Independent tests prove lack of frequency hopping with XPS

[JimC-MD]

	Quote: Originally Posted by XJet
	What difference does it make? If a commonly available 2.4GHz video transmitter (of which there are many thousands (or perhaps tens of thousands) sold and used world-wide every year is able to take out a system in the way I've observed, it's not really relevant if it's rule-compliant or not. Walking up to some poor flier who's left with a pile of smoldering wreckage as a result of being shot down and saying "it must have been an illegal transmitter" isn't going to put that bird back together, replace the engine or restore a life that may have been lost if it took someone out on its way to oblivion. This is especially true if those flying FASST and Spektrum/JR continue to fly, apparently unaffected. While it might be nice to dwell in a world where everybody lives by the rules and all the relevant standards are rigidly adhered to I think we have to be a little more pragmatic when large amounts of money and human lives are involved. If someone's weighing up the various 2.4GHz options I think it's a safe bet that they'll be more likely to opt for a system that shows the highest-level of resistance to legal (and illegal) interference -- or have I got that wrong? This is why we need some objective, comparative tests which subject each of the available 2.4GHz options to a range of controlled conditions designed to measure their resilience to variouis forms of interference. Having access to this information can only be a good thing. There are standards for 2.4GHz -- although they do tend to vary somewhat in different countries (namely power, spectral density, etc). The point you raise however -- in respect to the legality or otherwise of an interference source, makes it very clear that one would be silly to rely on having those "standards" protect you. They won't stop you being shot down. Just talk to JD about the numebr of completely legal 2.4GHz sources that can adversely affect all 2.4GHz systems (including XPS). There are definitely flying fields around where *legal* 2.4GHz traffic has made model-flying on this band either impossible or decidedly unwise. So clearly, even when the standards are rigorously adhered to, there's no guarantee that a system won't be shot down -- simply because 2.4GHz is a bit of a "wild west" band where, so long as you adhere to the few rules there are, it's pretty much "every man/device for him/her/its self." Although the goal is to ensure that all 2.4GHz equipment "plays nicely with others" the permutations of possible combinations has already reached the point where any practical proof is a physical impossibility.

NOW we are getting somewhere.

If you want to blast a system for not having a robust enough link under adverse conditions, that is fine. We should understand how these sytems work and make choices based on that. But the "What do the rules matter" attitude does not fly with me. I will give you and example and see if you can grasp it. Remember the days when we went from wide channel to narrow channel spacing on 72? Basic halving of the Tx Rx signal to fit twice as many channels. Existing radios had to be checked and tuned to operate under the new rules. If someone came out with an obsolete Tx or a system that was mistreated and out of tune and they shot another Rx down, what do we have? Was the radio in the killed airplane junk and subject railings of people from all over? HELL NO. It was the fault of the crappy radio that was not doing the right thing. I am saying that if the issue is the crappy video systems not working by the rules THEN THEY NEED TO GO! and we need to improve the robust quality of our links...... Do you see the distinction here? What is the cause DOES matter. Improvements are always good. Tell the whole story and let people become informed

These discussions are so much like politics it really gets old. Half truths and spin. Everyone has a paradigm and sees things through a filter. I applaude people that look into things. Like seeing the information. Just realize that people will look at what you say and how you test and say, "what about this?" That is a good thing in the part of the US that I come from.

It is called learning and peer review and BS filtering. If it stands the test, all the better.

[1bwana1]

	Quote: Originally Posted by RichardCorby
	Wow!!! I'm getting scared to death of this radio control stuff. Nothing is going to save my investments in aircraft etc. All the technology is bad stuff. So I think I better give up this hobby that I've participated in for 40 plus years, and take up something safer. Maybe knitting. Unless I stick a needle in my eye I should be safe.

Richard,
Have you ever thought of flying control line? You won't get shot down.

