Independent tests prove lack of frequency hopping with XPS

[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?

[skubacb]

Neither defending nor condemning. I am adamantly against unproven claims, false accusations, made up stories.

If there is a fact great. If it is not a fact then don't try to make it so. The test that this thread is based on does not test for XPS hoping. Yet, the title would have you believe it does. JD never stated that the antenna was isotropic yet they claimed that spherical coverage was a lie. Yet, we do have spherical coverage. Claimed that a certain chip in XPS was over clocked. It was not. Claimed that the XBee chip could not do what is was doing. It can. Claimed the XBee chip could not jump. It can. So far none of the accusations has been proven true. Showing the ticking servo (fixed and only with the 9Z) is less valid than keeping a Spectrum v1 around so you can see the elevator go randomly down. Claims that failsafe does not work. I've tried turning off my TX with an A/C in the air. It works. Claims that they could not link multiple RX with the TX. I have twenty RX and two TX and have always been able to link them. The list of unproven lies and and just plain BS goes on and on.

On the aircraft in question, I am still not certain about the cause, nor have I come to an absolute decision. Is 1800 to 2000 flights with those two enough. I just don't know. I continue to fly XPS, as I continue to fly Spectrum. I am not so sure about using my Fasst equipment until Futaba has the courage to take some more positive steps, rather than a wet towel over the AC.

What I want is proof of a specific error or problem not conjecture, stories or lies. If there was a specific flaw it would be lost in all the trash being posted.

[bodywerks]

Haven't been following the XPS saga lately. Has anyone been able to prove any XPS claims valid? To me, the people that are posting stuff showing inconsistencies in XPS claims are valid unless it can be proven otherwise. I am no rf engineer, but I am not seeing any smoke and mirrors in the tests I have seen.

[XJet]

	Quote: Originally Posted by skubacb
	Neither defending nor condemning. I am adamantly against unproven claims, false accusations, made up stories.

Like "a patent-pending 8-element antenna" that can't be found?

Like a system that "will hop away from interfering signals" but can't be demonstrated to do so by either JD or independent testers willing to put their names to such tests?

Come on, if there are any "unproven claims" around, they come from the mouth of JD.

	Quote:
	If there is a fact great. If it is not a fact then don't try to make it so.

Well at least we agree on something. Please ask JD to point out where his mythical 8-element antenna is and fulfill his promise to show the original XPS system hopping in response to potential interference. Extraordinary claims require extraordinary evidence - and we've seen nothing.

	Quote:
	The test that this thread is based on does not test for XPS hoping. Yet, the title would have you believe it does. JD never stated that the antenna was isotropic yet they claimed that spherical coverage was a lie. Yet, we do have spherical coverage.

No, with a quarter-wave groundplane antenna (which is what the XBeePro uses) you have a toroidal radiation pattern with deep dimples at each end. JD has claimed a spherical pattern but has never fronted up with the 3D plots to prove this and DigiKey have told me (and others) that it is indeed a toroidal radiation pattern with deep dimples at the poles. JD made a *big* noise about the antenna pattern for XPS being something special -- it's not -- it's just a plane quarterwave groundplane. When proof was requested for this extraordinary claim it (like the hopping proof) was simply never forthcoming.

	Quote:
	Claimed that a certain chip in XPS was over clocked. It was not.

I've not seen the proof of this either - just more *claims* from JD.

	Quote:
	Claimed that the XBee chip could not do what is was doing. It can.

Of course the XBeePro chip can do what it's doing -- it just can't do what JD said it would (which it isn't doing).

	Quote:
	Claimed the XBee chip could not jump. It can

I certainly never claimed the XBee could not jump -- I simply said it could not jump in the way that JD was claiming (ie: in response to an interfering signal and we still have no credible proof of that, despite JD's promises to provide it.

	Quote:
	So far none of the accusations has been proven true.

