[ASK] Precautions needed for a noob with a spectrum analyzer - Page 1
Forum section: electronics / beginners

author: BravoV
author_rank: Super Contributor
timestamp: March 14, 2018, 10:15:03 am
content: Recently by luck, scored an used bench type 9KHz - 3GHz spectrum analyzer, and as noob regarding this fine piece of T&M equipment, I have read few precautions needed (more to read), and think I need to hear experienced members here regarding your wise advice.This is my SA's input :Click to enlarge.So please excuse few 1st noob questions :- Is it important to always use the so called "DC Block" adapter on the input to reduce the risk oftypical noob's mistake? Or any other comments on this.- Aware there are so many "cheap Aliexpress" type sales on this DC block, are they "decent" for this SA ? Yes, I'm currently lurking & stalking a 1st tier branded used DC Block online. Or any other suggestion ?- What is the RF Surge Protection ? As locally I got an offer of one of this, can I use this "temporarily" to secure the SA instead of a real DC Block adapter as this needs time to score a good one yet relatively cheap, and no, I can't afford a new one.- Or any other suggestions or advice for a noob, please.Thanks in advance for your help.

author: tautech
author_rank: Super Contributor
timestamp: March 14, 2018, 10:30:57 am
content: You'll need the official datasheet to be sure how much the input can handle.The SSA3000X models are rated similarly:Maximum input DC voltage +/- 50 VDCVDC isn't all you need be concerned about, more so max dB and that can be managed with internal attenuation (again check datasheet for how much is available) or external attenuation. 20dB is a pretty normal value to have on hand and it's the default (not max) internal attenuation for SSA3000X models.

author: BravoV
author_rank: Super Contributor
timestamp: March 14, 2018, 10:35:37 am
content: Quote from: tautech on March 14, 2018, 10:30:57 amMy SA official datasheet ->NS-30 Spec (PDF)

author: tautech
author_rank: Super Contributor
timestamp: March 14, 2018, 10:47:50 am
content: Quote from: BravoV on March 14, 2018, 10:35:37 amThe important stuff is there:QuoteQuoteNow you just need to learn how to drive it !Dive over to the SSA3000X thread and look at the excellent usage examples by rf-loop.https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/

author: tautech
author_rank: Super Contributor
timestamp: March 14, 2018, 11:22:13 am
content: BravoVFurther to just point out the modern approach is have an integral DC block which your unit by virtue of a 50V input rating will have.When I got my SA I had similar fears to you of damaging the input but with some little knowledge gained from members here and very careful initial small steps you will gain confidence as to what you can do with it.Achieving useful results on the display with just a near field loop is a safe way to make progress and become familiar with the UI before advancing to actual connection to a DUT.Play it super safe and conservative to start with and you'll be fine.

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 14, 2018, 11:53:13 am
content: That arrestor isNOTa DC block, it is a lightning arrestor and will happily conduct DC because most GPS antennas do have a preamp built in.What you need is a DC block which is simply said a capacitor, the trick is to get a capacitor that is big enough to not attenuate the lower range of the SA (9 KHz).So check the specs of any DC block you are going to get and see if the lower range is acceptable for what you are going to feed the SA with.

author: tggzzz
author_rank: Super Contributor
timestamp: March 14, 2018, 01:12:27 pm
content: Quote from: PA0PBZ on March 14, 2018, 11:53:13 amAnd linear enough that high voltages don't change its capacitance, thus changing the low frequency cutoff and/or creating harmonics.QuoteYes.Don't try to make your own. For RF (as opposed to audio) look at Minicircuits.

author: Shock
author_rank: Super Contributor
timestamp: March 14, 2018, 02:36:20 pm
content: Gotta measure em all! Went through a similar process when I got mine though I'm mainly interested in ULF to LF. I think it is common sense, similar to a scope you need to have an idea up front of the characteristics offset/amplitude of the signal you are measuring before connecting the front end, try not to use the instrument as an exploratory tool and use attenuation if necessary. You also have ratings on adapters and termination and need to be mindful to "err on the side of caution".These links have some tidbits, but it would be nice to see some deep dives on the subject. I'm always interested in how not to destroy gear. A nice project would be to make a few RF pads and a diode detector circuit.http://literature.cdn.keysight.com/litweb/pdf/5989-8791EN.pdfhttps://www.criticalcomms.com.au/content/test-measure/article/protecting-test-equipment-from-rf-damage-1405796639#axzz59jBWCOaYhttps://cdn.rohde-schwarz.com/pws/dl_downloads/dl_application/application_notes/1ma201_1/1MA201_9e_spectrum_analyzers_meas.pdf

author: mnementh
author_rank: Super Contributor
timestamp: March 14, 2018, 04:03:41 pm
content: So what is the "probe power" for? A FET high-impedance probe, or an active attenuator probe of some sort?mnemEvery day you learn something is not a wasted day.

author: Shock
author_rank: Super Contributor
timestamp: March 15, 2018, 01:06:12 am
content: Quote from: mnementh on March 14, 2018, 04:03:41 pmIt's a power source for compatible high impedance probes.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 03:17:51 am
content: Quote from: tautech on March 14, 2018, 11:22:13 amThank you, I thought I was too paranoid, as current the SA input N connector is the 1st and the only one in the house, and currently I just powered it on as don't have anything and the ball to connect anything into it yet.What is "near field loop" are you talking about ? Mind elaborate further ?

