I'm looking for a spectrum analyzer for EMC analyses. I've come across this spectrum analyzer:
Would this be a good buy or not?
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.)
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Typical resolution BW is 300khz for EMC (or was). As long as your just pre scanning and not measuring precise power levels, then 250khz should be ok. You should use the rBW that CISPR specs out.
You might want to look to see if there is any automated scanning capabilities. So you can scan from 10hz to 3ghz in one shot. We had the old tek analyzer that did that, which was nice. With 300khz BW the scan took a few minutes.
Cheers
Too expensive. Look on eBay for some old AVCOM units. Of course, you don't supply enough information for us to really help you...
I'm a big fan of "fix it in software." BUT EMC is tricky business. You need to be very aware of the testing methods and equipment used for the qualification tests. If you use different methodology/equipment, you need to UNDERSTAND the differences/limits in that technology.
You can't just design in more margin just in case their reading might be higher than yours...and still meet your cost/schedule goals.
Failing the first qualification tests on your prototype can be EXPENSIVE. Failing the qualification tests on the first unit of that 10,000 unit production build can be CATASTROPHIC.
Look at risk/reward and do the math. If this is a toy for your bench, it can be very helpful and save you trips across campus to your test facility. If this is your ONLY test method, you've got some math to do.
Saving a few bux on the front end will get you a smile from your boss. Shutting down sales will get you a frown from personnel at your exit interview. "Somebody on the web told me it would work," will be of little help.
What puzzles me most is that people pay hundreds of Dollars for broken
20+ years old equipment and over $2000 for a 15 years old HP analyzer without any warranties.All this while you can buy a new analog Atten Spectrum analyzer (with TG) for about $700 and a couple of hundreds $ more buys you the USB analyzer I mentioned. So either people are paying way too much for old gear or the new gear I mentioned has serious flaws.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
I have been out of campus for a while :-)
My prefered route is to find & fix potential problems, take a pre-compliance test, fix things and then go for the final test. And fix things. The 'problem' is that I'm on my own now so I need to invest in a spectrum analyzer. I don't want to depend on lending/renting one. Since you can spend money only once I'd like to spend it as wisely as possible.
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
Of course, some of us actually need good performance. My HP 8568B has
-110 dBc phase noise at 1 kHz offset--good luck getting that with a USB gizmo.
But do keep thinking that way...that's what keeps boat anchors so delightfully cheap!
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs (atsign) electrooptical (period) net http://electrooptical.net
I am quite certain that the USB part is merely the interface to the software applet that allows you to display the data that the actually device gathers. So, it comes down to that device, and the 'gizmo' is likely quite a lot smaller and quite a lot less refined than your HP. The HP has decades of knowledge behind it. The gizmo is a stab at that same capability and feature set.
But it isn't due to the fact that it uses a computer and USB to look at the data. It relates to how the data is gathered by the 'gizmo' itself. There is a chance it is better, but not likely.
Sorry, but I don't think you thought that one through too well. :-)
The HP is far heavier than the gizmo. Hell, the gizmo would probably float if it were a sealed case. Certainly no anchor.
Anyway, the new Agilent stuff is cool. High function and good looks. They look nice in the racks next to the other equipment.
[snip]
Below this it also says:
Sounds like a fractional-N synthesizer with integer-N boundary spurs.
My 20+ year old Marconi 2383 SA has better performance in these areas.
At $700 the best you can usually get with a new unit is a non-PLL oscillator in there. Which will likely have the stability of Camembert cheese on a hot summer day. The Signal Hound might have a PLL though. But, quote "There is also a thermometer for temperature corrections, allowing accurate amplitude measurements over the entire operating temperature range". Umm, yeah, well, I have never had or designed RF gear where the gain would noticeably drift with temperature ...
Yep. I couldn't have said it more succinctly. For example, the performance of the HP3585 baseband analyzed is IMHO unrivaled to this day. So is the Tektronix 2465 scope.
Right on!
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
My point, exactly. Spending wisely is not always the same as "cheapest thing I can find." You really need to understand how the thing works and whether the thing produces equivalent results in the desired application. You'll find out at the first EMC test, but you've already spent the $$ by then.
I worry about "artifacts" in a cheap, doitinsoftware solution. You certainly CAN doitinsoftware, but not cheaply.
The thing that may save your bacon is the small dynamic range you need. If you set the reference level for the standards limit, you really only need 20dB of dynamic range. You don't even care about the accuracy or artifacts of stuff much lower than the limit. All this assumes that the digitizing is done AFTER a lot of input bandwidth filtering. Othrwise, you can't even count on small dynamic range.
I'd consult the vendor and ask them for some testimonials from people using their product for EMC pretesting.
I've been considering the idea of buying a Tek 2465B and had found this link, earlier. Now that you bring this up to my mind again, I'd like to post the link and some of the text there:
"I bought a 2465B (or so it appears) from a calibration outfit in CA USA. The unit had fresh calibration. Attempting to measure a signal in the 400MHz range, I didn't like what I saw. I opened the case (again ;-)), and noticed at the A1 PCB part number - 671-0720-08 -a 2445B PCB, not a 2465B PCB.
"I queried the seller, and this is what he claims:
'Tek made 2445B and 2465B with only one internal difference: a 2445B has a bandwidth choke on the backside of its main A1 board etched into the printed circuitry of the bare board. This was also true of the 2445A 2465A pair, and the original 2445 2465 pair introduced in 1983.
'For the privilege of not having that bandpass limiter, Tek charged clients $2000 more, but was too lazy to make 2 really different scopes. So since 1985, when I discovered Tek's laziness, I have earned my living upgrading the 3rd digit from 4 to 6.
