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We've learned a lot about the use of DSM in all applications of RC modeling. While DSM
solves 98% of the RF-related issues that plague 72/75MHz bands (being shot down, shooting
others down, model-generated interference, external interference, etc.) there are still
opportunities to maximize your DSM experience through use of these "best practice" ideas
Here's more detail on each of these concepts
The #1 problem encountered by DSM fliers: inadequate power supply. Unlike PCM, where servos
get "crunchy" at voltages as low as 2.5 volts, the digital system used in DSM shuts down at
3.2 volts. 99% of fliers have no problem, but when you do, it's a toughie. New QuickConnect
software allows restoration of your radio link the instant voltage is restored.
When your model is worth thousands of dollars, why skimp and save $30 for an extra remote receiver?
Why using multiple remote receiver is important.
Having additional receivers increases your chance of having a perfect RF link, pure
and simple. More is better. And when you have correct polarization (see DO polarize
when possible) things get even that much better.
Plus there's the irrefutable benefit of having redundancy - something no single
receiver can match.
With the Flight Log, you won't just think you're getting great
performance, you'll know it. It'll give a feeling of confidence you can't
have with other 2.4GHz systems.
What is the Flight Log, and why is it important?
The Flight Log is a device that plugs into the data port of the receiver and records
the fades, frame losses, and the extremely rare hold. (Data ports are available on
current 7 channel and up receivers.) It'll allow you to tell how well your DSM system
is working in the plane. Most of the time, it'll confirm that you're getting near-perfect
performance. But in some cases, it'll act as an early-warning system (especially if you use
the technique described in "Do a first flight relatively close in with flight logger".)
Basic description of Fades, Frames, Hold (in the Flight Log)
Fades: when a particular receiver does not receive a good packet of information (frame).
With the patented MultiLink system, all receivers work simultaneously, so an individual
fade is little concern. High fade numbers indicate that a receiver is not getting
the information, which is sometimes unavoidable.
Frame: When the Flight Log records a frame loss, it means all receivers failed to get
a good packet of information simultaneously. Small frame losses are common and to be
expected. However, large numbers, (over 50 or more) should be investigated.
Holds: In the rare occurrence your system encounters 45 consecutive frame losses,
a hold will be triggered. How long does the hold last? Holds last until the next
frame of good information your system sees then your control will be returned. Unlike
early PCM systems, there's no delay with DSM - no re-booting, no nothing. This is why
in the rare instance we have seen a hold, itisn't noticeable, because control has
already been re-established. That said, anytime a hold is discovered, it should be
(tip) When flying sailplanes and electric racers, we've noted that we can induce Flight
Log "hold" simply in the process of landing - especially if one lands a long distance
away. The model is safely on the ground, but the antennas might be in grass. This can
cause a hold to occur in the Flight Log, even though by the time you pick up the model,
everything is normal. Test this by clearing the Flight Log, have an observer watch the
"hold" screen and move the transmitter back away from the model.
It doesn't take much to do a quick range check. It's extremely rare that a radio won't
range test. But since we don't have to worry about engine-on interference, it won't take long
to do a simple range test to assure everything's working right. Simply hold the button in,
walk backwards at least 30 paces before you fly a new model.
There's more information on our website "Advanced Range Testing" for those who'd like
to explore greater detail in range testing.
Like all radio equipment, range is proportional to an inverse square. That means
range is non-linear. At a certain point, the signal drops off rapidly. But how far is
far enough? We've flown giant-scale models over a mile away, so the range of the
DSM system is quite proven. But in challenging models (those with lots of carbon
are the worst) you can increase your chances of success dramatically if you keep your
first flight relatively close in. Then land, check the numbers on your Flight Log, and
try another flight farther out. Then, farther out again. Taking a progressive approach
is the best way to reduce risk and improve your odds.
The short leads provided with most Spektrum receivers are good for small aircraft,
but if your plane is larger, use the longest leads possible. On many GS aircraft, put
one remote back in the tail as far as you can reach. Run the other one forward, or
high behind the canopy.
