Checking ASK modulation on 868mhz remote - Page 1
Forum section: electronics / rf-microwave

author: vespaman
author_rank: Contributor
timestamp: January 19, 2024, 12:02:06 pm
content: Hi all,I am trying to find out issues with a 868mhz transmitter design, and I thought I should ask here, since you guys knows lots more about this than I  do.In essence, I am developing a receiver for these "garage door remote control" type keyloq transmitters for a customer. It is their transmitter (from a China supplier).I can receive data but it depends much on how the transmitters are held in users hands, and some are better/worse than others.In the transmitter, the ASK modulator is fed by 400us pulses from a microchip keyloq, coded as PWM. (Each data bit is 3x400us long, where the mid 400us decides it the databit is 0 or 1.The ASK modulator is a 6 pin metal smd part marked "DROC", which I have not found any data on.The frequency is changing a lot depending on how they are held while pressing a button, but I think this is not my main problem, I suspect the ASK bit time is messed up - i.e. the modulation is not proper the full 400us.In my receiving end, I use a radio receiver chip that does internal processing of the data, and therefore I'm kind of blind, so I need to understand how the ASK looks "in the air", in order to mitigate the problem.My scope is only 200MHz, so I doubt it will be much useful here. But I have a "Siglent SSA3021X Plus" at hand, but I have never used the modulation analyzer in it, and when I look at it, there's a lot of stuff going on that I don't understand...I also have a SDRplay RSP1A laying around in a drawer, that I haven't used for a long time.So my question is really simple (not sure the answer is, though!):What would be my best way forward? Should I be able to set up the Siglent, or is that a dead end (I have read about lots of limitations of the modulation analyzer)? SDRplay with some software?Or something else?All input and ideas, appreciated - I'm getting close to giving up on these transmitters.

author: wasedadoc
author_rank: Super Contributor
timestamp: January 19, 2024, 12:41:29 pm
content: ASK (Amplitude Shift Keying) is just carrier on/off.

author: vespaman
author_rank: Contributor
timestamp: January 19, 2024, 01:46:49 pm
content: Yes, but how to dig deeper into the signal properties in the air?

author: A.Z.
author_rank: Super Contributor
timestamp: January 19, 2024, 03:05:58 pm
content: Quote from: vespaman on January 19, 2024, 01:46:49 pmDid you consider using an SDR and then, if needed, writing some code to process the received signal ?Tools like GNUradio and/or RedHawkSDR may be useful in the latter case

author: RFDx
author_rank: Regular Contributor
timestamp: January 19, 2024, 05:11:59 pm
content: Quote from: vespaman on January 19, 2024, 01:46:49 pmWith "Universal Radio Hacker (URH)" you can capture/record the transmissions of your remote control and then do the analysis in the time domain. Works with a RTLSDR dongle, SDRplay etc.https://github.com/jopohl/urhhttps://hakin9.org/universal-radio-hacker-investigate-wireless-protocols-like-a-boss/

author: vespaman
author_rank: Contributor
timestamp: January 21, 2024, 01:26:39 pm
content: Quote from: RFDx on January 19, 2024, 05:11:59 pmWow!That was a super solution, a very useful program that I have added to my toolbox! It solved my problem

author: A.Z.
author_rank: Super Contributor
timestamp: January 21, 2024, 01:37:11 pm
content: well, as I already hintedhttps://redhawksdr.org/

author: vespaman
author_rank: Contributor
timestamp: January 21, 2024, 01:47:36 pm
content: I briefly looked at that, but even the webpage could not describe exactly what it was. Said to be a support thing for developing own radio applications (which I am not interested in).Granted, it was not very clear. Even the picture was so low res, so it was not possible to see any details..Does it bring anything that urh does not bring straight out of the box?Cheers