Kiwi's XPS test results are up.

[JimDrew]

	Quote: Originally Posted by Daemon
	Short answer, using the current 2.4Ghz XBee modules. No. Because it is two way, the satellite receivers are at best, dumb, and at worst a liability. They can't transmit ACKs without interfering with the main Rx's ACKs (you'd actually be creating multipath interference at the source) so if the main Rx antenna is blocked, and the satellite receiver antennas are not, the Tx will still think it has lost the link, even though the Rx is still getting signals from its satellites. That'd be ok, if it was meant to always be a one way system, but it's not.

People forget that we use only the XBEE hardware. The firmware is our own, and if you look at the chipset used with the XBEE, you can clearly see that multiple receivers can be used and the ACKs will not collide.

	Quote: Originally Posted by Daemon
	As for hopping, it can be done, but it's always going to be *slow*, again because the two way nature gets in the way and it's tough for both ends of a two way link to know for sure if the link is 100% broken or only 50% broken, and you risk more by hopping when it's 50% broken than you would by staying put.

That is completely wrong. We can support 5ms frames, complete with ACKs and change frequencies every single frame. Frames are typically every 22ms. Think that is slow, well I have some news for you. Spektrum frequency hops every frame between two frequencies. They don't "lock on" to two channels as they claim. Every 22ms, the data is transmitted to the other frequency. Interesting too, since their FCC ID clearly shows their system to be a DSSS configuration. Part 15.247 clearly states that any device changing frequencies faster than once every 400ms/dwell is required to occupy no fewer than 15 channels. Hopping every frame is not legal by these rules. When I added the "hop on saturate to foil the bench testers code", I asked for clarification from the FCC on the hopping speed and we either have to transmit with a psuedo-random 15 frequency algorithm, or we can not hop faster than roughly once every 300ms, which is actually faster than the 450ms spacing we had in the original hopping code. So, it was a benefit to look into this.

[KrisW]

	Quote: Originally Posted by JimDrew
	People forget that we use only the XBEE hardware. The firmware is our own, and if you look at the chipset used with the XBEE, you can clearly see that multiple receivers can be used and the ACKs will not collide. That is completely wrong. We can support 5ms frames, complete with ACKs and change frequencies every single frame. Frames are typically every 22ms. Think that is slow, well I have some news for you. Spektrum frequency hops every frame between two frequencies. They don't "lock on" to two channels as they claim. Every 22ms, the data is transmitted to the other frequency. Interesting too, since their FCC ID clearly shows their system to be a DSSS configuration. Part 15.247 clearly states that any device changing frequencies faster than once every 400ms/dwell is required to occupy no fewer than 15 channels. Hopping every frame is not legal by these rules. When I added the "hop on saturate to foil the bench testers code", I asked for clarification from the FCC on the hopping speed and we either have to transmit with a psuedo-random 15 frequency algorithm, or we can not hop faster than roughly once every 300ms, which is actually faster than the 450ms spacing we had in the original hopping code. So, it was a benefit to look into this.

Is it possible that Spektrum has two transmitter sections in each module, retransmitting the same data and encoding, but on two different frequencies? Seems like every Spektrum receiver I've ever seen has two antennae. . possibly two receiver sections per unit??

hmmmmm. . something to think about, eh? Not that I know. . just that the possibility seems plausible if there are laws and such against single transmitters doing certain things.

After all this time, I'd expect JD to have something better to throw our way than "but. . but. . but SPEKTRUM. . .etc etc etc. . . ."

so, the question then remains, IF XPS is so. . . agile. . .WHY doesn't it ever hop??? AndIF you coulduse multiple receivers. . WHY don't you do it?

Anyone ever seen a video proving that it can, or does? I certainly haven't.

[aviti]

	Quote: Originally Posted by JimDrew
	People forget that we use only the XBEE hardware. The firmware is our own, and if you look at the chipset used with the XBEE, you can clearly see that multiple receivers can be used and the ACKs will not collide. That is completely wrong. We can support 5ms frames, complete with ACKs and change frequencies every single frame. Frames are typically every 22ms. Think that is slow, well I have some news for you. Spektrum frequency hops every frame between two frequencies. They don't "lock on" to two channels as they claim. Every 22ms, the data is transmitted to the other frequency. Interesting too, since their FCC ID clearly shows their system to be a DSSS configuration. Part 15.247 clearly states that any device changing frequencies faster than once every 400ms/dwell is required to occupy no fewer than 15 channels. Hopping every frame is not legal by these rules. When I added the "hop on saturate to foil the bench testers code", I asked for clarification from the FCC on the hopping speed and we either have to transmit with a psuedo-random 15 frequency algorithm, or we can not hop faster than roughly once every 300ms, which is actually faster than the 450ms spacing we had in the original hopping code. So, it was a benefit to look into this.

