Independent tests prove lack of frequency hopping with XPS

[Flyfast1]

	Quote: Originally Posted by buttface
	The system is still usable of coarse but should only be limited to foamies that you don't care about.Even then then it not the best for them either.I don't understand why lots of people are still using it in there glow planes and giant planes after knowing about all of the bad stuff with XPS. They continue to fly ticking time bombs and stand up for the product.But then people do dumb things every day and I for the life of me cant figure that out either. I read the local paper today .A man parked his car in the middle of rout 7 bridge and jumped plummeting to his death.I wonder If he was trying to prove every one wrong that told him he couldn't fly.The XPS users just keep using it hoping to prove it works for them.Why do something that obviously puts you at RISK ???

Because it's far safer than any 72Mhz system. Those who have studied the system understand this.

-Ed B.

[JEFFRO503]

	Quote: Originally Posted by Flyfast1
	Because it's far safer than any 72Mhz system. Those who have studied the system understand this. -Ed B.

I completely disagree with this also.

why.....because the XPS is just like 72mhz it doesn't hop correct/ Ok they are the same that way.....BUt safer.....i think not. The band on the 72mhz is a lot wider i believe , and XPS ( or any 2.4 ) is a narrower band. Which is why spektrum and futaba fasst HOP. Unlike XPS that gets a total blackout when the aircraft is coming towards them , because the freq was blocked by the motor....HAHA!! Whatever. I have flown 72mhz for quite some time , and the motor has never blocked the signal. JD ,mentioned to the guy who lost his 40% , that it was his fault because he mounted the redeiver in the wrong place....."behind the motor". Jesus.......where else are you going to put it?......duct tape it to the top of your canopy?

[Daemon]

Just to clarify something. Most people associate the terms "wider" and "narrower" with
the bandwidth (range of frequencies used by a single channel).
2.4Ghz channels are *much much* wider bandwidth than 72Mhz.
72Mhz uses about 5-10KHz per channel.. 2.4Ghz RC systems use more than 1Mhz per channel
(they all split it up into different width chunks).

What you're talking about is the actual wavelengths, which are generally referred to
as "shorter" or "longer". 2.4Ghz is a shorter wavelength, and thus tends
to be blocked and/or reflected by smaller objects.

But you can't use that as the only criteria to compare them.

For a fair comparison you have to talk about their relative resistance to noise due to factors such as
Analog versus digital.
Simple FM versus spread spectrum (DSSS specifically).
Retransmits.. and so forth..

It's an interesting question. I've had many issues (some fatal to the aircraft) with
various 72Mhz Rxs (too many to list here). Some are proven reliable, some are nothing
but trouble. I've been shot down several times over the years, but I still fly 72Mhz in my
most prized, fastest aircraft (300mph capable), because they're proven
to work in/around 100% carbon. I fly XPS in two of my foamies at speeds up to 155mph
and in those applications I've had no problems at all, other than its high power
consumption (sucks my small glider batteries dry fast).

So, if for the sake of argument, we were to agree that the shadowing issue can be
avoided in certain aircraft (non-carbon, and relatively easy to get away from large bit of metal),
then is there any reason to conclude that a single channel, non-hopping DSSS system is
better or worse than 72Mhz? Any reason to believe that XPS is more susceptible
to external interference than your average 72Mhz Rx? Keep in mind, I fly somewhere
where 72Mhz Bergs (all of them), and Sombra Shadow 3s/SL-8s synths, and Polk Seeker 6 synth all fall from
the sky, only a stones throw away, so I know for a fact that severe 72Mhz interference
exists.

ian

[BaldEagel]

	Quote: Originally Posted by wrightme
	Can't comply. It IS to give a balanced view. Why do you care if I am in the thread or not? Just because I fly XPS without troubles? Go ahead and look through the whole thread. What does any of it really have to do with the subject? At the time of the OP, there was no such data forthcoming, and from the OP, there is still no data. Kiwi has provide a test since then. Why am I here? Why don't you ask Kiwi where he got the XPS TX module for his testing. Why should I not be here? Are you the gatekeeper? I have as much right to be here as you do. Why are YOU here?

I did not say you should not be here, I just asked why you where and so late in the day, I am here because my Graupner IFS system kept locking me out in flight and plainly just does not do what I was lead to belive.

Your view as mine is biased not ballanced.

Mike

[buttface]

Lets not get all irrational hear now...