[XJet]

	Quote: Originally Posted by JimC-MD
	NOW we are getting somewhere. If you want to blast a system for not having a robust enough link under adverse conditions, that is fine. We should understand how these sytems work and make choices based on that. But the "What do the rules matter" attitude does not fly with me.

I still argue that if you find yourself staring at a pile of busted balsa, ply and fiberglass that used to be a giant scale model, you're not going to get any comfort from being able to attribute it to some unknown party who must have broken the rules.

Much better that someone did the tests and warned you that the gear you're using (whatever it is) may be deficient in some way that could make you more vulnerable to such interference.

Basically, if we could simply rely on folks to follow the rules we wouldn't need seatbelts or airbags because nobody would ever fail to give-way at an intersection, pass on a dangerous bend or drive while drunk.

But hey, we're pragmatic enough to realize that "better safe than sorry" is the best attitude on the roads and so it should be with RC gear.

If you choose to drive without belts or bags and have a smash, I don't think the fact that the other driver was drunk will provide any practical consolation if you're left facing life in a wheelchair.

As I've said all along, we need some objective tests and comparisons of the various 2.4GHz systems so we know how each handles a set of well-designed situations that may occur either as a result of "legal" or "illegal" interference.

What's wrong with that?

[KrisW]

Okay, 2.4 is looking more and more dangerous. . for whatever reasons. . increase in signals and interference above 50', stray "badly tuned" 2.4 systems floating around, the frequency hopping features not being as good as they seemed to be. . more and more big corporations using 2.4 and taking up more bandwidth. .. . .

900mhz is looking okay. . for now, but it's only a matter of time until it gets overused/abused, right?

72 mhz works, but you can get shot down by people ignorant of the frequency pins, or other stuff on the 72 mhz band

27 is truly dangerous.

5.8 ghz has an even shorter range than 2.4

Control line can get shot down by a frayed wire.

Free Flights sometimes just fly away. .

There's a lot of money, time, effort, and research being done to make our hobby, and our tenuous radio links, better. I'm sadly shaking my head in disbelief that no one seems to have finally produced the magic pill that will resolve the problems of interference and glitches. Just look at this thread . .tons of posts, and no one has the answer, but all that appears is more and more questions and doubts.

I'm thinking of developing a neural interface helmet, that uses boosted telepathic signals on the Terahertz range to link to a borg receptor on the aircraft. That way, the only possible lockouts are from my own brain. Someone said that still happens. . may as well make it the ONLY way it can happen.

But seriously. . anyone else have any bright ideas on how to solve all the problems? I certainly don't, but thanks for all the gret information, that has made me even more doubtful of technological innovation. I'm actually kind of depressed that all this effort, and money, and time, still has not solved the problem in a satisfactory manner.

[Foamaholic]

How about 2.4, 900, and 72 all-in-one tx and rx? Then if there is a problem with one the others will work.

[dqman40rock]

Now that is an idea. That seems possible. Why not creat some kind of 99% redundant system.
We can throw the telepathic thing in as a plaseabo.

[XJet]

	Quote: Originally Posted by KrisW
	But seriously. . anyone else have any bright ideas on how to solve all the problems? I certainly don't, but thanks for all the gret information, that has made me even more doubtful of technological innovation. I'm actually kind of depressed that all this effort, and money, and time, still has not solved the problem in a satisfactory manner.

I can't believe that the AMA hasn't approached the FCC for a small slice of dedicated spectrum that can be allocated solely for model RC use.

Sure, this might cost money - but amortize it across all the model-fliers and you'd find that it was a pretty small price to pay for security against having your 40% gaser shot down by some kid with a park-flier or some quite legal burst of sustained noise on 2.4GHz.

Given that only a handful of models can fly at the same field at the same time, only a very small chunk of spectrum would be needed for a narrow-band system (like we've been using for decades) and the shoot-down problem could easily be handled by smart transmitters that automatically negotiate an available frequency at power-up (even the Polk Seeker synth transmitter listens before it will transmit and refuses to emit RF if the chosen channel is in-use).

