandwidth, the select input attenuation to keep the strongest peaks attenuated to -10dBm at least (i.e. if you see peaks up to +10dBm, you should select an internal attenuation of at least 20dB) and only then narrow down frequency/span/RBW parameters. If you just "play along" and keep input levels within the SAFE range, you can also decrease attenuation and observe how too strong signals at the active input circuitry will affect the spectrum. Eventually, the SSA will start "buzzing" at you to notify that the input signal is too strong. But this all happens long before dangerously high levels are reached.

Cheers,
Thomas

Optimal "mixer level" (level after internal step attenuator) for normal use is -20dBm in SSA3kX. (depending some other settings and needs for measurements quality (including unwanted productions by mixer etc)  also bit higher can use)

I do not know what is 1dB compression level in Siglent.

Because sometimes it is boring to use Keysight material, here from Anritsu
It is good that user know this kind of things least roughly for his analyzer.

With signal under test try set SA input attenuator so that not exeed 1dB compression level.

[amdnra]

rf-loop: So if the internal attenuator does not change the level or anything else on the display, then what's the point of having it? TurboTom says it is there to adjust the signal so that it works within the linear region. Ok fine, but this implies that the displayed signal moves either up or down, and not stay at -25db as my previous example.Please someone address this Specific point

[TurboTom]

It´s been mentioned more than once in this thread: The SA displays signal level at the RF input N connector, not what it "sees" at the input of the active frontend. The attenuator is physically placed in front of the active circuitry and since the SA "knows" its settings, it shifts the measurements up and down on the screen accordingly (it does much more than this to compensate for internal gain deviations from the ideal flat line -- that´s why every digital SA has extensive internal calibration tables that are unique to every machine).

Cheers,
Tom

[amdnra]

it shifts the measurements up and down on the screen accordingly

Exactly! Then the damn thing does not stay at -25db!!
Answer this question please: If the signal does not change one bit from the aforementioned -25db with either the Attenuator ON or OFF then of what use it relly is and how can you tell that the Internal Attenuator is on? Does anybody understand the question??

[TurboTom]

I guess most members here understand your question and also see the point where you find it difficult to understand what the SA is doing and why it has to have the attenuator and comensates its setting on the display.

First of all, consider the SA as an instrument to show you the spectral RF power at its input connector over a quite wide dynamic range and also over a decent frequency span. It´s a black box, what´s going on internally is basically irrelevant.

The parameters that you can adjust on the SA are there to either "zoom" into the signal at the frequency range that you´re particularly interested in (center frequency, span, bandwidth) or to compensate for the instrument´s shortcomings dynamics-wise. And that´s what the preamplifier or the attenuator are for.

The "real" dynamic range of an SA´s signal processing section may be, let´s say 80dB (-100dBm to -20dBm, depends on the selected bandwidth and of course on the amount of effort put into the circuitry). Yet, you want to be able to measure in the range of maybe -120dBm to +20dBm, which is a span of 140dBm. It becomes immediately obvious that with the available signal processing hardware, this isn´t directly possible and definitely not so in a single setting. If you attenuate the input signal so the strongest components of +20dBm won´t overdrive the SA´s front end, you´ve got to attenuate the signal by 40dB. Yet, now the lowest signals that won´t vanish in the SA´s noise floor will have to be stronger than -60dBm. So as long as there are signal components as strong as +20dBm, you SA cennot resolve any components lower than -60dBm. If oyu made sure there are no powerful signal components at the SA´s input, you can reduce attenuation and maybe even activate the 20dB preamplifier, effectively lowering the noise floor fo the SA to -120dBm. Yet this means, signals as low as -40dBm may already overdrive the input of the SA and cause harmonics or intermodulation.

Consider the attenuator a parameter of the vertical position of the "window of interest" that you can slide over the "real" spectrum at the SA´s input socket. Thsi should make clear why the reported signal strength must not change when you change the SA´s internal attenuator setting.

Hope this helps to clarify the situation.
Cheers,
Thomas

[amdnra]

Thomas: I appreciate the fact that you are taking the time to explain things... but it is still not all clear because I see the tendency not to answer the questions posted but instead people go on with their own explanations and tangents. To be clear I'm not being ungrateful, quite the contrary but one wishes to have one's questions answered as posted, to clear some sticking points.

Now let me ask you a SA question: If you have a signal sitting at, say, -20db and the User adds an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. Or would it? From previous replies I gather it would still show -25db. 
In other words, the addition of discrete internal attenuation by the User does not show up as having any kind of effect (since the signal STILL shows -25db). Then what's the point if nothing changes on the display!! (I did this with an Anritsu model MS2721B).
I'm not concerned here about when the SA does its own special switching for Internal Attenuation that is automatically chosen by the unit itself; I'm talking about the User programmable input from the keypad of the instrument to set the Internal Attenuator to some value.
Please advise.Thanks

[nctnico]

Now let me ask you a SA question: If you have a signal sitting at, say, -20db and the User adds an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. Or would it? From previous replies I gather it would still show -25db. 
In other words, the addition of discrete internal attenuation by the User does not show up as having any kind of effect (since the signal STILL shows -25db). Then what's the point if nothing changes on the display!! (I did this with an Anritsu model MS2721B).

