Independent tests prove lack of frequency hopping with XPS

[XJet]

	Quote: Originally Posted by BoneDoc
	XJet, So what did you do on your testing? So far, you've been telling us of what XPS does NOT do, but not HOW. Curious minds want to know and get to the facts. If you have the time to make counterpoint arguments, surely you'll have the time to at least write about your methods. I'm no fanboy as I do not own XPS. I have Spektrum right now, and I have issues as well from time to time (2 receivers died). Please publish the facts.

Because it becomes very easy to start lapsing into rather technical jargon (which benefits nobody except other tech-heads), I intend to make a video that will demonstrate the XPS frequency-hopping situation in a way that is easy to see.

I was first alerted to the problem when we were experimenting with 2.4GHz video-senders on a UAV wth an XBeePro -based telemetry system onboard.

If I turned the video sender on first, the XBeePro modules would work just fine, giving all the required range and no data-loss.

However, if I turned the XbeePro link on first, then turning on the video system would cause massive data-loss (over 99%). I realised this was because the XBee system is not frequency hopping and has no intrinsic ability to change frequencies when encountering interference.

I decided to see if the XPS modules had this frequency-change firmware so I repeated the experiment with an XPS receiver onboard.

As before, turning on the video system first produced a working link with acceptable range. The XPS worked fine.

However, when I turned on the XPS system first and checked it was working fine, it all stopped as soon as I turned on the video-sender.

A quick check showed that the video sender was operating on the same channel that XPS was choosing as its default at startup and that when exposed to this kind of sudden increase in noise, it would simply stop working.

This wasn't front-ened overloading or anything else , it was simply a case of the video-sender's transmission clashing with the XPS transmitter.

I then performed some other tests to see how far the video sender and XPS system had to be
separated before this didn't happen -- and found that even with 100 yards separation, the problem persisted.

The possibility that this XPS receiver was faulty had not been discounted but I now have another in my possession (thanks to a kind FG member) and I'll re-test with both units.

If I had a lot more time at my disposal, I'd set up a spectrum analyzer and invest a few days on this but I have to earn a crust too and we're on a tight timeline with an upcoming UAV tender so I'm already burning the candle at both ends.

However, I expect to produce something that will allow folks to see with their own eyes what's going on. If I get the chance I'll also upload some of the noise profiles from our own airfield which show the quite marked difference in 2.4GHz RF activity at ground-level versus altitude.

[bgold]

I should be patient

[XJet]

	Quote: Originally Posted by jonkoppisch
	Interesting. Thanks! I take it that the xbee modules are from wireless routers and such? What is the range of a typical 2.4 wireless router? Does it have the same strength as the xbee modules being used for rc? If so, with everyone getting wireless routers for their home networks, say 3 or 4 in the area, could this cause any interference? As I understand it, ground clutter would weaken or thin a lot of the signals but as you say, once you're in the air?

The XBeePro modules are designed primarily for the creation of data links and networks. The "range" of an XBeePro pair is "up to" a mile on the ground and more in the air -- that's not really an issue. Even with 10mW output (versus the 60mW standard output of XPS) you'll get far more range than you'll ever need on 2.4GHz.

Wireless internet *can* be an interference issue but most home routers are relatively low-powered and, because they're usually operated indoors, tend to emit only small amounts of RF beyond a hundred yards or so.

What can be more of an issue are things like powerful cordless phones (legal and illegal) operating in someone's back yard and thus clearly visible to a model and broadcast wireless internet. We have a commercial wireless internet service in the town where we test our UAVs and it has a profile on three of the XPS's 12 channels. It has three large radiation lobes, one of which comes very close to the airfield itself and you can observe the noise-levels rise significantly when you fly through it.

Even a BlueTooth mobile phone could potentially cause problems if it's activated in your pocket (or that of someone near you) while on the flightline. If it transmits on the frequency XPS is using, it could in theory obliterate the acknowledgment data sent back from the XPS receiver to the transmitter. If XPS doesn't get these acknowledgments it resends the data several times because it thinks the receiver never got it. This chews up more of the timeline. I don't know what happens if the timeline is almost full but I expect it *would* impact on other XPS systems also using that channel.

Other potentially worrying sources of interference are leaky microwave ovens and commercial 2.4GHz data-links -- or perhaps even a plane on 72MHz that's flying with a 600mW video transmitter onboard and is operating from the same field as you. I have a video sender here that completely obliterates the XPS system at significant ranges (I'll be testing this further in the New Year).

If you've got a 2.4GHz cordless phone or home network you've probably already seen just how much unwanted interference can occur between 2.4GHz devices. It's not uncommon for even a perfectly good microwave oven to kill the throughput on a home wireless network and likewise with the cordless phone.

If you've got diversity antennas or satellite receivers on your 2.4GHz gear then the effects of these interfering signals is likely to be much less -- since one of your antennas should be getting a strong signal from your transmitter at all times. With a single quarter-wave whip however, the chances of the valid signal being overwhelmed by an interfering one increases due to multi-pathing, polarization conflicts and dropouts caused by antenna null-points.

