Kiwi's XPS test results are up.

[dick hanson]

	Quote: Originally Posted by Pale Rider
	So is there any DIS-advantage to using the channel-hopping FAAST system ?

other than you you don't get the advantages of the DSM2 system - no-none I have seen- both work just fine

[chewy]

Yes: expensive rx's. But if you can afford them, then that won't matter.

chewy

[dick hanson]

	Quote: Originally Posted by chewy
	Yes: expensive rx's. But if you can afford them, then that won't matter. chewy

what does the price of em have to do with anything?
Are you inferring that thaey are better because they cost more?
or that you are really paying more than they are worth?

[Chris F]

	Quote: Originally Posted by dick hanson
	what does the price of em have to do with anything? Are you inferring that thaey are better because they cost more? or that you are really paying more than they are worth?

Don't be so defensive, I expect Chewy is saying that if you're on a budget the extra price might be a disadvantage. Not all of us have bursting wallets.

[Kiwi]

Probably one of Spektrums strongest points is the great variety of receivers but I really doubt that the playing field will remain lop sided for very long. In market driven economy articles of equal performance and size tend to level out.

It just takes time and the cream is always on top of the warm milk. First in gets the best bite of the cherry but that wont last forever.

[chewy]

	Quote: Originally Posted by dick hanson
	what does the price of em have to do with anything? Are you inferring that thaey are better because they cost more? or that you are really paying more than they are worth?

It doesn't matter if you only buy 1 set, and no other rx. But, if you are like me and have to replace 10+ rx's, it adds up.

Corona has a new FHSS module/rx out for testing. Don't know how good it is, though. And I betcha they are MUCH cheaper. We shall see and I am not in any hurry to splurge on a new system, or I will end up sleeping with the dog.

chewy

[Al Czervik]

I must say that the level of knowledge here goes so far over my head that I might as well be reading Chinese.

Fortunately from the info that I have been able to piece together, I have found it wise to give Futaba FASST a try..and fortunately my 8 channel combo and additional receiver came in the mail today.

It mentions nothing with receiver mounting other than staying away from carbon fiber and having both antennas form a 90 degree angle. Would it be good to mount the Futaba setup high in the canopy as well?

[USN_POPS]

	Quote: Originally Posted by Al Czervik
	It mentions nothing with receiver mounting other than staying away from carbon fiber and having both antennas form a 90 degree angle. Would it be good to mount the Futaba setup high in the canopy as well?

I flew DX-6 for nearly a year, and another 2.4 full range system for nearly a year. I fly only electric, and I make it a point to place my receiver as high as possible in the plane. On both systems.

2.4 has a problem with any mass, and a battery pack or motor can cause blockage of signal in certain attitudes.

So by having the RX high, and doing a 360 degree range check you can pretty well insure that you have good signal at all times.

[Garland]

Ok I feel like a snookered XPS customer, sucks but hey...I came to FG to get the whole XPS story.

Now 2.4g experts lest whisper to each other for a sec...
hypothetically take all other brands of 2.4g off the table as they dont exist now..

If you had to fly your most prized $$ aircraft using only XPS, for 500 flight hours, what steps would you take to reduce lock outs knowing the 2.4g environment like ya'll do?

Now even more interesting Q:

With all ya'll skills... if using only the XBee chips, can ya'll team up and do what JD hasnt done and create XPS to fulfill all the Telemetry, Sat Rx's, chan hopping etc.......CAN XPS DO ALL THESE THINGS?? Is xBEE capable of all this?

Or is all this just a marketing hype experiment on JD's part.

I'm military, and the only way to get a good threat level assessment is to find out from poeple I feel are experts/know their Caca... What they would do with XPS were it mission critical? Go or No Go?

How bleak is it? How hostile can 2.4g spektrum get for non hop?

How can a XPS user protect themselves?

[Mike Busutil]

Chevy.......Ford........JR......Futaba, Everyone has their own preferrences and all the companys are going to say they have the best system, we just have to pick one and go fly, this whole hobby is a big risk with any equpment we use, If that worries us too much we should get into a less stressfull hobby like sailboats. I happen to put my trust in the XPS with my 50% Edge 540.


Nice job Kiwi

[Daemon]

	Quote: Originally Posted by Garland
	hypothetically take all other brands of 2.4g off the table as they dont exist now.. If you had to fly your most prized $$ aircraft using only XPS, for 500 flight hours, what steps would you take to reduce lock outs knowing the 2.4g environment like ya'll do?

