In late 2005, Spektrum introduced the RC world to Digital Spectrum Modulation 2.4GHz technology (DSM) for park flyers and electric helicopters with the Spektrum DX6 transmitter and AR6000 DSM receiver (see Fly RC, March 2006). Together they offer the freedom of crystal-free, pin-free, interference-free performance for your small models. With the recent introduction of the DX7 transmitter and AR7000 receiver, Spektrum has made this same technology available to models of any size and speed.

I’ve had the distinct honor of testing the new Spektrum DX7 in a wide variety of airplanes for the last few months, and the new DSM2 technology has absolutely blown me away during this time. I have flown everything from small park flyers to 35 percent gas giants with this radio, all without a single glitch. The DX7 link is so solid, it is uncanny. Gone are the inevitable twitches and dropouts we have taken for granted with 72MHz systems. Let’s take a look at DSM2 technology, the DX7 transmitter and AR7000 receiver, and how they promise to revolutionize the way you fly model airplanes of every size.

2.4GHz REFRESHER

What exactly is the big deal with this new 2.4GHz technology? How can it possibly be glitch-free, and how can I just “turn on” with total disregard for a frequency board? It all begins with the manner in which the 72MHz and 2.4GHZ (2400MHz) bands are regulated. As you are aware, traditional 72MHz systems share the frequency band with many users, and interference is a mere power switch away if another user activates his radio on your frequency. The FCC also allows high-power users to locate in-between the channels dedicated for RC use, which can cause interference. Normally, 72MHz works very well as our receivers are great at weeding through all the noise, but interference, whether man-made or as a result of onboard electronics, does happen.

When the FCC and other international bodies got together to come up with the rules for the new 2.4GHz frequencies, they took an entirely different tact. Instead of a frequency free-for-all, they decided to require all 2.4GHz capable devices to interface with each other, ensuring multiple users couldn’t occupy the same frequency concurrently. Now, as you turn on your new DX7, it scans all 80 channels in the band, finds two that are free, locks onto them, and begins transmitting. Your transmitter simply can’t interfere with other systems, and other transmitters can’t interfere with your system. Finally, the DX7 is immune to traditional RF noise caused by ignition systems and onboard electronics because the “noise” they create is in a completely different frequency range. My experience has proven to me that the DX7 and its DSM2 modulation is the most secure, glitch-free radio system on the market today.

The AR7000 dual receiver has two components. The main receiver body has the servo connector block, The smaller satellite receiver is attached with a six inch extension so that it “sees” a different RF environment. In use the antennas should be extended straight out of their respective receiver bodies and mounted 90 degrees opposed to each other.

DSM2 MODULATION

Based on the success of the DX6 and its DSM technology, Spektrum incorporated the second-generation DSM2 modulation into the new DX7 system. In addition to significantly increasing the range of the system, they’ve also increased the system’s speed and resolution, dramatically improving signal processing and latency. The result is a radio system that responds to your inputs faster than any 72MHz system on the market.

My personal experience mirrors this claim. As a cautious modeler, I slowly ramped up during testing from smaller park flyers to my larger gas-powered models. Each test model was flown back-to-back—first with my standard 72MHz system, followed by the DX7 with identical mixing, rates and expo. In each case, the model flown with the DX7/AR7000 combo responded every bit as quickly and precisely as my fastest 72MHz system. From my perspective, variations in system response and latency are emphasized during maneuvers that require highly stick-pattern driven inputs like the rolling harrier—and in several cases, my timing had to be accelerated to compensate for the responsiveness of the DX7 system.

The DX7 switches are conveniently located and easy to access. The helicopter version moves the three position flight mode switch to the left side.

TWO SETS OF EYES — THE AR7000 DSM2 RECEIVER

The original AR6000 DSM receiver used two integral receivers, each individually and independently tuned to different unique channels to ensure that if one channel lost frames, the second would maintain a secure link between the model and radio. The new AR7000 DSM2 receiver takes that redundancy one step further. The AR7000 has a second “remote” receiver in addition to the main receiving unit on the receiver’s PC board. The remote satellite receiver is attached to the main receiver with a six-inch lead.

As with the DX6, the DX7 bind button on the back of the transmitter is used to key a receiver to the transmitter and for range testing by reducing the transmitter output.

The basic premise is that two eyes are better than one, and when separated by a short distance, the receivers see slightly different RF environments that, when combined, offer a far greater level of precision and accuracy. Data from both receivers is processed by the AR7000’s onboard software, resulting in the clearest RF picture possible. This innovation dramatically improves the system’s precision, but more important, it improves its range by allowing it to be used in virtually any size or speed of model.

