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There have been quite
a few defining moments throughout the history of RC,
but the impact of any product or technology isn't
always immediately apparent. Vehicles such as the
original RC10 and the T-Maxx didn't achieve cult
status until some time after their introduction.
Electronic speed controls (ESCs), Ni-Cd batteries,
peak-chargers, RTRs and dozens of other developments
had been around for years before everyone realized
that each represented a pivotal moment in the
advancement of RC. We don't need the benefit of
history to tell us that the introduction of the new
Spektrum DSM system will profoundly change the future
of RC. The days of buying and changing crystals,
waiting for a frequency clip during practice, random
interference and almost all the other shortcomings of
current radio technology, will be history. The new
Spektrum system also promises to usher in technology
that has never been available in a radio system.
There's a lot to look forward to; you just have to
open your eyes and watch it unfold.
The Spektrum DSM replaces your existing transmitter
module and receiver, and plugging it into your radio
advances it light-years ahead of current technology.
Current systems in the U.S. operate on 27 and 75MHz;
the Spektrum DSM operates on the ultrahigh 2.4GHz band
(2400MHz), and there are 79 channels available. RC
cars now have 79 channels on a band that is inherently
more stable and universally accepted throughout the
world. If this article stopped right here, that alone
would be huge news. You could stop reading right now
and know that running and racing RC cars just became
exponentially better. But the aforementioned barely
scratches the surface of this new system's benefits.
We've tested this new system and talked extensively
with the experts who developed it to give you the
complete scoop on this fantastic new technology.
DECIPHERING DSSS AND
FHSS
The FCC requires that any device that operates on the
2.4GHz spectrum is required to have some type of
"collision avoidance" technology, which is a
fancy way of saying that it absolutely can't interfere
with other devices operating on the same frequency.
It's technology that's never been available in the RC
car market, but now it's the basis of what makes the
Spektrum such a significant leap in technology. There
are two standards of this so-called collision
avoidance, each with a different approach to
guaranteeing reliable operation. Although it's a
little techy, it helps to understand the differences
between the two methods that provide incredible signal
stability and security against interference–so
here's the scoop on "FHSS" and "DSSS."
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MANUFACATURER'S
SPECIFICATIONS
DSM
SYSTEM
> Frequency band:
2.400 to 2.4835GHz
> Channels: 79
> Channel spacing:
1MHz
> Bit rate:
15.626kbp
> Range: 3,000 ft.
> Latency (response
time): 5.6ms
>
Resolution/channel: 4,096
steps
DSM TRANSCEIVER
> Weight: 0.40 oz.
(11.3g)
> Dimensions:
1.62x1.06x.57 in. (41.2 x 27.0
x 15.3mm)
> Input voltage: 3.2
to 9.6V
> Channels: 3
> Current
requirements: 40mA @ 4.8V
> Antenna length:
3.6/8.5 in.
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The
Spektrum DSM system costs
about $160 and consists of a
transmitter module and
receiver. Extra receivers can
be programmed to work with the
same module and are available
for $80 each.
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FREQUENCY-HOPPING SPREAD SPECTRUM (FHSS). The
FHSS standard means that the radio system rapidly
jumps from one channel to another using a random
sequence of channels. Here's how it works: a code at
the end of every string of data sent from the
transmitter to the receiver tells the receiver the
next channel in the sequence. For example, the
transmitter might "tell" the receiver,
"left, left, left, left, switch to channel
51." The signal jumps randomly from channel to
channel hundreds of times per second. Other systems
using this standard use different random sequences,
and although there's a remote possibility of crossing
channels, the resulting interference would last only
milliseconds, so you wouldn't be able to detect it.
