Independent tests prove lack of frequency hopping with XPS

[Toumal]

I know. But in all fairness, that picture alone doesn't prove anything except that there was an XPS system in the plane and that it crashed. It's akin to FASST crash reports. "My plane just went out of control" - well there's more to a flying plane than just wings and a receiver, a hundred things can go wrong in the air.

However, the fact that XPS didn't activate failsafe, and the motor also didn't cut out, kinda points to a problem with XPS. I say kinda, because I won't risk a lawsuit on those statements


And BRAVO to the competition organizers for doing the right thing. If FASST were to have similar problems, I myself would want to see the same steps taken to ensure safety.

[jonkoppisch]

I didn't say anything.... I just posted a picture from the thread showing one of the planes wrecked that was using xps/ifs..

There's no 'fairness' about it. I didn't claim anything. I think the thread and the results speak for themselves, don't you?

[BZFrank]

	Quote: Originally Posted by Toumal
	Individual incidents should not be taken as definite proof for anything.

True, but at the competition in Leipzig where this image originates there were two pilots with IFS/XPS, both with two planes. *All*these planes crashed due to radio problems - and whats worse some flew away at high speed without triggering the failsafe, one crashed only meters from a highway - and that seems to be the main cause for the current ban. There were no problems reported on the other eleven 2.4 Ghz systems that were in use at the same time and location.

[seattle_helo]

	Quote: Originally Posted by capgains
	What is antenna diversity, and what does it do for you? I mean, I understand the way the Spektrum has the 2 pieces of one, and that FASST has 2 whips, but do you really need it, or is it more of that warm fuzzy type stuff? Personally, I don't care if it has no antenna if it works.

Just to elaborate on what's already been said, diversity receivers do several important things. One is to prevent phase drop outs where radio signals bounce around and hit the antenna 180 degrees out of phase and cause the signal to drop out. This problem is not a matter of range, it can happen anytime in a non-diversity system. Since a diversity system uses at least 2 antennas (by definition), the odds of having phasing cancellation on both antennas simultaneously is nearly impossible. To prevent phase cancellation the antennas only need to be a minimum 1/4 wavelength apart to be effective. Diversity receivers can also help extend the range since they offer the signal different paths to find the receiver. While 1/4 wavelength spacing can be enough at a minimum, for maximum benefit the antennas should be spaced further apart to present a bigger 'target', so to speak. This is where Spektrum/DSM really shines as you can position the satellite receivers in strategic areas to always provide line of sight RF coverage for the entire aircraft in any attitude. I often see comments online that attempt to bash the satellite receivers as some kind of weakness in the design or as an added burden or inconvenience. It is not a weakness of any kind but rather a very practical and well done implementation that is dictated by the way in which RF works. It is true that having to install a few satellite receivers is a bit more work, but the substantial and very important payoff is that you can have an ideal diversity setup and very robust RF link- as we can prove by monitoring our Flight Log data. In complex models with lots of metal, wiring and other components that can reflect or absorb RF, having separate receivers, and more importantly, physical space between them, is a very beneficial arrangement.

I'm running two JR R1221 receivers (for true receiver diversity) in my latest turbine heli and it has a total of eight satellites!





Among many other things, the single antenna design on the XPS receiver is reason alone I would never, ever use such a system.

nick

[BZFrank]

	Quote: Originally Posted by seattle_helo
	To prevent phase cancellation the antennas only need to be a minimum 1/4 wavelength apart to be effective. Diversity receivers can also help extend the range since they offer the signal different paths to find the receiver.

Yep. Allow an addition: In case of FHSS systems like FASST multipath issues ("phase cancellation") are not as large a problem as in DSSS systems because the nulling effect changes with frequency for a given location. So just by hopping around on the band it will hit a frequency where phases do not null out anymore. That one of the reasons why FASST has no satellites - it does not need them (as much as Spektrum do or XPS should).