The point is to stay in the measurement region with the least distortion and thus the best measurement results.

[amdnra]

and how's that going to be possible when the display does NOT change one bit from before and after the attenuation? remember, per you folks it is still pegged at -25db

[CJay]

In simple terms the SA nulls out the -25dB and displays the signal levels as it is presented to the attenuator, not the front end of the SA.

As others have already explained, that can be useful if the input signal is going to overload the SA and cause the front end to create distortion.

If you stick an external 25dB attenuator on the SA and don't tell the SA it's present then the indicated level will correctly drop 25dB.

[amdnra]

If you stick an external 25dB attenuator on the SA and don't tell the SA it's present then the indicated level will correctly drop 25dB.

Alrighty...CJay: then What happens when you have a -25db signal present and then you stick a 25db Internal Attenuator on the SA and the SA knows it's there, Pray tell? According to the group in the know here, nothing Happens!! It stays at -25db!! It changes nothing

[idpromnut]

Now let me ask you a SA question: If you have a signal sitting at, say, -20db and the User adds an 'Attenuation Level' of -25db
then the signal on the screen should shift and show the signal sitting at -45db. Or would it? From previous replies I gather it would still show -25db.

<snip>

On my older HP that has an internal attenuator, it is a bit clearer what is going on here. On my SA, the attenuator knob also has the "reference level" setting, and both change when you change the attenuator setting. So if the reference level is say 10dB (that is what the strength of a signal that touches the top of the screen, where the reference level is, would be), and the attenuator is set to 0dB, then if you feed in a -25dB signal, you should see the top of your signal reach the -25dB mark on the screen, -35dB from the reference (this is important!).

Now, you decide to change the attenuator setting to -20dB. This will /at the same time/ change the reference level (i.e. what the top line of the screen means) to -10dB. Now that same -25dB signal being fed in is into the SA is at the same relative "place" on the screen, but the scale is different, it is now at -45dB. But it is /still/ -35dB from the reference level, so as people have been saying, your signal strength has not changed, how ever the reference level combined with the attenuator setting have now brought that signal lower in an absolute sense, but on the SA screen, it should still be the "same" relative to the reference level (which is at the top of the screen). 

In other words, the addition of discrete internal attenuation by the User does not show up as having any kind of effect (since the signal STILL shows -25db). Then what's the point if nothing changes on the display!! (I did this with an Anritsu model MS2721B).
I'm not concerned here about when the SA does its own special switching for Internal Attenuation that is automatically chosen by the unit itself; I'm talking about the User programmable input from the keypad of the instrument to set the Internal Attenuator to some value.
Please advise.Thanks

Again, the internal attenuator allows the user to bring the input signal down in absolute strength to a point where the instrument has better performance and you can get more detail about the characteristics of that signal. You are right however, that from a relative display perspective, there should be no change (i.e. the signal will "look" the same on the screen) but the measurement scales will change and different performance characteristics of the SA will come into play.

Whether the instrument automatically or the user manually adjusts the internal attenuator, the above still applies. If you wanted to further protect the instrument from a particularly high input signal (i.e. a +100dB signal where your SA has a max of +30dB input), then you would need to use an external attenuator. You might at the same time use the internal attenuator to adjust what level of signal is applied to the SA front end to gain more accurate measurements (so for example, a 100dB of external attenuation, and then 20-30dB of internal attenuation to bring the signal down to the optimal strength for analysis).

Cheers,
id

[nctnico]

and how's that going to be possible when the display does NOT change one bit from before and after the attenuation? remember, per you folks it is still pegged at -25db

It is about the signal which goes into the spectrum analyser's first mixer. That will be attenuated! It is the same as using a 1:100 probe on a modern oscilloscope. If you tell the oscilloscope you use a 1:100 probe it will multiply all numbers on the display by 100.

[amdnra]

To member id: Read reply number 13 by myself and reply number 14 by DaJMasta . Comment on whether reply 14 makes sense

[idpromnut]

To member id: Read reply number 13 by myself and reply number 14 by DaJMasta . Comment on whether reply 14 makes sense

I will need to recheck my setup at home; I'm pretty sure that the relative signal position on the screen will not change, but that the vertical scale will change (on my SA). The signal reaching the SA after the internal attenuator will be reduced in strength and this is reflected in the change of vertical scale.

[CJay]

If you stick an external 25dB attenuator on the SA and don't tell the SA it's present then the indicated level will correctly drop 25dB.

Alrighty...CJay: then What happens when you have a -25db signal present and then you stick a 25db Internal Attenuator on the SA and the SA knows it's there, Pray tell? According to the group in the know here, nothing Happens!! It stays at -25db!! It changes nothing

And the group here is correct, the signal will still display as -25dB even though the signal presented at its input is -50dB (which is a nonsense because dB has to be relative to something, be it uV, watts, milliwats etc.)

