When we look back on the year 2007 I think we'll use just a couple of numbers to sum up our flying memories... 2.4! We may add the letters GHz (gigahertz) after these numbers and we'll all nod knowingly and agree that 2007 was the year that saw one of the biggest changes in decades to the way we operate our models. Yes folks, I predict that 2007 will be known as the year of the 2.4 gig'.

What am I talking about? Well, you may have seen the adverts, you've possibly perused the R/C internet forum threads and you could well have read the revised 2007 BMFA Handbook. If not, then now's as good a time as any to know that the 2.4GHz 'spread spectrum' R/C system is here and it can do things that our faithful old 35MHz equipment simply can't contemplate. The words revolutionary and ground-breaking have been used in relation to this technology and unless you've got your head buried firmly in the sands of our vintage past, you'll be wanting to know what all the fuss is about.

TALK BACK

2.4GHz, or 2400MHz if you prefer, is a frequency band that requires the various components of the equipment to interface with each other. In short, transmitter and receiver communicate in a way that, until now, has not been realised in the R/C world. Accordingly, radio equipment of this type offers decided advantages over that which we currently use.

The DX7 isn't to be confused with the earlier DX6 which, as a park-fly system, offers limited range for about £100 less. We're going to take a look at the DX7, see what it'll do, and explain the various functions and the terminology employed. Next time around we'll report on what we think of it in practical use at the flying club and, moreover, in control of our guinea pig airframe.

REVOLUTIONARY?

Although it would be easy to sound like a jaded hack and employ a healthy dose of cynicism in describing the Spektrum DX7, I won`t because quite frankly the range of features the system offers is very impressive. Mind you, before I go too far I will just add that, for me, the most tempting part of the whole deal is the price - £270. Now, initially that sounds a trifle high for a basic 7-channel computer radio, but when the full capabilities of this little bundle are realised, I for one find it eminently acceptable, not least because the set is packaged with a quartet of digital servos.

Right then, empty your mind, prepare to soak up some new words, phrases and techniques and let's get started. We’ll go straight in and look at the main features that differentiate the DX7 from a standard 35MHz set and see if it deserves to be called revolutionary.

I guess that one of the advantages of being the first manufacturer to bring out a spread spectrum radio is that you can patent a host of terms and names in the hope that they'll become generic in much the same way as William Henry Hoover's splendid vacuum cleaner. In this feature, then, I'll use the manufacturer's terminology for the system functions, simply because I wouldn't otherwise have a clue what to call them!

  • Dualink. This is the way in which the transmitter and receiver talk to each other. At switch-on the transmitter scans the 2.4GHz band and finds an open signal (channel) to lock on to. It then repeats the process and locks on to a second. The model is therefore protected by having two links with the transmitter, if a problem is encountered with one, the other link keeps the model flying. The BMFA handbook alludes to the fact that there are effectively 80 channels available in the 2.4GHz band and at two per model, enough to fly 40 aircraft at the same time. Plenty for everyone and, effectively, a cheery bye-bye to transmitter control.
  • Binding. The term used for the way in which the transmitter and receiver get to know each other and work together. Here, the transmitter teaches the receiver only to work with the model memory that it's programmed for. Once 'bound' the receiver will only operate with that particular model memory and, thus, its allocated model. In other words it's impossible to fly the wrong model by accidentally forgetting to change the model memory. To achieve all this a small Bind plug is inserted in the switch harness jack and the receiver and transmitter systems are switched on. An illuminated button on the back of the transmitter is held down while the Tx is switched on, and to signify connection the button flashes. Similarly, the LEDs on the main receiver and satellite receiver glow solid to indicate that all is well at the model end. The bind plug can then be removed. It's worth noting that the Bind button has a secondary purpose to help with range testing. When pressed it reduces the DX7's output power, whereupon at 90ft from the model (button depressed) total control should still be evident.
  • Smartsafe. When the binding process above is being undertaken, the position of the sticks should be at fail-safe. In this way the receiver can memorise the stick settings as a default in the event of signal loss.
  • Latency. This is the name given to servo response time. The system boasts more synchronicity between the flyer and model. This is all down to the improved response time that a 2.4GHz system brings. Traditional transmitter systems use a linear method of transmission which sends information one channel after the other, whereas the DX7 transmitter sends information to the receiver simultaneously. Perhaps not a feature that will be noticed on the average Sunday hack but competition pilots should appreciate snappier and more precise control when used with appropriate digital servos.
  • AR7000 receiver. As you can see, the receiver has grown cat’s whiskers. The system effectively has said receiver and a satellite receiver linked with a short wire, the main unit housing the traditional Futaba / JR / Hitec servo pins. As you'll see from the photos, aerials are practically non-existent, each unit having just two short 30mm lengths. So, another advantage then: users of this system will no longer have to consider how they hide a lengthy receiver aerial! After all those years of struggling with wires, rubber bands and aerial routing issues, this seems almost unbelievable.

    Data from both receiver and satellite aerial is handled by the AR7000's software to ensure that one clear signal is processed, although in pursuit of this the two units should ideally be placed perpendicular to each other in the model. It's worth noting, mind, that the manual marks this as 'preferable' rather than essential. It also notes that the aerials should be adjusted so they're at 90 degrees to the receiver side. Ok, that's a lot to take in, let's pause for breath and have a look at what the DX7 has to offer from a user`s perspective.

