How spread spectrum RC systems can share the same part of the 2.4GHz band

[SaToMojo]

Thank You Professor Bruce ;)

[SphinctersForever]

So here is a question: I haven't flown anything in probably 15 years, and I have a very nice Futaba 7UAP "PCM 1024" system in the old 72 MHz band, I think it's channel 14. I used to have a Great Planes Super Kaos 60 that I flew the heck out of with it and it was a great radio. If I go flying somewhere (where no one else is around) am I likely to get hammered by modern radios? Can I still fly with it at an organized field using the frequency queue board as we always did before?

[xjet]

@SphinctersForever (I'm posting from my other YT account but it's me) -- yes, of course you can still fly your old gear. In fact, there's never been a better time to fly 72MHz because the band is almost deserted because so many other people have shifted up to 2.4GHz.

[SphinctersForever]

@xjet Thanks! I'm glad to hear that. Not that I wouldn't probably upgrade in time (the newer systems seem to have much smaller flight-side components than the older ones did), but it's good to know that I can get back in using my old equipment, much of which was top-of-the-line (and expensive!) way back when I last flew.

[jonathanglass]

This is a brilliant video giving a clear explanation of a tricky concept. 10 out of 10 for the instructional technique. To simplify this in such a way, with a small amount of artists licence, shows just how valuable Bruce's input is to our hobby. Well worth another donation from me!!

[hot4plasma]

Excellent video! What more can I say than really great explanation. Please stick to this medium of communication, because you are very good at this! Have faith that you'll make money enough to keep your talents on the web.. thanks for making this, it really helped me understand.

[lesdeuxciel]

Gray code (aka state diagram for binary code) was used in the earliest days of semiconductor designs due to possible errors from single transistors failing to stabilize across a bank of them arranged as a memory register. Gray code enforced change of only One bit at each clock pulse: 0000 0001 0011 0010 0110 0111 0101 0100 1100 1101 1111 1110 1010 1011 1001 1000 0000 Motorola may hold a patent on its use for microcode in microprocessors. Nixdorf may have something, too...

[gruntboy50]

i just want to say. I have learned more in your 10min youtube video than in an entire semester of communication theory. That was incredibly educational.

[struggleforlife]

This is very educational.

Could you please go into de details of 'fasst' versus 'dsmx'? There are just too many pseudo experts telling different stories about these systems, mostly in an attempt to make sense of it themselves or make the 'other' system look bad.

Explanation would be greatly appreciated (and I will repost it in the dutch forums).

[TheGrandmasterT]

i have a question!? am driving a rc car with a spektrum dsm dx2.0 transmitter. and a buddy of me driving with a spektrum dx3s. i am drivin about 5 minutes and he switched on his transmitter and he could drive my rc car. how could this be???????

[RCcunuk]

thanks Bruce, you have dumbed it down enough so that I can understand the basics of how it works. Very informative

[catamaranman333]

Bruce, I am doing some preliminary research into a new Tx for FPV to replace my 72Mhz radio. Range is my priority. Without taking too much of your time, is there a specific video or videos that I can begin with to help me understand the myriad of options I have? I love the idea of having modules that I can switch back and forth between Mhz and Ghz even UHF? I'm an idiot when it comes to all the letters. Thinking about fhss, dsss, afhss, makes my head hurt! I just want to fly far, far away!

[marhar2]

This is great... hope you do a lot more of these!

[RCModelReviews]

@freemanchris1 Actually, GFSK modulation is not that uncommon in DSSS systems.  The original FlySky (iMax) 2.4GHz DSSS system used GFSK modulation to create its DSSS system The issue is whether there are spreading codes added to datastream to provide the "spread" and without them the bandwidth of the signal at the data-rates we're talking about here is *significantly* less than the 1MHz seen for the AFHSS signal. Remember Futaba call their system FHSS too -- but it's an agile DSSS system.

[catamaranman333]

@freemanchris1 I'd love to see your video on the subject...

[nlimchua]

I'd like to see more of these. Nicely done!

[rolgarcia1]

will the OrangeRx Spektrum DSM2 Compatible receiver from hobbyking work with a spektrum dx5e?

[RCModelReviews]

@freemanchris1 If you examine the Test Report you'll see on page 13 that the 20dB bandwidth for the Hitec's transmissions are about 1MHz -- which is typical of a DSSS signal. My own tests also show there is a DSSS energy profile to the system's transmission on each of its chosen channels. Nowhere in the FCC report (that I was able to find) did it define this system as FHSS. Yes, the term AFHSS was used but that's Hitec's "trademark" for their agile DSSS modulation system.

[oakleymac1]

I have a DX6I I bought it because at the time it offered 2.4g 10 model memory 6 channels and mixing for v tails also the push and roll system for just £130 evrything else at the time 2.4g was much more expensive. But now I'm thinking of upgrading what will give me the most reliable signal out of all the 2.4g range of transmitters. Also what would be another option for cheap recievers ? great video I know nothing about radio signals and electronics this is very hepfull.

