Independent tests prove lack of frequency hopping with XPS

[jonkoppisch]

I'm sure that this has been brought up, something to remember is that...

xps uses 1 antennae and locks to 1 frequency.... If you get noise or locked out then you end up with what everyone is discussing. Frequency hop???? So far it's a no???

specktrum uses 2 antennas and 2 frequencies. Apparently the way it's setup is that if there's noise on 1 it still has the 2nd (probably locked on a separate apart frequency) + it checks each against the other. If the noise is a short burst then the first is clear to use again. Frequency hop???? No...

fasst uses 2 antennas and multiple frequencies. It's constantly switching and error checking so that if it does see noise it disregards and goes on to the next known frequency. Frequency hop???? Definite Yes!

Just a logical, visual comparison shows that spektrum and fast systems should be 2X as reliable just by using twice the antennas and twice the frequencies for redundancy, right???

[aviti]

The funny thing about it is that after I have read a bunch of info on this, I can't find out if XPS claims it hops or not. I think the jist of what I have read is, it will hop if the noise level gets to a certain point but not if it gets there rapidly. Seems like whatever the findings are by X-jet or others, XPS will say they said that. Maybe I just can't read or understand well enough and someone can clear up for me what exactly XPS is stating about frequency hopping.

[sweetpea]

	Quote: Originally Posted by jonkoppisch
	It's constantly switching and error checking so that if it does see noise it disregards and goes on to the next known frequency. Frequency hop???? Definite Yes! Just a logical, visual comparison shows that spektrum and fast systems should be 2X as reliable just by using twice the antennas and twice the frequencies for redundancy, right???

I don't think it matters if it sees noise or not. FASST hops freqs regardless if its a good signal or not. Time will tell if this is optimum.


I do agree however that more antennas are more reliable for signal reception though. (kinda of why I wish XPS would release the telemetry unit with the satellites rx's they talked about before the system ever became available).

Then it boils down to 3 systems with mulitple antennas(disregarding ASSAN for the moment)

XPS 1 ch but hops when needed (assuming gradual vs burst)
Spektrum 2 ch and stays
FASST hops all the time

For me your choices would then logically be XPS or FASST and if you already own a radio that is not Futaba then XPS is your choice.....as far as redundancy
If you own Futaba then you have 2 choices. (again this assumes that XPS releases the satellites regardless if they say they are needed or not. The customer says they want them)


As long as we keep the thread civil and Xjet posts his results after the new year this thread should remain open.

[jonkoppisch]

According to this chart it does but with condition...

On this page they say.. http://www.xtremepowersystems.net/xtremelink.php

Frequency

• 2.4GHz ISM bands, using intelligent frequency hopping.
• Spherical RF radiation technology eliminates the need for multiple receiver antennas.

The XtremeLink™ uses all of the available frequencies in the ISM band through an advanced patent-pending frequency hopping technique

[XJet]

	Quote: Originally Posted by exeter_acres
	50%.... no flames needed...... this entire thread is a "hesaid, he said" thread..... no substance...... Mods, any reason to really keep this going?? the WHOLE thread is speculation

Excuse me?

I said (after observation and testing) that XPS doesn't appear to frequency hop as advertised.

Jim Drew, the guy who designed and sells the system admits it doesn't frequency hop when hit with sudden high levels of interference.

So an independent tester *and* the manufacturer both agree on this basic point -- yet we still have folks saying "where's the proof" and this thread has "no substance".

Hell, if the manufacturer admits to the fault why on earth would you doubt it? Why would the manufacturer admit to such a major flaw if it weren't true?

And (in light of the number of crashes that fit the profile of a "sudden rise in noise on the frequency used by XPS") isn't it rather important that people are made aware of this limitation just as it was important people knew about the low-voltage reset threshold on the Spektrum gear?

[jonkoppisch]

It's funny. According to the chart there are several iffy or twisted points...

Like the integrated single antennae (like that's a negative )

The resolution I believe is set by the transmitter right? Ex, a 14mz has a higher resolution than a 9c.. So the resolution advertised becomes reliant upon the transmitter??

The receivers pending has been a running joke for quite awhile

Operating voltage range is inaccurate... I'm sure that spektrum is lower than stated and fasst has been tested down to 2.4v

Support for all transmitters??? Maybe they do now but last I knew they didn't

BTW, this chart has been on the site for over a year if I remember right...