	Quote:
	Added: Does a wireless router/network etc use more time on the frequency also? So instead of only using 10% it might use 30% or 70%??

This depends on how much data is being transferred. If the network has (say) a 2Mbps maximum throughput and someone is sucking down a large file at full bore then that cbannel will be very highly utilized with very little space left on the timeline for anything else. That's one of the reasons that wireless internet connections tend to be so variable in their performance - as more people start using them they slow down a lot as the timeline becomes filled.

[aviti]

Some guys like to question X-jet because they think he has an axe to grind with Jim Drew but right or wrong, I'm glad someone that knows more than most of us is questioning this. There are others in the industry that know what's what with this stuff but they can't really comment on a competitor's system. It would be nice if we had a lot of non-biased experts like our own RC consumer reports but we just don't. I hope some other folks with the qualifications will also look at this.

[KrisW]

	Quote: Originally Posted by Kiwi
	Something I find a bit unnerving here is I remember clearly in the early days of the Web spamming on the benifits of XPS was the fantastic amount of channels available to this setup. I seem to recall it being stated that you could technically fly hundreds of models at the same time and get no interference between them. I am neither for nor against any manufacturers attempts to provide a reliable and robust RC system but I do find 12 channels a seriously small number of available frequencies. I know someone is going to say yeah but!!! You never have 12 planes flying at the same time but by god you can easily have more than 12 transmitters turned on in the pits if everyone thinks they are never ever going to shoot someone down or cause a problem. What happens when transmitter No 13 gets turned on.?? Does it just fail to link up or does it squeeze someone out with a weaker transmitter signal.?? Again I am not taking sides, nor do I want to open pandoras box but seeing as we have someone with a seriously indepth knowledge of 2.4 Ghz radio systems its an opportune time to ask I think??

Actually, the total numbr of frequencies would be about 6, to have totally clutter free, uninterrupted signal on BOTH channels in a pair. . . NOT GOOD.

Now, since an identifier string is encrypted, theoretically you can still have 78 pairs of frequency, with each half of the pair being stepped on by conflicting signals, but not matching the other half's PCM encryption, and so being ignored. . in THEORY....... and in theory keep flying . . ..

Theory often conflicts with reality .. and reality always wins.

[KrisW]

	Quote: Originally Posted by aviti
	Some guys like to question X-jet because they think he has an axe to grind with Jim Drew but right or wrong, I'm glad someone that knows more than most of us is questioning this. There are others in the industry that know what's what with this stuff but they can't really comment on a competitor's system. It would be nice if we had a lot of non-biased experts like our own RC consumer reports but we just don't. I hope some other folks with the qualifications will also look at this.

I really like X-jet . .he's knowledgeable, intelligent, educated, AND his posts are LONGER than MINE!!!!.


Finally, someone in MY league ! !

[Kiwi]

Tony

I have to whole heartedly agree with you and thats why I am moderating this forum like a hawk. I dont want it to go off the rails as there is a lot of knowledge being shared here and everyone at least has the right to observe and ask Xjet questions as we go.

On a side note but intersting just the same I was taliking with someone last week who is feild testing the FASST system on a high end Futaba radio. At his field they had a spectrum analyser running and also had some Spektrum radios operating. He was telling me how you could clearly see the two channels the Specktrum had locked into and when you turned on the FASST system you could see it pretty much black out the screen as it checked and skipped channels at light speed.

I´m sure once FASST becomes mainstream next month there will be tales of disaster and issues until people become accustomed to them.

In the mean time I am sitting back, watching and patiently waiting for Xjet to show us how the XPS system works and any issues it may have or not have.

[3ddd]

xjet i must say you finally gave me something i can bite into other than just(i ran some test)thankyou and keep going,i am still listening

[sweetpea]

Very good posts Xjet......

With the way you described the your test though, it doesn't appear to lend to freq hopping. It more sounds like you saturated the spectrum, it also doesn't say that you had a device to see if it actually hopped. Maybe it hopped to the next adjacent freq which also was covered by the device as far as power and harmonics. I wonder if FASST or Spektrum would have failed the same way in this test.

Because the important part of this to me is a feature that stands out....If it is hopping and it doesn't help I'd like to know. If its not, hopping but all the other 2.4 systems fail in the same test.....that's not great news but then you are no worse off than any other system . And lastly.....how does each system react in this scenario....immediate failsafe or sluggish controls than failsafe etc...All of this will help people decide which unit is better for their needs

I don't doubt that you got the system to fail.....I just question why it failed and if any of the other systems would have done any better in your test.

