Aerocam is an airborne video system developed to transmit live video pictures from a model aircraft to the ground. The system consists of a small video camera and transmitter mounted on board a model aircraft. The transmitter sends picture and sound via a small antenna to a receiving system on the ground. The picture is demodulated by a receiver, recorded on a VCR and viewed on a television set. Aerocam has been developed over the past five years into a reliable system that gives excellent results.
The transmitter operates at 1250 MHz and uses FM modulation. The RF
output power is approximately 0.5 watt which is sufficient for this application and has a
theoretical range of 15 kilometres. It is the heaviest component weighing in at
approximately 500 grams. It requires 9-12 volts DC and draws approx 700 milliamps.
The transmit antenna is a 1/4- wave monopole which is compact and lightweight and radiates
the signal in nearly all directions. As the transmitter operates in an Australian amateur
radio band, an amateur radio licence is required to operate the transmitter (my callsign
is VK1TMG).
The receiving system consists of several components. A 1/4-wave monopole antenna attached to a tripod receives the transmitted picture. The signal is then amplified by a low noise amplifier with a 0.9 dB noise figure and fed into the receiver. The receiver is an old surplus satellite receiver which tunes to 1250 MHz and FM demodulates the video and audio to baseband signals. These signals are then fed to a VCR which records them. A portable TV set is used to monitor and view the signals. The receiving system is powered from 240 VAC which is provided by an inverter connected to a car battery. The receiving system can run directly off a 12 volt car battery.
The colour video camera is a small module consisting of a printed circuit board with a lens mounted directly on it. It has automatic exposure and shutter control so no adjustments are necessary. The lens has a wide viewing angle (85 degrees) which is ideal for this application and has a fixed focus which is set to infinity. The camera operates from 7-13 volts DC, draws approximately 160 milliamps and outputs composite PAL video. It is mounted in an aluminium case to protect it from damage in the event of a crash and to shield interfering signals. The camera itself weighs 60 grams. The camera, case and cable weigh 150 grams.
As nearly 900 milliamps of current is required to operate the camera and transmitter, battery considerations are important. Eight "AA" nicads with 700 milliamp-hour capacity are used. The batteries operate the camera and transmitter for approximately 45 minutes. The battery pack weighs 240 grams. The total weight of the payload is 900 grams. This is light enough for most .60 sized aircraft.
One area of concern is possible interference to the R/C receiver from the high level
signal generated by the video transmitter. In order to ensure electro-magnetic
compatibility between all airborne components, ferrite beads are placed in power and
signal leads and shielding is used wherever possible. The transmitting antenna is mounted
away from the R/C receiver and it's antenna. In practice, no interference has been
experienced when using two different types of JR PCM receivers.
A switch, activated by an unused channel, is used to turn Aerocam on and off via
the R/C transmitter. This is a safety feature to keep the plane under control if the video
transmitter interferes with the R/C receiver. If interference occurs, the transmitter can
be turned off either manually or by the receivers failsafe circuitry.
As for the cost of the system, the camera cost $400 (commercially available), transmitter parts were $100, battery $30, tx switch parts $10, antenna parts $20, receiver $200, receiver amplifier $40, VCR $200, TV $300, 12V/240V inverter $200. So, for around $1,300 and with electronics / radio knowledge, you could also have your own Aerocam system.
Aerocam has been placed in an aerobatic aircraft and a Piper Cub and the results have been excellent. There are plans to place Aerocam in a helicopter and glider in the near future.
The files below contain video footage taken using Aerocam. The files are reasably large and may take some time to download. The videos are in Microsoft AVI format.
Takeoff.avi (2.3 MB)
Flyover.avi (0.9 MB)
Aerocam was designed, built and flight tested by Mark Griffin,
Canberra, AUSTRALIA: mark.griffin@ties.itu.int.
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