Independent tests prove lack of frequency hopping with XPS

[Kiwi]

	Quote: Originally Posted by Eflyer_75214
	Hey Kiwi, You buy very expensive servos eh. Per the web site, the Wi Spy 2.4 is $399 and the v1 is $199. Course, when comparing that to a large size model, it is not an expensive item I would guess. For us guys that go with smaller models, would be a good club purchase. Really appreciate the time you are putting in to testing the radios. Will you be able to obtain one of the new Airtronics RDS8000 units to add to the test group at some point? Thanks again, Ron

Ron, sorry for the false info there mate. I was referring to the www.nutsaboutnets.com scanner and software. Thats about $90 but I'm not using it as the driver seems to have issues. Monday I hope to fix that with some help from them and we will be on the road again.

Apologies mate.

[ricoalonso]

Kiwi / Xjet,
Just FYI: you may consider to do additional testing for XPS with different power settings in the Tx module and/or different country settings in the Rx. Someone seems to show that it hopped. Pls check this thread in RCG and read posts specifically starting on post #6 http://www.rcgroups.com/forums/showthread.php?t=815913

Unfortunately, the same person has another post later about his crashed plane with XPS, but one interesting item to note is that his unit seems to be set for another country and the Tx is transmitting at lower power. Here's the other thread: http://www.rcgroups.com/forums/showthread.php?t=816378

Thanks
^R^

[Kiwi]

OK guys,

A day of tinkering and coming to grips with the scanner software and systems.

Sunday is my fly day so I launched myself out of bed early and off to the field I went. Trusty laptop in hand and no plane. Had a prop fail last week and new one wont be here till Wednesday plus I had a new guy to train so it was still an enjoyable day.

OK one of the things I want to do this year is profile the flying fields I visit. Just for my own interests sake and nothing else so the first place was home of course.

Well the field is about 2 miles from an active runway with heavies coming in and out two or three an hour. Military base, loaded with new equipment including F16's etc. So I expected some pretty reasonable traffic as those guys own the airwaves pretty much.

The following screen shots show what the day had in store. Pretty much clear skies. No 2.4Ghz traffic to speak of. We look pretty good here for any system.

What that shot is showing is:
1. the lower graph shows the average traffic in solid green with the peaks or spikes in blue. The yellow line is the live action.

2. the upper graph shows the duration and intensity. Now you can see some faint smokey lines that show some far off traffic but nothing that would would allow you see what it is or suffer any events from. Again this is at ground level + 9 ft so what your airplane will see could and should be a little more. Where this is there are no trees and the ground slopes away for miles. There's not much chance of anything being hidden from the scanner here.

[Kiwi]

OK

I was getting ready to come home when a friend and very adventurous young guy turned up with his powered sail plane and on board video system. Yes you guessed it. 2.4 Ghz. Perfect for another test.

I already had the clean scan so this would show what an on board video setup can do to ruin your day.

This system is on WiFI channel 8 and as I said before this channel thing is really just a rough way of saying where about the signal might appear, its definitely not a precise science with the things I have tested so far.

So lets explain what the scanner is showing.

Lets start in the upper window. Near the center but the highest image (red, green, yellow) line shows the receiver being turned on. You can see it sends a very strong signal when its switched. Its close to channel 8 but more a 7 or a 6. OK the receiver is on but it only fired that burst of energy and then waited.

Twelve seconds later the video transmitter is turned on and you can see what it done. It hit three channels and then locked in. That smokey line above channel 9 shows the spectrum and strength it is using.

Going to the lower graph you can how strong and how spread out that initial burst of energy was. It took up four bands but only for a millisecond. Not enough to knock over a healthy 2.4Ghz RC system.

Something that is new to me and one of the reasons I find playing with this stuff so interesting is that a flat graph like this does not really tell the whole story. 2.4 Ghz appears to be three dimensional. That is the frequency also has depth. So you can have a lot of traffic on one channel so long as one of the transmitters does not hog that frequency with a 100% duty cycle.

I have some new software that I hope will show you how that works. It scans the X axis and Y axis and also the third access (D for me) but you techies will have a better name for it.

So here's what happens when someone arrives at the field and turns on a 2.4 Ghz video system.