I'm really looking forward to more of your testing in the new year......And post some more on how you setup your test and what your looking to accomplish.....not everyone online has no experience with electronics and radio freqs so the data and technique are just as important as the results only

Its a shame I don't live anywhere near you as I'd lend my equip to the test....72mhz, Spektrum and XPS (sorry don't own a futaba radio)

[Kiwi]

	Quote: Originally Posted by sweetpea
	....not everyone online has no experience with electronics and radio freqs

But I bet you your last dollar that there are a darn site more who dont know than do. There are also a whole lot who know enough to be dangerous.

Thats why its good to sit back and let the man show us what he found and in a manner that the dont knows will soon know.

[Chris]

	Quote: Originally Posted by gmilo
	I for one lost faith in X-link when JD claimed that the 1st delay in introduction was due to a delay in receiving plastic receiver enclosures from the Asia supplier that 'were in transit'.....this transit time turned out to be about 6 months. Just a bold face lie IMHO that I didn't appreciate as a reasonably intelligent consumer. When I go 2.4, it will be JR or Futaba, but not XPS

Same here. It was delayed too long. And anybody with 1/2 a brain knows it wasn't because the freight ship got lost in the middle of the ocean.

Then--when they FINALLY got some inventory--I couldn't buy it. They had issues with the shopping cart. The rumor was that somebody had gone in and placed thousands of units in their cart--thereby making all the inventory "spoken for" and unavailable to the rest of us.

I find it positively amazing that a guy with the knowledge to design, build and manufacturer an RC system such as this, cannot get a simple website shopping cart set up correctly. It's total BS. Something fishy was going on. Having a shopping cart and internet commerce system set up to make purchases and collect money is not rocket science. It's not new technology either. But for some strange reason, XPS couldn't figure out how to sell their product after it arrived in the states.

Ummmmmmmm, no thanks. I tried to buy it when it had been here and available for just a few hours. But, THANK GAWD!!, I couldn't purchase anything because of the shopping cart snag.

I'm now a happy user of Spektrum.

Just do a google search for JD and read all about his past business ventures. Read about how he sold business' in the past and left users high and dry when they needed support and warranty work. Read about his prior delays with regard to getting products available for the market. Read about the delays and the broken promises. Read about the claims and then about the REAL facts about what his products could and could NOT deliver.

Makes no difference now weather XPS works or not. I wouldn't buy a square of toilet paper from that guy if I was stuck on the toilet in a public bathroom. I'd rather use my finger. At least I could wash that off when I was done and get on with my life.

Did I sugarcoat anything?

[KrisW]

	Quote: Originally Posted by Chris
	Same here. It was delayed too long. And anybody with 1/2 a brain knows it wasn't because the freight ship got lost in the middle of the ocean. Then--when they FINALLY got some inventory--I couldn't buy it. They had issues with the shopping cart. The rumor was that somebody had gone in and placed thousands of units in their cart--thereby making all the inventory "spoken for" and unavailable to the rest of us. I find it positively amazing that a guy with the knowledge to design, build and manufacturer an RC system such as this, cannot get a simple website shopping cart set up correctly. It's total BS. Something fishy was going on. Having a shopping cart and internet commerce system set up to make purchases and collect money is not rocket science. It's not new technology either. But for some strange reason, XPS couldn't figure out how to sell their product after it arrived in the states. Ummmmmmmm, no thanks. I tried to buy it when it had been here and available for just a few hours. But, THANK GAWD!!, I couldn't purchase anything because of the shopping cart snag. I'm now a happy user of Spektrum. Just do a google search for JD and read all about his past business ventures. Read about how he sold business' in the past and left users high and dry when they needed support and warranty work. Read about his prior delays with regard to getting products available for the market. Read about the delays and the broken promises. Read about the claims and then about the REAL facts about what his products could and could NOT deliver. Makes no difference now weather XPS works or not. I wouldn't buy a square of toilet paper from that guy if I was stuck on the toilet in a public bathroom. I'd rather use my finger. At least I could wash that off when I was done and get on with my life. Did I sugarcoat anything?

Not at all. . . want to borrow some clover honey?

[sweetpea]

And I thought we were going to keep this civil.

[Chris]

	Quote: Originally Posted by KrisW
	want to borrow some clover honey?

Sorry Kris, I don't know what that means.

I have no interest in the XPS system, so the results of XJet's testing really don't matter to me. Just had to point out, or joggle some memories, with regard to all the problems in actually getting this product to the market. And I would encourage anyone thinking of purchasing one of these systems to do some research on the company before buying the product. You might need warranty work some day.

I have no doubt that if I ever need service on a Spektrum product, all I have to do is ship it to Champaign, IL. with a brief description of the problem. Weather it be next week or in 10yrs from now, I'll get it serviced if it ever needs it.

I'll stay out of this one from now on. Carry on gents.

[Kiwi]

All Righty, back on track guys.

Dont take sides on this one. Lets see if we can get some sort of independent and obvious well intended analysis done here.

In another thread someone asked why we could not have some sort of product assurance testing done by members. Here´s a chance to prove we can be independent enough and mature enough to test a product and get an unbiased result.