Richard Putnam 1 Posted March 25, 2013 Share Posted March 25, 2013 Hi, can some one tell me what mode our 2.4 GHz transmiters use? is it FM, AM,double side band supressed carrier? nowhere on the internet can I find the information. I have even contacted Spektrum they were very polite but refered me to their Q&A page. A block diagram of the Tx would be a help. And Why, because I am giving a talk to an amateur radio club. Thanks Richard Quote Link to comment Share on other sites More sharing options...
Masher Posted March 25, 2013 Share Posted March 25, 2013 Hi Richard You should Google Spread Spectrum and Frequency Hopping which will give you the background - mind you, the radio ameteurs will probably be ahead of you on that one! Quote Link to comment Share on other sites More sharing options...
Olly P Posted March 25, 2013 Share Posted March 25, 2013 It is a type of FM. The system uses multi frequency (either hoping or spread) FM data bursts with IP addressed packetised data. Olly Quote Link to comment Share on other sites More sharing options...
Masher Posted March 25, 2013 Share Posted March 25, 2013 To be a bit more helpful, try this to start you off: http://www.rcmodelreviews.com/spreadspectrum01.shtml Actually, this article could be the whole of your talk - if you're an engineer it will make sense but, IMHO, it is not exactly simple for the non technical person Edited By Masher on 25/03/2013 10:49:09 Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted March 25, 2013 Share Posted March 25, 2013 Most 2.4Ghz RC manufacturers use some version of Direct Sequence Spread Spectrum (DSSS) apart from Futaba FASST, I understand this uses Frequency Hopping Spread Spectrum (FHSS)There is some good info here, there is a "next page" link at the end of each section.**Link**Edited By WolstonFlyer on 25/03/2013 10:48:44 Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 25, 2013 Share Posted March 25, 2013 Some misinformation here. The packets aren't IP addressed and Futaba fasst IS dsss, the which it moves around the band instead of staying on fixed channels. Best to avoid the technicalities unless you're 100% confident. The hams will have it down pat. Maybe make the session interactive - ask about their video activities, compare our permissions with theirs, mention 27mhz and sun-spot cycles, the origins of UHF R/C and its demise (mention the ham Wood & Douglas kits that some UHF R/C gear was based on, several will have built W&D kits), talk about the use of carbon in moulded models and the challenges that presents, mention diversity on 2.4g and redundancy used in big models... hope these ideas help Cheers Phil (G4PHL) Edited By Phil Green on 25/03/2013 11:19:06 Quote Link to comment Share on other sites More sharing options...
Richard Putnam 1 Posted March 25, 2013 Author Share Posted March 25, 2013 Thanks all for your replies. thanks Phil for your ideas Yes I remember the Wood and Douglas kists. I was going to talk about diversity I will add Redundancy to the list. Our LiPo Batteries servos etc. I have also made up a simple slide show. Then some helicopter flying followed by fun on the simulator. Richard G0ILN Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 25, 2013 Share Posted March 25, 2013 We find a good introduction is the spark transmitter and "Coherer Receiver" which started the whole radio communications thing off. If you want to take anything from our website as examples, feel free - **LINK** Cheers Phil Quote Link to comment Share on other sites More sharing options...
John Privett Posted March 25, 2013 Share Posted March 25, 2013 Posted by Olly P on 25/03/2013 10:44:57: The system uses multi frequency (either hoping or spread) FM data bursts Amusing typo, Olly! I take it that's the mehod Spektrum use, whereas everybody else uses 'hopping'! Quote Link to comment Share on other sites More sharing options...
Olly P Posted March 26, 2013 Share Posted March 26, 2013 John - D'oh - must proof read.... Ref the IP addressing, that is perhaps an over simplification, they are however source identified packetised data - otherwise when my Tx 'hopped' onto the same freq as another then the Rx's could get confused. this doesn't happen on a modern system due to this ID signature - hence why we need to bind the Rx and Tx. Quote Link to comment Share on other sites More sharing options...
Richard Putnam 1 Posted March 26, 2013 Author Share Posted March 26, 2013 Hi Phil, I have a feeling you have had articles in some of the magazines? Your website is amazing In the late fifties I was into CL combat RC was out of my league but we used to try free flight and had hours of fun with Ebenezers. Our engine of choice was Oliver Tiger for Combat flying and then I got interested in girls ,that was the end of aeromodelling ! Until retirement . Back to the present day and my talk. I had booked one of our older members to talk about the early days of RC but unfortunatly he has family commitments and can't make it. But I have more than enough info to fill the hour and a half slot. 73 Richard Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 26, 2013 Share Posted March 26, 2013 >Posted by Olly P on 26/03/2013 11:22:03 >Ref the IP addressing, that is perhaps an over simplification Its really more of an over complication Olly, we're down at the physical and datalink layers here. >they are however source identified packetised data Yes the guid identifies the packet source, but this is more akin to MAC addressing than IP. > otherwise when my Tx 'hopped' onto the same freq as another >then the Rx's could get confused. That doesnt happen, no two sets are on the same freq for long enough. Remember this is wideband, huge deviation and with dsss several changes of frequency per bit. Any frequency clash would be fleeting, not even enough to resolve a single bit of data, because chipping code (of which the guid is a significant part) ensures that all systems spread differently - in fact uniquely. Couple this with the very low duty cycle and the result is that several systems can happily cohabit the same arbitrary channel. Similarly with FHSS such as Frsky, though dwelling significantly longer on a channel than does dsss, its still a wideband signal, widely deviating in frequency from that channel centre - any clash is therefore brief and on the next hop is gone anyway. >This doesn't happen on a modern system due to this ID signature > - hence why we need to bind the Rx and Tx. Partly true, but its not just because the guid 'labels' the packet. Its also because the guid contributes to the whole unique spreading sequence. Cheers Phil Edited By Phil Green on 26/03/2013 14:29:02 Quote Link to comment Share on other sites More sharing options...