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 03:19:40 am
content: Quote from: PA0PBZ on March 14, 2018, 11:53:13 amThanks, noted. As I suspected.Quote from: PA0PBZ on March 14, 2018, 11:53:13 amNow, finding the "right" DC block that is good enough for my SA input range and also cheap, that is the hard part.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 04:19:35 am
content: Quote from: tggzzz on March 14, 2018, 01:12:27 pmNoted, especially the DIY one, definitely its not in my plan.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 04:22:51 am
content: Quote from: Shock on March 14, 2018, 02:36:20 pmShock, thank for the links and docs. Yes, I've watched the Alan's one hence the DC Block hunt.Curious, what kind of SA you have that does ULF to LF ?

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 04:24:57 am
content: Quote from: Shock on March 15, 2018, 01:06:12 amYep, and still don't have any idea what kind of connector is that ?Attached below the close up shot and it's outputs rating.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 04:33:03 am
content: Reading one of the Keysight document above, on the highlighted text, what is that ?Sort of a shorting cap for the N connector ?

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2018, 04:47:32 am
content: Quote from: BravoV on March 15, 2018, 03:17:51 amYou've a few options so I'll just give you some links in which to get a handle on them and then decide whether to buy something or DIY.https://www.eevblog.com/forum/projects/diy-magentic-field-probes/https://www.eevblog.com/forum/testgear/new-affordable-emc-probe-set-at-a-bargain-price-from-ariel-rocholl's-lab/https://www.edn.com/design/test-and-measurement/4380475/Near-field-probes-sniff-circuitsObviously if you need accuracy characterized probes are the way to go but I'd suggest you DIY from a loop of coax.That will at least get you started and give you a 'feel' for how to use a SA.You can use these on scopes too but you don't have the BW like a SA has.

author: Shock
author_rank: Super Contributor
timestamp: March 15, 2018, 04:47:48 am
content: Quote from: BravoV on March 15, 2018, 04:22:51 amHP 3580a 5Hz-50kHz and I also have a HP 3581c selective voltmeter.Shown here but my HP 3580a has the balanced input (takes both balanced and non balanced sources) and battery option.

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2018, 05:02:54 am
content: Let me just say I'm no wiz with a SA, just that I've had to come up to speed some due to wanting/needing to sell them.Read as much as you can, not just the links I've added and try to get a handle on those here that 'know their stuff'.I've mentioned one already and there's several more following whose opinions I deeply respect.Look here:https://www.eevblog.com/forum/testgear/kirkby-calibration-kit-alternatives/It can be a deep rabbit hole but it is fun.

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2018, 05:07:21 am
content: Quote from: BravoV on March 15, 2018, 04:33:03 amNot all SA's are created equal....sensitivity, input robustness etc.Check if the KS has:Quote

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 05:08:44 am
content: Quote from: tautech on March 15, 2018, 04:47:32 amGreat links, thanks again Rob.I guess I will be busy reading and gathering more infos especially on the DIY field probe 1st.Quote from: tautech on March 15, 2018, 04:47:32 amAccuracy on RF part is not my priority now, as this purchase is never planned, I didn't even expect to own a SA.It really changed a lot in my learning direction.My highest scope bandwidth is only at 400 MHz analog, this 3 GHz thingy is really quite a big jump in my T&M inventory.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 06:00:18 am
content: Quote from: Shock on March 15, 2018, 04:47:48 amCool piece of equipment, ULF & LF .. no wonder with battery option for low noise stuff.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 06:06:05 am
content: Quote from: tautech on March 15, 2018, 05:02:54 amYes, I'm aware of few fellas here looking the way they share/post their knowledge, that I believe are RF kung-fu masters.Quote from: tautech on March 15, 2018, 05:02:54 amDamn, I'm now just walking thru the hole's gate ...

author: vk6zgo
author_rank: Super Contributor
timestamp: March 15, 2018, 06:22:29 am
content: Quote from: BravoV on March 15, 2018, 04:33:03 amBasically a load of bollocks ! ( as far as ESD is concerned)We used to carry spectrum analysers all over the state without caps on the connectors.If you havep them, though, by all means use them, as they protect the thread on the outside of the "N" connector.( BNCs are worse, even though they don't have threads, they are much more prone to daThe problem is that, unless they are captive to the instruments

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 06:32:42 am
content: Related to BNCs , other question, attached below the rear ports, I do know common types like serial, VGA, printer port, GPIB too, and the 10 Mhz reference clock BNC, its capable of as input or output.How about these BNCs ? Do I need a special extra precautions on these ? I am not saying like hooking up to mains voltage, but are they also ultra sensitive sort of like the main input ?Mechanically wise, I know how to protect BNC as I have lots of those silicone caps for BNC.