[Kiwi]

Gents the reason I have not posted the test on the XPS yet is that now that I understand a little more about this I need that 3D software to see that I am in fact flooding the XPS system. Example: If my Airhorn is only using up 50% of the cycle time that would leave XPS with the other 50% and likely not enough to force the hop.

In the test carried out on RCG the entire frequency was swamped, slowly and quickly. XPS never moved. I somehow think I wont make it move either but what I have found that even hitting the same frequency (say Ch 1) that XPS is running on it does not always go into fail safe. That tells me there may be holes in the signal I am generating and XPS uses those holes.

So far this is all speculation but the new software should be running tomorrow and the information will be a whole lot more complete.

At least we are on it guys and the results will follow I promise.

[KrisW]

	Quote: Originally Posted by Kiwi
	OK I was getting ready to come home when a friend and very adventurous young guy turned up with his powered sail plane and on board video system. Yes you guessed it. 2.4 Ghz. Perfect for another test. I already had the clean scan so this would show what an on board video setup can do to ruin your day. This system is on WiFI channel 8 and as I said before this channel thing is really just a rough way of saying where about the signal might appear, its definitely not a precise science with the things I have tested so far. So lets explain what the scanner is showing. Lets start in the upper window. Near the center but the highest image (red, green, yellow) line shows the receiver being turned on. You can see it sends a very strong signal when its switched. Its close to channel 8 but more a 7 or a 6. OK the receiver is on but it only fired that burst of energy and then waited. Twelve seconds later the video transmitter is turned on and you can see what it done. It hit three channels and then locked in. That smokey line above channel 9 shows the spectrum and strength it is using. Going to the lower graph you can how strong and how spread out that initial burst of energy was. It took up four bands but only for a millisecond. Not enough to knock over a healthy 2.4Ghz RC system. Something that is new to me and one of the reasons I find playing with this stuff so interesting is that a flat graph like this does not really tell the whole story. 2.4 Ghz appears to be three dimensional. That is the frequency also has depth. So you can have a lot of traffic on one channel so long as one of the transmitters does not hog that frequency with a 100% duty cycle. I have some new software that I hope will show you how that works. It scans the X axis and Y axis and also the third access (D for me) but you techies will have a better name for it. So here's what happens when someone arrives at the field and turns on a 2.4 Ghz video system.

Spiffy-kean. . neato. . ultra coolio. . . . .keep it coming Kiwi

[Pale Rider]

Great info Kiwi!! Looking forward to reading more..

Here is a question--does Spektrum toggle back and forth between the 2 channels it picks when it first links up ? Meaning during a flight if the first channel is swamped and it goes to the second channel, does it stay locked onto it (2nd channel) for the duration of the flight ?

[jonkoppisch]

Someone else may have made the xps system hop although it's under strange circumstances...

	Quote: Originally Posted by Eddie-extra
	Hi, Ok I'll try to repeat todays results.... Tested equipment in garage prior to taking it down the field, had a friend over with his Futaba system so thourght we would try and see if there was any issues with cross talk interferance or the like, I had my XPS system powered up and working on my plane without the TX aerial connected, the usb Analyzer on my computer was monitoring the 2.4 bandwidth showing my TX on channel 10 and a few other much smaller signals probably the local computer networks etc. My friend then powered up his Futaba TX to see if would 'interfeer' in any way there was no noticable problems with the XPS system apart from a slight increase in servo buzz he then touched the XPS receiver with his Futaba aerial (extreme i know) whilst the xps Tx aerial was still not connected again no perceivable problems with the xps system. During this time the readout on the USB analyzer showed all the channels were now varying/ peaking with signal which wasnt there previously. The Futaba was then turned off and all the channels returned to no significant signals except a strong signal on chanel 20 and nothing on 10. The XPS system was still working. We then went to the field and flew.... my system had a lockout due to range problems his flew perfectly.....

http://www.rcgroups.com/forums/showt...13#post9125803

[ricoalonso]

Kiwi,
Since someone from RCG was able to make XPS hop by using the FASST signal as the noise source, maybe aside from your plan of subjecting the XPS to a '3D' noise that you can also consider subjecting XPS to a repeatitive (off-and-on) low-level noise.

