Hi
OK, backing up a bit. For a spectrum analyzer you do it fairly simply. You put a 50 ohm termination on the input and see what you get. The floor will be some number in dbm per square root Hz. This is also called "normalized to 1 Hz" on some analyzers. As you change bandwidth settings on the analyzer, the displayed number will change if you do not have a "normalize to bandwidth" button on the scope. If you don't have that button you will also need to calculate the actual noise bandwidth of the filters in the analyzer. That can be more or less exciting depending on the vintage of the analyzer.
Next up is video bandwidth. This is just an averaging process. Depending on how it is done in your specific analyzer, there may or may not be a correction for it. On older analyzers there is also a video peak to average correction (don't ask if you have a modern unit).
So let's assume you now have an analyzer that is calibrated and properly measuring noise in dbm / sqrt(Hz). You take a look and you might be getting -171 dbm. If so your analyzer has a 3 db noise figure front end. You might also get -131 dbm. In that case, your analyzer may still be in spec. It all depends on which one you bought and which options you got with it. Before we ever do anything with an antenna, there could be a 40 db delta....
Now we grab an antenna. At least it says it is an antenna. Consider that a half wave dipole at 1 MHz is 150 meters long. That thing in your hand is *not* quite the same thing, regardless of what it says it's lower frequency limit is. If you are reading low frequencies, you are using a probe rather than an antenna. The probe is likely either designed for E field or H field pickup. It has some magic calibration factor of "this field equals that dbm" buried in the spec sheet. It may have a 20 db amp with it, it could have a 60 db amp. There's another 40 db delta
We move up to a frequency (say 500 MHz) where we *can* build an antenna. It's either a monopole or a dipole. We read up on all the design details and have the directivity and gain all worked out. We hook it up to our -171 dbm analyzer and in the quite spots we get .... -171 dbm. Everyplace else you get discrete signals that are related to this or that. You can see the local TV stations. You can see all sorts of stuff. How well can you see them? It depends on your building construction and where you are in the building. I have seen people claim (and the FCC actually accept !!!) that they have 120 db buildings.
So what will you read in your experiment (after calibration) ... -171 to -91 with the 80 db fudge factors above. Does this matter? ... err ... do your people carry around cell phones? If so, the phones are likely checking in with this and that on a regular basis. When they do, you have at least +20 dbm on your analyzer. Do you have an in-plant pager system (RF not audio). Any bets what happens when it goes off? Same issue with in-plant cell repeaters. Then there's WiFi (outside your band).
Assuming you have tossed out all of everybody's RF gear on a permanent basis, what is reasonable? No matter how hard you try, the broadcast stations are going to be there. If you can hunt down every source in your lab and get them below what the broadcasts peak at. That's about as good as it gets. Good luck tracking down that final UPS that's spraying crud from DC to light ....it can be done .. just keep at it.
Bob
With a spectrum analyzer, what is a good method for determining the local noise floor (in the lab area around the spectrum analyzer)?
I don't want to derail the discussion so this is just a brief interruption for a light hearted thought....
after following some of the posts here I came across this:
http://m.ebay.com/itm/AGILENT-KEYSIGHT-HP-8510C-SYSTEM-SCALAR-AND-VECTOR-ANALYZER-/131727315933?nav=SEARCH
http://www.keysight.com/en/pd-1000002059%3Aepsg%3Apro-pn-8510C/vector-network-analyzer?cc=US&lc=eng
I'm wondering if one of these might be able to get the equivalent of 2 scopes credit toward the 20 scope merit badge?
ok, returning now to the original thread in progress ...
I don't want to derail the discussion so this is just a brief interruption for a light hearted thought....
after following some of the posts here I came across this:
http://m.ebay.com/itm/AGILENT-KEYSIGHT-HP-8510C-SYSTEM-SCALAR-AND-VECTOR-ANALYZER-/131727315933?nav=SEARCH
http://www.keysight.com/en/pd-1000002059%3Aepsg%3Apro-pn-8510C/vector-network-analyzer?cc=US&lc=eng
I'm wondering if one of these might be able to get the equivalent of 2 scopes credit toward the 20 scope merit badge?
ok, returning now to the original thread in progress ...
Hi
If you get one of those (or a similar vintage unit) the display is it's main weakness. They go dim and are a bit expensive to replace (If you can find them). They also have a tendency to have been used by some guy named Bob in an auto test system. Said knuckle head ran tests on them constantly for years. The poor relays in the attenuators got a real work out ... they also are a pain to replace.
The same issue applies to some generations of spectrum analyzers. The ones with relay attenuators (not knobs, not solid state switches) do have a wear out mechanism. It shows up often as one range bring wrong.
Bob
I don't want to derail the discussion so this is just a brief interruption for a light hearted thought....
after following some of the posts here I came across this:
http://m.ebay.com/itm/AGILENT-KEYSIGHT-HP-8510C-SYSTEM-SCALAR-AND-VECTOR-ANALYZER-/131727315933?nav=SEARCH
http://www.keysight.com/en/pd-1000002059%3Aepsg%3Apro-pn-8510C/vector-network-analyzer?cc=US&lc=eng
I'm wondering if one of these might be able to get the equivalent of 2 scopes credit toward the 20 scope merit badge?
ok, returning now to the original thread in progress ...
I did some calibs on my Rigol DSA 815 recently...using a Boonton 4210 -4b Power meter and an HP8753D as a sweep (CW) gen.
I did a full range cal to 'smooth' the response down to around 0.1 db precision via the correction constants entries in the Rigol. Took < 30 cal points.
Of course, for tighter ranges of interest I'd have to do another set of cals to optimize the results, but it can be done, in about 30 mins!
Ok, onto the subject at hand.
I can get the Rigol down to -150dBm/Hz or so with a small VBW (300Hz), internal preamp on, and a 1Mhz span which takes abt 25 secs to sweep.
I hope to use this approach to doing NF work:
http://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1000001900:epsg:faq&nid=-536902970.536880671&id=1000001900:epsg:faq
Perhaps I'll score a calib. noise source one day.
Hmm, can you suggest a type of diode that's not too hard to source? I could get 1 and select from them for a decent unit.
I have some 2n2369 on hand which are fast avalanche, (as per Jim Williams pulse gen for scope cals). Also some high Ft (up to 25Ghz) transistors.
Anyhow, this document was very interesting as it describes the build of noise gens as well as their cals.
http://www.w1ghz.org/noise/noise99.pdf
Ok, and i understand soldering the SMT , top dow, provide s a shorter& straighter inductance path.
Ok, went fishing for RF transistors in stock. Have several of each.
BFR93A - 6Ghz SOT23
BFG540W - 9Ghz SOT-343
2.5GHZ GaAs FET AF002-32
BFP 650 - 42GHz NPN
http://www.infineon.com/dgdl/Infineon-BFP650-DS-v01_01-en.pdf?fileId=db3a30431400ef6801142743b0330715
BFG21W - 18Ghz, SOT-343R
BFG 425W - 25Ghz, SOT343R
Ok. I have this wideband amp:
http://www.minicircuits.com/pdfs/ZX60-6013E.pdf
Some of these as well:
http://www.minicircuits.com/pdfs/ERA-2SM+.pdf
I can try to copy this assy with FR4 0.8mm.
http://www.minicircuits.com/pcb/WTB-408-2+_P02.pdf
But this Ebay item seems better for my app...given the gain:
252075077721