According to Spektrum's designers, there are two
significant elements of the current FHSS standard that
make it less than ideal for RC applications. First,
the latency time (response time) with the FHSS
standard is typically about 50 milliseconds. For
reference, the Airtronics M8 out of the box has a
response time of about 12 milliseconds, and the
ultra-fast Futaba HRS system clocks in at about 8
milliseconds. The fastest FHSS-based systems the
Spektrum crew tested had response times of about 25
milliseconds, which is more than twice the response
time of a standard M8. The second drawback is the
system's response to interference. In the event of
signal interruption, it can take 2 to 4 seconds for
the transmitter and receiver to resynchronize. The
inability to control a moving vehicle for up to 4
seconds would obviously be unacceptable.
DIRECT SEQUENCING
SPREAD SPECTRUM (DSSS). This is the system used by
Spektrum. The DSSS standard is unique in that it hunts
for and locks into a single channel; there isn't any
channel-hopping. When the transmitter is turned on,
the module scans and locks on to any channel that is
not in use. Because of the 2.4GHz spectrum's collision
avoidance requirements, locking into one channel
requires different anti-interference measures than
those implemented in FHSS systems. A DSSS-based system
spreads the RC data over a wide bandwidth using a
pseudo-random noise code. The receiver knows its
transmitter's spreading code and can distinguish its
intended radio signal. Spreading has the additional
benefit of digitally increasing the range of the
system for the same power. A further security method
particular to the DSM is the use of a globally unique
identifier code (GUID). This code is encoded into
every RC data packet. The GUID is one of 4.2 billion
potential codes; there aren't even 7 billion people on
the planet.
STEPPIN' OUT
Any radio system that processes signals digitally has
a defined number of steps (servo positions) throughout
its range of travel. The 1024 standard was made
popular by Futaba's PCM radios, they have 1024 steps
across the range of control movement. For example, if
a servo connected to a Futaba PCM system were to start
from the full left position and sweep all the way to
full right, the movement of the servo would be broken
down into 1,024 steps. It usually happens so fast that
it's virtually seamless. The Spektrum has 4,096 steps
of resolution, a little less than four times that of
any other popular system.
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The
Spektrum DSM module is simply installed in
place of the factory module in selected radio
systems. Our test system is installed in the
Airtronics M8, but it will be available for
most popular radio systems that include a
factory module. "Binding" the
receiver to the module is a quick one-step
process, and it's the only setup required to
make the Spektrum fully functional. The high
2.4GHz frequency means the short antenna seen
on the module is all that's required. The
collapsible standard antenna isn't functional
as long as the Spektrum module is installed,
so it can be removed if desired.
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The
Spektrum receiver is installed and outwardly functions in much the same way as
a standard receiver. The magic that happens inside the housing is transparent
and rock-solid in terms of reliability. Like the transmitter module, the
receiver needs only a short 3.6-inch antenna for maximum radio range.
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The
Spektrum receiver includes a single setup
button, which is used to "bind" it
to the transmitter during initial setup. Two
holes molded into the housing permit different
antenna routing depending on the installation.
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The inside of
the Spektrum receiver features a double-deck circuit board (see below) and
high-tech surface-mounted processors. All this horsepower is used to process
the signals sent back and forth between the module and receiver.
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SPEKTRUM
Q&A
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IS
THE RESPONSE TIME FAST ENOUGH?
Latency (response time) is a measure of how
long it takes from the time you move the
steering wheel or throttle to the time the
servos or the speed control react in the car.
Even in sport radios, it's often so fast that
the delays are undetectable, but for the
people who race their radio stats, the
Spektrum has the fastest response time ever—5.6
milliseconds.
DO I STILL NEED TO
IMPOUND MY RADIO?
The Spektrum's ability to seek an open channel
and its other robust anti-interference
features mean that Spektrum-equipped radios
don't have to be impounded. They can't
interfere with conventional radios, and they
can't be turned on within their own band
unless there's an open channel, so only
paranoia and faulty logic would land your
radio in the impound, but some tracks may
still require that you hand over your
transmitter.
WHAT ABOUT FREQUENCY
CLIPS AT THE RACETRACK?
The technology of the Spektrum will eventually
eliminate the need to monitor frequency usage.
