Independent tests prove lack of frequency hopping with XPS

[ben_beyer]

I lost a new plane (7th flight I beleive) to an XPS lockout. I just had to watch it's last few seconds before it hit the ground and I was still holding the stick in the proper directions to correct it. If I ever do 2.4 again (I've since gone back to 72), it will be Futaba or JR/Spektrum. Does anyone know if when the primary channel on JR/Spektrum will change to an open frequency once it finds one open?

I've heard that the system picks two channels and doesn't move but others have said that when the primary gets knocked out, it goes to the secondary until a new primary is established. Just looking for clarification.

[prizzy]

I can't wait to see the actual data, then there will be something concrete. I hope the rhetoric will not shut this thread down.

[Wayne]

	Quote: Originally Posted by exeter_acres
	Do they hop if you use a123 batteries?

Now thats funny right there..

[3ddd]

	Quote: Originally Posted by Wayne
	Now thats funny right there..

--guess we will have to wait for dick h to chime in to find that out

[ninjazx7]

as someone who is looking at going to 2.4 i find this thread interesting. dont screw it up!!

[XJet]

	Quote: Originally Posted by sweetpea
	Again.......you are only talking about one reason for the system to hop.....High noise levels. XPS never expected to see these levels.....and as we all see......here is a side effect to that along with the antenna. very unfortunate

Then XPS didn't spend much time analyzing the 2.4GHz band at an altitude of more than 100 feet. It's not at all uncommon for rapid changes in the noise level to occur -- primarily as a result of some new device being powered-up somewhere. On the ground it's a whole different story because buildings, trees and even natural terrain features often shield other sources of 2.4GHz radiation.

And, based on some of the reports of failure appearing in this thread (and elsewhere) it appears that this lack of frequency agility *has* cost people models, the symptoms and circumstances corresponding exactly with what you'd expect in such cases.

As use of the 2.4GHz band increases, this will become even more common and an airborne receiver is exceptionally prone to such interference because 2.4GHz is primarily line of site and an aircraft, given its elevated position, has a very large "view" once it's airborne.

	Quote:
	Trust me, I had a long talk with XPS face to face after my crash (feels like years ago). I asked about the freq hopping and it was explained to my satisfaction. It worked pretty much as I expected it would.

The problem is that, based on past track record, it becomes very hard to believe anything JD says. His tendency to delve into a fantasy world of spherical patent-pending antennas and other hokum means that one should interpret his claims with a healthy degree of skepticism.

DId you actually see one frequency hop?

	Quote:
	But I would still like to see your results to compare them to what I saw when I had issues. Do they pertain to me?

I'm in the process of setting up a new test-rig that I hope will make things very clear, even to lay-persons and provide irrefutable evidence -- not that this is necessary now that JD has admitted the flaw.

	Quote:
	XPS has also stated that there is a software fix coming very soon for the noise floor freq hopping. Please tell me, you plan to re-accomplish your tests then as well.

Don't hold your breath -- this is actually a *very* difficult problem to solve with the XBeePro modules. How does one end inform the other which channel it's changing to when all communications between the two has been lost?

You could just switch to a previously agreed channel -- but there's no assurance that it too isn't also affected (while others remain clear). There's also the fact that if you've got several other XPS systems also flying and they're also hit -- every system might try to use the same fall-back channel with clearly indeterminate results.

Why not just scan all 12 channels and then pick the quietest one to hop to?

Because what's quietest on the ground may not be what's quietest in the air so the transmitter and receiver could end up on different channels, each waiting for the other to appear.

There are ways around the problem -- but none are as reliable or effective as the solutions opted for by Futaba and Spektrum.

I hope Jim comes up with a suitably effective fix -- but I doubt he'll send me a system to verify the claims he makes for this amended firmware so we may never know for sure.

[brn2fly]

	Quote: Originally Posted by exeter_acres
	Do they hop if you use a123 batteries?

ROTFLMAO nice touch

[exeter_acres]

[brn2fly]

	Quote: Originally Posted by ben_beyer
	I lost a new plane (7th flight I beleive) to an XPS lockout. I just had to watch it's last few seconds before it hit the ground and I was still holding the stick in the proper directions to correct it. If I ever do 2.4 again (I've since gone back to 72), it will be Futaba or JR/Spektrum. Does anyone know if when the primary channel on JR/Spektrum will change to an open frequency once it finds one open? I've heard that the system picks two channels and doesn't move but others have said that when the primary gets knocked out, it goes to the secondary until a new primary is established. Just looking for clarification.

Currently the JR/Spektrum picks two open channels and stays on them. It does not change channels after being turning on. Futaba frequency hops(among the channels). I think it changes frequency 500 times a second.

[Pale Rider]

	Quote: Originally Posted by exeter_acres
	Do they hop if you use a123 batteries?

Nope--they would long-jump

Now with Li-ion--yes they would just hop.

[brn2fly]

	Quote: Originally Posted by Pale Rider
	Nope--they would long-jump Now with Li-ion--yes they would just hop.

But Li-Ions have endurance!

[Pale Rider]

	Quote: Originally Posted by brn2fly
	But Li-Ions have endurance!

nothing that some performance-enhancing substances can't cure--oh wait thats baseball

[brn2fly]

	Quote: Originally Posted by Pale Rider
	nothing that some performance-enhancing substances can't cure--oh wait thats baseball

LOL

[dick hanson]

try Bonerall

[martin18152]

Beware of military radar, frequencies are classified; however fall with in the GHz range. They are very powerful and their scatter frequencies might be a problem. If you are near a military base, I would watch using a non frequency hopping system.