How about the AMA approaches the FCC to see what bureaucracy and costs are involved in grabbing a single MHz or even 500KHz of bandwidth somewhere?

Remember that all this fancy SS technology on 2.4GHz is really only there to try and solve the frequency clash and interference issues that would effectively disappear with such a auto-negotiationg system on a dedicated chunk of spectrum.

Thoughts?

[Mithrandir]

A laser can be a very secure means of communication...

[XJet]

	Quote: Originally Posted by Mithrandir
	A laser can be a very secure means of communication...

True, but if you think the propagation issues with 2.4GHz and RC models are tricky, just try using a laser and you're in for a whole bag of issues :-)

[RH1N0]

	Quote: Originally Posted by JimC-MD
	OK XJet. Here it is STRAIGHT to YOU. What are the rules for 2.4 use? Does that video system you are saying knocks out the XPS conform to standards for 2.4? I am talking in the US. That is where I am so that is what I care about. Are there standards for 2.4? What are they? Do you know? If you do not and can provide us with no references I am through with this thread. Hope you all would understand why. GDay

Not sure why you persist with complaining on this thread when 5 seconds on google will provide the info you seek. But I can understand why someone would avoid answering the question on here since their response is likely to be thoroughly scrutinised etc.

I suggest you start here and do some reading: http://en.wikipedia.org/wiki/ISM_band. Then perhaps you could summarise what you have learned from your research and post any specific questions you may have.

No offence intended - just a friendly suggestion

[Jamieman]

I am learning a lot here.

[KrisW]

	Quote: Originally Posted by XJet
	I can't believe that the AMA hasn't approached the FCC for a small slice of dedicated spectrum that can be allocated solely for model RC use. Sure, this might cost money - but amortize it across all the model-fliers and you'd find that it was a pretty small price to pay for security against having your 40% gaser shot down by some kid with a park-flier or some quite legal burst of sustained noise on 2.4GHz. Given that only a handful of models can fly at the same field at the same time, only a very small chunk of spectrum would be needed for a narrow-band system (like we've been using for decades) and the shoot-down problem could easily be handled by smart transmitters that automatically negotiate an available frequency at power-up (even the Polk Seeker synth transmitter listens before it will transmit and refuses to emit RF if the chosen channel is in-use). How about the AMA approaches the FCC to see what bureaucracy and costs are involved in grabbing a single MHz or even 500KHz of bandwidth somewhere? Remember that all this fancy SS technology on 2.4GHz is really only there to try and solve the frequency clash and interference issues that would effectively disappear with such a auto-negotiationg system on a dedicated chunk of spectrum. Thoughts?

let me pu on my neural interface helmet here. . the one connected to the keyboard.


Okay. . Switch ON dfypoihyp[oisdsdoifsp[ofhosipjnp[ojh[osisdafjs[oihsdfpoids-0987-0297-4012379-034598-034;lkj;lgsdja09asfd7-08


OOps .. that didn't work so well. . need more coffee.

I'm sure the AMA works close with the US Federal Government (FCC) concerning the frequencies we use. They spent a long time, the last time, lobbying and fighting for the setup we currently use here in the USA. It would take some searching, but I'm sure there would be something in the 400-600 mhz range that would be very clear interfering signals of any sort. Of course, there are the secondary and tertiary harmonics problem associated with certain frequency bands, but it does seem reasonable to find a band that is pretty much free.

On the other hand, concerning International attention on the subject, some countries do RC on their own assigned frequencies (35 mhz?), so engineering transmitter modules and receivers for yet another frequency band (like 500 mhz)that is not truly Internationally recognized as being set aside for RC ONLY would not be financially feasible, or advantageous. 900m and 2.4g are internationally recognized, making it a lot easier for the RC radio companies to jump right in with compliant hardware. Why no one thought to use 900 mhz instead of 2.4 ghz is really strange, though. I've seen only a few items (cordless phones) for 900 mhz.

