Real time spectrum analyzers - Page 1
Forum section: electronics / testgear

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: April 13, 2021, 01:11:08 pm
content: HI,since now I am equipping a lab at home I want to replace some instruments, like my old R&S FSA spectrum analyzer.I was searching for some newer spectrum analyzer that I need for the lab at home, nothing too special because if I need to do some fancy at work I have plenty of equipment to do so, like "my" beloved FSV40 full opt.And I found this rigol RIGOL RSA3015E that is a real time spectrum analyzer, never used one and I was wondering whats the difference between a real time spectrum analyzer and a spectrum analyzer to understand if I really need one.Also this particular model is any good? I know that rigol has some firmware problems, also because I own some rigol equipment.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: April 13, 2021, 01:58:34 pm
content: Deep Voice Guy from Rohde & Schwarz has my favorite explanation:These days Rigol and Siglent (and SignalHound -- I have a SM200B that I love) offer this capability at a much lower price. Of course, I have yet to see an implementation from the economy players that matches the quality of the implementation from Keysight or R&S. Color grading, resolution, update smoothness, ability to really crank the juice on the spectrogram, triggers, etc are all much better from the Big Players. Still, these are exciting times, and it might well make sense to spring for an RTSA!That said, once a spectrum analyzer has a powerful digital IF, typically they don't expose IF Out anymore because they want to steer you towards their own software solutions. Analog IF Out is good for time correlating signals on an oscilloscope, using a SA as a filter / downconverter, digitizing and steering signals into GNU Radio, etc. So, as always, there are tradeoffs.

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: April 13, 2021, 02:19:21 pm
content: Quote from: jjoonathan on April 13, 2021, 01:58:34 pmWow deep voice R&S guys has given a very good explanation.Also about the implementation of R&S, I love their instruments, I work on a daily basis with their equipment, with ZVA, RTP scopes, FSV SA, PSU, SMB and on and on, great user interface and all.But if you have some problems, like changing hdd, SSD, they charge you up to the sky. Also you cant calibrate them you need R&S kits that costs an entire fortune, if I remember correctly the cal lab of R&S down here to make only the SAs costs something up to 3ml.That said you pay qualityI also use other scopes for example from LeCroy up to (If I remember correctly, I used them less often) 10GHz, but the R&S interface makes all the difference, also because LeCroy scopes are fricking heaters lol

author: jjoonathan
author_rank: Frequent Contributor
timestamp: April 13, 2021, 03:00:14 pm
content: Yes, that is my experience as well: Rohde & Schwarz spectrum and network analyzers aren't cheap but they feel like they have received much more iteration on professional workflows. Your first time shopping for a professional SA you balk at the R&S premium and then a few years down the road you visit a trade show and see them demo a feature that would have easily justified the price had you known up front that you would need it or that other vendors' implementations of the feature were missing a critical sub-feature. This happens two or three or four times and then you join the cult of professionals who insist on R&S upfront.It is unfortunate that hobby applications do not support the same "pay a lot of money to avoid wasting time" calculation. At least we have options these days!

author: mawyatt
author_rank: Super Contributor
timestamp: April 13, 2021, 05:01:22 pm
content: It's really good to see more folks becoming interested in Real Time Spectral Analysis, and at a price point where individuals can consider acquiring instruments. The R&S video is an excellent example of the usefulness of RTSA, thanks for posting jj. Maybe can save up enough to get one of these RTSA somedayRTSA was usually for special applications in the distant past like or work back in 1982 using custom CCD devices (convolvers) as a core for a RTSA based upon the Chirp Z algorithms, or the decade old Single Chip Spectral Imager utilizing imaging chip concepts to capture an "image" of the RF spectrum similar in fashion as our phone cameras (can post more details if interested).Best,

author: tautech
author_rank: Super Contributor
timestamp: April 13, 2021, 05:16:14 pm
content: The marketplace has changed rapidly and some really versatile instruments of this type are available now.This snapped remotely directly to my PC from the other side of town examining a mates WiFi spectrum with his SSA3075X-R.Not only is this a RTSA but an ordinary SA, VNA and a DTF tester.A step up in frequency along with RTSA capability from the popular SVA1032X.

author: 2N3055
author_rank: Super Contributor
timestamp: April 13, 2021, 05:56:15 pm
content: Quote from: mawyatt on April 13, 2021, 05:01:22 pmYes please !!

author: Bud
author_rank: Super Contributor
timestamp: April 13, 2021, 06:31:52 pm
content: Quote from: tautech on April 13, 2021, 05:16:14 pmSorry tautech but what problem that allowed you to solve?

author: 1design
author_rank: Regular Contributor
timestamp: April 13, 2021, 07:07:41 pm
content: If you only need a real time SA ad no TG or VNA functionality, I think the best price/performance product today would be the Tek RSA306B.https://www.tek.com/spectrum-analyzer/rsa306You get 40MHz of real time BW, free VSA SW, a 6GHz frequency range and plenty of other functionality for under $5k in the US.It is also in a portable and robust form factor that can be operated from a laptop and fits into any backpack or bag.With RSA's it is more about the functionality of the VSA than anything else. Looking at the nice temperature graded display is rarely the thing that nails down the problem. Demodulating the signals correctly, having a robust VSA implementation is what really brings in the value. When you measure actual OTA signals, they almost always have impairments(higher phase noise, multipath fading, doppler spread, etc.). How the SW deals with them differentiates between the good, band and ugly implementations.The TEK VSA is ok, but still not as good as Keysight and R&S. Take it from someone that has been using them to demodulate real world signals for the past few years to pay the bills.I haven't tried any of the budget ones yet, but wouldn't bet my pay on them.In the lab we have R&S and Keysight, in the filed, the budget RSA306B does the job very well and has proven reliable.A good video showing its functionality by W2AEW:It showcases how much other functionality you need past just looking at the spectrum.

