Independent tests prove lack of frequency hopping with XPS

[XJet]

Several independent tests (by different parties) has proven that the XPS system does *not* reliably frequency hop (in fact no frequency hopping has ever been recorded by independent testers).

Even XPS themselves have admitted that when confronted with a sudden rise in the noise level (or a strong interfering signal) XPS will not hop frequencies -- meaning loss of control and lockout.

This issue was raised initially on RCG and once the evidence began flowing, the posts were deleted by JD.

To put this in perspective however, it doesn't mean that XPS isn't a practical 2.4GHz solution -- it simply means that it *is* more vulnerable to some forms of interference than either Spektrum or Futaba.

Futaba, thanks to its constant frequency-hopping remains virtually unaffected by any strong signal on any of its 250 or so operating channels.

Spektrum uses two channels from a selection of 80 so a strong signal on either one of those signals will not cause loss of control because the other frequency will continue to deliver data.

XPS however, starts off on the back foot because it only has 12 frequencies available to it (versus 255 on Futaba and 80 on Spektrum) and absolutely no way of coping with a sudden sustained interference source.

From a practical perspective, this means that if you fly from a remote field with little or no other 2.4GHz activity around then XPS is no better or worse than any of the others.

However, if you fly in an environment where the noise profile of the 2.4GHz band is both cluttered and highly variable then the XPS system becomes significantly more susceptible to interference than its peers.

The reality is that something as simple as one of those 1W 2.4GHz video transmitters up to a mile or so away could knock your plane out of the sky by suddenly dumping on the frequency XPS has chosen to use. Spektrum wouold fall back to its second channel, Futaba would simply hop past the noise -- XPS coudl well have nowhere to go and fall into failsafe.

This revelation could explain the few instances where XPS-equipped models have flown perfectly well for hundreds of flights and then (seemingly inexplicably) locked out and crashed. It also explains why some folks have no problems until they opt to fly from a different location.

It may also explain why some folks (such as a handful in France) lost several models to XPS while Futaba and Spektrum systems operating at the same time were unaffected.

So, if XPS is working well for you -- that's great, long may it do so.

However, be aware that you *are* more vulnerable to the sudden appearance of strong noise or interfering signals.

JD initially admitted that this was a problem and that XPS was working on a fix -- then seemed to have a change of heart and deleted many posts in the thread where the evidence was presented.

He then began trying to discredit those who did the tests and presented the evidence (if you can't argue the message, shoot the messenger).

[Reza]

Very interesting XJet. Thank you for sharing. This does explain a lot of things. Some of our friends in the hobby think all these 2.4 Ghz systems are the same! This is not the case! There are different algorithm and engineering behind these systems and we can not associate failure of one to other/s and discredit this whole 2.4 technology!

Thanks for the info.

[Reza]

BTW, could you post a link to these individual tests or is there any way we can get more info how these tests were run and concluded?

[XJet]

I'm planning on doing up a YouTube video over the holiday break so I can document my own tests. I'll post a link.

[3ddd]

i for one hope you can prove what you are saying.you have blasted xps so much if i were jim and you made one little mistake i would sue your a$$ off my friend.just my 4 cents

[notorious_benny]

Sue for what??? Its not illegal to dispute, debate,test anothers technology.
Sueing seems to be the favourite pastime over there in the US.

[excelpoint]

	Quote: Originally Posted by XJet
	I'm planning on doing up a YouTube video over the holiday break so I can document my own tests. I'll post a link.

Looking foward to your tests. Ive ben looking at going 2.4 for a while but have still to make up my mind. I'm leaning towards the Futaba stuff for my 12Z at the moment. As Benny said, I cant see any reason for you to be sued. Keep the info comming

[jonkoppisch]

Here's what JD said...

	Quote:
	Yesterday, 10:31 AM Report This Post to a Moderator · #52 JimDrew Xtreme Power Systems Join Date: Jun 2005 Location: Lake Havasu, AZ Posts: 4,089 The frequency hop requires a rise in the noise floor over a number of frames. A sudden saturation will reset the noise "counter" and not switch at all. I have been testing new code that would allow a swap with a sudden saturation. We plan to release that early next year and will show this and other new items at the AMA show in January. This would cure the case where there was a video camera or other high powered radar device turned on and left on.

[exeter_acres]

	Quote: Originally Posted by Reza
	BTW, could you post a link to these individual tests or is there any way we can get more info how these tests were run and concluded?

Come on...you should know... if it is printed on the Internet,,,then it must be true

[Pale Rider]

	Quote: Originally Posted by notorious_benny
	Sueing seems to be the favourite pastime over there in the US.

You got that right my friend!

[sweetpea]

I would like to see these "independant" tests as well. And where Spektrum and Futaba systems part of the test? If not, these tests have not proved one system better than another.

We all could create a test on Spektrum to show that it can't handle voltage issues very well but without including all the other brands it means nothing. The other brands claims of being better could actually be worse. Same with what your saying about Freq hopping.

Did your test look at how fast Spektrum looks to its second freq? Or did it look at how close the 2 freqs are where an overflow of signal may effect both? How about Futaba hopping.....what if it hops to numerous used freqs in a row? Or if the noise floor is high as well? What if it can't detect the signal interference?

If your going to bash one........bash them all please.

And once Futaba has been out for a year or more and starts putting up the numbers that XPS and Spektrum have.....we shall see their weak points as well.

