Radio equipment - Hucknall MAC

There has been for some time now, concerns that radio gear inside a carbon fibre model might not have the range it should have. The carbon shields' the transmitter signals, and therefore reduces controllable range. Modellers with planes constructed in Carbon Fibre are advised to ensure the Rx aerial runs completely outside the carbon fuselage.

There has been recent scares with users of the new 2.4 gig radio gear experiencing the same problems. Even though the kit is interference free, if a signal cannot reach the receiver via the aerial.... it will fail. Ensure that all of the Rx aerial leaves a CF model as soon as possible.

The frequency table is now coming along, but I still need the rest of you to let me know yours. Please email me with all of the frequencies that you use, or intend to use at Hucknall. This will assist you in the purchase of crystals in the future, and newcomers can see the free channels, and avoid clashes. Let me know if now have 2.4gig radio, and remember to paint a cloths peg black and mark it with your name for the peg board.

2.4 GHz radio equipment - BMFA

OFCOM have issued the necessary permissions and changes to Government legislation which allow the sale and use of approved equipment transmitting on the 2.4 GHz band at 100mw maximum radiating power in December 2006.

Equipment on this band is already selling in large numbers and will soon start to appear at the club field or flying event. At this early stage only one manufacturer is offering equipment on this frequency, however indications are that more will take advantage of this new technology in the near future.

Below are a few points for your guidance on operation and integration within your normal flying activities, however always remember the final decision on any matter relating to the safety of a flight rests with the pilot.

The Spektrum DX6 is a 6-channel computer system designed to be flown exclusively with parkflyer airplanes and micro/mini helicopters. Using 2.4GHz Spread Spectrum DSM (Digital Spectrum Modulation) technology, the DX6 system includes a nicad-equipped transmitter, a micro 7-gram AR6000 receiver, and four lightning-fast sub-micro S75 servos.

With the 2.4GHz, you can say goodbye to frequency pins, getting shot-down, or shooting someone else down for that matter. Plus, you'll never have to wait for a frequency pin again. And that's just the beginning of the benefits of operating on the 2.4GHz band.

When using this system, (which operates just like you'll never have to worry about "noise" coming from your motor or speed control (or anywhere else on your model) affecting your radio's performance. Why? It's simple. Motor and model-generated noise has no energy above 300MHz. . Your DSM system operates nearly eight times higher in the frequency range (see chart.) Fact is, you can mount your AR6000 receiver directly to any speed control. It just doesn't care and won't be affected a bit.

And because the signal is pure digital, it means that glitches are a thing of the past too. No more annoying glitches that shatter the confidence and cause you to worry about crashing. They're a thing of the past too.
Not to mention the nasty intermodulation issues that have plagued 27, 72 and 75 MHz like 2IM, 3IM and adjacent frequency. They too, can't affect DSM.

And to top if off, the equipment you see here is all solid state. There are no pots to tune, nothing to ever degrade in performance, adjust or need tuning.
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To understand the full benefits of the DSM system and its operation in the 2.4GHz band, it helps to review the 72MHz band we're currently flying in, and compare how the FCC rules are different between the two.
As you know, our 72MHz channels are spaced in 20Khz spacing. Our output is limited to 750mW (most manufacturers have output a lot lower than this to avoid intermodulation (inadvertent mixing of signals.) That's all fine and dandy, but FCC authorized high power industrial users to locate right in between our channels. Now, undermost situations, this isn't a big issue. Our receivers have to be very selective and sensitive to "find" our low power output signals. Normally, everything works well. But occasionally, industrial transmitters (some of these put out 50,000 Watts and more) can slip a bit off frequency. Guess who gets hit? (That said, it'd only be realistic to point out that most of us who analyze radio interference find model-generated noise is a much more common problem than high-powered industrial operators. But does it happen? Sure.)

FCC adopted a similar system with the 900MHz band - they mixed high power, narrow band users. It worked pretty well, but not perfectly. So when FCC devised the 2.4GHz rules, they set about a completely new system: they mandated that all 2.4GHz devices will transmit at less than 1 Watt. This prevents high power transmission from causing interference over great distances.

The FCC also mandated that transmitters using Spread Spectrum must have the ability to check for, and find an open frequency on the 2.4 band (there are 80 channels, spread in 1MHz spacing.) before transmitting any signal.

So when you turn on your DX6 transmitter, it scans the 2.4GHz band and picks two frequencies which show the least activity. That's right, there two frequencies used with the DX6 system. (see explanation of DuaLink technology.)

Since all devices on the 2.4GHz band are required to avoid other users (or else they wouldn't receive FCC type acceptance) there is no chance that another type of device using 2.4GHz can cause an issue with your radio. It just can't happen. They all work by the same rules.