author: tautech
author_rank: Super Contributor
timestamp: April 14, 2021, 01:15:12 am
content: Quote from: Bud on April 13, 2021, 06:31:52 pmNone at all.This particular unit did not pass through my hands as it was sent directly to one of Siglent's beta testers from the factory and as it was my first experience with any SSA3000X-R albeit remotely I grabbed the screenshot of the RTSA menu for my own reference.However the SSA3000X-R along with SSA300X Plus and SVA1000X models all have many features including demodulation capabilities as per below:

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2021, 02:40:46 am
content: Quote from: 2N3055 on April 13, 2021, 05:56:15 pmSome time ago we discovered while studying certain SOTA nanometer feature size CMOS processes that they could capture and hold a charge on the gate similar to the way FLASH memory works by captured charge, but obviously not held as long. This charge would produce a given drain to source current if properly biased. In effect a single small MOS transistor could act as a very high speed sample & hold circuit. While investigating this effect we also discovered that the drain to source current could be "remembered" even if the drain to source voltage bias was removed, then reapplied a some later time.By forcing the signal input input current thru a biased MOS device connected as a transconductor (gate connected to drain) a gate to source voltage Vgs is established to support the total drain current and this Vgs can be sampled by another like device to produce a scaled drain current, with the scaling being the Width/Length and Finger ratio. This concept leads to an "RF Pixel" similar to an imaging pixel, whereas each pixel can be sequentially sampled and held as time marches on (an imaging chip all the pixels are "exposed" simultaneously where the RF Pixel is sequentially "exposed"). These become time samples from a discrete time continuous amplitude RF signal sampling process, so a type RF Memory.A analog FFT is implemented on these RF memory samples as a current mode algorithm in DTCA format, where the additions and subtractions are performed in the current domain and the multiplications are performed by dedicated MOS device size scaling. Following the camera chip imaging concept the frequency domain outputs from the FFT "bins" are digitized with multiple parallel SAR ADCs, one for each frequency bin.For example, a 1 megapixel RF imager sampling at 20GSPS produces a 10GHz Nyquist range with 20KHz resolution with FFT updates at 50us, or a 10,000 pixel version with 2MHz resolution with updates every 500ns. One concept was to use smaller imager chips looking for signals of interest, followed by high resolution imagers to resolve signal details. Some time after the discovery & concepts patent applications were created which unfortunately fell on a company acquisition transition and the patent process was never followed thru after they closed our R&D center. Hopefully someone will pick up on this and follow thru with the development, I know of a DARPA program that was working on analog FFTs awhile back, so likely others are also involved.Anyway, here's some old pages from a PP presentation that may help show the concepts.Best,

author: Bud
author_rank: Super Contributor
timestamp: April 14, 2021, 03:28:52 am
content: Quote from: tautech on April 14, 2021, 01:15:12 amI am still struggling to understand how is this useful for a HOME Lab. The OP's question was in the context of a home lab. These capabilities are totally useless for home/hobby use case.

author: mawyatt
author_rank: Super Contributor
timestamp: April 14, 2021, 02:44:27 pm
content: Quote from: mawyatt on April 14, 2021, 02:40:46 amCorrection, evidently a patent was issued, patent US10161975 "Method and System for RF Spectral Imager on an Integrated Circuit". Either we weren't informed (unlikely), or misplaced the patent notice from awhile back and forgot (likely since our memory has been fading lately)Best,

author: Bicurico
author_rank: Super Contributor
timestamp: April 14, 2021, 03:04:42 pm
content: Quote from: Bud on April 14, 2021, 03:28:52 amWell, you could use your consideration for ANY test equipment purchased for home/hobby use.Of course I disagree with you. You need to understand that people have different interpretation of what a home/hobby lab is and what's it purpose.The picture that tautech posted, shows for instance a Constellation Diagram, which shows modulation errors, normally due to reception, cable or distribution problems. You may be a hobbyist developing your own amplifier, modulator, etc. and may be interested in this. A Constellation Diagram is interesting for something as simple as satellite DX (reception of difficult TV/Radio broadcasts via satellite).A realtime spectrum analyzer will basically show you sporadic signals, which a sweeping spectrum analyzer will miss. This is clearly shown in the R&S video.A home/hobby use might be the development of GNU Radio sink to implement 4G, 5G, WIFI, etc.Consider that home/hobby might include amateur/academic research,Also, another application might be for self-education. This is actually the main reason behind me buying test equipment. It often allows learning for less money and you get to own the equipment.Regards,Vitor

author: NiaDebesis
author_rank: Frequent Contributor
timestamp: April 19, 2021, 12:17:14 am
content: Quote from: Bicurico on April 14, 2021, 03:04:42 pmExactly same reasons here.I work with RF every day, is so fascinating, somethimes I can do some researches at work, but as you know at work you have to do something ahah, so I have my personal lab at home well equipped with a lot of RF equipment often gathered for free, for example TWT amplifiers, PNA from Keysight, PLL analyzers from Agilent, phase noise from Aeroflex that works up to 26GHz and have a phase noise of -170dbc, that is stuff maybe a little bit old but that works perfectly fine.