Since of course you are only going by what a company tells you their system does. Xjet refuses to believe in the comments of XPS (which is his right) but takes blindly what Spektrum and Futaba says and has no "independant" tests on them? Why not? Do you think we aren't interested in those results?

I'm not saying XPS is all that.....Nor am I saying that about Spektrum or Futaba. I am saying that all 3 systems are far better than 72mhz as far as interference is concerned. Which is why I went to 2.4 to start with.

[exeter_acres]

Do they hop if you use a123 batteries?

[Edge 540]

.

[luv2flyguy]

It's Christmas for goodness sake!!
Why can't we all just get along!

[XJet]

	Quote: Originally Posted by sweetpea
	I would like to see these "independant" tests as well. And where Spektrum and Futaba systems part of the test? If not, these tests have not proved one system better than another.

I suspect the problem is that to some folks, JD is God and XPS is a religion based on faith. Anyone who questions that faith by raising points of fact gets roundly demonized for their trouble.

I have no doubt that even when the evidence is posted, the XPS devotees will claim it was rigged, or that the two XPS systems tested must be both faulty, or that Mars was in the seventh house, etc, etc.

That's fine, I don't expect to convert the fanboys, my only goal is to provide everyone with more objective information on which to base their decision-making.

	Quote:
	We all could create a test on Spektrum to show that it can't handle voltage issues very well but without including all the other brands it means nothing. The other brands claims of being better could actually be worse. Same with what your saying about Freq hopping.

Untrue. Nothing Spektrum or Futaba does has any bearing on the fact that XPS does not have robust frequency agility or frequency redundancy.

	Quote:
	Did your test look at how fast Spektrum looks to its second freq? Or did it look at how close the 2 freqs are where an overflow of signal may effect both? How about Futaba hopping.....what if it hops to numerous used freqs in a row? Or if the noise floor is high as well? What if it can't detect the signal interference?

Again, this is not really relevant. A spectrum analyzer shows clearly that Spektrum uses two independent frequencies, both of which carry the data-stream. Likewise, others have already tested and proven that Futaba does indeed use frequency hopping.

	Quote:
	If your going to bash one........bash them all please.

Sorry Sweatpea but that's fanboy talk. I'm not "bashing", simply pointing out that yet another one of XPS's claims is unfounded. If I were making claims against XPS as wild as the claims that are made for it by JD -- then I'd be bashing.

	Quote:
	And once Futaba has been out for a year or more and starts putting up the numbers that XPS and Spektrum have.....we shall see their weak points as well.

And indeed, I'll be looking at Futaba's system when time/finances allow. However, neither Futaba nor Spektrum are making claims that defy the laws of physics (spherical antennas) so have to admit to being less confident of finding such wild misrepresentations.

	Quote:
	Since of course you are only going by what a company tells you their system does. Xjet refuses to believe in the comments of XPS (which is his right) but takes blindly what Spektrum and Futaba says and has no "independant" tests on them? Why not? Do you think we aren't interested in those results?

Okay Sweatpea, as a fanboy, you're not interested in learning of the weaknesses of XPS -- that's fine. But I think (and posts here seem to confirm) that others are.

You'll note that I have never said "XPS bad, don't buy" -- I've simply done my best to objectively point out that XPS has another rather significant weakness when compared to its competitors.

This weakness has been admitted by JD and he's even said he's working to fix it. My question would be -- if it's not broken, why would you waste time fixing it?

I notice since I presented my evidence, JD has taken to trying to question my skills and experience in the RF field -- making childish remarks relating to the fact that I have a jet-powered gokart (relevance??)

The fanboys also refer to anyone who dares question their faith or the word of JD as "self-appointed experts"

Well...

If you recall, I questioned XPS's antenna claims right back at the beginning, when JD was swearing black and blue that the tiny quarter-wave whip in the transmitter module as all that would ever be needed for bullet-proof operation.

Then, suddenly that wonderful quarter wave *wasn't* actually good enough for all situations so now XPS sports an external dipole.

I also queried XPS's lack of diversity antennas or satellite receivers, but those criticisms were roundly discounted as rubbish by JD. Then, as if by magic, XPS announces the upcoming release of satellite receivers.

I then queried this "essential eight element antenna" that is apparently a magic feature of XPS and unqiue to it. Even when I posted side-by-side images of a stock XBeePro module and an XPS one with no sign of a magic antenna -- I was told I was wrong.

When I asked therefore, for the name of the testing lab or university that determined the effect of this miracle antenna -- there was absolute silence.

Obviously I know absolutely nothing then... right?

These are the reasons that I treat any claim made by JD with great skepticism and dismiss the ravings of the fanboys as being akin to that of a religious cult..

	Quote:
	I'm not saying XPS is all that.....Nor am I saying that about Spektrum or Futaba. I am saying that all 3 systems are far better than 72mhz as far as interference is concerned. Which is why I went to 2.4 to start with.

You're right -- in some countries (such as the USA), 2.4GHz may be better than VHF but there are countries where frequencies have been specifically allocated for model control and in those places, providing the clubs have effective frequency controls in place, 2.4GHz may *not* be the best alternative because it really is a "free for all" band.

As I said in the first posting to this thread, XPS will likely work fine for most people but users ought to be aware that there's no contigency for the sudden appearance of a strong interfering signal on the frequency XPS has selected at boot-up time. In this respect it is inferior to its competitors.

It s a free world though and I invite people to purchase and use whatever they want.