Put the Rx far from anything that might block the signal, like somewhere
in the middle of the tailboom far from motor, batteries, carbon frame etc.
Unfortunately my most prized high $$ aircraft are all 100% carbon fiber fuse and wings
so XPS is simply not an option, and I've not seen any 2.4Ghz system work
with 100% carbon planes without serious modifications (either to the plane
or warranty voiding mods to the Rx antennas)

And because very bad things can happen if it ever loses power at the same time
it loses the signal for a second (zombie state), put the servos on the other side of an
opto-isolator and give the Rx its own power supply, or second battery as a buffer.
There's a DIY circuit that you could use. Diagram attached.
The main power basically just keeps the Rx battery topped off, and if
the servo draw ever draws the main power supply's voltage down, the Rx
voltage stays high (the diode prevents the servos from ever drawing against
the Rx's battery). If you can eliminate any possibility of a low power reboot,
you up the odds of staying alive through intermittent loss of signal by
quite a lot.

	Quote:
	Now even more interesting Q: With all ya'll skills... if using only the XBee chips, can ya'll team up and do what JD hasnt done and create XPS to fulfill all the Telemetry, Sat Rx's, chan hopping etc.......CAN XPS DO ALL THESE THINGS?? Is xBEE capable of all this?

Short answer, using the current 2.4Ghz XBee modules. No.

Because it is two way, the satellite receivers are at best, dumb, and at worst
a liability. They can't transmit ACKs without interfering with the main Rx's ACKs
(you'd actually be creating multipath interference at the source) so if the main Rx antenna
is blocked, and the satellite receiver antennas are not, the Tx will still think it has lost
the link, even though the Rx is still getting signals from its satellites.
That'd be ok, if it was meant to always be a one way system, but it's not.

As for hopping, it can be done, but it's always going to be *slow*, again
because the two way nature gets in the way and it's tough for both
ends of a two way link to know for sure if the link is 100% broken or only 50%
broken, and you risk more by hopping when it's 50% broken than you would by
staying put.

There are good reasons for it being a two way system, and it wouldn't
work as well as it does if it wasn't, but it hampers its ability to do proper satellite receivers, or to
hop quickly and effectively.

There is another option. There are new 900Mhz Xbee modules which use
FHSS instead of DSSS. They're still two way, so they have the advantage
of being able to retransmit when there are single receiver multi-path issues (what I call
temporal diversity), but they hop *all the time*, like FASST or Airtronics FHSS.
900Mhz has better range, less multi-pathing and are blocked by
less types of material.

	Quote:
	Or is all this just a marketing hype experiment on JD's part.

Exaggeration.

	Quote:
	How bleak is it? How hostile can 2.4g spektrum get for non hop?

Spektrum is a brand name.
The 2.4Ghz spectrum can be very hostile to a single channel system, but it's
actually fairly rare. We've got a zillion single channel devices (stuff
that only picks a channel at power up and stays on it) and they rarely
get knocked out completely. But my test with 2.4Ghz video Tx's show that it is possible.

ian

[XJet]

	Quote: Originally Posted by Garland
	If you had to fly your most prized $$ aircraft using only XPS, for 500 flight hours, what steps would you take to reduce lock outs knowing the 2.4g environment like ya'll do?

I'd have a spectrum analyzer at my side and keep a close eye on it to try and get an idea of what the noise profile of the area was. Even better, I'd fly an SA in one of my 72MHz planes and see what the environment is like from the model's perspective.

If it were relatively benign I'd feel much happier about committing a valuable model to XPS.

	Quote:
	With all ya'll skills... if using only the XBee chips, can ya'll team up and do what JD hasnt done and create XPS to fulfill all the Telemetry, Sat Rx's, chan hopping etc.......CAN XPS DO ALL THESE THINGS?? Is xBEE capable of all this?

The best you can hope for in terms of frequency agility is a system that might work some of the time but there's no way to create a system that'll guarantee (once a link is established) to hunt out a free piece of 2.4GHz spectrum and switch to it in all cases when using the XBee/Pro modules.

	Quote:
	Or is all this just a marketing hype experiment on JD's part.

I'm picking that a lot of the more outrageous claims made by JD for XPS (patented 8-element spherical antenna, on-demand frequency hopping, etc) are simply an attempt to mitigate (through hype) the obvious limitations of the system he's shipping and try to give it bullet-points when compared to its competition.

For example, when questioned about the lack of diversity, JD says "don't need it" because of this magic antenna and the reliable-transport layer intrinsic to XBee. Well the reality is that although the reliable transport layer will *help* mitigate the effects of multi-pathing it's not going to do a thing to prevent shadowing by CF structures, engines or other large RF-opaque elements of a model.

Another example: Spektrum offers redundancy by using two channels and FASST offers to exploit *any* clear-spot on the band by constantly frequency-hopping. XPS has neither feature and the XBeePro modules were never designed to operate on dual frequencies or constantly hop. To try and mitigate this, JD came up with the story that a patented algorithm would hop on "potential interference" thus allowing the system to switch to a less noisy channel when required. Clearly this isn't the case (or at least not in a reproducible way).

