Independent tests prove lack of frequency hopping with XPS

[Kiwi]

Step 5.

Turn on the Transmitter and get a link.

Here you can very clearly see the red and yellow signal being recorded in this case on Channel 11.

[Kiwi]

Step 6

Now its time to get things moving or hopping with a little bit of luck. What I done here was place the sig gen in traverse and set it running. As this moves across the channels one at a time in a sequential motion slowly sneaks up on the XPS signal. I really figured if anything was going to make XPS move this would as its a rising noise floor and moving slowly, thus giving XPS lots of time to call for a channel change and out run the danger.

Nothing happened. It rode out the interference and never moved.

[Kiwi]

Step 7.

Try another way. This time I set up the sig gen to pulse on the same frequency as XPS was locked into. I figured seeing as slowly raising the noise floor did not have any impact I would hit the actual channel with pulses. Again these were set to 5 seconds on and 5 seconds off. Here my thoughts were it has to move under this scenario as it has thousands of milliseconds and lots of gaps to escape from that demon interference I was firing at it.

The yellow bands clearly show the whacks of interference I was firing at the XPS.

Again it just stubbornly refused to move to a clean channel. It stayed stuck in the mud so to speak.

[Kiwi]

Step 8.

Well there was only one more way to jolt this thing onto another channel and that was hit it with everything. Full on burst on the same channel, no rising floor. I knew this had not worked for others but if I did not try it then it left a gap and room for debate.

So full strength 2.4 on Ch 11 and still it did not move.

[Kiwi]

Well that about does me on XPS folks. I will not say it does not hop channels as there may be a way that it can. But so far I have:

Raised the noise floor slowly
Pulsed on the same channel
Drowned it with interference

And none of those scenarios causes XPS to swap to a cleaner channel.

SO what's my verdict.

If XPS hops channels then please someone show us on this site and in this thread how, why when and where because I cannot force it to do so, no one else has been successful in doing so. I'm buggered if I know how. I'm out of ideas and scenarios.

I personally would not use this system until its proven.

XPS cannot be made to HOP under reasonable test conditions and circumstances that should force a frequency change.

So after all that I turned off the sig gen and yes sir. XPS was still happily firing away on channel 11.

No thank you.

[aviti]

Thanks Kiwi. I read the post above quoting JD on when the system would hop and either it doesn't make any sense or it's way over my head (quite possible as I'm far from an expert). Does anyone else understand what the heck JD is talking about?

[Kiwi]

Tony,

I'm bilingual and I cant understand it either mate.

Its pure waffle without the cream.

[1bwana1]

Kiwi,
Thanks for your efforts, very interesting. Today, XPS posted a response to the frequency hopping questions. I'm sure you read it. What I would like to see is whether the lack of hopping in the situations you tested in is meaningful to us as fliers. If I read it correctly, XPS implies in their explanation, that the only level of interference that would cause their system to fail, would also cause all of the other 2.4 systems to fail. Does the XPS system see through the interference and continue to offer control, or does it lock out. Since XPS seems to be stuck on one channel, if it fails due to interference then you crash. Spektrum has two channels, so I am assuming that it would continue to work. FUTABA FAAST would probably hop right through it and continue to work. I would really like to see tests on each that would prove, what to an untrained user like me, seems obvious.

Thanks,
STEVE

[cadconversions]

Do you have a futaba / spektrum system to try the similar test on? Also, did the XPS system completely lock out during the test or come through? You never really said one way or the other...

[sweetpea]

Looking forward to the same round of testing against both Spektrum/Fasst/ASSAN.

its getting interesting now!

[Eflyer_75214]

It would be much more interesting if Jim would simply have a 3rd party such as a University or a lab test the system to show that it does or doesn't hop. Basically, put up or shut up. Would make his existing users much more comfortable if they can show it hops and stop the detractors.

Ron

[sweetpea]

In his "Sticky" he put up with his answer to the recent threads he mentioned conditions that would make it hop.

"Does it hop? Yes, it does. Can you make it hop? Probably, but it is going to require some very specific situations for it to occur.

The hopping is predictive, based on the noise floor over a period of time. When the noise increases at a particular rate and pattern, a new frequency can be selected. Can be? Yes, if there are no good frequencies to use, hopping can be more of a problem than not hopping.

So, how did we determine the noise rate and pattern? By flight testing at various locations, including Las Vegas - which we believe has the highest noise floor in the U.S."


I simply asked......."I think this is what most of the so called experts want explained. They want to know the rate and pattern."

It remains unanswered. I for one don't care to see his tests of it hopping. Just explain what conditions are required....plain and simple.

[Daemon]

The problem with the question of "what do the other systems do" is that
we already know what they do with respect to hopping. Spektrum doesn't claim to hop,
(or at least it never moves from the two frequencies it chose at startup)
and FASST hops constantly whether it's needed or not.

One thing not mentioned in the preceding series of tests is how XPS responded
to all this noise? Did you have a link the whole time, or did it lose the link and
drop to failsafe?

I ask because obviously if it maintained the link through all your tests without
going to failsafe, then JD would just say "it's so good that it doesn't' need to hop". Of
course I've knocked it into failsafe about 40 times in the last 24 hours, testing
with my 2.4Ghz video Tx, but I'm curious if your noise generator is doing
that or not.

I think what everyone else is asking for now is a test of responsiveness.
XPS, Spektrum, FASST all running at once, and then run the same series
of noise generation tests across the whole spectrum and see how each system
responds. Loss of link, sluggish response, or completely normal.

BTW, the test you didn't do that, Jim claimed would induce hopping, is
a gradual rise of the noise floor to the point where it does harm to the link,
followed by a small decrease. I think the logic being, that it needs to know it's
in harm's way, but still be able to tell the Tx that it needs to move.

ian

[buttface]

	Quote: Originally Posted by XJet
	Well I"m just trying to throw JD a lifeline here. Obviously, no matter what I, Kiwi or anyone else says in respect to XPS, JD's happy to simply reply by saying "it hops" and then it becomes a "he-says, she-says" situation that likely leaves a lot of people unsure who to believe. If a truly independent testing organisation gets involved, the whole debate over antennas, hopping etc becomes finalized and we'll have something solid to go on. It strikes me that this is by far and away the simplest solution to a complex and important problem. Or do I have this all wrong?

It is apparent that you are NOT bashing JD,how ever hard it must be!And YES we just want some good solid proof.Role in the independent testing organization !!!!I think we deserve some solid proof!You are on the right track Bro! You make sense to me!

[Daemon]

On a side note, JD and others familiar with the Xbee modules have stated that the Rx
drives the whole channel selection process. It's not looking for the Tx at all. It scans for a
channel with a low noise floor at startup and then sits there transmitting "Hi, I'm on
channel X bound to Tx Y, come find me". When Tx Y is turned on, it just scans through all
the channels looking for the Rx sending the message that matches its GUID (really the MAC
of the Xbee module). If you turn the Tx on before the Rx, then the Tx just goes into
perpetual search mode, until the Rx is turned on, does it's own channel scan, selects a
free channel and starts broadcasting its message for the Tx to find.

Could be interesting to see what happens on the spectrum when you turn the XPS Tx
on without the Rx.
Do you see it transmit at all?

ian