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Old 10-21-2005, 06:37 AM   #1
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Say good-bye to frequency conflicts!!!

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"In case you missed it - From Model Aviation Magazine – May or June 05

BPL, pager transmitters, 2-way communications, noisy electric motor brushes, ignition noise, two transmitters on the same frequency, metal-to-metal noise, bad bearings, all have one thing in common; they all can potentially interfere with your RC system. Wouldn’t you like to say “good riddance” to all these problems? You’d better hang on tight, because we’re in for an exciting ride!

We’re about to witness the biggest step in the evolution of our RC control systems since digital proportional hit the RC world. That was a long time ago, longer than I’ve been in the hobby.

Those that have been paying attention to the RC car world know what’s coming. The RC car hobby has been blessed with a new system for the RF link between the controller and the model called “spread spectrum”. Let’s call it SS. Introduced last year; the first SS system began with a replacement RF module for the existing transmitter and a new receiver for the model. With this, the engineers have been able to work out the potential bugs in such a new innovation. I imagine the car guys were guinea pigs in this grand adventure when it started, like anything revolutionary can be, but just take a look at what it’s done for them in the long run. Now, it’s time to take the next step and put SS into our airborne systems.

Spread spectrum communication is the form of RF communication link that’s used for cordless phones, cell phones and wireless links for laptops. It spreads out the transmitted information to a large number of RF frequencies instead of using just one. There are several methods of doing this, but for now I won’t get into it because I don’t want you falling asleep while reading this. This is an exciting time!

Our traditional RC systems use just one frequency for the RF link to our models. That brings with it a host of problems. Another RC transmitter on the same frequency, a pager transmitter in between our frequencies or a badly tuned RC transmitter on the next RC channel can all jam the guy trying to fly the model. Also, because the receiver is concentrating on a single frequency, anything else that generates enough noise on that frequency can interfere. Motor brushes, ignition noise, bad bearings and metal-to-metal noise could disrupt that precious link to the model.

The requirements for SS operation in the 2.4 GHz band are written such that everything that uses that band must follow the rules and must get along when operated simultaneously. The math whizzes worked this all out in the rules and regulations from the FCC. There are several authorized types of SS that are available for our use, and I won’t get into the details here, but they must all work together in order to get certification. Systems that operate on that band must be “collision proof”, in other words, when signals do happen to cross, they will ignore each other and keep working. It really does work. That’s why several people with wireless links from their laptops can sit together at the airport, surf the Internet, and they don’t interfere with each other. The SS systems we will be using work on the same principle.

A spread spectrum system uses frequencies on 2.4 GHz and spreads the information over that broad band of frequencies instead of concentrating everything in a narrow bandwidth. With the huge bandwidth available comes an advantage. The same information can be repeated a lot more often (redundancies) and checks and balances (checksums) can be incorporated. Anything picked up by the receiver that doesn’t add up right gets tossed out. It happens so much more quickly than our present systems that the occasional drop doesn’t matter. Basically, SS is immune to interference from traditional narrow band sources that thrive in our 72 MHz RC band. The receiver is also locked electronically to that transmitter so they won’t glitch from signals from other transmitters, even if the signals happen to “collide” momentarily during operation.

The AMA is being pro-active in this adventure for several reasons. First, and foremost, is safety. We will be testing the systems as they become available. We must make sure that it is at least as reliable in our type of environment as our current system. We will look at simultaneous pilots flying in close proximity, according to our safety code. We will look at how far away we can fly the model. Adjacent field distances will also be checked out. Cooperation with other equipment on the 2.4 GHz band will also be verified. Suffice it to say that our current frequency management with boards and pins will change. We have the cooperation of the manufacturers involved to make sure that everyone is on the same page when it comes to the use and management of this new technology. Needless to say, it is in the manufacturer’s best interest to make sure that everyone is happy and safe as well. The manufacturers have representatives that sit on the Frequency Advisory Council that works in conjunction with the Frequency Committee.

I’ll stop here, but stay tuned. I don’t want anyone getting glassy-eyed. There will undoubtedly be as many articles written about this as there were about digital proportional back in the good old days. I put together a list of Q&A’s that may help answer questions and dispel rumors.

Enjoy the ride, and be sure to thank all the wireless manufacturers for developing the technology that the RC manufacturers are now taking advantage of.

