How Digital Spread Spectrum Radio Control Systems Came To Be
2.4 GHz Digital Spread Spectrum Radio Control System.
The following is an explanation of how AUAV developed the worlds first production Digital Spread Spectrum RC system for the remote controlling of Unmanned Air Vehicles(UAV's) and Radio Control model airplanes. You have most likely heard that Horizon Hobby was the first to produce a production Digital Spread Spectrum RC system this is not true
AUAV was the first I'll explain how and why.
Why We Chose Digital Spread Spectrum Technology.
First we chose digital spread spectrum for it's tight security and outstanding ability to reject intentional or unintentional radio frequency interference, this is a very big advantage when comes to controlling a UAV or a Radio Controlled model. Digital Spread Spectrum technology is not new it has been around for many years. It's first use was primarily by the military in the 1940s and 50s for communication systems to send and receive secure data. It has only been since about 1985 that it's been available for use by the general public
What we were planning to do.
We were looking into conducting a flight of a 10 ft UAV to an altitude of 30,000 ft.
After giving this task a great deal of thought, one of our biggest concerns was how do you insure that you have relievable control of the aircraft.
We had planed to fly most of the flight under autonomous control but we still wanted to have the ability to take over manually or make changes in the flight profile should the need arise.
We came to the early conclusion that hobby type radio control systems did not have sufficient protection against intentional or unintentional interference. Our concern was that while the aircraft was at altitude it could be subject to higher levels of natural or man made radio frequency interference, and without some form of protection it would be very easy to lose control of the aircraft with devastating results. The biggest concern that we had was if unknown to us a 2nd. 72 MHz hobby R/C transmitter was transmitting on the same frequency that we would be using to control our aircraft and if the operator of that 2nd. transmitter flipped the same switch on his transmitter that we were using on our transmitter to activate the autopilot, we may not be able to override his input and could lose control of the aircraft.
We reviewed the technology that was available to us and decided to use Digital Spread Spectrum. We then started developing what is now the Grand Daddy of all of the Digital Spread Spectrum Radio Control Systems that are being produced and sold to the RC hobbyist the world over.
What we developed was truly a unique system that has many levels of protection from interference. During the testing phase of the system development, we designed and built a solid-state A/B switching system that could be used to transfer control of the test aircraft from the experimental digital Spread Spectrum radio control system over to a 72 MHz system. We did this in case of component failure in the digital spread spectrum radio. This was a safety issue as well as a financial one we did not want to endanger anyone on the ground and we couldn't afford to lose the test aircraft with all of the equipment onboard. On page 2 of this report you can see photos of the prototypes of the Digital Spread Spectrum Radio Control System.
The first version was cobbled together as a proof of concept version it worked so well that we decided to build a 2nd version. Version 2 was built using a Plastic Radio Shack project box and control sticks from an old Futaba G series transmitter.
Version 3 was built using transmitter cases and control sticks from Silvertone Electronics Sydney, Australia and became our production version. The current version # 4 is our Frequency Redundant Digital Spread Spectrum R/C Control-Link. There's a version # 5 in the works as I write this but I won't go in to what it will entail, I will tell you that it will be even more innovating than anything ever seen before in the radio control industry.
Some Of The Advantages Of Using Digital Spread Spectrum Technology To Control UAV's And Radio Control Models
After reviewing the following information it will be clear that the Digital Spread Spectrum Radio Control System is a very unique system in that it offers many levels of protection from intentional or unintentional, natural or man made radio frequency interference.
Spread Spectrum Frequency Hopping
The transmitter and receiver are constantly changing channels by a predetermined sequence. They are preprogrammed to hop through 25 channels to avoid interference from natural or man made radio frequency interference. For example, if channel 12 has interference on it, the system would only be on that channel for such a short time that the pilot will not even notice a glitch of the controls.
2.4 GHz Frequency Band
This is 33 times higher than the 72 MHz radios that are currently used to fly model aircraft, this allows us to use smaller antennas on the receiver with higher gains than the wire antennas that are currently used on 72 MHz systems. The higher frequency insures that we will not have interference from a model radio control transmitter that may be near the flying site.
Unique Spread Code
If a second spread spectrum frequency hopping transmitter were transmitting on the same 2.4 GHz band, and even using the exact same set of frequencies, the spread code ( hopping sequence) would have to be identical as well as time sequence matched to this system to cause interference.
Each of our DSS Transmitters and Receivers use a unique addressing for that is assigned to only that Transmitter and Receiver
Digital Data Format
The control data that is sent over this type of system is true digital data and is for all practical purposes immune to outside interference (in the manner that we use this system) . Even if a second spread spectrum frequency hopping transmitter were transmitting on the same 2.4 GHz band with the same hopping sequence the servo decoder board would still have to receive the exact same digital data in the correct format before any of the servos would move, this is the 5th. level of protection that we integrated into the system.