Spektrum Wireless Telemetry System
for smartphones are all the rage. Many product manufacturers are providing apps as part of the package. What makes
this particular app cool is that it is part of a wireless telemetry system offered for remote controlled models.
It used to be that a modeler was satisfied just to have reliable communications from his transmitter to his
airborne receiver. That is especially true these days when the total value of an airplane, engine, and associated
hardware can easily exceed $2,000. The guys who build incredibly detailed scale aircraft that reflect many
hundreds of hours
of building, painting, and detailing a WWII era B-17 bomber or a twin-turbine F-15 model put it all on the line
the moment the plane is put in motion. Any failure of the receiver to properly decode the transmitter's signal can
- and often does - result in total loss of all their effort. RF interference has in the past been the most
prominent cause, either from nearby unintentional radiators or from dopes who switch on their transmitter
operating on the same channel (the FCC reserves 50 frequencies exclusively for airborne R/C).
for the modeling community, sometime around the turn of the century (21st, not 20th) some smart engineers figured
out how to build reliable radio control systems that operate in the 2.4 GHz ISM band using
spread spectrum modulation. The quantum barrier to be tunneled over/around was sufficient range while keeping
within the FCC's maximum power output specification. Redundant receivers with separate, orthogonally oriented
antennas provided the largest part of the solution, but the availability of more sensitive receiver ICs played no
small part. Frequency hopping and direct sequence spread spectrum is being used by competing manufacturers, and a
couple have even implemented a combination of both; I'm not sure how the processing gain is calculated in the
I'll return to the telemetry and smartphone app part of the story. A couple years ago R/C system manufacturers
began offering receivers and stand-alone airborne transmitters that talk back to the earth-bound transmitter in
the pilot's hands. Onboard sensors report battery voltage and current (complete with low battery warning alarms),
engine/motor temperature, RPM, altitude, airspeed, motor power for electric-powered aircraft, signal quality, and
a few other functions. Parameters display on the large LCD screens that are a part of the more expensive
transmitters (some more than a 1kilobuck). The entire flight can be recorded for playback later.
Spektrum™ STi™ Telemetry
for iPhone®, iPad® and iPod touch® is a stand-alone receiver that does not require a suitably equipped transmitter
to operate - it simply plugs into your device. That allows a helper to monitor critical functions for you while
you concentrate on flying the airplane. It is not unusual on sophisticated model aircraft to require an assistant
to operate auxiliary functions like flaps, bomb release mechanisms, machine gun firing, brakes, etc., so having a
helper for monitoring onboard conditions is not a new concept.
Do I have one, you might ask? No, not yet.
Time just does not permit me to justify the cost at this time. As soon as some company from China buys
RFCafe.com for a couple million dollar$, then I'll be getting
one right away. It would be nice to get one to do a teardown report, though.
The inventions and products featured on these pages were chosen either for their uniqueness in the RF engineering realm, or are simply awesome
(or ridiculous) enough to warrant an appearance.
All Featured Product Archive Pages:
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Posted August 5, 2011
1996 - 2018
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas
and reference material while performing my work as an RF system and circuit design engineer.
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