Featured Product Archive
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.
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Apps 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).
Fortunately 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
former case.
Now 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.
The
Spektrum™ STi™ Telemetry Interface 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.
Posted August 5, 2011
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