Kiwi's XPS test results are up.

[zoomer260]

	Quote: Originally Posted by Daemon
	I appreciate the work put into the tests but without actually testing the responsiveness of the system during the test, I don't see that it proves much of anything. Yes it could not be made to hop, but what we don't know is if it really *needed* to hop. I assume XPS Tx antenna was on and it was running at full power during all the tests shown in the video. If the Rx was still maintaining full control (which we don't know because nobody checked), then there's no reason it would need to hop. Why would we expect it to? If it was totally blocked by the noise (which we also don't know), then it would not hop, by design, per admission of JD. And frankly, while JD and apparently Kiwi too thinks it's a silly idea to hop *after* onset of failsafe, that is frankly the only case I care about. That's the only time it makes sense to me. "Potential noise" is just too nebulous and you could easily get yourself in more trouble hopping when it's not absolutely necessary (still maintaining control but there's more noise than there was before) than waiting until the link is actually lost long enough to cause failsafe when you *know* that it can't get any worse. And as for "first tier" versus "second tier" systems, with the implication that Spektrum having two frequencies to XPS's one (100% better) makes it first tier is still a bit short sighted. I watched a Spektrum DX7/AR6100 combo lock out and fall out of the sky twice the other day in a non-motorized Easy Glider. After our ground testing with very surprising results, and my subsequent thread in the Radio forum on RCG, I come to learn that if a Spektrum AR6100 Rx (maybe all models) loses the signal on both channels for any reason for more than about a second, it goes off into la la land and scans for the Tx on all 80 channels (assuming that the Tx has been turned off and back on) and may not find it for another 5, 10, 15 (and in my tests 25 and 40) seconds before it finds it. People are telling me this is "normal" behavior. And no, we're not talking about the known low voltage reboot issue, for which there is a fix. We reproduced this behavior on a fully charged 6V battery pack, on video. All it needs is anything blocking the Rf signal (range/orientation/shadowing of Rx or Tx) for more than 1 second. At *least* XPS always hot-links instantly as soon as the Rf signal can get through again. The other model Spektrum Rxs basically try to avoid this issue by having better diversity (more Rxs and/or more widely spaced antennas), and that's better, but if the link is lost anyway, then you're still screwed for that 5-15 seconds while it scans and I don't know of many planes that can survive that long without control. That's not Tier 1 behavior as far as I'm concerned. BTW, with regard to 2.4Ghz video transmitters. *Most* people still use 100-200mW. More people these days are buying 500mW units, and only a small handful of people use 1-2W systems. Anything above 100mW requires a HAM license to use legally. A 500mW video Tx placed between XPS Tx and Rx will easily swamp the signal if it's on an overlapping "channel". And contrary to what Kiwi said, the video transmission is fully analog and consumes pretty much 100% of the bandwidth on its channel 100% of the time.. It may look similar to the rectangular shaped spectrum of say a Wifi router but it is *not* spread spectrum, it is much higher power density, it does not play nicely with *anything* close up. If I turn my video Tx on on certain channels inside the house, it will just kick everything off my Wifi router instantly. In terms of making XPS upset, a single 2.4Ghz video Tx of sufficient power is a pretty good noise generator (I've got a bunch of videos showing how I used mine). You can vary the distance between them to increase and decrease the noise floor gradually. Anyway, back to the topic at hand. I still think the "How do these systems actually react to noise" (as in what they actually do, rather than what the manufacturer claims they do or don't) would be more useful. Test like this. 1. Increase noise floor on all channels used by the system until onset of failsafe. How much does it take? 2. Increase noise on all channels used by system gradually while monitoring actual responsiveness. Do they slow down? Do they get glitchy? Intermittent.. etc 3. Repeat test 1, and then immediately shut off all sources of interference and see how long it takes before they become responsive again (based on my testing, we'd see XPS come back instantly, and Spektrum take however long it takes.. 5-15 seconds). After the change that JD is talking about in the software to make it hop after onset of failsafe, that might make XPS take longer to relink because it has to scan (like Spektrum does now). 4. Introduce noise that is narrower than the SS channel, overlapping that channel, and see how it reacts. Basically testing the spread spectrum ability of each system. XPS has 12 wide SS channels so may be more resistant to narrow band interference, than Spektrum for instance. FASST has very narrow invidividual channels, but it sort of simulates one big fat channel that covers the whole spectrum. I agree with XJet's assessement of how it'd probably react to interference. Saturate half the spectrum, it'll run at 50% responsiveness. We're talking about ability to work through noise to gauge whether the designed in capabilies are any good. If we discovered that XPS could function normally through twice the level of noise on its single channel, than Spektrum can on its two channels, would that level the playing field? ian

All the questions about XPS could be handled in a single post by JD.

