Independent tests prove lack of frequency hopping with XPS

[Kiwi]

Gents,

I have all the tests and videos pretty much finished. I just need to get the related banner adverts done for the forum as all the scanner equipment and signal generation stuff was very kindly donated to FG so we could get the best possible results yet keep it simple enough for a laymen like me to understand. I owe them the decency of telling everyone where to go and buy one of these things if you want one or your club wants something.

No sneak previews until thats ready sorry but facts that are well known is;

FUTABA hops and never stops.
SPEKTRUM looks for and selects two channels with as much spacing as possible.
ASSAN is a single channel non hopping system.
IMAC (not tested) but is the ASSAN hardware.
AIRTRONICS (not tested)
XPS, cant make it hop so far.

The vids are interesting and show a lot that I cant explain in words. Sorry for being slow here guys but time has been pretty hard to get lately with the business demanding a mega amount of attention. But its nearly done, lock stock and barrel.

[BaldEagel]

According to a pic in one of the UK mags, Graupner are about to come out with a dedicated RC set using the IFS technology, this is XPS in all but name, it would seem that Graupner have expended quite a large investment in the JD system, I have through my supplier been keeping Graupner UK up to date on development here, at this time they have my module and Rx and are testing to see if it works, I have asked that they give me unequivical proof that it hops not just that it works.

As Graupner are quite a large supplier of RC stuff, I would think that their international reputation could be given a substantive blow by the results if it is proved to not act in accordance with their own advertising, so I don't hold out much hope that they will come back with a result showing the unit's lacking, what I am hoping is that after testing, they show good will and return my monies.

Mike

[dick hanson]

	Quote: Originally Posted by Kiwi
	Gents, I have all the tests and videos pretty much finished. I just need to get the related banner adverts done for the forum as all the scanner equipment and signal generation stuff was very kindly donated to FG so we could get the best possible results yet keep it simple enough for a laymen like me to understand. I owe them the decency of telling everyone where to go and buy one of these things if you want one or your club wants something. No sneak previews until thats ready sorry but facts that are well known is; FUTABA hops and never stops. SPEKTRUM looks for and selects two channels with as much spacing as possible. ASSAN is a single channel non hopping system. IMAC (not tested) but is the ASSAN hardware. AIRTRONICS (not tested) XPS, cant make it hop so far. The vids are interesting and show a lot that I cant explain in words. Sorry for being slow here guys but time has been pretty hard to get lately with the business demanding a mega amount of attention. But its nearly done, lock stock and barrel.

I am not surprised that there are new comers - look at the new teeeeny toy models from ParkZone - these 3 gram radios are --2.4 DSM2- and compatible with the Spektrum radios -a new budget 5 channel is also available .
With all the stuf on th market - how someone new could NOT get it right -at even very low price -would really surprise me I have two ofthe Cessnas -two radios each is 2.4 -you can watch em link up - and -one will NOT fly the other
I mentioned to JD last summer that the real threat will come from VERY low cost model toy builders
mebbe I am wrong -
I fly DSM2 in everything and nary a problem.

[Daemon]

	Quote: Originally Posted by Kiwi
	AIRTRONICS (not tested)

As the name Airtronics FHSS implies, it also hops and never stops, and will hop
right into severe interference and out again, like FASST. My testing with
a 500mW 2.4Ghz analog video Tx + XPS + Airtronics FHSS show the latter
hopping into the middle of the video transmission every 2 seconds or so.
It may be a pseudo random hopping sequence, but it also appears to repeat itself
on a very regular cycle. Wish I had an FASST system on hand to test the same way
to see if it does the same thing.

ian

[Reckless Loony]

	Quote: Originally Posted by jonkoppisch
	Interesting post... It probably wont last long though... http://www.rcgroups.com/forums/showp...&postcount=127

He also posted at the end of this thread

[Flyfast1]

	Quote: Originally Posted by Daemon
	As the name Airtronics FHSS implies, it also hops and never stops, and will hop right into severe interference and out again, like FASST. My testing with a 500mW 2.4Ghz analog video Tx + XPS + Airtronics FHSS show the latter hopping into the middle of the video transmission every 2 seconds or so. It may be a pseudo random hopping sequence, but it also appears to repeat itself on a very regular cycle. Wish I had an FASST system on hand to test the same way to see if it does the same thing. ian

Interesting, so the Airtronics FHSS system has no adaptive FH. Even in the presence of severe interference on certain channels it continues to use those channels.

-Ed B.

[JimC-MD]

I thought on the pictures loaded up of the Futaba working along with the XPS and Noise unit such you could see Futaba doing the same thing. You could distinctly see the small spikes of the Futaba signal right through the XPS system and the noise signal. If it avoided any potential area of other transmissions, then it would not get much done in a noisy or active area, I would think. These are not the same types of communication as old systems. Just because there is something on a "channel" does not mean you cannot get your message across. Right? If you are thinking or been told that the Futaba system will "hop around" the noise that is out there, the scan image does not support that claim. Look at it closely and you will see the 30 odd spikes right through the other signals.

[XJet]

Since none of the FHSS systems currently in use for RC model use are bi-directional they are not adaptive.

There's no way for the transmitter to know that there are bits of the spectrum which are noisy from the receiver's perspective so they simply use a pseudo-random hopping sequence regardless of other activity on the band.

This isn't a problem however, since the presence on the timeline of each frequency is so low it won't interfere with any other system and the packet-losses that may occur as a result of noise are so small as to be inconsequential under normal circumstances.

It's a simple and pragmatic solution that works well in practice.

[4*60]

...

[XJet]

	Quote: Originally Posted by 4*60
	Inconsequential! Proof please?!