The important bit is 'it changes nothing on the SA display' because the SA is adjusting the scale to take that attenuator into account by adding +25dB to the displayed figures.

This is really very simple and I'm begining to wonder why or even if you're having a hard time understanding it.

[amdnra]

Aha! Eureka!!  nctnico takes the cake when bringing up the scope probe analogy. That's all it took. Finally got it.

 

   This is really very simple and I'm begining to wonder why or even if you're having a hard time understanding it

I have never used a Spectrum Analyzer before (that's the reason I'm here at the Forums asking questions. Because I didn't know. Duh ) And Yes, it is very simple when somebody explains it intelligently and provides a common and good example.
and About the last part of your quote, Strange you included a stupid implication after your previous decent posts. There's no need to post anything if all you're going to offer is some veiled insult.
Thanks to all that tried to help.

[CJay]

Aha! Eureka!!  nctnico takes the cake when bringing up the scope probe analogy. That's all it took. Finally got it.

 

   This is really very simple and I'm begining to wonder why or even if you're having a hard time understanding it

I have never used a Spectrum Analyzer before (that's the reason I'm here at the Forums asking questions. Because I didn't know. Duh ) And Yes, it is very simple when somebody explains it intelligently and provides a common and good example.
and About the last part of your quote, Strange you included a stupid implication after your previous decent posts. There's no need to post anything if all you're going to offer is some veiled insult.
Thanks to all that tried to help.

Simply put, it was beginning to feel like you were trolling, there were numerous explanations that if read and thought about gave the correct reasons and explanations of the behaviour you would see.

[tautech]

All make very good points and offer sound advice of SA usage. While I'm no expert and only have a year or two with SSA3000X, hard wired connection into the RFin port should be first attempted with extreme care. Answers above indicate the reasons why.
Initial use can wisely be restricted to weak coupled inputs until confidence and familiarity with the UI.

Yesterday while exploring Peak from a recent discussion on the forum, I had local spurious emissions via a coax sniffer loop on the display. Settings and attenuation were such to have peaks well within the dynamic range displayed but occasionally I noticed something at ~900 MHz. Cell phone I suspected as it was in my shirt pocket.
I shifted the coax loop and as it came close to me the cell handshake with the cell tower and immediately the SA warned of excess input......loop and phone had 300mm separation. 

These SA things are super sensitive........use with great thought and care.

[nctnico]

For some tests you may want an RF limiter. A couple of months ago I spoke to someone who blew up the input of a SA using a LISN without limiter while measuring a DUT which produced a lot of output on the LISN.

When not in use I have a 50 Ohm terminator on the input of my SA.

[amdnra]

All good points. Thanks guys 

[usagi]

you may also want to protect your SA with a DC blocker if you are sending in completely unknown signal source.

[Bicurico]

Indeed.

Investing in a Spectrum Analyser does not stop with the purchase of the device itself!

You have to consider buying a lot of tools, too:

1) DC Blocker
2) External switchable attenuator (prices go from around 50 Euro to infinite, according to specs)
3) Cables (kind of stupid using bad cables on such an expensive device - especially if low quality cables attenuate or distort the signal you want to measure - this gets increasingly expensive, the higher the frequency)
4) Adapters: you get N-type connector, but want to measure a DUT with SMA, F, whatever connector... Get adapters!
5) The N-type connector of your spectrum analyser is not exchangeable. Wear it out and you have a problem. Best to get a connector you screw onto it, which acts as a sacrificial connector.
6) Probes: I am not into measurements and certification of electronic boards, but if you want to carry that out, you need probes.
7) Get a cover, bag, whatever to avoid your precious instrument from accumulating dust.
Signal generator
9) Noise generator
10) Power meter (wish I had one)
11) ...

Cheers,
Vitor

[Electro Fan]

Hi. I've been looking to get a Spectrum Analyzer.
The choices at this point are:
Used Anritsu MS2721B
Used Rohde & Schwarz FSEA30 20Hz to 3.5GHz
New Rigol DSA832E-TG
New Siglent SSA3032X
All include the Tracking Generator
Trying to get something with an LCD display and stay around $2500 give or take
Any ideas or advice? Thanks

Pretty late to this thread and there are definitely newer models that might have longer useful lives but HP / Agilent had a few LCD models with some pretty good specs.

https://m.ebay.com/itm/HP-Agilent-Keysight-8560EC-007-Spectrum-Analyzer-2-9GHZ-Wth-30-Day-Warranty-/191899485592?hash=item2cae19c598%3Ag%3ADbQAAOSwPCVX7aNg&_trkparms=pageci%253A4c3f7429-a3e3-11e7-8511-74dbd1804dbc%257Cparentrq%253Ac5de39e515e0abc2e0e98027ffdb4cd5%257Ciid%253A12