Kiwi's XPS test results are up.

[easytiger]

	Quote: Originally Posted by Kiwi
	Tiger, All's well mate but honestly something we cannot do is delete a post then reinstate it. Not even Max's wizardry was capable of that. I suspect we had some kind of glitch or it was something with your PC as that post has been there all the time, I mean physically anyway. Thanks a lot anyway for your input and comments. I'm sure that there are those that will never believe facts no matter how you present them and that is problem belong em. (Taken from my very poor remnants of Pidgen English learned in Papua New Guinea many years ago)

Hmmm...well...it all kind of relates...to someone who has no technical knowledge, Jim Drews claims are as indistinguisable from magic as aircraft were to the Cargo Cultists. You say it hops, and they beleive. No matter how much scientific proof refuting the claims you present, the Drewists will just dismiss it, because their faith is not based upon science in the first place, but a beleif in magic. Same way those Johnfromists kept building bamboo hangars up until the Sixties, waiting for planes full of "cargo" to arrive.
As far as those who, at this point, still beleive in XPS, well, him b'long XPS, powerful magic make fly, when plane crash, only b'cause gods angry, no nothing problem XPS.

[jonkoppisch]

Whew.. Heating up a little over on the xps site...

http://www.rcgroups.com/forums/showt...=8#post9833090

	Quote: Originally Posted by bergaliv
	Yeh, the thread got deleted again from XPS forum. I've never met such an arrogant person that tries to sell something in my life. He's treating existing customers, and potential customers as if it's their good luck to be able to buy something from him. And since they are so lucky, they should never raise any questions, no matter how obvious the lies about the system are. That such a man was able to sell he's system, based on lies, to a company such as Graupner just blows my mind. Well, at least my thread got the truth out of Mr Jim Drew. The system was never designed to jump to the next channel in case of trouble. I'm so upset by the way he's deleting threads, not answering questions, and flat out lies, that I will file a formal complaint to the Swedish authoritys first thing tomorrow. I urge everyone to do the same. The laws in Sweden are NOT "one of a kind". Close to all countrys have laws that states that the burden of proof lies with the manufacturer/agent of a product. They HAVE to provide proof that their product does what their marketing says. I just can't belive that Mr Jim Drew has the stomac to actually go out to meetings, and meet people face to face, when he has been proven to lie about most everything. Not even he's so called 3 college degrees at age 17 can be proven, since there's no records of that. It's just as surprizing that RC-Groups allow such a company to keep their forum here. RC-Groups are a place for honnest people, that share a passion for this hobby. We now have proof, from mr Jim Drew himself that he has been lying about he's system all along. I think i stayed civil in my posts in the XPS forum, giving XPS every chance to do the right thing before file a formal Complaint. The first answer given was Quote Jim Drew "We are not concerned about this, as we know how the system works." Well, if things go like they usually goes after filing a complaint, we will know IF it works. Sorry for the long post, i'm just mad right now.

[Kiwi]

	Quote: Originally Posted by easytiger
	Hmmm...well...it all kind of relates...to someone who has no technical knowledge, Jim Drews claims are as indistinguisable from magic as aircraft were to the Cargo Cultists. You say it hops, and they beleive. No matter how much scientific proof refuting the claims you present, the Drewists will just dismiss it, because their faith is not based upon science in the first place, but a beleif in magic. Same way those Johnfromists kept building bamboo hangars up until the Sixties, waiting for planes full of "cargo" to arrive. As far as those who, at this point, still beleive in XPS, well, him b'long XPS, powerful magic make fly, when plane crash, only b'cause gods angry, no nothing problem XPS.

Well looks like you have some knowledge of PNG that many others would not have picked up on. To know about the cargo cult means you have either read well or visited the place.

Which one??

As for things hotting up Jon it was only a matter of time. One way or the other the nuts and bolts of the XPS system will come out.

[tadawson]

	Quote: Originally Posted by jonkoppisch
	So you have to start loosing control for 11 seconds before it will do anything..... By then, it's too late! Even if you're flying a cub

Ah, no . . . . "rising noise" does not necessarily imply that is it strong enough to affect operation . . . merely that it is increasing. Keep in mind that XBEE/XPS can look at the noise floor between packets and read it even when well below the TX signal level.

- Tim

[tadawson]

	Quote: Originally Posted by XJet
	But the problem is that (as the tests prove) it *doesn't* maximize range under the conditions that count -- strong on-channel interference.

Or that the test have simply overloaded the front end of the RX, preventing the code from working. Most of the tests I have seen have had the "offending" signal TX right on top of the RX, which can't be good from that standpoint.