(For more information on the Spread Spectrum story, see Dan Williams article in July Model Aviation.)

How each receiver recognises its transmitter

Instead of using a bind button like the surface Spektrum receiver, the AR6000 actually uses a plug to put the receiver into the binding mode. Simply plug the jumper in, hold down the DX6’s bind button when you turn it on, and bingo, its setup. Things don’t get much simpler than this.
Each Spektrum transmitter has a GUID (Globally Unique Identifier) code. Binding is the process of programming the receiver to recognize the GUID of a single, specific transmitter. Binding teaches the receiver the specific GUID of that transmitter so that the receiver will only listen to the information from its previously bound transmitter and ignores everything else. With over 4.2 billion GUID codes, the chances of having a interference from another transmitter is virtually impossible.

It is usually only necessary to bind the receiver once. The only time it'll be necessary to re-bind is if you wish to use a different transmitter, or you want to change failsafe positions (see next section.)
How tough is it to bind? Not very. Just….

1) Put the bind plug into the BAT port of the receiver
2) Power up the receiver
3) Press and hold the bind button on the back of the Tx while turning on the transmitter.

That's it - nothing complex or mysterious.

With the DX7 you’ll be able to fly anything from micro electric helis, to big gas-powered IMAC planes without regard to frequencies and free from fear of interference. Calling this kind of thing “revolutionary” just doesn’t cut it. It is nothing less than a quantum leap in RC technology that will change how you fly forever. Never again will the availability of a frequency pin dictate when you can take off. Never again will you have to ask, “What channel are you on?” Never again will your flying experience be interrupted by model-generated RF noise, interference from commercial broadcast towers, or anyone on another RC system.

About the only problem you and the rest of your club will have when you all start flying with Spektrum® is what to do with the frequency board.

Unlike most first-of-its-kind innovations, DSM2™ is not an unproven concept. It is based on the exact same Spektrum 2.4GHz DSM® (Digital Spectrum Modulation) that RC car racers as well as micro electric and parkflyer modelers have been enjoying for at least two years now. Like DSM, DSM2 provides an impenetrable radio link that’s immune to every known type of RC interference. And because it operates at 1024 bit resolution, it provides the kind of locked-in response that will have you feeling more connected to your model than ever before.

AR7000—Spectacular Signal Clarity

AR7000 dual receiver that comes with the DX7 is key to the system’s incredibly robust RF link. Comprised of a compact main receiver that is linked to an even smaller satellite receiver by a 6” lead, the AR7000 acts as a pair of extremely sharp RF “eyes” that each take in a slightly different view of the signal environment. Information from both receivers is then processed by patent-pending Spektrum software that takes information from each receiver and combines it to form the most vivid “picture” of an RF signal than has ever been possible in RC before.

What’s more, there are no long pesky antennas to accommodate. The AR7000’s short 3” antennas don’t require any external exposure, so installation is an absolute breeze.

ModelMatch and ServoSync – Extra Safety and Precision

DSM2 and the AR7000 aren’t the DX7’s only marvels. Spektrum engineers have come up with two more patent-pending innovations that you’ll wonder how you ever lived without—ModelMatch™ and ServoSync™.

ModelMatch puts an end to the “wrong model” syndrome. Almost everyone that flies RC has, at one time or another, crashed, or seen someone crash, because they neglected to verify the model name on the transmitter display in their preflight check. With the DX7 a unique code is embedded in the signal so that if the wrong model’s name is on the screen, the model’s controls simply won’t respond.

ServoSync is an ingenious new feature that actually re-sequences the bits of data the DX7 transmits based on the type of mixing you select. So, if you have a dual elevator on your big Extra or a 3-servo CCPM setup on your heli, ServoSync will see to it that those servos working together receive their impulses together. The result is more synchronized servo movement which translates into an undeniable, locked-in feel when you fly.

AR6000 Compatible

DX6 owners, and anyone else who flies small electric models, will be pleased to know that the AR6000 receiver works perfectly with DX7 too. In fact, the AR6000 will actually benefit from the DX7’s signal speed, as well as ModelMatch and ServoSync. So whatever the aircraft in your collection, be it a .60-size heli or a 15-ounce foamie, you can fly it with the DX7.

Q: What is the range of the DX7, and can I fly large scale airplanes and large gas- or glow-powered helicopters with the system?

A: The DX7’s range is beyond visual limits, allowing even giant-scale airplanes and unlimited class sailplanes to be flown to the limits of sight. The AR7000 receiver incorporates a second remotely mounted receiver that sees a slightly different RF environment. This remote receiver is the key that allows sophisticated aircraft of all sizes and types to maintain a solid RF link out to the limits of sight.