Very nice helicopter! BTW

Frank

[Toumal]

	Quote: Originally Posted by jonkoppisch
	There's no 'fairness' about it. I didn't claim anything. I think the thread and the results speak for themselves, don't you?

Oh absolutely. I'm just saying that they could file suit for people claiming that a particular crash was caused by XPS, and it would be difficult to prove that in court, hence I would be careful with such statements.

That said... In my opinion, XPS should have the advertising blurbs corrected to tell the truth - or be recalled completely. I don't think that it's in any way more safe than 72/35MHz. Quite the opposite, in fact.


@seattle_helo: Good point - and your helo build is excellent, a feast for the eyes. Get a paintjob for this bird, damnit!

[capgains]

Wow.... beautiful looking install there. I wish I could make my installs look that clean.

[Dustflyer]

Speaking of diversity, ever notice that even wireless guitar and microphone rigs use two antennas?

Wouldn't want to lose that crucial guitar or microphone signal now, would we?

Don't worry; however, it's perfectly safe to control a 50 pound airplane on 2.4Ghz with a single receiving antenna as long as it has "spherical radiation technology!"

Legal disclaimer: Attorney's take note, the comments above are for entertainment purposes only.

[GBR2]

Hey Dustflyer, remember JD has said:

"By the way, we have 9 antennas total (8 internal and 1 external) ......."

The 8 internal antennas though are so well hidden that it puts the "where is Waldo" drawings to shame.

Legal disclaimer: Attorney's take note, the comments above are for entertainment purposes only.

[wrightme]

	Quote: Originally Posted by jonkoppisch
	I didn't say anything.... I just posted a picture from the thread showing one of the planes wrecked that was using xps/ifs.. There's no 'fairness' about it. I didn't claim anything. I think the thread and the results speak for themselves, don't you?

Similar tactics are used by Michael Moore. You are in good company.

[skubacb]

	Quote: Originally Posted by Toumal
	Scubacb: This is the third time I've read you writing a reply that ignores either everything or parts of what was said earlier. For the 10th time: We are not talking about hopping on saturation. We are talking about hopping on interference. Kiwi's test does not saturate the receiver, it merely occupies the same channel as XPS, and XPS fails whereas Spektrum and FASST keep working without a hitch. What part of that sentence is it that is unclear or, after Kiwi's video, remains open for debate? Why is saturation being brought into this over and over? @ss40: If video evidence is not good enough for you, then I suggest you test for yourself. It's not hard to do, and it's the only way you can be sure that what we say is true. As for being lied to by the manufacturer... I dunno about you, but if I buy a 25C LiPo pack, and it dies when I pull 20C, then that pack goes back for replacement or I get my money back. When a car is advertised with 2 airbags but they don't inflate on a crash, that car is going to be recalled. Since frequency hopping is an important safety feature on a free-for-all band such as 2.4, I'd say this is something no responsible model pilot should just ignore out of convenience.

Tomoual, You are obviously slow to understand. No matter how many times you try to make Kiwi's test something it is not it is still saturation and not a test of XPS hoping. Duh, go and read about what causes XPS to hop. Kiwi's test does not test for XPS hoping.

Just because you want XPS to do something other than it was designed will not make it so. How many times do you need to be told this? Do you just not understand the difference between saturation and interference? Do you even understand the difference between white, pink noise versus the digital packages used by current 2.4ghz RC systems. Obviously, not!

If frequency hoping is so important then don't use Spectrum. Also, today's 2.4 ghz systems are required by the FCC to be non-interfering. Please go read some more about how this environment works before coming to more illogical conclusions.

[bodywerks]

Gotta be honest, Scuba - for a guy that has lost at least two planes due to a loss of radio control while under the 'command' of XPS, and who also knows I lost one for the same reason on a maiden flight, you sure are defending them adamantly. Haven't you stopped using X-link altogether now, except for maybe foamies?