[jonkoppisch]

	Quote: Originally Posted by sweetpea
	I don't think it matters if it sees noise or not. FASST hops freqs regardless if its a good signal or not. Time will tell if this is optimum. I do agree however that more antennas are more reliable for signal reception though. (kinda of why I wish XPS would release the telemetry unit with the satellites rx's they talked about before the system ever became available). Then it boils down to 3 systems with mulitple antennas(disregarding ASSAN for the moment) XPS 1 ch but hops when needed (assuming gradual vs burst) Spektrum 2 ch and stays FASST hops all the time For me your choices would then logically be XPS or FASST and if you already own a radio that is not Futaba then XPS is your choice.....as far as redundancy If you own Futaba then you have 2 choices. (again this assumes that XPS releases the satellites regardless if they say they are needed or not. The customer says they want them) As long as we keep the thread civil and Xjet posts his results after the new year this thread should remain open.

I wasnt implying that fasst didn't hop if it was clear, just that it always checks between the 2 frequencies for any noise or corruption

I believe that any 2 antennae receiver would be better than 1. So far it appears despite the claim that xps hops it's indicating the opposite so it appears to be at the biggest disadvantage. I would pick fasst as 1st choice as (not mentioning the same qualities that all systems have in common)

it uses more frequencies for reliability,
has by far the easiest to set failsafe (although it's just on the throttle channel),
it has battery failsafe which none of the others have (which I rate as one of the single most important options 2.4 should have given their inherent vulnerability to low voltage)

2nd would be spektrum as, hey, 2 channels are better than 1!!!!
It has model match
extra remote antennaes

xps if theirs absolutely no other choice and you're using smaller models..

Added: I remember when I first got the xps. I was reading all of the threads and quite a few people were having trouble setting the failsafe. They were inadvertantly setting the power setting to the lowest and having problems. If I remember right, jd even changed some of the software because of this issue. I decided that I wasn't going to mess with the receiver programming to avoid any chance of that....

[BoneDoc]

Who is to say that continuous hopping is optimal? What if the next two channel FASST hops on to is jammed? How dies it know where else to hop to?

[50%plane]

	Quote: Originally Posted by XJet
	Excuse me? I said (after observation and testing) that XPS doesn't appear to frequency hop as advertised.

"Independent tests prove lack of frequency hopping with XPS"

	Quote: Originally Posted by XJet
	Jim Drew, the guy who designed and sells the system admits it doesn't frequency hop when hit with sudden high levels of interference. So an independent tester *and* the manufacturer both agree on this basic point -- yet we still have folks saying "where's the proof" and this thread has "no substance". Hell, if the manufacturer admits to the fault why on earth would you doubt it? Why would the manufacturer admit to such a major flaw if it weren't true? And (in light of the number of crashes that fit the profile of a "sudden rise in noise on the frequency used by XPS") isn't it rather important that people are made aware of this limitation just as it was important people knew about the low-voltage reset threshold on the Spektrum gear?

Seems more like you opened the thread waiting to spill your goodness, and 11 pages later, you still don't offer assertive proof of your accusations. Exeter is correct. It is still just a "he said, she said" thread offering no substance. I don't know your past, but it seems like you're on a anti-XPS tirade, at least from what I read in this thread.

Have a good day!
Chris

[jonkoppisch]

http://www.rcgroups.com/forums/showp...8&postcount=52

JimDrew
Xtreme Power Systems


Join Date: Jun 2005
Location: Lake Havasu, AZ
Posts: 4,105


The frequency hop requires a rise in the noise floor over a number of frames. A sudden saturation will reset the noise "counter" and not switch at all. I have been testing new code that would allow a swap with a sudden saturation. We plan to release that early next year and will show this and other new items at the AMA show in January. This would cure the case where there was a video camera or other high powered radar device turned on and left on.

[Dan767]

Regarding the antenna(s) that XPS system uses. From what I can see, not the best. The picture below is what the broadcast pattern looks like from your antenna. They are both vertically polarized in the XPS system when the receiver is mounted upright. When you roll, the "hole" at the top of the torroid, ("the doughnut" so to speak)and the antenna is pointed at the plane, the signal is at it weakest, causing a null. The reception is weak, causing a possible loss of link between the receiver and the transmitter.

A high noise floor shouldn't cause frequncy hopping, particularly when you're rolling or when the aicraft position causes a weak signal. The receiver gets fooled, thinking the signal is lost, or the noise floor has increased,when in fact the noise floor has remained the same, but looks higher because the signal is weaker. A hop during this event would causes a lost link between the transmitter and the receiver, and loss of control.

From what little I know.

[jonkoppisch]

Oops.. You must not have read about the "The XtremeLink's™ proprietary spherical RF radiation pattern"

That's interesting.. It seems like a rough spot for a single channel unit in that you don't want the hop every time that the plane does an aileron roll (may or may not give a seconds hesitation due to what it takes to do the hop? Surface control info, mod id scan, noise level scan, available freq scan, co-ordinate with module to hop info....) but you don't want it to be locked out indefinitely either. So do you have it hop every time that it sees any noise or loss of signal or leave it locked in??

Maybe I'm totally off base...

You would think that you stand a better chance of surviving with a dual channel unit?