Looking at the provided link for the ITU frequencies http://en.wikipedia.org/wiki/ISM_band you can see hoe difficult it would be to put something out there on any sort of higher frequency other than 2.4g that would be acceptable internationally.

I'm guessing this is one of the reasons 2.4 was picked by Spektrum, and why everyone else felt compelled to follow along in copycat fashion. Also the original equipment was meant only for foamies, and they wanted to get radios on the market that would not interfere with the 72 mhz stuff, so that the modelers could fly anywhere, any time, they wanted to. Great for Foamies, that fly in close. . not so great for $8,000 IMAC birds that are 2000 feet out in the middle of a roller. There were even discussions about how it's a really BAD idea to try to use a DX6000 for a gasser, due to limited range and other considerations. Back then I did it, with an 84" plane, just to prove it could be done, and I had no problems for the 10 test flights I tried it, but things have changed since then, and I have not done it since.

Seems to me, if dedicating to a new frequency band is not 100% totally reliable, foolproof, and idiotproof, as well as advantageous from marketing and financial considerations, it would be a BAD idea. It would not be the first time society has followed an idea because the first permutations were really good. . and then it fell apart for whatever reason later on. So, it looks like we are, because of the ITU, kind of stuck with 2.4g. . .

It will be intersting to see how much 2.4ghz stuff has "issues" at Joe Nall this year. 500+ pilots. . 1500-2000 aircraft ..

Anbother link, giving information concerning 900m versus 2.4g frequency usage:

http://www.digi.com/support/kbase/kb...detl.jsp?kb=64

Note the higher power, and 7 mile range, of the 900mhz band, versus 3 miles on the 2.4ghz.

[klhoard]

X-Jet,

Could you make a SS scheme on the 72Mhz freq.'s?

[RMaia]

	Quote: Originally Posted by JimC-MD
	OK XJet. Here it is STRAIGHT to YOU. What are the rules for 2.4 use? Does that video system you are saying knocks out the XPS conform to standards for 2.4? I am talking in the US. That is where I am so that is what I care about. Are there standards for 2.4? What are they? Do you know? If you do not and can provide us with no references I am through with this thread. Hope you all would understand why. GDay

From the little understanding I got from the 2.4 concept, sounds like the spectrum is all there, free for everyone to use. Most devices will look for a free channel and transmit on that channel, for a time that depends on the device. Some will transmit there for as long as they are on, others will change to another channel somewhat often and others will stay on a single channel for as little as a fraction of a second. So, if it happens that your Tx chooses a free signal that later on, another more powerful device decides to transmit on (it may have checked the spectrum, and due to the ground clutter issues X-Jet mentioned, it may have not "seen" your Tx signal, so it assumes that channel is free) and this new and more powerful signal is "seen" by your Rx (due to the plane being on the air) and being more powerful effectively "blankets" your Tx signal, if your Tx/Rx link doesn't change to another frequency channel, you've got trouble...

From the understanding I got, this hypothetical device would be perfectly legal, as it decided to transmit on a frequency which appeared "free" for it. It's not at fault if during it's power up scan it could not "see" your Tx signal due to it being blanketed by a building or something else in the path between your Tx and said device. If this is a kind of device that transmits on the same channel as long as it's on, if your Tx quickly changes it's frequency, you're fine. But if it doesn't change, you've got a lockout...

I believe that the possibility of such a scenario happening is low in a percentage factor, but figuring out the number of 2.4Ghz devices out there and combining with the number of 2.4 radios, it's very reasonable that problems will occur. Take 0.1% of 100 thousand and you still have 100...
It's somewhat like the jackpot, your chances of winning are very low, but someone will win, no matter how small the chances are of you being the actual winner.

[jonkoppisch]

Crap!!! One of these days I'm going to win that jackpot.... It wasn't the other day though