Masher Posted March 26, 2013 Share Posted March 26, 2013 Ahhh........... You can't beat a good bit of technical flagellation - takes me back to my corporate days! Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 26, 2013 Share Posted March 26, 2013 >Posted by Phil Green on 26/03/2013 14:11:43 >Similarly with FHSS such as Frsky, though dwelling significantly >longer on a channel than does dsss, its still a wideband signal... a typo, but I missed the edit window! Masher, Olly, sorry - wasnt meant to be confrontational... my apologies Phil Quote Link to comment Share on other sites More sharing options...
Olly P Posted March 26, 2013 Share Posted March 26, 2013 Phil - no problem - I tend to deal with slightly more 'advanced' systems than used in the RC world and tend to forget which stream I'm working in when explaining things! Essentially then, the Tx switches frequency very quickly and the info it sends has a stamp on it to id the sending tx, these elemenets in combination along with the available spectrum width mean that Rx's will not pick up the wrong Tx. How is that then? Edited By Olly P on 26/03/2013 16:46:54 Quote Link to comment Share on other sites More sharing options...
Simon Chambers Posted March 26, 2013 Share Posted March 26, 2013 Posted by Phil Green on 26/03/2013 14:11:43: Partly true, but its not just because the guid 'labels' the packet. Its also because the guid contributes to the whole unique spreading sequence. This is true for DSM2/DSMX but not every RC system. Those that don't use DSSS modulation (e.g. FrSky/Hitec/Futaba S-FHSS/others) the ID is merely the address of the data packet to decide if the system will either use it (if what is expected) or chuck away. Those systems also define their hopping channel sequence to the receiver during binding. In answer to the OP, 2.4GHz systems use all sorts of modulation techniques - most of the RF chipsets can switch between different ones. Here are two datasheet's of popular RF chipsets: TI CC2500 - Supports 2FSK/GFSK/MSK/OOK modulation. Hitec/Futaba/Frsky/Graupner/Corona/Radiolink/+others use this chipset. Page 17 is the RF block diagram. Cypress CYRF6936. Supports DSSS/GFSK modulation. Used by Spektrum/Multiplex/Walkera. First page has the RF block diagram. Si. Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 26, 2013 Share Posted March 26, 2013 Agreed, thanks Simon. There remains one mystery - how Corona claim to get DSSS from a CC2500, a native FHSS chip! Cheers Phil Quote Link to comment Share on other sites More sharing options...
Shaunie Posted March 26, 2013 Share Posted March 26, 2013 As the Spektrum system operates on two frequencies simultaneously is this handled by one Cypress tranceiver chip? I can imagine that two chips would cause problems with antenna splitting/combination, crosstalk etc. Shaunie. Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 26, 2013 Share Posted March 26, 2013 Its a single Cypress chip and it doesnt actually transmit on two frequencies simultaneously, the chip has only one synthesiser and is only capable of generating one freq at a time. So it sends a frame on one channel then the same frame again on the second channel. Of course this all happens very quickly so appears to be simultaneous. Cheers Phil Quote Link to comment Share on other sites More sharing options...
Richard Putnam 1 Posted March 28, 2013 Author Share Posted March 28, 2013 Hi Phil, just to say my talk to the radio c lub went off without a hitch. Best lecture they had ever had! So obviously I was very pleased with the result. And a lot of it due to this thread. Some of the professional blogs on line were way off the mark but reading your comments and a few others and the links I was able to get my head round all the concepts. Many thanks to all who have contributed to this thread have learnt a lot. Many thanks Best 73 Richard. G0ILN Quote Link to comment Share on other sites More sharing options...
Phil Green Posted March 28, 2013 Share Posted March 28, 2013 Well done Richard, presenting isnt an easy task, sounds like you did very well. I'm a bit of a wallflower, I leave all the talking to Shaun ! (-: Cheers Phil Quote Link to comment Share on other sites More sharing options...
Glyn R Posted March 29, 2013 Share Posted March 29, 2013 Ask silly question! Quote Link to comment Share on other sites More sharing options...
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