Modems
Radio modems allow for a digital uplink and downlink from the aircraft. During development a downlink was established with the video transmitter, and an uplink using spare channels on the RC transmitter. Now with a Radio modem changes to gains and waypoint positions can be made on the laptop during flight. Initial testing was done using a Coronis Wavecard which showed very good results. Testing has now begun using a Maxstream 9Xtend, which has shown great range and reliability. Waypoint moving, as well as flight plan block changes have been done. Gains have been adjusted as well.
Aerocomm AC4868-250M
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Pinout
| AC4868 20-pin Header | Name | Color | Tiny Serial-1 | Notes |
| 2 | Tx | green | 7 | (Note 1) |
| 3 | Rx | blue | 8 | (Note 1) |
| 5 | GND | black | 1 | - |
| 10+11 | VCC | red | 2 | +3.3v |
| 17 | C/D | white | 3 | Low = Command High = Data |
Note 1 : names are specified with respect to the AEROCOMM module
Documentation
Maxstream XBee Pro
These relatively cheap and light modules implement the ZigBee/IEEE 802.15.4 norme. They allow up to 1 mile range(Paparazzi tested to 2.5km). The main drawback of using such 2.4Ghz modules for datalink is that it will interfere with the 2.4Ghz analog video transmitters and a inevidable decrease in range when in proximity to any wifi devices.
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Pinout
Documentation
Maxstream 9XTend
These larger units have been tested on the 900Mhz band, but are also available in 2.4Ghz. They are a bit on the heavy side(~20grams) but give good performance at range. They have adjustable power settings from 100mW to 1W. Testing has shown range up to 2 miles with 100mW.
 9XTend USB Modem |
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 9XTend OEM Modem |
Pinout
Documentation
Coronis WaveCard
These relatively inexpensive and light modules implement a Coronis proprietary protocol. Low power consumption - high latency - I would not recommend these modules mostly because of the low quality of the distribution and support. The documentation is rather poor and not easily available.
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Documentation
Video Transmitter Telemetry
In order for the UAV to transmit video from an onboard camera, a video transmitter is needed. The paparazzi AP sends all telemetry data down with the video on the audio channel portion of the transmitter. This means that the transmitter must have an audio channel. These vary in power, and thus range, and run normally on 2.4Ghz. Small UAVs can get about 600m of range from the 50mW version, and extended range can be achieved using units up to 1W. Weight for these units varies from a couple grams to about 30 for the 1W with shielding. Please check for your countries regulations on 2.4Ghz transmission, as each is different.
Antennas
Here are some examples of lightweight and efficient 868MHz antennas developped by the RF laboratory at ENAC.
