EEVblog Electronics Community Forum
Electronics => RF, Microwave, Ham Radio => Topic started by: vespaman on January 19, 2024, 12:02:06 pm
-
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 [currently] 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... |O
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! :D):
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.
-
ASK (Amplitude Shift Keying) is just carrier on/off.
-
Yes, but how to dig deeper into the signal properties in the air?
-
Yes, but how to dig deeper into the signal properties in the air?
Did 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
-
Yes, but how to dig deeper into the signal properties in the air?
With "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/urh (https://github.com/jopohl/urh)
https://hakin9.org/universal-radio-hacker-investigate-wireless-protocols-like-a-boss/ (https://hakin9.org/universal-radio-hacker-investigate-wireless-protocols-like-a-boss/)
https://www.youtube.com/watch?v=kuubkTDAxwA&list=PLlKjreY6G-1EKKBs9sucMdk8PwzcFuIPB (https://www.youtube.com/watch?v=kuubkTDAxwA&list=PLlKjreY6G-1EKKBs9sucMdk8PwzcFuIPB)
-
With "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.
Wow!
That was a super solution, a very useful program that I have added to my toolbox! It solved my problem :-+
-
well, as I already hinted
https://redhawksdr.org/
-
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