Dedicated spectrum aanalysers - Page 1
Forum section: electronics / beginners

author: imolas3
author_rank: Newbie
timestamp: November 09, 2020, 10:13:13 am
content: HiI am not new to electronics but am new to dedicated spectrum analysers and wonder if they are useful to me. Basically, i find the FFT functionality of digital scopes that i can afford to be pretty poor (understatement)I wondered if a dedicated spectrum analyser such as the Siglent SSA3021X that was reviewed well by Dave is any use to someone working at relatively low frequencies in audio to maybe a few MHzI am put off with the 9kHz to (insert RF frequency here) ranges which suggest NOT DC to RF, when i want great performance at DC to maybe a few hundred kHz - definitely DC up, not 9kHz up (and i want the 10Hz resolution here too of course)Am i looking at the wrong kit for my needs?thanks

author: Kibabalu
author_rank: Regular Contributor
timestamp: November 09, 2020, 10:24:18 am
content: For low frequencies spans starting at DC and low required dynamic ranges the FFT functions of DSOs are more than sufficient. If you need to measure at higher frequencies up to many GHz and you need a high dynamic range to capture lower power signals beside of higher power signals you need a spectrum analyser.If you want to go for an SA, it usually doesn't goes down to DC, you'll need in addition something called 'low frequency converter' for mixing eg. the DC to 1MHz range into the measurement range of the SA.My recomondation for you is using the FFT function of a DSO.

author: David Hess
author_rank: Super Contributor
timestamp: November 09, 2020, 12:10:33 pm
content: While it is possible to DC couple an RF spectrum analyzer by changing the arrangement of the first mixer, performance is limited due to high flicker noise.High resolution low frequency spectrum analysis is done by instruments like dynamic signal analyzers like the SRS SR785 or Keysight 35670A. A 16-bit USB DSO might be suitable except that the software is likely very poor for this application. USB audio analyzers like the QA401 might be suitable except also for the software issue.

author: imolas3
author_rank: Newbie
timestamp: November 09, 2020, 12:41:33 pm
content: ThanksThat is sort of what i expected, but the FFT on scopes is not great in that the display tends to be a bit poor and tricky to read well. Most times i end up putting an ADC on the signal and then doing the FFT in code or Matlab, but i'm getting lazy

author: imolas3
author_rank: Newbie
timestamp: November 09, 2020, 12:43:53 pm
content: Thanks DavidI'll look into those device you mentioned - interesting to see if i can get what I'm looking forMight be a nice project to make a dedicated front end for my 16-bit NI acquition unit

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 09, 2020, 01:16:55 pm
content: what DSO you?

author: mawyatt
author_rank: Super Contributor
timestamp: November 09, 2020, 01:48:15 pm
content: Analog Discovery 2 has 14 bit ADCs and supports an FFT and CZT (Chirp Z Transform) according to the specs, which might support your low frequency needs. I haven't used the the AD 2, nor the software, so just speculation on my part.The SSA3021X Plus, which I do have and use, is an excellent device for higher frequency RF use, even at 100KHz.Like you mentioned I wanted to cover the DC to RF/MW range, so I use the SDS2102X Plus FFT for the lower frequencies and the SSA3021X Plus for the higher ranges. The DSO actually performs much better than you might expect from the 8 bit ADC. I've done an number of tests on my particular DSO and quite impressed by the accuracy and dynamic range (10 bit "extension" is very effective), and the Bode Plot capability is a nice added feature (extended DR by scaling).Best,