You don't have to worry about frequency clips
on the drivers' stand, and race officials
won't have to scan the system to see if it's
on a legal band because it's global, and it's
fixed. Nobody will need the
"funnies" anymore. Can I bind extra
receivers for use with my other cars? You can
bind an unlimited number of receivers to the
same transmitter. Extra receivers are
available for a retail price of about $80
each.
WHICH RADIOS WILL
WORK WITH THE SPEKTRUM?
At the time of our testing, the Spektrum for
the Airtronics M8 was the only one available,
but by the time you read this, modules should
be available for the KO EX-10 Helios and EX1
Mars, the Futaba 3PJ and 3PK, the JR 756 and
R1 and the Hitec Lynx 3D, CRX and SRX.
IS IT LEGAL OVERSEAS?
International acceptance of the 2.4GHz band
means you can use the radio system that you
use at home overseas. Current radio technology
requires a module and receiver tuned for
approved frequencies that are often unique to
one country or one part of the world. In
addition, all 2.4GHz devices (RC and
everything else) are limited to a maximum of 1
watt of transmitting power, and that
eliminates the potential of your RC signal
being crushed by powerful 100,000W signals
from industrial users as it could on the 27
and 75MHz bands.
HOW SUSCEPTIBLE WILL
IT BE TO INTERFERENCE?
Interference with the Spektrum is highly
unlikely. The 2.4GHz band is very far from the
spectrum in which most model-generated
interference occurs. Motor arcing, metal parts
contacting each other, noise from a speed
control and the vast majority of interference
that comes from within your RC car happens
mostly below 300MHz. At 2.4GHz, the Spektrum
is immune from the nuisances that plague our
current radio systems, and that eliminates the
need for anti-interference measures such as
capacitors and other devices. There are also
numerous defenses against other potential
interference sources. As previously stated,
all devices using the DSSS standard must have
the ability to seek an unused channel. In the
unlikely event that defense is bypassed, the
GUID would reject any signal that didn't have
the proper ID. If a rogue signal was on the
same channel and somehow managed to be using
the same ID, it would have to be on the same
part of the band as the Spektrum unit. The
band has the equivalent of 100 data paths
(think of a 100-lane freeway). The interfering
signal would have to be in the same
"lane" or on one of the adjacent
lanes for it to have a chance to break in (and
even then, the built-in fail-safe would save
you). Basically, interference is just this
side of impossible.
HOW MANY CHANNELS ARE
AVAILABLE?
The 27 and 75MHz bands currently in use in the
U.S. have 6 and 30 channels, respectively.
Although that's technically enough channels to
do what we have to do, the burden has always
been having enough spare sets of crystals to
be reasonably certain that you'll have an open
one when it comes time to race with 10 or more
other cars. The Spektrum has more than twice
the number of channels, so there's no need to
spend extra moola for channel changes. The
number of available channels is determined by
the Spektrum developers, and there's plenty of
room on the band to add more channels down the
road, but it's inconceivable that more would
ever be needed. The distance between the
channels allows many simultaneous streams of
information from optional telemetry devices.
WHAT ABOUT CELL
PHONES, CORDLESS PHONES, WIRELESS ROUTERS,
ETC?
All wireless devices on the 2.4GHz have to
include collision-avoidance technology—no
exceptions. There could be 20 cordless phones,
as many wireless routers and a multitude of
other devices, and the result would be the
same: no interference.
IS ANY PERFORMANCE
LOST DUE TO THE SHORT ANTENNA?
The high-frequency 2.4 GHz band requires a
short antenna. The Spektrum receiver comes
with an 8.5-inch antenna, and it's every bit
as effective as the really long antennas
included with the 27 and 75MHz receivers. In
fact, the included antenna is 8.5 inches long
so that it can make its way out of a receiver
box. According to the instructions, it can be
cut to 3.6 inches for touring cars and other
installations without any loss of performance.
The antenna should be installed so it stands
vertically, but it doesn't have to come
through the body at all.
IS THERE A FAIL-SAFE?