[BaldEagel]

	Quote: Originally Posted by Daemon
	So, if for the sake of argument, we were to agree that the shadowing issue can be avoided in certain aircraft (non-carbon, and relatively easy to get away from large bit of metal), then is there any reason to conclude that a single channel, non-hopping DSSS system is better or worse than 72Mhz? Any reason to believe that XPS is more susceptible to external interference than your average 72Mhz Rx? Keep in mind, I fly somewhere where 72Mhz Bergs (all of them), and Sombra Shadow 3s/SL-8s synths, and Polk Seeker 6 synth all fall from the sky, only a stones throw away, so I know for a fact that severe 72Mhz interference exists. ian

Ian

Being in the UK we fly on 35Mhz, the field I fly on has proven RF interferance problems, PPM gets glitches in approx four different areas of the site, these have been mapped as being in line with communication towers on either side of a large river adjacent to the site, these towers are not in sight of the flying field, when I installed my Graupner IFS system, this is XPS in Europe, I experienced lock out in the same areas that produce glitches for PPM, this to me proves that the IFS/XPS sytem does not hop to a different frequency when experiencing interferance which is what I understood it would do from the advertising for the system.

The main reason for being on this site is to accumalate sufficient information to allow an informed and weighted responce to Graupner who at this time refuse to reinburse me, however, the Trade Descriptions Act in Germany is more stringent than in the UK and I am hopefull of a succesfulll conclusion.

Mike

[ricoalonso]

After reading most of the posts (both positive and negative in both RCG and FG) regarding XPS, I honestly think (my opinion, of course) that the only advantage (at present) of XPS over 72Mhz is that the pilot does not have to check the frequency board before he/she turns ON his/her Radio system.

^R^

[Wojcigitty]

	Quote: Originally Posted by Wojcigitty
	Yes, it is able to coexist on the same frequency as another 2.4 ghz device, and it is a lot "smarter" in how it's bound receiver-to-transmitter. However, it's to be expected that, out of nowhere, another device could start broadcasting on the same frequency as XPS and use up all available bandwidth. FASST and Spektrum have methods of dealing with this. It's NOT expected that all of a sudden another device could suddenly take a single frequency on 72 MHz without warning. 72MHz systems are not designed to be frequency-agile, and when properly used (frequency control is implemented), they do not need to be. 2.4GHz systems ARE supposed to be frequency-agile, and even when used properly, they DO need to be.

I would still rather use 72 over XPS.

[aviti]

If something sounds too good to be true, it probably is. I've thought that since the first time I heard XPS's claims and it sure seems to be correct in this case. Oh, and by the way XPS cheering section, there are other valuable threads on this site other than the XPS ones, might be worth checking out...welcome to the site.

[Julez]

72 relies on the frequency to be very clean. There is no other equipment on 72 other than RC radios, so the frequency is usually clean, unless someone shoots you down, that is.
2.4 relies on the ability of the reciever to cope with a lot of noise. We are not the only ones on 2.4, but this is usually not a problem, als most 2.4 systems can cope with interference very well due to antenna diversity and frequency agility.
If a 2.4 system now lacks both these features, 2 of the main advantages are gone, making this system a lot less safe.
Therefore, I tend to agree that a decent dual conversion PCM 72 system is superior to XPS.

[ricoalonso]

Agree, and you said it better Julez, for the average pilot to understand the current situation.

Thanks.
^R^

[JEFFRO503]

	Quote: Originally Posted by BaldEagel
	Ian Being in the UK we fly on 35Mhz, the field I fly on has proven RF interferance problems, PPM gets glitches in approx four different areas of the site, these have been mapped as being in line with communication towers on either side of a large river adjacent to the site, these towers are not in sight of the flying field, when I installed my Graupner IFS system, this is XPS in Europe, I experienced lock out in the same areas that produce glitches for PPM, this to me proves that the IFS/XPS sytem does not hop to a different frequency when experiencing interferance which is what I understood it would do from the advertising for the system. The main reason for being on this site is to accumalate sufficient information to allow an informed and weighted responce to Graupner who at this time refuse to reinburse me, however, the Trade Descriptions Act in Germany is more stringent than in the UK and I am hopefull of a succesfulll conclusion. Mike

Oh holy hell!! Until now , i didn't know Graupner and XPS we're the same unit. I haven't read much good stuff about this system either......that explains it.


And mike , i wish you the best of luck with getting some money back for whatever aircraft you lost due to this system.