A: DSM2™ technology is Spektrum’s second-generation proprietary spread spectrum protocol. DSM2 (Digital Spektrum Modulation 2nd version) is optimized to allow all types and sizes of aircraft to be flown. With DSM2, latency has been greatly reduced and, in fact, the system offers faster response time than any brand of 72MHz PCM system.

Q: What is Model Match? A: Model Match™ (patent pending) prevents the pilot from flying a model using the wrong memory. During binding (the process of teaching the receiver the specific code of the transmitter), the receiver actually learns and remembers the specific model memory that is selected during binding. Later, if the system is turned on and a different model memory in the transmitter is selected, the system will not operate. This prevents the disastrous issue of trying to fly a model using the wrong model memory. Simply selecting the correct model in model memory will cause the system to connect. The AR6000 parkflyer receiver is 100% compatible with the DX7.

A: Yes. The AR6000 receiver included with the DX6 works perfectly with the DX7 transmitter. The AR6000 receiver is designed for parkflyer and Mini helicopter use only and, even when used with the DX7 transmitter, the AR6000 must only be used in parkflyer type of aircraft. The Model Match feature functions perfectly when using the AR6000 with the DX7 transmitter.

A: The included 1500mAh transmitter battery offers nearly 6 hours of flight time in the DX7 transmitter.

A: Yes. All popular brands of three-wire servos, including digitals and even high current draw digital servos, work with the DX7 system.

A: The AR7000 incorporates two receivers; an internal receiver is located on the main board, and the extra part you’re referring to is actually an external receiver. Mounting the external receiver in a slightly different location with its antenna oriented in a different direction greatly improves the RF link in difficult environments.

AM, FM, PCM and now DSM. Spektrum’s newly released DSM (Digital Spectrum Modulation) system advances RC radio technology to the next generation. Based on an optimized version of Direct Sequencing Spread Spectrum, DSM offers pure digital control providing an impenetrable radio link that’s immune to all types of interference. And with 4096 bit resolution and 5.6ms response time, the DSM system offers seemingly infinite accuracy and instantaneous response for a totally connected driving experience.

For the highest security levels of radio communications, NASA, the U.S. military and government agencies like the CIA and FBI rely on Spread Spectrum technology. Whether guiding unmanned reconnaissance aircraft over enemy territory, controlling satellites in space or communicating critical mission orders to the battlefield, the impenetrable secure link that Spread Spectrum coding provides makes it ideal for these decisive security applications.

Collision avoidance eliminates the possibility of more than one Direct Sequencing Spread Spectrum system from transmitting on the same frequency. Here's how it works: When the transmitter is turned on, the system scans the 2.4GHz band looking for an open channel. 79 channels are available. When an open channel is found, the system locks in and transmits on that channel as seen below.

This process takes about 2 seconds. In the unlikely event an open channel is unavailable, the transmitter continues to scan without emitting a signal until an open channel becomes available. The transmitter will remain on that selected channel until it's turned off. Each individual module is factory programmed with its own unique serial code called GUID (Globally Unique Identification code). Once a receiver is programmed to a specific module (called binding) the receiver will only recognize that module ignoring signals from any other sources. And with over 4 billion possible GUID codes, it's virtually impossible for a receiver to listen to anything other than its bound transmitter. When the receiver is turned on, it scans the 2.4GHz band and searches for its specific transmitter's encoded signal. When found, it locks in on that channel. If the signal is lost, the receiver goes into a hold mode, positioning the servo to a preset fail-safe position until the signal is reacquired.

If the receiver is turned on before the transmitter, it will continuously scan the band until the encoded transmitter signal is present. During this period, the receiver drives the servos to the preset fail-safe position. All Direct Sequencing Spread Spectrum systems are required by the FCC to incorporate active collision avoidance, making it impossible and illegal for more than one transmission on a single frequency.

BINDING Each module has it own unique code (called GUID). The receiver must be programmed to a specific module so that the receiver will only recognize that module, ignoring signals from any other sources. This process called binding is push-button-easy and takes only about 30 seconds. During the binding process the servo fail-safe positions are also set. It's necessary to bind the receiver to the module during first installation and is recommended when the receiver is moved from one car to another. Multiple receivers can be bound to a single transmitter module, common when using one transmitter to operate several models.

Numerous clubs have experienced radio interference over the past few months, not least ourselves at Hucknall. With local expertise, and countless test days, we are convinced that wrapping the Receiver in some sort of radio impervious material..... AND earthed to your RX battery negative (To create a Faraday cage) will minimize the problem.

Any airborne interference that could render your Receiver components in-active...... like microwave flooding from mobile telephones and phone mast dishes, should be shielded against.