If you can't dazzle them with brilliance, baffle them with BS. Thanks for clearing all this up Jim. I'll put my Spektrum gear up for sale and convert to XPS immediately if not sooner.

[JimDrew]

	Quote: Originally Posted by KrisW
	so, the question then remains, IF XPS is so. . . agile. . .WHY doesn't it ever hop??? AndIF you coulduse multiple receivers. . WHY don't you do it? Anyone ever seen a video proving that it can, or does? I certainly haven't.

The reality is that we don't fly models on a bench, and certainly not within inches of a WiFi device hooked to a computer. The power output required to cause what is demonstrated here while flying would cause the saturation of the entire 2.4GHz band (above and below 2.4GHz), and not a single frequency. A good example of this is the flying field in Davis, CA. The Nexrad that sits just a few miles away from the field transmits on 2.7GHz, yet 750,000 watts appears to bleed over so badly that none of the 2.4GHz systems will work. They won't even connect if they are within a mile of the tower. Hopping when there is nowhere to go is a bit foolish, and that the reality of the environment that we use our radio systems in.

According to the FCC, you are not allowed to even attempt to transmit data if the noise floor exceeds a certain threshold (-36 db). In the bench testing that has been done, our system may not be prevented from receiving data, it may no longer be transmitting data. I just read the forum here, and I ordered two of the Airhorns. We use 2.4GHz video transmitters for testing here now. We have a couple of more issues to wrap up with the FCC and we can release the new firwmare that will make the bench testers happy. A lot of work for a simple show. I can't wait to see what's next.

The current hopping algorithm was created by using real world tests to generate a noise pattern that must occur. I am not sure how you would generate this pattern with the Airhorn, and since I am not yet familiar with the Airhorn, I can't speculate how you would accomplish it. I do know that if you take off on channel 1 and you land on channel 7 (as some have already reported), then obviously something must have occurred. If the system didn't hop at all, we wouldn't have a few angry customers who used 2.4GHz video cameras on board that were remotely activated. The system can hop on to the same frequency range that the camera uses while it is off. Switching it on, yields a lock out since there is a complete saturation of the frequency, and the receiver is programmed not to move in these cases as typically enough power to cause the lockout means the entire band is wiped out. The solution: don't use a 2.4GHz camera with any 2.4GHz system.

Our antenna's spherical radiation pattern (recently confirmed again with anechoic chamber tests) provides an omni-directional antenna. With this antenna and our bi-directional communication, we have not found a genuine need for multiple receivers. However, to appease the masses, we will be releasing satellite receivers. These are part of our telemetry package, which allows up to 64 devices to be connected to the telemetry port. So, you could have up to 65 receivers in your aircraft. This does not add "antenna diversity" (which everyone claims to have a patent pending for), it adds redundant receivers in case of primary receiver failure.

[klhoard]

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I think you're yelling into an empty stadium, JD. . .
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[XJet]

	Quote: Originally Posted by JimDrew
	The reality is that we don't fly models on a bench, and certainly not within inches of a WiFi device hooked to a computer.

Sometimes the only way to test for certain conditions in a repeatable scenario is to emulate potential "real-world" situations on the bench. You don't do that?

	Quote:
	The power output required to cause what is demonstrated here while flying would cause the saturation of the entire 2.4GHz band (above and below 2.4GHz), and not a single frequency.

I strongly disagree.

	Quote:
	A good example of this is the flying field in Davis, CA. The Nexrad that sits just a few miles away from the field transmits on 2.7GHz, yet 750,000 watts appears to bleed over so badly that none of the 2.4GHz systems will work. They won't even connect if they are within a mile of the tower. Hopping when there is nowhere to go is a bit foolish, and that the reality of the environment that we use our radio systems in.

Have you actually determined if this is due to sidebands on the 2.7GHz signal or simply front-end overload in the receivers?

	Quote:
	According to the FCC, you are not allowed to even attempt to transmit data if the noise floor exceeds a certain threshold (-36 db).

That's odd -- because testing seems to indicate that XPS *does* continue to transmit, even when noise levels far exceed the -36dB you quote. Does that mean you're not FCC-compliant?

	Quote:
	The current hopping algorithm was created by using real world tests to generate a noise pattern that must occur

Are these "real world tests" related to the ones you did before claiming that a transmitter dipole was completely unnecessary?