Q: Will my current equipment become obsolete?

A: The first system uses existing transmitters with a new RF module, but the receiver must be new.

Q: I like operating one transmitter with multiple models, which means that I will have multiple receivers. What will I do with this system?

A: Each system has its own way of dealing with multiple receivers, but generally the receiver will be programmed one way or another to only listen to that transmitter signal, so that in the even that “collisions” in the spreading signals occur, the receiver will only listen to its transmitter.

Q: Will this new system affect systems on the current frequencies?

A: The new systems work on 2.4 GHz, a long way from any of our current RC systems on 72 MHz, 50 MHz and 27 MHz. There will be no interaction, but that is one of many things that AMA will verify.

Q: Will our 72 MHz or 27 MHz RC frequencies go away?

A: There are no plans for giving up our RC frequencies on 72 or 27 MHz. Your current equipment is safe!

Q: The AMA Safety Code specifically calls out the bands and frequencies that I can use. Will I be able to use my new SS system at my AMA chartered club?

A: The AMA goal with the system testing is to make changes to the safety code as necessary to accommodate the new systems. The AMA wants to encourage the technology, not hinder it.

Q: Will I be able to use my new SS system in competition?

A: The AMA will examine changes necessary to accommodate competition both nationally and make recommendations and work internationally with the FAI.

Q: Will I be able to bury the antenna inside my scale model?

A: This may depend on the manufacturer of the radio system as to where the antenna may be placed inside the model. At 2.4 GHz, and with models at just about any orientation during flight, the receiver antenna is obviously a critical element. This was a definitely a design issue during development and may continue to be so as the systems evolve.

Q: How many transmitters will be able to operate simultaneously at my field?

A: This is something that must be worked out as part of the testing. Transmitters must work together as part of the requirement in the standards. Just how many at a time can operate reliably is still to be determined and may depend on the type of SS technology that they use. There is a point where the band can “fill up” with all these SS signals, and each type of system may start to degrade in performance, called “graceful degradation”, but no one will get locked out. Depending on the SS system, each transmitter will listen before starting to transmit its SS signal so that it can cooperate with the other transmitters and not interfere. This is part of the “getting along” process.

Q: Will my cell phone or pager cause interference with the new SS system?

A: Cell phones and pagers, if using the same 2.4 GHz band as the new SS systems, must follow the same rules. They must get along. To be certified, they must comply with the rules and get along so they won’t interfere with each other.

Q: Will cordless phones cause interference at the field?

A: All equipment on the 2.4 GHz band we’re using “must” work together. Because of the spread spectrum characteristics, they will ignore each other.

Q: Will my servos respond slowly during any time with SS?

A: The slowness of response is called “latency”. It’s the time it takes between movements of the stick to movements in the servo. The SS manufacturers, as part of their design effort, are making sure that their system will operate at least as well terms of latency as our current systems. As the band begins to fill up from many transmitters on the band doing SS, there may become a time when there are so many collisions that latency is compromised. This is part of what AMA will be looking at for safety reasons. Depending on the form of SS being used, this may never be a problem.

Q: Will my club be able to get rid of the frequency board at our field?

A: Probably not as long as anyone flying at the field continues to use traditional RC systems. In reality, that will continue for a long time. If your club hosts contests or fly-ins of any kind, traditional systems will continue to show up during the registration process. You don’t want to be turning these people away.

Q: Will our club still need a transmitter impound?

A: If traditional systems are still being used at your club, the impound will be necessary. If, however, you have one of the new SS systems and go to a fly-in or contest, you may still be required to turn your SS transmitter in to the impound, based on that club’s rules. Don’t give them grief; it’ll take some time for all to get used to the new ways of dealing with SS.

Q: Is this truly RC nirvana?

A: Well, although it appears that way right now, everything eventually shows up with some compromises. Nothing is perfect. There may be issues; we just don’t know what they are yet. Suffice it to say that SS will continue to evolve and it may come to a point where we can just worry about dumb thumbs again. "
Ron Mattiuz

Flying Tigers RC Club
"Flying an airplane is just like riding a bike...except it's harder to put cards in the spokes"
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Old 10-21-2005, 09:18 AM   #2
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If it lives up to its promise, there will be another excuse gone for that unexplained crash. Just fingers, or bad connections, both of which come back to the operator. That may not be good for me.
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Old 10-21-2005, 09:31 AM   #3
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Originally Posted by Dave Holmes
If it lives up to its promise, there will be another excuse gone for that unexplained crash. Just fingers, or bad connections, both of which come back to the operator. That may not be good for me.
LOL, thats funny
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Old 10-21-2005, 01:56 PM   #4
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The author of this article is a little over optimistic of what 2.4Ghz and DSS have to offer. I just want to pull this article down closer to reality.