[catamaranman333]

@oakleymac1 2.4Ghz is not the best option if range is what you are looking for. Try UHF, higher Mhz radios like Futaba 433Mhz, or something like the dragonlink system. I also bought a Dx6i because thats what everyone else was buying. I use it but wish I had paid a bit more for a modular Futaba system that can be Ghz or Mhz depending on the module you use. My DX6i works about 2km away on it's best day. I can get double that with the cheap 72Mhz radio that came with one of my RTF planes.

[oakleymac1]

@catamaranman333 Sorry I'm not looking for range but I do want a radio that is going to give me a reliable signal that wont break. At my club a few people lost there planes due too losing the signal so I'm looking to go for something that will give me the strongest signal possible with cheap recievers but thanks anyway I did'nt know you could get 433mhz or uhf will need to start learning about radios one day.

[catamaranman333]

@oakleymac1 Yup, stick with 2.4 Ghz if cutting interference is the goal. I have a spektrum DX6i that, while it has worked flawlessly for me, some report problems with glitches. If it's really a problem at your field maybe go with Futaba or JR...

[daveyedgar]

well done!!

[startazz]

Great info and well explained Bruce and any chance of showing us the viewers how the fail safe works and and what happens when it kicks in ;-) thumbs up.

[zombienumber13]

thanks for the video, very informative and simple is better

[cgwd]

Thanks for this, makes things a lot clearer.

Does FrSky use this PN code as well as the "hopping" throughout the band?

[wallaguest1]

and whats the difference between FHSS and DSSS? looks the same to me

[RCModelReviews]

@wallaguest1 "true" FHSS uses a very narrow signal like our old 72MHz signals which hops around all over the band. Interference can totally wipe-out the very narrow signal in parts of the band. DSSS uses the much wider (inverted funnel shaped) signal which is spread out much wider so is harder to interfere with. Today's RC systems don't use true FHSS -- they use a DSSS signal that hops around the band so you get the benefits of FHSS *and* the benefits of DSSS.

[cgwd]

@RCModelReviews Do you know if FrSky's ACCST technology uses a DSSS signal as well? (their site only says it is channel shifting)

[sankushinde]

@RCModelReviews this is definately not DSSS .what u are explaining is a pure form of FHSS. Spreading in DSSS means multiplying the baseband signal at low bitrate with a random sequence at high bitrate. This new signal which is the product of the two signals has a higher bitrate than the baseband signal. This is how the signal is spread.

[jbx907]

no wonder i could scan the freq using the freq counter ^_^

[lewandlo]

Wow very well explained . very simplified ,even for a lug like me heheeh. I wish my math teacher explained things like you ....heheh. Thanks you Sir.

[tankshermanator]

Fantastic video thanks Bruce, very informative :o)

[jsnhart]

wow really great video. cleared it up for me!

[pinzgauernorcal]

great video what are the chances of two or more people having the same PN code?

[yittymitty11]

@pinzgauernorcal probly depends on how many variations there are but as he said the pn code is much bigger than what he drew

[pushinold]

Excellent graphic representation. This explanation clears up a lot of misconceptions that I had. Keep posting these short videos when you can. They allow me to show others the advantages of these systems.

Bryan

[simscody3]

Hi rather starting new videos how about finishing the ones you said you were going to like the 9x frsky mode, after all that why i donated

[RCModelReviews]

@simscody3 That video is being edited as I type this. The DIY vids are a *lot* harder to make and edit than a simple presentation like this (which took about 15 minutes). Quite often with a DIY vid I have to go back and re-shoot some shots because they're not clear/obvious enough when you look at the footage later in editing. Doing it properly sometimes that takes a little longer.

[fisherboom]

@simscody3

How about you have a little respect and give Bruce a break.

[BMSWEB]

Great explanations ! Very helpful

[rcralphpfister]

nice one!!

[PHeMoX]

Excellent video. How does the PN code translate to what people often call the Spektrum 'exclusive' (at least people tend to state so) 'ID' code or should it be considered the same thing?

In short, I'm wondering how much the various systems actually differ from the other DSSS systems out there. A pure marketing issue?

Also, isn't the Hitec Adaptive Frequency Hopping Spread Spektrum (AFHSS) on for example the Aurora 9 a somewhat more true frequency hopping system?

[RCModelReviews]

@PHeMoX All the current RC systems use a DSSS signal -- which is at the heart of this explanation. Systems such as FASST, DSMX, AFHSS and the other "hoppers" simply move that signal around so that it's not sitting in one part of the band all the time. The term "frequency hopping" as applied to RC systems is not truly correct -- it should be "constantly agile DSSS" because all RC systems actually use DSSS, it's just that most of them also constantly change the DSSS frequency.

[PHeMoX]

@RCModelReviews Thanks for clearing that up, I appreciate it. So basically all frequency hopping does differently is change the location of the small frequency band it would normally use the PN coded transmissions on.

I think the fact that the visual representation show the average over time makes stuff somewhat confusing when it comes to frequency hopping. Basically it doesn't use multiple channels (frequency peaks on a different location in the spectrum) at the (exact) same time, right?

[tswitz65]

Nice job Bruce. Being in mobile telecommunications I can appreciate the simplicity in which you explained it. Excellent!

[briguy99]

Nice explanation, thank you for sharing.

[WalneyCol]

cool :)