He has chosen not to (for obvious reasons I think) and you can be sure "if" he has sold any units lately those people are completely new to the hobby or don't have internet.

His total lack of response (in this forum) and total BS in others tell all we need to know about XPS in "the real world". Too many others to choose from. One would be enough.

[USN_POPS]

	Quote: Originally Posted by zoomer260
	All the questions about XPS could be handled in a single post by JD. He has chosen not to (for obvious reasons I think) and you can be sure "if" he has sold any units lately those people are completely new to the hobby or don't have internet. His total lack of response (in this forum) and total BS in others tell all we need to know about XPS in "the real world". Too many others to choose from. One would be enough.

I think JD is doing well enough to not bother with the nit pickers in this and other forums. I'd ignore it as well. When he does give explanations they get buried in junk by the naysayers, some of whom have not even used or own an XPS system.

And your statement about those buying the XPS is BS as well. The XPS is designed for more high ended gear than most New People are willing or able to afford. I have yet to see a newbie show up at the field with a Futaba 9C. And the guys that I know using XPS are flying some pretty expensive planes successfully, and using high end radios with XPS modules.

My 500 plus flights over the past year have proven the system to me. Thats not BS, it's fact. And I dont need Videos and techie proof of the system. I consider the proof to be in the flying of a system.

[DesertHucker]

	Quote: Originally Posted by RichardCorby
	I think JD is doing well enough to not bother with the nit pickers in this and other forums. I'd ignore it as well. When he does give explanations they get buried in junk by the naysayers, some of whom have not even used or own an XPS system. And your statement about those buying the XPS is BS as well. The XPS is designed for more high ended gear than most New People are willing or able to afford. I have yet to see a newbie show up at the field with a Futaba 9C. And the guys that I know using XPS are flying some pretty expensive planes successfully, and using high end radios with XPS modules. My 500 plus flights over the past year have proven the system to me. Thats not BS, it's fact. And I dont need Videos and techie proof of the system. I consider the proof to be in the flying of a system.

I was with you untill mine locked out and it was in a high end system and plane.
good bye to $5k

[Chris F]

	Quote: Originally Posted by RichardCorby
	I think JD is doing well enough to not bother with the nit pickers in this and other forums. I'd ignore it as well. When he does give explanations they get buried in junk by the naysayers, some of whom have not even used or own an XPS system. And your statement about those buying the XPS is BS as well. The XPS is designed for more high ended gear than most New People are willing or able to afford. I have yet to see a newbie show up at the field with a Futaba 9C. And the guys that I know using XPS are flying some pretty expensive planes successfully, and using high end radios with XPS modules. My 500 plus flights over the past year have proven the system to me. Thats not BS, it's fact. And I dont need Videos and techie proof of the system. I consider the proof to be in the flying of a system.

This thread is about testing different 2.4 GHz systems, if they work as advertised and how they compare to each other. Kiwi and others are doing their best to be unbiased and only report what they find. Please lets not let this thread become a fanboy or "naysayer" thread and stick to the technical facts. The fact that XPS works for you and that you have had 500 successful flights is good news for you, but not relevant for most people watching this thread. If you have some proof that XPS can frequency hop as advertised I'm sure people will be interested. I'm impressed with how neutral this thread is compared to other forums concerning XPS and I hope it stays that way. I believe this thread is getting as close to the truth as any I have seen and I trust Kiwi and many others here call it as they see it without bias.

[BZFrank]

	Quote: Originally Posted by Four Stroker
	Am I completely missing something here ? You guys are getting excited about the loudest system at 100 mW vs. the wimpy system at 90 mW.

Its 100 mW for the throttled EU version of the DX-7, the DX-7 US version sends +3db on top of that and more (~ more than double the power).