Tin foil may work but is flimsy and alloy boxes require fabrication in a workshop. We then discovered a material that is used to screen test facility rooms from microwave signals. Since the testing of this material, we have sewn bags from this cloth, and soldered a wire to its side so as to connect it to the earth of the Rx battery. Pilots with the receiver wrapped AND earthed to the battery black wire, have experienced no interference at all at our flying field. Either the problem has gone away, or we have found an antidote to alleviate the problem...... either way, we are happy.

See our "For Sale" section......... I think there may be something on there that I may be talking about.

Folk are always selling on, and buying used transmitter and receiver Xtals at Swapmeets and other sites like ebaY. Be warned...... Don't buy them unless you know their source and history. This tiny metal box looks strong enough to withstand a bash, but once you understand what it actually is, you may have a different opinion on the matter.

The circuit involved in producing the 35MHz transmission is known as an oscillator. This circuit produces an alternating current at a particular frequency. The circuit is made to oscillate by alternately charging a component, which stores energy, and then discharging the energy via a resistor. The energy storage can be either in a capacitor, an inductor, or both. The resonant frequency depends on the value of the capacitor or inductor and the resistance. The problem with this type of circuit is its stability.

The frequency will alter with variations in both temperature and voltage. A crystal is therefore used which acts like an electronic tuning fork. Inside the casing of a crystal, there is tiny and very delicate piece of piezo material. This material has the characteristic that when a charge is applied it changes shape. With the charge removed it reverts to its original shape. When a crystal is put in an oscillator circuit it acts as a regulator, maintaining a very precise frequency. This becomes the channel number that we all know.

Circuits vary in configuration, and crystals vary to suit the type of oscillator circuit they are intended for. Different manufacturers have slightly different ways of creating the intended circuit, and hence the crystal required for the final channel. The crystal can be likened to the frequency tuning knob on the radio, but it will vary slightly from make to make of radio. Without getting too technical it is sufficient to say that the correct manufacturer crystal must be used in your radios. The use of another manufacturer’s crystal is a definite NO unless the packaging specifically states that it can be used in your equipment. In some cases the circuit will work on the ground and for a range check, but after take-off the frequency may be shifted, and / or, be unstable and may even radiate onto an adjacent channel.

Manufacturers quote the phenomenon of ageing, where the frequency is known to drift with age, and this differential gets worse over prolonged time. If the components are as delicate as described above, then it stands to reason that after a heavy landing, the Xtal may have been damaged without your knowledge.

For the sake of a £5 replacement, surely you aircraft would be safer with a new Xtal onboard. Some reported radio interference may actually be credited to poor Xtal management.

Change your dented, rusting and mismatched Xtals NOW before it is too late, you have been warned !

We take our batteries for granted, or at least those that sit in our models...... hidden out of sight, often never to be removed until the demise of the plane. The transmitter will usually sport a power / voltage meter and modern Tx's even have a beep to warn of low power.

The receiver pack however may get charged on a Friday, ready for a weekend flight, weather permitting. If we don't get to fly that model, do you check the power in the pack the next time you do fly that model? You may be forgiven for placing the pack on charge to just boost up the volts on the morning of the flight, but consider this.

The charger that you may have received with your radio set will probably be adequate for the 500 maH pack that cane with it. It was usually recommended to leave the charger connected for 14 hours for a full charge. Now ask yourself this ! What Milliamp hours rating has the pack got that you use today? 800 maH, 1200 ? If a 500maH pack took 14 hours with that charger then a 1000maH cell will require a 28 hour session. You will either need to modify your charging times or use a charger that can output a greater amperage rate. Maybe use your flight pack charger if you have one.

Some folk buy a new battery pack, be it for the Transmitter or the Receiver... charge it and expect better performance than their old cells. It is not always going to be the case that from an initial charge your pack will be great. The first charge needs to be at the lowest amperage rate that you can charge at, and for a considerably longer time than you would normally take. any cell will require a number of charging cycles to get it to its peak performance. If your charger can do an automatic cycle then that will prolong the life of the pack.

If NiCad's are used heavily for long flying sessions there is less need to cycle. However, if a battery has been stored for several months, say during a winter lay-up, it is a good idea to cycle them a couple of times before flying. It is advisable not to let the pack go completely flat, as a cell may be damaged beyond repair. This information applies to NiCad and NiMh cells, and attention to LiPo cells is addressed elsewhere on this site.

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2.4 GHz radio equipment - BMFA

How each receiver recognises its transmitter

AR7000—Spectacular Signal Clarity

ModelMatch and ServoSync – Extra Safety and Precision

AR6000 Compatible