Installing the AR7000, like the AR6000, is very straightforward. Simply mount the primary receiver with foam tape or a foam wrap anywhere in the fuselage, or in the case of a helicopter on the main radio tray. Mount the remote receiver with either foam tape or servo tape at least two inches from the primary receiver’s antenna array. In a perfect world, each receiver’s 1.25-inch antenna array would be mounted perpendicular to the other. I’ve tried to emulate this ideal, as well as tried much more casual installations, without a noticeable difference in performance. The receiver has slots for up to seven servos, so for airplanes with multiple servos per channel, you can use Y-harnesses, Matchboxes, or an external unit like the Smart-Fly Power Expander. I’ve successfully flown the AR7000 many times in my 10-servo, 35 percent Giles powered with a DA-100 gas engine, and I’m convinced that the AR7000 is capable of flying any model requiring seven or less channels, even including complex giant-scale gas airplanes.

INNOVATIVE FEATURES — MODEL MATCH AND SERVO SYNCH

We’ve all done it, but only some of us will admit it. You know exactly what I am talking about. That’s right, taking off with the wrong model selected on our computer radio, of course. Technology to the rescue—with the DX7, this event is a thing of the past. For those of you familiar with the DX6, you know that each receiver is “bound” to an individual transmitter. The process is quick and easy, and is a primary feature of the DSM technology linking the receiver with a specific transmitter identification code, ensuring that the receiver responds to that transmitter alone.

The DX7 takes binding one step further. When binding an AR7000 receiver to your transmitter, the receiver also remembers the specific airplane model you have actively selected on the DX7. That receiver will now only respond to the DX7 when that model is selected and active. With the DX7, it is finally impossible to fly with the wrong model selected in the transmitter. This feature also works with the original AR6000 receivers. In fact, while the AR6000 retains its original restriction for park flyers and small electric helicopters, all of the new features described here also apply to the AR6000 when used with the DX7.

Servo Sync is the other major innovation incorporated into the DX7. Traditional radios use a very linear transmission methodology, simply running sequentially from channel one through, in this case with a seven-channel transmitter, channel seven. This causes slight delays, depending on the type of mixing used. For instance, on a larger dual elevator servo model, it isn’t uncommon to use channel selections that are far apart, for instance, channels two and seven on your receiver. This can result in a perceptible lag between the two surfaces during quick or extreme deflections.

The DX7 eliminates this with a feature called servo sync. Basically, the DX7 looks at the different mixes selected, and re-synchronizes the data so that servos that need to move together actually move together. A good example of this is a 120-degree CCPM three-servo head on a helicopter. The DX7 knows the head type mixing selected, and sends all three head servos the correct data at the same time. The result is as precise a feel as I’ve ever experienced in any radio system.

DX7 PROGRAMMING SPECIFICS

Clearly, the most compelling feature of the DX7 system is the fact that it offers the security, speed and precision of spread spectrum technology to models of all sizes, so it might be easy to overlook the fact that the transmitter itself is a really nice, feature-packed mid-level sport radio. So the question begs, how capable is the transmitter? Based largely on the new JR 7202, the Spektrum DX7 offers all of the mixing and programming flexibility that the vast majority of the modeling community could possibly need or reasonably use. As I mentioned earlier, I’ve flown the DX7 in a wide variety of airplanes. These have included small park flyers, traditional .60 size club models, and even my 35 percent IMAC aerobat. In each case, I found the DX7 to be a capable radio that was not only easy to program, but also very intuitive to operate.

Here is a typical AR7000 installation for a giant scale model. I located the satellite receiver up on the bulkhead with a little double-sided foam tape. The SmartFly power expander distributes signal and regulated power to the various servos.

The DX7 is available in two versions: airplane and helicopter. Both share identical programming options, differing only in switch layout, so each can fly helicopters and airplanes equally well. The DX7 includes a 1500mAh pack, allowing up to six hours of operation between recharges, a substantial upgrade over the DX6. The pilot interface is very logical, using a toggle switch and confirmation button along each side of the large LCD display. Like the 7202, there are two basic programming menus: system setup mode and function mode. System setup options include model selection, head type for helicopters, wing type for airplanes, and other “administrative” functions; function mode options include dual rates, exponential, and both helicopter and airplane appropriate mixing options including three (helicopter) to six (airplane) programmable mixes. For more on the programming capabilities of the DX7, take a look at the December 2006 issue of Fly RC for my review of JR 7202. Other than broadcasting on different frequency bands, the radios, for all intents and purposes, are the same.

The DX7 transmitter antenna hinges 90 degrees and can be rotated to either side for compact storage.

Overall, the DX7 offers a very capable radio system that when combined with the AR7000 full-range receiver will meet the needs of the vast majority of modelers, all in a glitch-free and affordable package.

CONCLUSION

In my 23 years of RC modeling, I’ve seen technology that claimed to be the next great thing come and go many times over. Some products, however, make their mark in such a way that they completely redefine the market.

I would offer that the Spektrum DX7, with its 2.4GHz full-range DSM2 technology, is such a product.

After operating the DX7 for the last few months, I’m completely sold on the DX7—not one single glitch in well over 150 flights.

The confidence of knowing that you can’t be “shot-down” by an errant signal is hard to put a value on. For my peace of mind though, at $349.99, the DX7 is an absolute steal.

Links

Spektrum, distributed by Horizon Hobby, www.spektrumrc.com, (800) 338-4639

For more information, please see the source guide in the magazine.