SDS2000X+ Trigger Mode RF Demod - Page 1
Forum section: electronics / testgear

author: eloso
author_rank: Regular Contributor
timestamp: February 13, 2024, 01:57:30 pm
content: Hi,I have viewed Keysight videos and instructions on using a pattern matching timeout trigger mode to demodulate ASK RF. In particular, Manchester Encoded although the same principle should apply to any ASK RF signal.App note :https://assets.testequity.com/te1/Documents/pdf/keysight/AutoKeyFobCommunication-an.pdfVideo :The technique is to set up a trigger on the condition where the rising or falling edge has a significant time gap after it before the next rising/falling edge. This would mark the end of a burst of carrier.The method necessitates the detection of all subsequent multiple trigger points within the same capture. By using the BNC trigger output to feed another channel, a logic level replica of the ASK signal appears on the screen.Seems pretty neat and I wanted to replicate that with my Siglent SDS2504X+.But I can't get it to work. It appears that once the first trigger has occurred after arming, the scope either does not bother detecting subsequent triggers - or it detects them but doesn't send them to the trigger out. So I don't get a nice replica of the demodulated waveform.I left wondering about a few things now.1. Is this little hardware demod trick outlined by Keysight something that is in general use ?2. Does the Siglent work in a different way to the Keysight and thus not able to replicate this process ?3. If the Siglent can't replicate this trigger process, does anyone have any other bright ideas about how to implement it on the Siglent ?Obviously I can do it outside of the Siglent and in fact moved my project forward by doing just that. I used an external envelope demodulator. You can see from the two below screenshots that it works nicely. I reproduce them to aid in understanding what I am trying to achieve, lest I haven't made it very clear.So really this question is a point of curiosity and learning for me and maybe there are others who might take an interest also.ThanksEloso

author: 2N3055
author_rank: Super Contributor
timestamp: February 13, 2024, 02:20:50 pm
content: Quote from: eloso on February 13, 2024, 01:57:30 pm1. Yes. It is a trick because Keysight have little memory2. Yes, trigger out works differently.3. You don't need to replicate anything. You have 100X more memory. You simply capture it directly. If you want to use scope as ASK detector, you cannot do that. Your AM demodulator is the solution.As a sidenote, I used AM demodulator even with Keysight to save channels. It's just simpler. I have a Testec cheap RF demodulation probe.. Works well enough.

author: ebastler
author_rank: Super Contributor
timestamp: February 13, 2024, 02:27:35 pm
content: Couldn't you simply demodulate via a Math function, like Lowpass(Abs(C1))? Then let the scope decode the result.I understood from the Keysight video that the main limitation there, and the reason to use the trigger workaround, was that "the Manchester decoder is hardware-based, so we need to demodulate the signal in hardware". Which I understood to mean that the decoder cannot operate on a Math result.But it can in the Siglent, right?Edit: Hmm -- I took a look at the datasheet, and it seems that decoding is limited to the hardware channels in the Siglent scopes as well. Measurements work on Math functions, but not the decoders; I had that mixed up.