A better test would be to put the TX something like 500 feet away, and the "offending" signal at, say 200, and try again . . . .

It's things like this that cause me to still tend to question the validity of the testing . . . since *nowhere* in flight (other than the self inflicted wound of on-board video) are you going to get an interference source 3 inches away . . .

- Tim

[jonkoppisch]

I know... But it's possible that can loose contact for several seconds, depending on when it's set to change.. & if it increases just a hair faster than what xps likes, then it doesn't matter. You'll loose contact reguardless, it wont hop you'll just be swamped..

[tadawson]

	Quote: Originally Posted by seattle_helo
	If you have no direct experience with 2.4Ghz systems, what basis do you have for making your observations? I'm curious why are you defending his idiotic claims after all that has been revealed? And an awful lot has been revealed indeed. It has been very well demonstrated that what he has claimed in the past is not true. He is now doing his best to "adjust" his terminology and essentially rewrite history to put himself and his products in a better light in lieu of this ever increasing scrutiny. If you have read this entire thread, which I acknowledge takes quite a bit of time, and yet you still think that his statements are clear, truthful and logical then we're definitely not going to agree on this. nick

A degree in communications and RF, and extensive experience in RF as and engineer for Motorola for a number of years and as a ham radio operator. Just because this is R/C, does not mean that the fundamentals of RF and radio change . . .

And I am not necessarily defending anything - just noting that the tests that I have seen are far from conclusive, and trying to explain things for those who may not have as deep a background. A lot of what has been stated (by both sides) I view as "plausable" . . . things still need to be definitively proven one way or another . . .

And for that, I sit back and wait . . .

- Tim

[tadawson]

	Quote: Originally Posted by jonkoppisch
	I know... But it's possible that can loose contact for several seconds, depending on when it's set to change.. & if it increases just a hair faster than what xps likes, then it doesn't matter. You'll loose contact reguardless, it wont hop you'll just be swamped..

No argument there . . .

- Tim

[Kiwi]

Tim,

What I dont understand is despite my very bush mechanic testing and testing by others in some very good labs no matter how you move a conflicting signal into the XPS channel you cannot make it move.

My setup was to gradually slide a converging signal sideways, for want of a better argument, into the fixed XPS and see if I could knock it off and make it look or a better cleaner channel. No matter how I tried it just would not do it. The guys who tested XPS in a lab had the tools to slowly increase the noise over a 20 second span. Still it did not move. XPS stubbornly hangs on until it looses sufficient packets to go into fail safe. But it never once tried to hop. Not in mine or any other testing that has been carried out.

What I did not refer to and wont do so in video is it was possible to get XPS to go into a zombie state but its not repeatable. Just sometimes it went blank. No failsafe, just a plain last position hold lockout. I reset and reprogrammed the receiver many times to be sure it was not me because it was possible to program the Rx to go to last position hold for 5 seconds then to fail safe. I needed to sure I was not seeing the 5 second hold as a zombie state. With the Rx set at 1 second it would happen.

But despite all the testing and supposed overloading of the front end etc etc etc it still does not deny the facts and that is FASST and SPEKTRUM both continued to function under the exact same circumstances that caused XPS to fail. Whether its a poor testing setup or just plain bigotry on my part, those two systems were absolutely bullet proof and XPS was NOT!!!!!

I would not use XPS in anything other than a foamie or a trainer that I knew I would be flying in an area far away from buildings and potential 2.4Ghz noise. Its that simple.

The TIER one products have antenna divesity, dual or frequency hopping plus a wad of things that just make them a superior and above all a safer system. To me its a simple no brainer. The price difference is negligible when you take the cost of building any model with a 50cc gasser or greater.

I for one will not take risks for a lousy $40 or $50 dollars in the radio system. Its only ten gallons of gas when all said and done.

I honestly hope XPS can come to the party and have a fully functional system that competes with the clear leaders in the technology today. But what they have now is a very fancy wireless router that speaks model airplane geek. Its not a designed from the ground up RC system and the others are.

[seattle_helo]

	Quote:
	A better test would be to put the TX something like 500 feet away, and the "offending" signal at, say 200, and try again . . . . It's things like this that cause me to still tend to question the validity of the testing . . . since *nowhere* in flight (other than the self inflicted wound of on-board video) are you going to get an interference source 3 inches away . . .

As long as all systems tested are subjected to these same conditions, it's a perfectly valid test case. It may very well be a worse case than what we would experience in the field, but that's fine. The fact that the RX front end may be overloaded is also fine- if the XPS is not selective enough while the other systems are then that's good to know.