One point I would like to clarify right now:

The article is wrong that different devices on 2.4Ghz "must" work together. This is NOT true. One of the operating conditions from Industry Canada in the back of my cordless phone manual is written as follows:

#2 This device must accept any interference including interference that may cause undesired operation of this device.

DSS is a hybrid of FM transmission whos purpose is to encrypt the outgoing transmission and improve immunity to interference. The carrier signal is still analog and is subject to the laws of the analog universe. I am saying they are still subjet to interference.

Is DSS a good system.................Yes
Is DSS infallible..........................No
Is DSS immune to interference....No (I only said "improve")
Is 2.4Ghz already too crowded.....Yes

This is an attempt by manufacturers to keep up the price of their products by offeringselling new technology at a premium.
I can say with confidence that there is nothing DSS can offer that will be miles ahead of what we already have. There will be some benefits here and there....but there will also be some drawbacks.

Thanks for the heads up Ron.
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Old 10-21-2005, 02:18 PM   #5
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Do we not already have most of this with PCM (pulse code modulation) tx' and rx's??
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Old 10-21-2005, 06:41 PM   #6
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There is also a problem with range!
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Old 10-21-2005, 07:09 PM   #7
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I think it's an excellent idea and a long time coming. Cell phones have been using this technology for two decades and the car guys have been using it for a few years now.

The problem with 2.4ghz though, too crowded as somebody else said. Think cordless phones, Bluetooth, Wireless 802.11g signals. home intercoms, etc.

Is DSS immune to interference....No (I only said "improve")
Well, the technology is there to limit it. Apple's AirPort wireless system uses a feature called "Interference Robustness" to filter out signals that are not 802.11g signals in high trafic areas. Not fool proof but it does help. There must be a more suitable frequency out there.

Do we not already have most of this with PCM (pulse code modulation) tx' and rx's??
I don't know too much about RC radio technology but I think I can say no. PCM radios send a clearer signal than FM as it allows the RX to 'double check' commands. There are also variable frequency modules for them. However, it won't select a clear channel for you.

The big problem with new technology (as one of the car guys told me) is a lot of "nostalgic" pilots are very reluctant to adopt it. Some guys still think cell phones and RC car transmitters interfere with their plane. Even if the bugs could be worked out, it still takes a while to get this stuff mainstreme.
Currently driving: HPI Savage X SS 4.6 / Traxxas Mini E-Revo
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Old 10-21-2005, 08:20 PM   #8
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TX power will be an issue. Every time you double the frequency, you need to increase the power by 4 times (the square) to achieve the same range.

DSS and PCM are both FM technologies and will obviously be digital. The big difference is DSS can use a wider bandwidth to gain noise immunity against random noise.
However if 2 transmitters were to be on the same frequency you will still get locked out due to the digital nature.

I am not so hot to see this technology emerging for RC planes even though I work with it every day and have seen benefits for other products. It is not bad for the RC car guys because range is not an issue and a lockout will not total their cars.
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Old 11-06-2005, 07:53 PM   #9
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I agree with Tech 1 and many of the comments above.

I feel that this is a ruse to sell new equipment at higher prices. The radio equipment we currently have is so good there is no need to buy different transmitters for different frequencies or dedicate a transmitter to each plane anymore.

Those who are concerned about 2.4 ghz range problems are absolutely right.

I have seen this degradation of range happen before, when the City I worked for changed from 145 mhz to the 800 mhz. The transmission range on hand held radios was severely compromised. They had to install several repeater stations to cure the range problems.
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Old 11-06-2005, 08:01 PM   #10
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New JR radio

I just got back from the JR indoor festival in Columbus Ohio. JR showcased this system at this event. We counted 27 planes in the air at one time on Saturday. The JR guys were flying all weekend with the new radio. I'll be getting one when they come out. The only feature missing for me is exponential on the rudder.
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