Since FASST is actually hopping all around the entire band, it will mean that it hit the frequency which XPS is currently using so many times in a given time period. So, maybe (just maybe) if XPS is hit by a 'repeatitive' short-burst, low-energy noise then eventually the hopping is triggered.

Of course, IMO, this doesn't make sense in real application.

Just a thought..
^R^.

Edit:
I just thought of this while posting in another forum... I think I remember XPS saying that the 'counter' is reset when there is a sudden rise of noise.

Now, that makes me wonder about this counter... is it a 'counter' of occurence? If so, maybe it's keeping count of the short-burst noise and a threshhold is set. Maybe once the count of occurences hit the threshhold then the hopping is triggered?
++++

[sweetpea]

	Quote: Originally Posted by JEFFRO503
	Sweatpea..what b do you mean they are the same? All older radios for ground control we're 27.something before the big switch to 75mhz. My M8 ( which is one of the top of the line radio's for surface) is 75mhz . Are you saying that 27mhz and 75 mhz is the same? i don't get it.

Nope......what I'm saying is Ch 4 is 27mhz. It doesn't matter if you are AM or FM. My M8 (I've got one also) is 27mhz FM. I have channels 1-6 in the case. 27mhz only uses Ch 1-6. Anything higher is 75mhz. (on ground freqs)


Here is a good link that will show you all the available freqs and the number that is associated with them.

http://rcsource.hobbypeople.net/faqs/freqlist.htm

[JEFFRO503]

	Quote: Originally Posted by sweetpea
	Nope......what I'm saying is Ch 4 is 27mhz. It doesn't matter if you are AM or FM. My M8 (I've got one also) is 27mhz FM. I have channels 1-6 in the case. 27mhz only uses Ch 1-6. Anything higher is 75mhz. (on ground freqs) Here is a good link that will show you all the available freqs and the number that is associated with them. http://rcsource.hobbypeople.net/faqs/freqlist.htm

AAHHH!!.....i get it! After running the 1/8 scale buggies and truggies for about 4 years , i didn't know this. thanks for the info man.

[sweetpea]

No prob.

Back to the Hopping of XPS......

This most recent test was a little vague on details but here is the skinny.

A guy turned on XPS...noted it was on Ch 10. Then he turned on a FASST system. He noticed RF on all the available freqs (though it was very low in power). Assumed it was FASST hopping around. He then turned off FASST and noticed that XPS was now on Ch 20(or was it 30?).

This wasn't a very technical test at all and it raises more questions.

[ricoalonso]

	Quote: Originally Posted by sweetpea
	No prob. Back to the Hopping of XPS...... This most recent test was a little vague on details but here is the skinny. A guy turned on XPS...noted it was on Ch 10. Then he turned on a FASST system. He noticed RF on all the available freqs (though it was very low in power). Assumed it was FASST hopping around. He then turned off FASST and noticed that XPS was now on Ch 20(or was it 30?). This wasn't a very technical test at all and it raises more questions.

Yes, someone from RCG had tested and noticed that his XPS system hopped from Ch-10 to Ch-20 after they turned on a FASST system, using it as a noise source.

This is why in my post #579 above, I am requesting Kiwi for another test scenario. I am just thinking, that maybe XPS is using a noise occurence counter and a threshhold set for occurences to trigrer a hop.

^R^

[jonkoppisch]

It wasn't quite that simple.. See post #578, but it did seem to change channels although later he had problems with the xps

[ricoalonso]

	Quote: Originally Posted by jonkoppisch
	It wasn't quite that simple.. See post #578, but it did seem to change channels although later he had problems with the xps

Yeah, that's right. I feel sorry for the person. He said he had a poor range-test and someone else pointed out that based on the spectrum graph he posted, his Tx module seems to be transmitting at low power. For now, the cause is still unknown but the poor range test maybe some clue.

But as for the hopping, I still think that maybe by applying multiple short-bursts, low-level (just enough for XPS to notice but not enough to lockout) noise to XPS for several times within a time period may trigger the hop. I think that's why JD made mention of a 'counter' being reset if the noise has sudden rise.

^R^