I'm sorry but the burden of proof lies on the shoulders of those making the extraordinary claims -- which is JD. He's provided *no* proof it hops in the manner originally described (in fact he's backtracked on those claims already). He's provided *no* proof of the mytical 8-element spherical antenna and DigiChip deny any such system on the XBeePro (why would *they* lie?).

	Quote:
	What I want is proof of a specific error or problem not conjecture, stories or lies. If there was a specific flaw it would be lost in all the trash being posted.

Well since you're so *hot* on proof -- come back when you have the proof that XPS hops as claimed and when you've got proof of JD's magic antenna. Let those who are making those extraordinary claims front up with the proof -- we've seen not a scrap of evidence in either case.

I expect your next posting to be rich with the requested evidence, after all, you wouldn't want to look like a hypocrite would you?

[Woketman]

	Quote: Originally Posted by XJet
	I expect your next posting to be rich with the requested evidence, after all, you wouldn't want to look like a hypocrite would you?

Well Scubacb, it looks like you have had quite the gauntlet laid in front of you! Please do not hesitate to prove Xjet wrong in a timely manner.

Silence? No evidence of XPS claims?

Just another Fanboy!!!

[Dustflyer]

I think this guy is just messing with us. The facts and evidence of the faultiness and unreliability of XPS are indisputable. When someone endlessly denies reality you have to question intentions. Scubacb is playing you guys like a violin. Unfortunately the song will never end as long as you continue to play along.

Scubacb? I wonder. Could he and all the rest really be JD under different member names? I am beginning to have my suspicions.

XPS is a creature, a multi-headed monster that only lurks in the darkness of internet forums. It lives and breeds there but never strays to the light of legitimate media outlets. Feed any of its heads and it stays alive. Maybe it's time to stop feeding it.

[jonkoppisch]

	Quote: Originally Posted by wrightme
	Similar tactics are used by Michael Moore. You are in good company.

Well, evidently they thought that 4 models lost to xps/ifs in 1 event was enough proof that something was wrong and banned them & this was one of the models that crashed.. Maybe it's not enough proof for you but it must be for them...



jd says that he's sold 50,000 systems now. I'm surprised that only 1 of them made it to seff.. Of course, if i remember right he also said that there were more xps systems atSeff than Fasst systems.. I still haven't seen any vids of xps stuff/demo's at Joe Nall

http://www.rcgroups.com/forums/showt...8#post10051888

	Quote: Originally Posted by JimDrew
	We were basing our 1 million flights estimates on only 20 flights per customer. We have sold tens of thousands of full systems and obviously even more receivers.

http://www.rcgroups.com/forums/showt...63#post9976763

	Quote: Originally Posted by JimDrew
	You need to get the numbers from Tony Stillman, the AMA district rep who ran the event. We were told at the AMA meeting at Joe Nall that we had more systems in use than Futaba. We also informed Tony that several of our customers came forward and admitted that they had their planes turned on, but sitting on the ground because they wanted to see if there would be any issues.

Got to wonder why they just turned them on and didn't fly them

http://www.rcgroups.com/forums/showt...25#post9976425

	Quote: Originally Posted by JimDrew
	We know that we had more of our systems in use than FASST systems for the world record. The event organizer has all of the numbers.

http://www.rcgroups.com/forums/showt...25#post9976425

	Quote: Originally Posted by IPFlyer
	SPOILER ALERT! Here are the official numbers as submitted to Guiness. http://www.rcgroups.com/forums/showp...&postcount=338 <insert> Hi All, Here's the final rundown. Everything has been double checked and all numbers add up. Final count, this is what I'll be sending to Guinness: 99 ( we had one person stand in the wrong line for counting) 2 pilots on 53 Mhz 4 pilots on 50 Mhz 41 pilots on 72 Mhz 52 pilots on 2.4 gig 1 XPS 1 Futaba 50 JR/Spectrum Those who did not make it. 5 2.4 Gig 6 72 Mhz One midair that only took out one plane One low battery fall out 4 who did not start the attempt 114 for the range check Thanks to everyone. <end> Yup, looks like a clear majority to me! LMAO!