    SUITS YOU?

    Does the DX7 seem familiar? JR 2610 users will certainly think so, the casing is shared by both brands. Despite its technological leap the DX7 has to compete in other areas and for us fliers, when it comes to transmitters, cosmetic appeal still counts in the purchasing decision.

    Visually the unit is appealing and looks a little different in two-tone silver - a colour less likely to show dust and dirt. It feels very solid and very well made, too. Even as a devout Futaba user I'm not too proud to admit that JR transmitters always have a quality feel to them and the DX7 continues that theme - the switches in particular are sturdy JR items and the digital trim switches easy to find 'eye's off', with a nice audible scale to accompany inputs.

    Like the two-six-ten the main sticks are quality items of a type not always found on comparable rival transmitters, and tension can be adjusted by removing the rear case. The stubby aerial is clearly a little different from the norm but not unattractive and the hinged fold mid-length is, as far as I can tell, for improved reception and storage convenience. Incidentally this aerial is plastic and not rubber, i.e. it is not flexible like those little stubby car radio jobs that were once the rage.

    At the rear of the unit you'll find a tidy chrome carry handle (I do hate it when the handle is moulded as part of the case) along with the bind / range test button and, of course, the battery cover. Incidentally, hidden beneath the latter you'll find a 1500mAh NiMH pack that, we're told, lasts 5 - 6 hours. Plenty for a full day of uninterrupted (by frequency clashes!) flying.

    The DX7's screen and programming system will again be familiar to '2610' users, indeed as far as I could tell they're practically identical. The screen itself could be a little brighter, although Spektrum`s characters are easy to read and the two rocker switches simple enough to use without reference to the manual every time a change is made.

    AT A GLANCE

    In terms of features, the DX7 is a mid-range offering on a par with the aforementioned 2610 or Futaba FF7 (7C) although with a generous 20 model memories compared to the ten found on the JR and Futaba. All the standard aircraft features you'd expect to get on a mid-range unit are featured, including: servo reversing, exponential, differential, sub trim, six programmable mixing functions, servo monitoring, assignable switches, V-tail, flaperon and elevon mix, aileron / rudder mix, elevator / flap mix, and others besides.

    Helicopter pilots won't be left wanting either: travel adjustment, throttle hold, dual rate and exponential, 5-point pitch and throttle curves with a selection of idle-up options, revolution mixing, rudder dual rate, CCPM swashplate mixing, three programmable mixing functions, and gyro sensing, are all there.

    AND FINALLY... Just a few points worth noting:

  • The system will operate with any commercially available servos, including digitals.
  • The receiver will work on any voltage up to 9V, the limiting factor being the capability of the servos to handle the current.
  • Range is reported to be beyond visual and all aircraft sizes can be accommodated, from small park flyers to large petrol aerobats.
  • The BMFA has recently issued some guidelines on the use of 2.4GHz at the flying field. These can be viewed on their website www.bmfa.org and, typically, major on the practice of good common sense with the rider that the effectiveness and safety of any equipment still relies on the care and vigilance of the user.
  • The AR7000 7-channel receiver has an individual retail price of £64.99 and is sold with its satellite receiver.
  • Interference noise at up to 300MHz is well below 2.4GHz, so long servo leads and power cables do not need choking / suppressing. Spektrum positively advise against it as suppressors can affect the signal.
  • Since only the case and switch set is JR, you'll not get very far sending your DX7 to a JR approved agent for a service. Helger Distribution will be your point of contact in the UK (see Datafile).
  • Erase the word crystal from your mind. You’ll never need another.

    TIME TO SWITCH?

    You don't need me to tell you that the DX7 is just a little bit special. The thought of a flying field free from frequency control muddles, switch-on shoot downs and mistakes of the model memory variety is very attractive. Many of us have lost models this way and just one crash is a crash too many.

    Above and beyond all of this is the promise of glitch free flight, time after time with the locked frequency offered by a powerful 2.4GHz system. It seems uncanny that almost overnight, this system will remove so many of the problems that we've grown accustomed to working around and managing for so many years. Take heed though, a flying system is only as good as the batteries that power it and many models are still being lost through poor battery care, so the DX7 isn't infallible. It can't provide you with a faultless installation - you have to do that - and it won`t fly your models for you!

    As a package I should just express some minor disappointments. The omission of a transmitter charger seems silly. The charging socket on the Tx has a reversed polarity uncommon to the majority of current sets, although JR owners will be able to use their current unit. Alas, others will have to purchase a specific charger or, I guess, buy a JR one. Moreover, the Tx battery connector is not of the standard type so the battery can't easily be removed for a fast charge with a commercial field charger. It seems a bit stingy not to include a receiver battery pack and neckstrap too.

    On the whole, I'm very impressed with the promise of this system, and although I can't justify changing all my R/C gear overnight, I do know that, providing this one ticks all the boxes of our air test then the next system I buy will be 2.4, no question about it. If you're new to the hobby or are upgrading then you really must give the Spektrum DX7 some serious consideration because almost overnight all current 35MHz sets are looking decidedly prehistoric.

    Full credit to Spektrum for this highly impressive piece of kit. Mind you, as I say, playing around with a new toy on the workbench is all very well but field testing is another thing entirely so check out our flight test to see how the Specktrum fares.