|Nov 26, 2014, 05:38 AM|
Joined Nov 2014
Gfsk/ppm, dsss, fhss
Hey guys (and girls),
I'm quite new to this whole field of radio controls. Even though I do have some (more or less) solid basic understanding of the whole thing, there are some things that confuse me which I was hoping you could pehaps clarify
1. Quite often I see people writing stuff like FHSS modulation or DSSS modulation. For instance, recently I've seen a thread here at rcgroups where someone has written 'they use GFSK/PPM modulation INSTEAD OF FHSS' without anyone questioning that sentence. What I don't get is this: GFSK is a modulation technique, right? As in: it is a technique of modifying a wave function (in this case by modifying its frequency) to encode some information on said wave, right? On the other hand, FHSS is NOT a modulation technique in the sense that it is used for encoding info on a wave, right? Isn't FHSS (or DSSS for that matter) always used ON TOP of some modulation technique (such as GFSK) for things like jamming resistance? Because if so, a sentence like 'they use GFSK instead of FHSS' just makes no sense since GFSK is in no way a 'replacement' for FHSS or vice versa, or am I completely wrong here?
2. This question is actually heavily related to my first question: I've opened up my own remote control, because I'm trying to figure out all the details of the radio communication out of curiosity. Doing this I found out that it uses a Cypress CYRF6936 chip for all the RF-related stuff. Looking at the documentation of the Cypress CYRF6936, it says that it has three modes: GFSK mode (where it doesn't use any DSSS), 8DR mode, DDR mode, SDR mode. For instance, for 8DR, it says that ' eight bits are encoded in each derived code
symbol transmitted. ', so I presume that in this mode, some form of DSSS is used. But again, DSSS per se is no modulation technique, right? So how can I find out which modulation scheme is used for the radio communication, ON TOP of which DSSS is applied? And secondly, how can I find out which mode my remote control is operating in?
I hope that my questions are clear and thank very much in advance for any hint
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