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2018, 06:38:44 am
content: Quote from: BravoV on March 15, 2018, 06:06:05 amYou'll be captivated by it in no time.This is where I started and following posts show my SA newbie ramblings and growing confidence.https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg984038/#msg984038Study the GUI's shown for the many little visible clues on usage.Sure yours won't be the same however the same usage principles apply.One thing, check your documentation for the existence of an 'excessive input signal' warning alarm.....it's a bit like the confidence added when wearing a safety belt.....it won't save the SA if you do something stupid but it will warn you if you're pushing the input. Only had mine go off once when using a near field probe and the cellphone in my shirt pocket decided it should handshake with a cell tower some 5km away.Yes, they arethatsensitive !Quote from: BravoV on March 15, 2018, 06:32:42 amNo, just treat them the same as they were on a scope.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 15, 2018, 06:40:09 am
content: Quote from: BravoV on March 15, 2018, 04:33:03 amNo, the caps you will usually see used don't short the connector, they just cover the whole thing so the centre pin can't touch anything.In my opinion, the ESD reason for their use is all bollocks!We carried Spectrum Analysers all across the State without covers with no adverse effects.If you have them, use them as they protect the connector against physical damage.I have seen caps used on BNCs much more often than on"N " connectors, as the former are more prone to damage.Their biggest problem is that, unless captive to an instrument, they will easily be lost.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 06:53:56 am
content: Quote from: vk6zgo on March 15, 2018, 06:40:09 amOk, noted, especially on NOT TOUCHING the central pin, thanks.Quote from: vk6zgo on March 15, 2018, 06:40:09 amIf its just for mechanical and dust protection, you mean sort of this cap right ? Example from Aliexpress ->N Dust Cap, its cheap too.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 06:58:54 am
content: Quote from: tautech on March 15, 2018, 06:38:44 amWow !I'm not talking working at high power RF transmitter, or even a walky talky, but are you saying even using the near field probe and probing near a silly cell phone can toast the SA input ?Btw, looking at the spec of my SA, is the sensitivity level common ?Again, as a noob, I basically have no idea or fully understand yet, reading the majority part of the specification sheet.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 15, 2018, 07:06:35 am
content: But wait! ---- There's more!!!Re DC Block:-Nice to have, but you probably won't use it a lot.Over the years, I've noticed that such devices are the most "new looking" in the SA accessories kitAn external attenuators is probably a more useful device, as I've seen SAs where the front end has been "cooked" from excessive input signal level, but not from the application of DC.A 20 dB attentuator is very effective for input protection.In fact, as a resistive device, it will also reduce the level of any applied DC, whether by enough to protect the SA is in the lap of the gods!

author: tautech
author_rank: Super Contributor
timestamp: March 15, 2018, 07:18:00 am
content: Quote from: BravoV on March 15, 2018, 06:58:54 amPossibly, but it depends on the sensitivity of the probe, proximity andinput attenuation settings....they are your biggest friend when gaining experience. Always use some when initially investigating a DUT !So what happened that day, homing in on DUT signals just fine and reducing input attenuation for a lower floor and greater displayed signal amplitude when it did the handshake. Lesson learnt leave phone somewhere else when using a SA !Input attenuation is just one of the things to get your head around but the most important. Be it external or internal you must keep in your mind where you're at. SA's are so sensitive you must manage the input signal to within safe limits that are BTW far less that anything your'll encounter on 1M scope inputs.Start chucking some #'s into this and you'll see what I'm on about:https://www.rapidtables.com/convert/power/dBm_to_mW.html

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 07:53:09 am
content: Quote from: vk6zgo on March 15, 2018, 07:06:35 amOk, say a decent DC Block that has a flat response on my SA frequency range is hard to find, or still very expensive. Still going to find one though, as I'm a complete noob, just so worry I accidentally toast the input.Now, we're talking bout attenuator, since my SA range is 9 KHz- 3 GHz, as they're so many choices, which one is the most suitable ?I mean say like examples between two that have spec of DC-3Ghz vs DC-10GHz, is higher one is better ? Or just a bit higher say DC-4GHz one, so the performance at 3GHz is still good enough ? Worry I may fall into trap for young player.Also correct me if I'm wrong if I've asked the wrong question, as I'm just starting to grip on these.

author: BravoV
author_rank: Super Contributor
timestamp: March 15, 2018, 03:14:34 pm
content: Quote from: tautech on March 15, 2018, 07:18:00 amThanks again, simple yet really important lesson for SA noob.Quote from: tautech on March 15, 2018, 07:18:00 amAgree, its just few days ago I just realized and understood clearly the "power" vs "voltage" as in SA vs scope, cmiiw.Scope measures voltage while SA measures power, that is one of the fundamental different, again, cmiiw.Of course on time vs frequency as well.Thanks again.