Can you show me where (outside of Futaba's ZGUID issues) a FHSS RC system has shot down another SS RC system?

Even second-tier systems such as XPS, Assan, iMax, etc will be unaffected by an FHSS system such as Futaba, because the signal is only present for an extremely short period of time and has a different chipping code even when it is on the same frequency.

If you're extremely unlucky you might lose one in a thousand data-packets as a result of an FHSS system stomping on your channel -- but I defy any flier to notice that level of loss in actual use.

Do any Spektrum users with the logging system active find they read a significantly higher number of lost packets when flying alongside a FASST system?

[dick hanson]

	Quote: Originally Posted by XJet
	Can you show me where (outside of Futaba's ZGUID issues) a FHSS RC system has shot down another SS RC system? Even second-tier systems such as XPS, Assan, iMax, etc will be unaffected by an FHSS system such as Futaba, because the signal is only present for an extremely short period of time and has a different chipping code even when it is on the same frequency. If you're extremely unlucky you might lose one in a thousand data-packets as a result of an FHSS system stomping on your channel -- but I defy any flier to notice that level of loss in actual use. Do any Spektrum users with the logging system active find they read a significantly higher number of lost packets when flying alongside a FASST system?

Yeh, Shakespere said it best "Much ado about nothing".

The basic setups make it almost like confetti just blowing thru
2.4 by nature of whut it is - allows lots of stuff to bounce around and not bother other signals --cause if it did it would not be allowed to play

[Cherokee Jim]

Hello All,

You might like to check out the Xbee Pro web site to study up on the Base of the XPS system.

Check out the following:

http://www.digi.com/technology/rf-ar...e-immunity.jsp

Receiver Sensitivity:

http://www.digi.com/technology/rf-ar...ensitivity.jsp



Frequency hopping is built into the Xbee Pro base system, need a little more info though to understand how they work their system.

There are a lot of people who are very happy with the XPS system and have a lot of flying time on the radio without problems. JD needs a glitch counter like Spektrum so we can see whats happening in the air - signal loss, frame misses, low voltage. I am bet far more folks will as always have 10,000 more problem with their batteries than with their XPS System.

Happy Flying,
Cherokee Jim Mahoney

[XJet]

	Quote: Originally Posted by Cherokee Jim
	Frequency hopping is built into the Xbee Pro base system, need a little more info though to understand how they work their system.

Jim, there is no need to shout -- the standard font works just fine!

I'm sorry but you need to go back and read what MaxStream (aka DigiChip) actually say about the XBeePro 2.4GHz modules.

They do *not* have frequency hopping built into the base system. What they do have is the ability for the user's firmware to select a different operating channel if required. That is a far-cry from frequency hopping.

Read the second page of the Spec sheet and you'll see that these are DSSS (Direct Sequence Spread Spectrum) modules, not FHSS (Frequency Hopping Spread Spectrum).

The user's software can set the channel on which the modules operate but to try and force them to become frequency-hopping systems by some software kludge would be a waste of time and create all manner of problems.

There are people here who know the XBeePro systems intimately (even better than JD) and the consensus is that the XPS system can't be made to offer robust frequency agility.

I also notice that was Jim's first post and that he's a new member.

[BaldEagel]

	Quote: Originally Posted by Cherokee Jim
	. There are a lot of people who are very happy with the XPS system and have a lot of flying time on the radio without problems. JD needs a glitch counter like Spektrum so we can see whats happening in the air - signal loss, frame misses, low voltage. I am bet far more folks will as always have 10,000 more problem with their batteries than with their XPS System. Happy Flying, Cherokee Jim Mahoney

The reason for that is all the people who are unhappy don't fly it anymore, the system does not glitch it holds the last command, never had a problem with an airbourne battery ever.

I made a commitement too the XPS/Graupner IFS system to the tune of over £500.00 that's approx $1000.00 it locked out four times on my interferance prone site and will not go back into another plane of mine, just for your information the Rx was mounted high in the canopy and all the leads where taken immediatly down to the bottom of the fus out of the way of the aerial.

Another JD fan asked to come on I suspect.

Mike

[KrisW]

[quote=Cherokee Jim;430896]Hello All,
You might like to check out the Xbee Pro web site to study up on the Base of the XPS system.
Check out the following:
http://www.digi.com/technology/rf-articles/interference-immunity.jsp
Receiver Sensitivity:
http://www.digi.com/technology/rf-articles/receiver-sensitivity.jsp

Frequency hopping is built into the Xbee Pro base system, need a little more info though to understand how they work their system.
There are a lot of people who are very happy with the XPS system and have a lot of flying time on the radio without problems. JD needs a glitch counter like Spektrum so we can see whats happening in the air - signal loss, frame misses, low voltage. I am bet far more folks will as always have 10,000 more problem with their batteries than with their XPS System.

Happy Flying,
Cherokee Jim Mahoney
[/quote]

Jim. . just a logical question in rebuttal to what you wrote.

If there was no problem with the XPS system. .

WHY ARE SO MANY PEOPLE COMPLAINING?????

People don"t complain about a system that works as advertised and has no problems, do they? Coming out and declaring "many people are happy with it and never have a problem" does NOT make it a good system when other people have all sorts of issues and lost aircraft while using it.

If it can't be a GOOD system 100% of the time, AND do everything that the manufacturer says it will, then it has issues, and those issues should be examined very closely.

Face it. . XPS has severe limitations. Those limitations make it something to be wary of. If you are truly conscientious and caring about your hobby, the limitations and problems associated with XPS will make you use another 2.4 system, simply to avoid the problems that so many people have encountered. NOT doing so, especially in very large or fast aircraft, is IMHO extremely irresponsible.