	Quote:
	I'm military, and the only way to get a good threat level assessment is to find out from poeple I feel are experts/know their Caca... What they would do with XPS were it mission critical? Go or No Go?

This is entirely dependent on the type of model you fly and where you fly it.

In a benign 2.4GHz environment the lack of hopping isn't a big deal, since there's not going to be any need to hop. However, if your environment is very active and the profile of the 2.4GHz spectrum is constantly changing by a significant amount then you could find yourself affected to a greater or lesser degree. If you're lucky it'll be momentary lockouts -- if you're unlucky it'll be failsafe all the way to the ground.

In a smaller and all wood/glass model the XBeePro's reliable transport layer will compensate pretty well for a lack of diversity since the main problem will be transient signal dropouts due to multipathing, antenna nulls and cross-polarization. However, if you're flying a larger model with CF, big metal engines or other components that can block the 2.4GHz signal then antenna/receiver diversity is essential and XPS falls down here.

The reality is that most flying fields are pretty benign from an RF perspective and most models are neither large nor fast enough to defeat XPS's lack of antenna/receiver diversity. That's how come there are thousands of satisfied XPS users who've never had a problem.

Not surprisingly however, a number of the unexplained XPS crashes seem to have occurred when a previously trouble-free model is flown at a different location for the first time. Perhaps this is an example of what happens when XPS encounters a hostile 2.4GHz environment and can't hop.

	Quote:
	How bleak is it? How hostile can 2.4g spektrum get for non hop?

Single-channel DSSS systems are quite resilient to interference but XPS has a few dice loaded against it. The lack of antenna/receiver diversity means that the received signal strength can vary wildly depending on receiver orientation, signal reflections, absorbent and reflective airframe components, etc. As a result of this I'd expect to see XPS having more momentary holds and lockouts than some of the competing single-channel DSSS systems such as Assan and iMax which both offer diversity.

There are no "bullet-proof" RF links, even Futaba's FASST system, although theoretically the most resilient of the lot *will* fail if there's enough noise around -- although the whole band would have to be pretty much saturated for this to happen.

	Quote:
	How can a XPS user protect themselves?

Depending on how much you want to spend you can:

1. Check your RF environment using an SA (from ground and air) to make sure it's not too hostile
2. Make sure your installation is *perfect* to reduce the effects of shadowing
3. If you suffer even a momentary hold/failsafe -- get down quick and find out why

The situation isn't too bleak for XPS users -- single-channel DSSS systems can work. I fly every weekend with an ultra-cheap Chinese 2.4GHz DSSS system and have no problems, despite the presence of a school WiFi network, public WiFi tower, a large factory with several 2.4GHz systems in regular use and a small suburb nearby with at least two 2.4GHz cordless phones and an unknown number of microwave ovens.

Of course even that ultra-cheap system has a satellite receiver as standard equipment to provide diversity.

I could easily fly my 30% Extra with this system -- but I won't. The biggest plane I'm comfortable using *any* single-channel DSSS system on is a 40-sized profile.

And this is where I think some people have a real beef with XPS and JD. He's grossly oversold the capabilities of the system.

The Chinese system I've been using for four months now makes no outrageous claims -- when you buy it you know exactly what you're getting and can make judgments as to what kind of model you're prepared to risk to it. By comparison, XPS purchasers are told that they're getting a system that's even better than Spektrum or FASST because it has a revolutionary antenna and the ability to hop away from interference before it even happens.

If (as has happened on a growing number of occasions) people believe that hype and then lose a model to the system's limitations -- finally discovering that the "fantastic" claims were untrue they get really angry (which explains why there are some former XPS users who are so vitriolic about the system and JD).

XPS is a fine 2.4GHz system when people are made fully aware of its limitations and it is used appropriately (with these limitations in mind) -- unfortunately the company persists in over-hyping its technology and capabilities. The result is the utter fiasco that has pretty much exploded in recent months as the facts are revealed, XPS raises its shields to deflect all criticism, and customers are denied any proof that they've actually got the features they've paid for.

Ultimately I guess the question you really have to ask yourself is:

How much would it cost to switch from XPS to something else and is that cost greater than the amount you're prepared to gamble by using a second-tier 2.4GHz system that could (possibly) cost you a model?

From a personal perspective, I don't see any point on penny-pinching when it comes to RC gear. If you're flying giant scale and spending $4K+ on a model, why go all miserly and use a second-tier radio system when there are better solutions on the market for only a tiny amount more?

Those who are enamored of their XPS gear say that the product holds its price really well so work out whether it's better to sell what you've got and pay a couple of hundred more for a system that will be far better equipped to protect your total investment from destruction.

Or you could wait -- I'm aware that there's yet another 2.4GHz system coming onto the market later this year from a very reputable European manufacturer who's already selling into the giant scale and turbine markets. They've offered to send me a sample unit and I'll test it as soon as it arrives. It might be great, it might not but it is another option.