On a different note, the non diversity RF scheme of the XPS system is reason enough to stay away from it, IMO.

nick

[XJet]

	Quote: Originally Posted by tadawson
	Or that the test have simply overloaded the front end of the RX, preventing the code from working.

Yes Tim, you may be right -- but that's *NOT* a good thing.

The adjacent channel rejection (ie: +/- 5MHz) of the XBeePro modules is a mere 23dB which is atrocious.

This means that any strong off-channel interfering signal has the potential to disrupt the link between transmitter and receiver. The XBeePro modules were never designed for use in a harsh RF environment (hence their use of a single relatively narrow DSSS signal), something that makes them even less suitable for RC model use.

You will note that neither the Spektrum/JR nor Futaba systems suffered from front-end overload or lack of selectivity in the way that XPS did. Regardless of the reasons or the test conditions, this conclusively proves that XPS simply does not have the same level of interference rejection that first-tier systems offer.

	Quote:
	Most of the tests I have seen have had the "offending" signal TX right on top of the RX, which can't be good from that standpoint.

But the RF output of the interfering device is *tiny* compared to the magnitude of some interfering signals -- and remember, the RC transmitter was also very close to the receiver (in model terms) so that all balances out.

	Quote:
	A better test would be to put the TX something like 500 feet away, and the "offending" signal at, say 200, and try again . . . .

But the whole thing about interference is you can't assume it's always going to be mild and well-behaved. By its very nature, interference is wild and unpredictable. What the tests have shown is that XPS simply can not cope with anything like the same levels of interference that first-tier systems can. This is an irrefutable fact -- regardless of how you might like to tweak the test conditions and it flies directly in the face of JD's own claims that XPS would continue working when other 2.4GHz systems were toast.

	Quote:
	It's things like this that cause me to still tend to question the validity of the testing . . . since *nowhere* in flight (other than the self inflicted wound of on-board video) are you going to get an interference source 3 inches away . . .

It's all a matter of ratios Tim.

A weak RF source just a few inches away can produce exactly the same field-strength as a more powerful source at some distance (especially if directional antennas are being used).

I can now see why JD is claiming that any strong interfering signal on 2.4GHz will saturate the band...

In fact it *wont* saturate the band, but the very poor adjacent channel rejection of the XBeePro modules means that it will *appear* (to XPS systems) that the band is saturated.

Other systems will carry on unaffected while XPS struggles to maintain an RF link (as the tests clearly proved).

[Simpleton]

Glad to see you're not really banned from the XPS forum on RCG, Xjet. Just more smoke and mirrors, I guess?

[XJet]

	Quote: Originally Posted by Simpleton
	Glad to see you're not really banned from the XPS forum on RCG, Xjet. Just more smoke and mirrors, I guess?

Another JD "mis-truth" me thinks :-)

[tadawson]

	Quote: Originally Posted by XJet
	It's all a matter of ratios Tim. A weak RF source just a few inches away can produce exactly the same field-strength as a more powerful source at some distance (especially if directional antennas are being used).

Obviously. But no matter what antenna is used, inverse-square losses still apply. I must admit, when I made my comment, I was thinking of the guy with the 3watt video TX that was practically touching the XPS antenna when he tested, and for a typical remote source to give that kind of field strength, well, is very unlikely, unless you are right on top of it. Let's admit facts here - most flying fields are not sitting right on top of NexRad sites and similar emitters, and the WiFi crap just can't do it, no matter what antenna you have on it not enough antenna gain possible at that distance with the input power limitations. Same with ATV - the distance will still reduce the field strength to a point that it won't be that hot. . . . For the other tests, I don't recall seeing any data on what field strengths were being used, so probably spoke a bit too soon.

And as far as Futaba and Spektrum, one of the things that has not been considered is that their performing under similar conditions may well be due to a better front end design, but it might also be due to a less sensitive receiver . . .

- Tim

[tadawson]

	Quote: Originally Posted by Kiwi
	Tim, What I dont understand is despite my very bush mechanic testing and testing by others in some very good labs no matter how you move a conflicting signal into the XPS channel you cannot make it move.

Yet the guys at Boing have claimed to have been able to do so, and others have seen it function in flight. Data that I cannot disregard - video or not. Video is so easy to fake, that I find it to prove basically nothing . . . . remember the guy with the vid TX that put out the hoax video that he got a hop? Looked just as credible as the rest . . .

- Tim