'The clock stays with the A5 board. The 2445B A1 board, once it has its bandwidth choke bypassed (I cut traces in 4 places on the back and spliced in 2 short straight wires to carry the signals from the DL100 delay line to the inputs of U600), can do 400MHz.
'The only other difference is to ground a contact (pin 23 J511) that tells the A5 processor board that it is now has a 6 instead of a 4 (as 3rd digit) that allows the 5nS/cm fastest sweep speed to be accessible, instead of just going up to 10nS/cm.
'This is what many of my 2465B clients have, but so far you are the only one to have noticed... '
"I looked at the circuits, and discovered a 3rd difference - the 2465B PCB has inductor L403, apparently for adjusting the HF circuit.
"Leaving aside the apparent legal ramifications of what he has been doing for 25 years, without disclosing to his customers, I would like to learn from the technical people here:
"1. If there are any other technical differences between the 2445B and 2465B A1 PCB's? 2. If the integrity of the A1 PCB has been compromised by cutting the PCB traces? 3. If there is any spurious interference of any kind caused by the new spliced wires? 4. If this modified 2445B A1 PCB is, in fact, functionally equivalent to a real 671-0722-08 2465B A1 PCB (disregarding Tek's marketing considerations), and if not, why not?"
Jon
I have. And man did I feel old there :-)
Some advice here: Research any new analyzer well. RBW, sensitivity and all that are not the whole game. A major factor is intermodulation, IOW how sturdy the first mixer and preamp are.
In that context this remark gives me pause: Quote "No external power supply needed - draws power from USB". Now that's only 2.5 watts max, doesn't instill much confidence. When this little power is available how can there be a nice fat DBM inside and a frontend with tons of dynamic range? Maybe they designed in some miracle? Lack of raw dynamic range can be utterly frustrating when you have to do noise hunts in the vicinity of powerful RF sources, whether they are outside your house or part of the DUT functionality (switch mode supplies et cetera).
Then there is the USB connection itself which can inject noise that can mess with your measurements. But that is usually "debuggable". Make sure you are allowed to ground the analyzer.
Longs story short, with the old HP boat anchors there isn't much research that needs to be done, other than determining the confidence level that you will receive a working unit where the first mixer didn't have a head-on collision with a pulse yet. Newer Agilent gear sometimes did not make such a great impression on me, I'd prefer the big old stuff such as HP8566 over those. Of course, the disks in your spine won't ;-)
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
I have been eyeballing the HP8920 series mobile analyzers as well. Not a great dynamic range but tons of other features. The problem is the weight (about 32 kilo) which essentially makes it non-portable. I almost bought one from Germany but I messed up the bidding on Ebay (the seller must be happy though).
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
I don't remember that one. But 32kg used to be called portable back then. Believe it or not but even the HP-3577 here has a handle. They didn't dare to call that one portable though :-)
For portability the little Rohde&Schwarz "tablet style" analyzers work well. But you need an IrDA-RS232 converter for those because IrDA has pretty much fizzled. The one I rented last time came with a cool backpack that can also be used to day trips on the bicycle.
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Here is something with a USB interface that might be useful on an electronics workbench:
-- You can't fix stupid. You can't even put a Band-Aid? on it, because it's Teflon coated.
It's been around for a year or two now, and I think the price is decent enough, but I've been dismayed that they don't give you more information about how it works internally. From reading the manuals, I get the impression that (unlike a traditional swept frequency spectrum analyzer) they're doing SSB demodulation in software, and since their opposide sideband rejection is (almost surely) rather less than their on-channel dynamic range, they use some software heuristics to try to sort out what a real signal is vs. just an image. For EMC work, this would worry me a bit in that you're looking at "noisy but powerful" signals, which I'd guess would be difficult for their software heuristics to deal with.
But I could be completely full of it here -- I've never used one in person. :-)
Their FAQ page here:
---Joel
Something like an HP 8561E from the '90s has significantly better specs than a Signal Hound there... and if you really want to give your chiropractor a lifetime of income, check out the 8568B.
Or you can get something like an Agilent N9020A for $35k+ depending on what options you want.
It all depends on what specs you need; anything where you need really narrow resolution bandwidths, low internal phase noise, or really high dynamic range makes prices go up quite rapidly.
I am a believer that in many cases when you're just starting out and don't really know *what* you need, performance-wise, you're best off getting something cheap and then upgrading once you've learned what you really care about rather than buying something spendy right off-the-bat and potentially finding you paid for a lot more (or something different) than what you really need.
When I was in high school I had a $500 30MHz dual-channel Taiwanese scope and honestly... even if I'd had been able to afford a Tek 2465B, it wouldn't have done me any more good than the Taiwanese model did.
---Joel
The SignalHound's internal oscillator says its phase noise is typically -55dBc/Hz at 10Hz out... I'd have to respectfully submit that NO WAY does that drop to -110dBc/Hz by 1kHz as Phil's 8568B does. :-)
The spectrum analyzers in the 8920 (and it's bigger-but-cheaper-eBay brother, the 8924C) aren't that great -- they're meant to let you see if a strong transmitted signal is present and gauge the bandwidth it's consuming, but not to check for fine little spurs that violate emission limits or only show up as very narrowband signals.
That being said, they *are* very useful pieces of equipment for a lot of other uses; at work we have almost as many of them as we do spectrum analyzers.
...and for 12V operation they're meant to be powered by a car or car battery as well -- my recollection is they draw something like 50+ watts!
---Joel
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