Frank

[Prof. Dr. YoMan]

@Frank:

Do you got the URL from rc-network or rcline, where Frank T. measured the power output of the US-DX7 a year or more ago?

I cant find it.

He clearly measured way more that 500mW peak power, as i remember.

[Four Stroker]

There were also reports that Graupner had measured nearly a watt. This could be settled easily by comparing a FASST to a DX7 to an XPS to an RDS8000 on a spectrum analyzer.

In other words Kiwi could tell us the definitive answer now.

[BZFrank]

It certainly depends on the measurement rules how much you get. You know that (US) FCC and (EU) ETSI rules are different.

[KrisW]

	Quote: Originally Posted by Four Stroker
	Am I completely missing something here ? You guys are getting excited about the loudest system at 100 mW vs. the wimpy system at 90 mW.

Actually, given the way the dB system works, a 3 dB transmission strength increase effectively DOUBLES the power output of a radio. 10dB's increases it 10 fold. So if the testers were seeing a 3dB increase in signal strength, it is an effective doubling of power output, form 100mw to 200 mw.

I'd be interested in whether Spektrum will sell a "U.S. Spec" TX module that takes advantage of the law in the US and puts out even more power. 500-800mw would be great, and literally unjammable by other items on the same band, within 1/2 mile of the transmitter.

[JKos]

> XPS has 12 wide SS channels so may be more resistant to narrow band
> interference, than Spektrum for instance. FASST has very narrow invidividual
> channels, but it sort of simulates one big fat channel that covers the whole
> spectrum.

I would like to correct this statement. While the XPS channels are spaced 5 MHz apart, the bandwidth of the actual signal is 1.6 MHz. Futaba also uses 1.6 MHz of bandwidth. Both Spektrum and the new Airtronics FHSS system use 1 MHz bandwidth signals. All of this is per the FCC test reports on file and publicly available.

And to clear up a few myths; none of our R/C 2.4 GHz systems use collision avoidance nor does Futaba FASST avoid any channels. Yes, their marketing seemed to claim that at first, but they've drastically changed the wording on that "feature."

Also, despite having a narrower bandwidth, Spektrum actually has more processing gain than Futaba; so it's not all about bandwidth either but also the chip to data rate ratio. I'm not sure of the processing gain of XPS and Airtronics.

- John

[KrisW]

	Quote: Originally Posted by Prof. Dr. YoMan
	@Frank: Do you got the URL from rc-network or rcline, where Frank T. measured the power output of the US-DX7 a year or more ago? I cant find it. He clearly measured way more that 500mW peak power, as i remember.

You can have a "peak" of 500mw, but the average signal strength is what matters more. If that peak is an extremely narrow spike in a much wider pulse, looked at with an oscilloscope, then it's kind of irrelevant. However, if that 500mw is across 75% of the pulse width, then it's a substantial amount of power, and more likely to penetrate harsh environments and be "heard" by the receiver.

I do not think I have seen an example of an actual XPS, Spektrum, or FASST information "pulse" shown on the web, yet. During Kiwi's video, we saw an extremely wide signal, that I think reflects an average of the pulse train width during the testing, not an actual single pulse. At the same time, you see a very narrow FASST signal bouncing around the spectrum with these teensy little spikes. Having done a lot of IFF, Radar, TACAN and other Com/Nav work in the past, I expect it would be possible to isolate the information pulse trains to sort out the individual pulses. After all, if I could see the individual IFF pulse trains at 1.03-1.09 ghz with equipment built in the 1960's, I'm sure todays technology allows us to easily pick out pulses in a 2.4ghz fixed frequency pulse train, and analyze them for strength, shape, and any non-square wave characteristics. It would be interesting to see how each manufacturer addresses these items, as well as do a comparative test of pulse strength and width. After all, wider, or taller, will make a signal able to penetrate interference better than narrower or shorter. .

[gareth.ky]

I doubt any of them are still sending an analog pulse train. Its probably all digitally encoded (and possibly encrypted). E.g. On the Spektrum Rx its a Wireless USB chipset. Your in the digital age now, all 01100100011010010110011101101001011101000110000101 101100 now. Why send a pulse train when you can send 11 bits (2^11 == 2048) per channel?