	Quote:
	If the system didn't hop at all, we wouldn't have a few angry customers who used 2.4GHz video cameras on board that were remotely activated. The system can hop on to the same frequency range that the camera uses while it is off. Switching it on, yields a lock out since there is a complete saturation of the frequency, and the receiver is programmed not to move in these cases as typically enough power to cause the lockout means the entire band is wiped out.

You keep making this claim and I continue to refute it. Your "real world" seems decidedly different to the one I live in and the one that many folks have to fly in Jim.

And if XPS's hopping algorithm is so good -- why, in the tests conducted here, did XPS stop working when JR/Spektrum and FASST coped without any problems? This must surely be the single most important question that needs to be answered. You won't try to dodge that one will you?

	Quote:
	Our antenna's spherical radiation pattern (recently confirmed again with anechoic chamber tests) provides an omni-directional antenna.

Please tell me where we can see the 3-dimensional plots of this pattern. I've asked for this data from you I don't know how many times but all you've offered is the 2D plots from Maxstream. If you now have that data (which you seem to be claiming) I'm sure we'd all like to see it for ourselves -- otherwise it's hearsay.

	Quote:
	With this antenna and our bi-directional communication, we have not found a genuine need for multiple receivers.

So how do you cope with shadowing in a large model where it's impossible to position the receiver so that the signal isn't going to be blocked by a major metal or composite structure from some angles. The antenna's radiation pattern doesn't matter one sack of beans if it's shadowed and the same goes for resending the data. If the receiver remains in the shadow, it will not receive the data and it's "lockout time".

	Quote:
	However, to appease the masses, we will be releasing satellite receivers.

Why don't I believe that this is the sole reason?

	Quote:
	These are part of our telemetry package, which allows up to 64 devices to be connected to the telemetry port. So, you could have up to 65 receivers in your aircraft. This does not add "antenna diversity" (which everyone claims to have a patent pending for), it adds redundant receivers in case of primary receiver failure.

So what you're saying then (if it's not diversity) is that the secondary receiver(s) will not function unless the primary receiver fails (otherwise it *is* diversity).

Will you be able to run telemetry *without* a satellite receiver?

Can you give us a timeline?

Can you also elaborate on the situation in Europe? Graupner appears to have been giving quite a few refunds and taking back XPS gear with increasing regularity there. Are there special issues in this market?

[zoomer260]

Shock and Awe. WOW !! Mr. Drew please show us how XPS hops. That is how this thread came to be. And how a single channel 2.4 system can be any better than half of one that uses two ? Or more ?

I have not been able to convert yet and I was all over your advertisements which are hard to find these days.

You want my money defend your product.

[Reckless Loony]

Here is something people might find interesting.

http://www.automags.org/forums/showthread.php?t=116538

The interview link is dead but reading that forum one notices that JD managed to get 3 degrees while he was still in high school. If the guy really did earn those degrees instead of buying them over the Internet including a degree in Electronic Engineering then why did he go on about the spherical radiation pattern?

This is the only way to get a spherical radiation pattern

http://en.wikipedia.org/wiki/Isotropic_radiator


There is a saying “A leopard can’t change his spots”. There is also Dr Phil who said (not exact quote) ‘A persons past behaviour is an indicator of future behaviour’

Here is a small snippet of JD’s past.

http://www.emaculation.com/forum/vi...0ac31a6838451ac

http://www.pbnation.com/showthread.php?p=26376318

http://www.automags.org/forums/showthread.php?t=116914

http://www.automags.org/forums/showthread.php?t=203358


Note his two previous businesses were Microcode Solutions and Wicked Air Sportz.

That should give an idea in the direction XPS is headed.


Now as for this hopping thing

The user manual for the Digi 2.4Ghz RF modules that JD uses

http://ftp1.digi.com/support/documen...5.4_v1.xAx.pdf

Now look at the XPS website

http://www.xtremepowersystems.net/xtremelink.php

“predictive frequency hopping technique”

Predictive?? You mean those modules have crystal ball technology or is there a clairvoyant circuit? How the hell are you supposed to be able to predict when a 2.4Ghz device gets turned on and off?

Try this next time your at the flying field. Get a pad and pen and sit down in the pits. Watch your fellow modellers turn on their radios and note this down in the pad also note those that are turning off radios. Pretend all these radios are 2.4Ghz sets. Once you have made a nice list (a table) see if that helps you in determining (predicting) those that are about to turn on their radio next and those that are going to turn off their radio next. You will find it will be pretty much random unless of coarse it is close to lunch and then most club members will stop flying for the club lunch barbecue.

So how are these Digi 2.4Ghz modu