Why it's important
Spreading the remotes helps assure that one or more receivers will always have a
signal. When we did our one-mile flight at Joe Nall, there were only a couple of
fades and frame losses. In preparation, we flew the model to .8 of a mile with zero
frame losses - a perfect RF link. That's because we employed all of the techniques
mentioned here, and they work.
Polarization is simple: it means putting the antennas in vertical, horizontal and
longitudinal axis (X,Y,Z, to some).
What this does is assures that at any time, one receiver will be oriented for
optimal polarization. This also contributes to why you should use three receivers
(or four) whenever possible.
Polarization isn't absolutely critical, but it sure helps to give lower numbers
(a stronger link). The results can be seen on the Flight Log.
While all Spektrum 9-channel-and-above receivers have multiple battery ports, you can
actually put multiple batteries into any Spektrum receiver. Simply choose two batteries of
the same size and capacity with two switches. A common misconception is that one can hurt
the receiver with too much current. Wrong. They'll handle over 30 amps. By using 2 batteries,
you halve the current on the battery connector, which is the weak link in the system (the
reason our engineers developed the AR9100 and R1222 receivers).
It's a good practice - it keeps the antenna straight and won't interfere with the operation.
You don't fly over your head, do you? Unless you're flying directly over your
head, orienting your transmitter in a vertical position - no matter what way you
hold your transmitter - will provide great results. How big a deal is this? For most
flying, it's a non-issue. But for optimization, keep the antenna from being pointed at the
Why it matters
Our lead engineer says the radiation pattern from the Tx antenna is apple-shaped -
the least output is out the tip of the antenna.
By routing your remote receiver wires away from noise sources (like ignition
batteries, switches, ESCs, ECUs) youll eliminate any chance of a form of
interference called inductance. While 2.4GHz systems are impervious to noise that
comes in through the antenna (RF noise), noise can still enter the system through the
leads for remote receivers (inductance) and even servo wires.
Compatibility is the key issue here. While economy servos may have worked fine with
older-generation radios, our field reps have traced a host of problems to non-JR
servos. JR servos are not only leaders in precision and performance, but they're very
tolerant to a wide range of voltages - both high and low - for maximum reliability.
For more fun and less fiddling, JR servos are the #1 way to go.
When initializing, early Spektrum receivers scanned the spectrum to find the correct
digitally encoded message - a process requiring about 2 seconds to complete. Not a big deal
on the ground. But when flying, should the voltage of the system ever drop below the
3.2-volt threshold, early receivers would require 2 seconds to "re-boot."
To solve this, Spektrum engineers devised the QuickConnect feature that automatically
stores the frequency in the receiver. This allows the connection to be restored the instant
system voltage is restored. Receivers with this software will flash in the event a power
failure is encountered.
One easy way to test your system for the QuickConnect feature is to get your system
working on the bench, and then simply cycle the power. If all your lights flash, you have
this feature in your software. Both the main receiver and remotes must have QuickConnect
software for this to operate.
In practice, normal systems with adequate battery "headroom" will never need or use
If you do see lights flashing in your model after a flight, please investigate
the source of the power issue before flying again.
They interfere with the signal to the servo, especially with higher voltage systems.
Using old batteries, without adequate voltage conditioning, is taking a big risk. Just
because they worked with PPM systems or PCM systems does not mean they'll work with your
new Spektrum radio.
We're not saying that you shouldn't use old batteries, only that you should know what
you're using (you should cycle the battery and know that it's within rated capacity) with
your DSM system. Old batteries that are in poor shape fail to deliver the current your
servos need resulting in voltage drops.
They should not be tampered with.
They can cause issues. Run the servo directly to the receiver, or use a reversed servo as a last resort.
The antenna output is "apple" shaped - that is to say, the lowest output comes directly out the tip of the antenna. For maximum output, keep your antenna away from the model.