Kiwi's XPS test results are up.

[KrisW]

	Quote: Originally Posted by wingster
	Daemon An excellent series of posts(376-#78) that review and synthesize the features of the Spectrum and XPS systems. Just as you stated, "It works for me so you're full of it" argument is the predominate response from spectrum users on various forums. They usually blame the pilot for a poor setup and won't acknowledge that the Spectrum system has issues. Keep up the good work!

Please list these "issues" concerning the AR7000 and AR9000/9100 series receivers or systems, especially those using the upgraded firmware or software. Please do not include the 6000/6100 series receivers (As Daemon did), since they are listed for park flyers only, and are not really intended to be as robust or hold link as well as the AR7000 or 9000 series units.

I'm really interested in what the "Facts" are. So far I've seen a lot of subjective
"It might . .it could. . " statements and subjective "Anal-ysis" of the Spektrum systems, but nothing that really nails it down. Saying that an AR6100 receiver had issues does not get much credibility, since the unit was probably well outside it's intended operating environment. I cannot recall anything at all being said concerning the updated AR7000/9000 systems.

[BZFrank]

	Quote: Originally Posted by Pale Rider
	Im interested in your results with the Spektrum stuff---find anything interesting ?

Well, I did not want to influence Kiwis measurements but as you ask:

I did test both the DX-6 and the DX-7, also throttled to EU limits. (~ 100mW for the DX-7). The DX-6 plays in a different league as it only uses low power ouput, so the following is about the DX-7. The DX-7 works by first doing an energy scan on the band and then selecting two channels - the two that show the lowest interference level.


Two separate DSSS channels of the DX-7

The system then continues on these two channels forever (until turned off). It does not change them during runtime. You can think of it as a kind of frequency hopping scheme, but only between two channels as it sends alternating on both.

The two channels helps the DX to cope with interference. As long as one still gets through control is maintained. If both are hit at the same time, it goes into failsafe.

There is also another trick the DX uses to get the message through. For all SS systems on the market it is the 'loudest' - it sends with the most output power on the least speading width. Where FASST is 90 mW and XPS is 60 mW the DX-7 is 100 mW (EU version) and even more ( ~ +3 db ) for the US version. You can see that also when comparing the signal in the analyser.

So metaphorical speaking: While FASST is elegantly hopping from door to door to tell its story, the DX-7 sits on the middle of the street and uses two megaphones to be heard. Both methods seems to work in the real world.

Frank

[KrisW]

	Quote: Originally Posted by BZFrank
	Well, I did not want to influence Kiwis measurements but as you ask: I did test both the DX-6 and the DX-7, also throttled to EU limits. (~ 100mW for the DX-7). The DX-6 plays in a different league as it only uses low power ouput, so the following is about the DX-7. The DX-7 works by first doing an energy scan on the band and then selecting two channels - the two that show the lowest interference level. Two separate DSSS channels of the DX-7 The system then continues on these two channels forever (until turned off). It does not change them during runtime. You can think of it as a kind of frequency hopping scheme, but only between two channels as it sends alternating on both. The two channels helps the DX to cope with interference. As long as one still gets through control is maintained. If both are hit at the same time, it goes into failsafe. There is also another trick the DX uses to get the message through. For all SS systems on the market it is the 'loudest' - it sends with the most output power on the least speading width. Where FASST is 90 mW and XPS is 60 mW the DX-7 is 100 mW (EU version) and even more ( ~ +3 db ) for the US version. You can see that also when comparing the signal in the analyser. So metaphorical speaking: While FASST is elegantly hopping from door to door to tell its story, the DX-7 sits on the middle of the street and uses two megaphones to be heard. Both methods seems to work in the real world. Frank

Great information Frank, thanks.

I just went over to RCU and went back to the beginning of the year, looking at all the posts concerning Spektrum. Not ONE that was not a problem with the users setup, from bad batteries to a system that glitched on 72mhz, so gee, it was glitching on 2.4 as well, to a few brownout cases to adding separation distance betweenthe satellite RX's. That's it, no "Major" issues to talk about.

I'm sure I could go back a lot farther and find instances of problems from before the firware upgrades, but current systems seems to be pretty much locked in and very reliable.

[Pale Rider]

Great info Frank..appreciate it--

[gareth.ky]

	Quote: Originally Posted by BZFrank
	Well, I did not want to influence Kiwis measurements but as you ask: I did test both the DX-6 and the DX-7, also throttled to EU limits. (~ 100mW for the DX-7). The DX-6 plays in a different league as it only uses low power ouput, so the following is about the DX-7. The DX-7 works by first doing an energy scan on the band and then selecting two channels - the two that show the lowest interference level. Two separate DSSS channels of the DX-7 The system then continues on these two channels forever (until turned off). It does not change them during runtime. You can think of it as a kind of frequency hopping scheme, but only between two channels as it sends alternating on both. The two channels helps the DX to cope with interference. As long as one still gets through control is maintained. If both are hit at the same time, it goes into failsafe. There is also another trick the DX uses to get the message through. For all SS systems on the market it is the 'loudest' - it sends with the most output power on the least speading width. Where FASST is 90 mW and XPS is 60 mW the DX-7 is 100 mW (EU version) and even more ( ~ +3 db ) for the US version. You can see that also when comparing the signal in the analyser. So metaphorical speaking: While FASST is elegantly hopping from door to door to tell its story, the DX-7 sits on the middle of the street and uses two megaphones to be heard. Both methods seems to work in the real world. Frank

Good stuff there. That answers one of my questions. Your comments on power output are exactly in line with what I thought was really going on and what I read the band rules in the US are.

A US DX7 should be able to transmit at up to 1 watt. A FASST system is capped at 100mw. Basically systems that lock on a channel must avoid transmitting on the channel if it is in use BUT as a trade off they get to use more power. Continuously hopping systems like FASST don't have that restriction, they can transmit anywhere BUT they must do so at lower power to avoid knocking out systems locked to a single channel.

Its a trade off, more volume or better interference avoidance. Since the band rules dictate that other devices shall not interfere with one another its a pretty safe bet to just use two high power channels. You shouldn't actually need more than one.

Rules in the rest of the world would seem to favor FASST. The power output cap is much lower so there is not as big an advantage in being the loudest.

[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.

[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.