modulation identify by using analyzer - Page 1
Forum section: electronics / rf-microwave

author: SAP85
author_rank: Newbie
timestamp: July 10, 2023, 04:41:52 am
content: Hi friends,I have a satellite receiver, spectrum analyzer and oscilloscopeAs I know my STB box demodulate QPSK. therefore If I connect RF out from LNB to analyzer, Is there any method to identify modulation technique using spectrum analyzer and oscilloscope?Thank you

author: pdenisowski
author_rank: Super Contributor
timestamp: July 10, 2023, 09:50:27 am
content: Modulation type and modulation order can easily be determined looking at a constellation diagram. I made an entire video series on the most common digital modulation types (ASK, FSK, PSK, QAM, APSK) as well as how to interpret constellation diagrams that show various types of impairments:Most people would use a spec an to look at constellation diagrams, but this typically requires some kind of vector signal analysis (VSA) functionality or option that is not common in lower-end spec ans.Also if you had access to the I and Q data (and the symbol clock), you could also display constellation diagrams on an oscilloscope in XY mode, but this is also not common and would almost certainly not be practical in your case.https://youtu.be/yFnJAkd0OBg?t=383

author: pdenisowski
author_rank: Super Contributor
timestamp: July 10, 2023, 09:59:34 am
content: Quote from: pdenisowski on July 10, 2023, 09:50:27 amMore of a vector diagram than a constellation diagram, but an example of how you can determine modulation type / order using a scope to create a constellation diagram (here, 8PSK)https://www.instagram.com/reel/Csb7hKjJe7Z/

author: xmo
author_rank: Regular Contributor
timestamp: July 11, 2023, 12:21:34 am
content: A couple of items that may be of interest:https://www.itu.int/dms_pubrec/itu-r/rec/sm/R-REC-SM.1600-3-201709-I!!PDF-E.pdfhttps://www.itu.int/dms_pubrec/itu-r/rec/sm/R-REC-SM.1600-2-201508-S!!PDF-E.pdf

author: pdenisowski
author_rank: Super Contributor
timestamp: July 11, 2023, 12:34:40 pm
content: Quote from: xmo on July 11, 2023, 12:21:34 amThanks for posting those links - those are great documents.Our (R&S) radiomonitoring division actually offers solutions for automatic signal classification, demodulation, and decoding, but these are primarily for mil/gov customers:https://www.rohde-schwarz.com/us/products/aerospace-defense-security/online-signal-analysis/rs-ca120-multichannel-signal-analysis-software_63493-52993.htmlBut given that the OP was interested in satellite signals, this would definitely be overkill-- nowadays most satellite signals are some form of APSK, which is easy to recognize with a VSA.

author: Bicurico
author_rank: Super Contributor
timestamp: July 11, 2023, 07:44:40 pm
content: Just an importante advice: Theo LNB loop through port of your satellite receiver will almost certainly carry 13/18V DC! This will break most spectrum analyser frontends. You need to use a DC blocker before making the connection.Digital satellite is normally modulated with QPSK (DVB-S) or 8PSK (DVB-S2).Just by looking at the spectrum you can in most cases guess which is which by the shape of the transponder. DVB-S transponders are "thinner" than DVB-S2 transponders.What you really want is a satellite field meter with spectrum and constellation diagram.Regards,Vitor

author: pdenisowski
author_rank: Super Contributor
timestamp: July 12, 2023, 09:39:06 am
content: Quote from: Bicurico on July 11, 2023, 07:44:40 pmThis used to be true, but most modern spectrum analyzers can tolerate relatively high levels of DC. For example, every current spectrum analyzer model from R&S can safely tolerate up to 50 volts DC at the input.Even the hobbyist level Rigol and Siglent models are also (according to specs) safe up to 50V DC.

author: RAPo
author_rank: Super Contributor
timestamp: July 12, 2023, 12:01:05 pm
content: IMSAI GUY has a very nice video on QAM64 Quadrature Amplitude Modulation.