I really hope for JD's sake , that if and when he comes out with that new 900mhz system , it works really good , and the way it is supposed to. If he can get the system to hop and stay linked up , i think he'll have a good system at a competitive price.

I know he'll never admit that the XPS system that's out now has a major flaw in it , but it would be nice to see him make good on a new system. I think he could save a lot of face and less lawasuits this way. I really , really hope that one of these aircraft don't lock out at the wrong time , and hit someone , possibly causing serious injury or death. Is it worth it i wonder??....i think not.

[JEFFRO503]

	Quote: Originally Posted by Julez
	72 relies on the frequency to be very clean. There is no other equipment on 72 other than RC radios, so the frequency is usually clean, unless someone shoots you down, that is. 2.4 relies on the ability of the reciever to cope with a lot of noise. We are not the only ones on 2.4, but this is usually not a problem, als most 2.4 systems can cope with interference very well due to antenna diversity and frequency agility. If a 2.4 system now lacks both these features, 2 of the main advantages are gone, making this system a lot less safe. Therefore, I tend to agree that a decent dual conversion PCM 72 system is superior to XPS.

Thanks for putting that into lamens terms for me Julez!! I don't understand how all the 72mhz , and 2.4 stuff actually works , but i can say , from reading through this entire thread , i have learned a lot. Now....i can't remember a lot of the "high tech stuff" , but at least i try to hehe.

[chewy]

	Quote: Originally Posted by Julez
	72 relies on the frequency to be very clean. There is no other equipment on 72 other than RC radios, so the frequency is usually clean, unless someone shoots you down, that is. 2.4 relies on the ability of the reciever to cope with a lot of noise. We are not the only ones on 2.4, but this is usually not a problem, als most 2.4 systems can cope with interference very well due to antenna diversity and frequency agility. If a 2.4 system now lacks both these features, 2 of the main advantages are gone, making this system a lot less safe. Therefore, I tend to agree that a decent dual conversion PCM 72 system is superior to XPS.

Julez,

Actually, from what I have read so far, it appears to me that SS systems has a few more advantages to help cope with other users on the same band

1. The spreading of the signal itself (as long as the channels used are not swamped)
2. The unique ID code (doesn't help if the channels used are swamped)
3. The time division routines and look-ahead (if implemented)


If the channels used are swamped then not matter what is used, the plane will crash, unless it has the frequency agility to get itself out of the way of the noise source.

So, actually 2.4 is a LITTLE bit better than 72MHz or 35 or etc, FM sets. FM cannot take much of ANY interference, whereas 2.4 is able to survive SOME interference.

chewy

[wrightme]

	Quote: Originally Posted by BaldEagel
	I did not say you should not be here, I just asked why you where and so late in the day, I am here because my Graupner IFS system kept locking me out in flight and plainly just does not do what I was lead to belive. Your view as mine is biased not ballanced. Mike

"Late in the day" is only relative to the time zone of the poster.

My view is open. I see shortcomings in the XPS system, but whether you want to believe it or not, it is much easier to provide a proof of something like an XPS hop than to provide a disproof. We have seen specific test instances where it does not hop; specifically with a noise source similar to 2.4 Ghz systems for RPV. I do see that such a noise source will cause a big problem for XPS, and that the tests seen so far DO prove that it will not "hop" away from such a source.

I fly out in the desert, and nowhere near such noise sources. It really does work for me, in several different airframes. The big problem I see in the RCG Vendor forum is that the "hop/no-hop" "discussion" ends up obliterating any hope of actual XPS users receiving any help from others about their installations and use. Invariably, someone who does not like XPS (or doesn't like JD, or claims, or...) sea-lawyers the information into submission. There are plenty of forums for that discussion. JD can run his vendor area the way he sees fit.

Those who "bash" XPS then belittle those who choose to use it. This does not help the hobby in any way at all. I once again contend that no matter which R/C system you choose for your aircrafts, each time any of us puts a model in the sky, there is a chance that control will be lost (for MULTITUDES of reasons), and a crash will ensue. The best course of action is to always fly in an area and in a style that does the best to minimize the impact of an impact.

Each system I see has SOME level of "flaw" that people experience. Choose which you wish, and fly. I do.

Biased? If you check back a page or two, you will find that I have posted that I am seriously contemplating going to Spektrum. I see that the two channels is more robust than one channel, and that multiple RX modules can provide fewer blind spots in an installation. If XPS comes out with telemetry and/or daughter RX modules prior to that, my decision will be much more difficult.