Raw data out of Hantek scopes (for VDSL line analisys)? - Page 1
Forum section: electronics / beginners

author: Anichang
author_rank: Newbie
timestamp: September 19, 2018, 06:58:29 am
content: Hi,I've spent a few hours searching for clues about this topic but I couldn't get a single drop of water out of this huge pool. I've an Hantek DSO4072S with USB device port; my first scope. Vendor docs are ... what docs!? So I finally decided to disturb you gurus and masters.My goal is to use that raw data in order to process that using my computer and get some spectrum analysis. As an example I'd like to analyze my VDSL line, as I'm having performance issues and the technician that installed it, told to my brother that there is some kind of signal drop at some point of the spectrum.For this purpose I've also an RTL-SDR dongle, but it doesn't look like I can use it for VDSL because it must be something that can go down to 100KHz; that's why I tought about the oscilloscope.Please enlighten me (without giving me fire),cheersEDIT: something likehttps://hackaday.com/2015/12/20/no-spectrum-analyser-no-problem/

author: bd139
author_rank: Super Contributor
timestamp: September 19, 2018, 07:20:17 am
content: I doubt that will be much use for VDSL analysis. Firstly when you connect it, it will inject a lot of noise into the line. By measuring it you are affecting it. Secondly VDSL uses many many carriers in the spectrum below 30MHz, up to 8192 with bandwidth of around 5KHz each. The sample size and rate of the scope is nowhere near enough to drag that down and process it.Really the best solution is to buy a router with a spectrum monitor built in. Here's the one on my Fritz box 3490:

author: Anichang
author_rank: Newbie
timestamp: September 19, 2018, 04:58:17 pm
content: Thanks bd139Quote from: bd139 on September 19, 2018, 07:20:17 am1) I've found people using ethernet/adsl line transformers, or just rolling cables around the line twisted pairs, ie: without connecting. In order to get direct sampling with an RTL dongle. They bypass the tuner frontend chip and connect the differential transformed signals directly to the pins 1&2 of the rtl chip. I mean: there are ways to avoid/reduce noise injection.2) BW: 5*8191 << 70MHz scope's bw. Is it correct?Quote from: bd139 on September 19, 2018, 07:20:17 amThis is another path for sure. I was already thinking to change the telco modem. But which one? I can't find a good VDSL2 modem on the market. I used to have a Drytek ADSL modem with spectrum monitor but that part was pretty raw; it didn't give me the feeling I could rely on it. And specialized equipment starts at around 400 bucks on aliexpress. But I can't spend that much for a single use of it.

author: Emo
author_rank: Regular Contributor
timestamp: September 19, 2018, 06:52:01 pm
content: Hi,Using a suitable modem with inbuilt statistics is the most affordable method. Keep in mind that the spectrum only shows up after correct handshaking and depending on capabilities and attenuation a physical connection will be established based on a certain profile.For field measurements dedicated instruments are available. For instance the TM600 which can check and report most parameters up to profile 35b(equals approx 35 Mhz spectrum) as well as several other smart measurementsEric

author: Anichang
author_rank: Newbie
timestamp: September 20, 2018, 05:39:14 pm
content: Quote from: Emo on September 19, 2018, 06:52:01 pmAgreed, but I need the raw data out of the scope for other purposes as well.More on 'suitable modem': the spectrum analysis isn't an advertised feature. It's pretty hard to figure out which ones have it and which ones have not.Moreover, my connection provider doesn't support external VOIP adapters, forcing me to their router; there are community efforts to sniff credentials and make a fake handshake using some python glue, but it isn't very reliable atm. And If you put together a price of a decent router and a decent VOIP ATA, it's about the same of the cheapest vdsl line testers. Consider also that I don't really rely on my telco's router for any feature more than NAT&VOIP, as I use my custom router right after it, before my machines.That said, I'd like also to learn something about my scope and get a way, in case of need, to turn it into a primitive spectrum analyzer. The scope can do FFT; it's ridiculous, but it does it. I mean: it's kind of 'half away' between the time domain and the frequency domain. Can't be that hard to make a step forward.