The positions of the steering and
throttle/brake channels are stored, so in the
highly unlikely event of signal loss, the
servos will return to the preset fail-safe
positions. Here's the bonus: even if your
radio gets stuck in impound, when you flip on
the receiver switch, the servos will still go
to their present fail-safe position. That will
be especially helpful when warming up gas
cars; you won't have to worry about the engine
revving too high when you look away.
HOW MUCH POWER DOES
IT REQUIRE?
The Spektrum receiver draws about 40mA. This
is higher than the 12 to 15mA drawn by
standard radio receivers, but when the servos
are drawing upwards of 1000mA, this is
insignificant. On the other hand, the module
draws only about 120mA, which is about 40
percent less than a standard radio. That means
you'll get long life out of the transmitter
batteries.
WHAT SHOULD I DO WITH
THE STANDARD ANTENNA?
Ordinarily, operating your transmitter with
the antenna removed or collapsed can damage
it, but the Spektrum module disables the
original antenna, so it can be run collapsed
or removed entirely.
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TELEMETRY IS HERE!
Horizon promises that telemetry options will be
available for the Spektrum system, and the first is
described on the Spektrum website spektrumrc.com:
"The first optional telemetry module will include
the ability to monitor real-time engine temperature,
engine rpm, speed in mph or kph, battery voltage,
signal strength and individual lap times. You'll even
be able to record the data and review it later on your
PC. We hope to have this telemetry module available in
early spring." It also indicates that the
information will be read on a hand-held display that
you or your pit man can read from anywhere on the
track to monitor engine performance.
TESTING THE SPEKTRUM
During a quick "binding" process, a button
on the receiver and one on the transmitter are pressed
so the two components can be synchronized, and that
ensures that the receiver will recognize only that
transmitter. It only takes a moment. It's wise to be
aware of other people binding their receivers and
transmitters in the immediate vicinity, but the
chances of a mix-up are slim. The binding range is
only 5 to 6 feet, and someone would have to be in
exactly the same stage of the process in order for
your receiver to "listen" to the wrong
transmitter. If there were a problem, you would just
have to rebind your system.
I installed the Spektrum in an XRAY T1 Factory kit and
spent quite a bit of time racing the car at Hobby
Chamber in West Haven, CT. The track's tall drivers'
stand places transmitter antennas inches from the
roof's steel trusswork, and glitching isn't uncommon
even with high-end radio systems. The Spektrum
performed and continues to perform flawlessly. It
simply operates glitch-free every time the car is on
the track.
Track interference should never be a concern, but we
have discovered certain hot spots where even the best
radios have been known to glitch or shut down due to
interference. One of the worst is the upstairs hallway
of our building. It's about 200 feet long and
notorious for trashing cars. It's surrounded with
fluorescent lights, copiers and printers that combine
to produce the toughest environment we've ever seen to
test a radio system. It's virtually impossible to make
it end to end for without hard glitches that can
re-kit a car in the blink of an eye. Even here, the
Spektrum performed transparently—no hits, no
glitches.
A more recent discovery is the area under my desk. My
computer, combined with an electrical outlet and a
gaggle of networking plugs, causes fierce glitching
even at close range when I set up radio gear on my
bench. This became apparent when we used the standard
M8 to pilot the cars in the new Virtual RC simulator.
After I had installed the Spektrum, the interference
disappeared.
The only function we could not test was the Spektrum's
channel-seeking capability, since we were not testing
it alongside other Spektrum users. But we can cite the
experience of factory team drivers who have been
racing with the system and say that it does perform as
promised—just switch it on, and the Spektrum does
all the channel-surfing.
THE VERDICT
The Spektrum system is an incredible leap forward in
radio technology that will reshape the future of RC.
Yes, buying a top-end radio and the Spektrum system is
expensive. That's the cost of advancing technology,
but things like this tend to become more affordable
over time, and it shouldn't be long before you see
this technology built into an off-the-shelf radio
system. Until then, the Spektrum brings the technology
to us today, and it works. No matter what happens in
the years to come, we can all look back on this moment
and know that we have witnessed history in the making.
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