Does it Hop? Yes it does
Does it Hop, Yes, it does.
Bij deze de reactie van Jim Drew (XPS):
With all of the so-called experts doing some bench testing, it is time to shed some light on the subject of our frequency hopping.
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.
Using a simple bench test to apply a high power signal (even slowly increased) is likely not going to make it hop. You will find that I stated this last year when we discovered an issue pertaining to having an on-board 2.4GHz video camera. If that camera is activated remotely and is on the same range of frequencies (occupying 4 of the 16 available frequencies) as the XtremeLink, there is no question that there will be a problem. The system will not hop in this case, even though there is a possibility of hopping to a frequency far enough away. But, if the video camera is high powered (500mw or more), it won't matter what you do as the entire noise floor is completely saturated. You will find that NO 2.4GHz radio system will work in this condition. Lower power video cameras can be made to work with our system by making a change to the hopping to include instant noise saturation, and *if* there is an open channel. In practical testing for the last 2 years, we have never seen this occur without it being an on-board 2.4GHz device.
While in Germany, we discussed the frequency hopping issue along with Graupner in a meeting with the technical director of the German equiv. of our AMA. "Dieter" agreed that a simple single band noise saturation test is no where near the condition that we fly our aircraft in, and that unless you have a high power device sitting directly on the receiver, there is nothing available short of Nexrad radar that can cause the level of interference necessary to cause a lock out condition. In Dieter's test, it took a 20db, 100% duty cycle CW wave, using a 15db gain directional antenna nearly touching our receiver antenna, for a failsafe condition to occur. To get this power level while flying a model would require extremely high power levels. Wifi, baby monitors, etc. can not even come close to generating this type of power. We agreed with Dieter when he mentioned that the entire noise floor being elevated is the only real danger for 2.4GHz R/C, and that affects every 2.4GHz system made. Hopping to a non-existant frequency is not going to do you any good. If a 2.4GHz device supports spread spectrum technology, it could be high power and in close proximity. It is only carrier based devices that could every present a problem. A 500mw DX7 transmitter on the same frequency as our 100mw system play nicely together, even when the antennas are taped together and range checked. Although the noise floor goes up, there is no "noise" if the spread spectrum encoding is working. The data gets through with no problems.
How fast can we hop? If you listen to the experts that would like to believe they know our proprietary product better than we do, we can't hop fast. Our system is capable of hopping every single frame, which is all that matters. But, in reality our hardware can change to a new frequency every 350us. However, FCC/ETSI/IC rules clearly state that unless you are hopping on 15 or more frequencies, your maximum hop rate can not be any faster than once every 400ms. We only have 12 channels available to us, so we are not allowed to hop any faster than once every 400ms. Some have been confused about the FASST's FCC ID being DSSS instead of FHSS. They simply hop within the specified time, making them legal. While in Germany, there was a lot of speculation about the Spektrum's hopping being illegal. The Spektrum supposedly does not really "lock on" to 2 frequencies, but rather transmits one time on each frequency separately with the single antenna, thus hopping on only 2 channels, and faster than once every 400ms. We have not really looked into this ourselves, so we don't know if it is true.
So, our system does in fact do what it is advertised to do. Is it "bullet proof"? No way... NOTHING is bullet proof, not even a direct hard line to the aircraft. It is extremely arrogant to believe a system is infallible as these are electronic devices which can fail. We believe that we still have the best system available. We have the only system that actually knows what is going on during flight, knowing when data is not received and having that data re-transmitted when it isn't. We think that is a far cry from reporting a 'fade'. Our electronics are built by a company with every ISO certifiication available, and each piece is x-rayed, optically inspected and compared via computer, and hand tested prior to packaging... all in the U.S.A.
What are our future plans? We will be changing our code to make the receiver boot-up less sensitive to the noise floor. This is why sometimes the LED flashes red on both the transmitter and receiver after powered up (requiring a power cycle of the receiver). Some equate this to losing the binding which really is not be possible. We will also be adding a new hop condition (when possible) for immediate saturation of 2.4GHz noise to accomodate the on-board remotely activated 2.4GHz video cameras.
Some have asked about the ID system we use. We actually pay for IEEE certified "MAC" addresses, like you would see on the Internet. Each 64 bit address is unique (never repeating). This gives us 2^64 possible ID codes that are locked into protected flash ROM, guaranteeing that we will never have a case where two transmitters could control the same aircraft.
Based on the number of systems sold to date and the average amount of flying done by a modeler on any given weekend, we now have millions of successful flights by our customers. Compared to the number of issues reported, we believe this number speaks volumes for the reliability of this system.
, Frequency hoppen is zo belangrijk omdat
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