On 3/15/98 10:17, tduffy at tduffy@sygnet.com wrote:
>The subject is radar controlled hobbiest airplanes.
RADAR-controlled? I assume you mean Radio Controlled.
>From testimony to date, we have been told that these hobbiest aircraft are
>controlled by a low power transmitter controller operating at about 1 watt of
>output power on 27 Mhz.
>
>The controlling 27 Mhz (1) watt signal essentially guides the hobby plane's
>maneuvers - while in flight - allowing it to be safely flown and landed.
This appears to be accurate, but I would think that anyone using a 27 MHz
radio must be into antiques. Today, nearly all RC radios (other than the
toy cars you find at Radio Shack) are 72 MHz. A few RC hobbyists are
hams, and they may have 50 MHz radios as well.
>The questions being raised are whether the establishment of an amateur radio
>station with 100 foot towers and full legal power operating on the parcel
>next
>door will cause destructive interference STRONG enough to "override" the
>aircraft controller 1 w signal thus causing the aircraft to crash in flight.
More likely is a crash induced by someone else on the same channel
turning on their transmitters while someone else is flying. It happens.
>Questions:
>
>1) How valid are the allegations and fears posed?
Not very.
>2) Will ALL amateur bands likely affect the 27Mhz controller?
Probably not, but it isn't impossible. The question in my mind is how
likely is it that someone is flying with a 27 MHz controller?
>(If the hobbiest planes have a wideband front-end receiver of poor selective
>design, an amateur KW signal operating on 28Mhz MIGHT possibly be a problem.
>Would a harmonic from 14Mhz also be an issue?)
A KW signal from 28 MHz might cause a problem, but any illegal CB signal
on the same or similar frequency running power would DEFINITELY cause a
problem. This is why nearly all RC aircraft have moved to 72 MHz.
>3) Does anyone out there have any experience with these hobbiest aircraft?
I used to fly them. Now I'm doing full-scale airplanes.
>4)Can anything be done to remedy interference/interaction issues that MAY
>ARISE?
>5) Has anyone out there run into this one before?
>6) If interference IS unavoidable, how far must the controller/planes be
>removed from the amateur site for SAFE operation?
Good question. Let's add afew points of information.
Most modern 72 MHz radios are either FM or PCM, and as such they show a
good amount of interference rejection. In recent years, the AMA
(Association of Model Aviators?) called for improvements in the
interference rejection of radios, and such radios should have a "gold
sticker" certifying compliance with these new standards.
As for safe distances, that depends. Given that an aircraft in flight is
relatively high (100-500 feet) it is subject to signals from a
considerable distance away. For this reason, aircraft receivers are
actually fairly good at rejecting unwanted signals.
If modelers are flying aircraft several miles from your installation, I
would not worry about it. If they are within a mile or so, there may be
some cause for concern.
Note that flying these devices takes considerable open space. There's too
much danger of running into trees, buildings or other obstacles. If
there's no known activity of this kind in your area, one wonders why it
was brought up. If there's a modeling field nearby, perhaps you can work
with them to see if interference might be possible. Or, in the worst
possible case, volunteer to curtail operations on certain bands when
you've ascertained that modeling operations are taking place.
Frankly, when you think about it, RC receivers are going to have a much
harder time filtering out multi-MW FM stations transmitting continuously
just a few MHz away than your puny, intermittitant KW transmissions half
the frequency away.
Unless someone can come up with people ACTUALLY USING 27 MHz RC radios,
this whole line of argument is probably specious.
Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@radio.org
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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