[Makers] UAV comms Jack Pittar jpittar at bigpond.net.au Tue Jan 11 11:47:28 EST 2011 Thanks for your inputs regarding communications equipment foud so far. To bring you up to speed, here is some info showing where we are at this moment. Plan so far: - Now till 1st Feb - Research options / requirements analysis. - 1st Feb till Mid May - Level 1 (L1) development. L1 is the minimum necessary to carry out the challenge. Only when L1 is achieved will any further enhancements be tried. We have broken the project up into five main areas. - Aircraft Platform (inc airframe, power system, actuators and payload) - Video - Mission Control System (inc on board processing and sensors) - Comms links (inc mast and tracking antennas) - Ground Station. (inc mission management) Since there has been some interest and assistance from the makers list, this email concerns the radio communications. System plan so far is to have 3 main transmission frequencies for L1: 1. Manual radio control : 2.4 gig. This allows us to do all development at a local model aircraft field, which is highly desirable, but it means we cannot use the 2.4 gig band for anything else. 2. Video: to be determined. 2.4 gig at the last resort. The problem is finding a license free frequency with enough power and bandwidth to cover the distance we need. A lot of commercially available equipment overseas cannot be used in Australia. Using a commercially available device to superimpose On Screen Data (OSD) on the video stream does not constitute digital telemetry. We expect to have to use a high gain antenna at the base station to receive the video, which means tracking the aircraft to point the antenna. The antenna pointing could be done manually, using the video signal, or using the navigation data from the telemetry. 3. Telemetry: To be determined. 2.4 gig at the last resort. Thoughts of WiFi. Duplex digital telemetry most likely. A high gain receiving antenna on the aircraft is difficult, but not out of the question. Regards, Jack. Here follows an excerpt from Dave. UAV Communications Limitations The specific class licence that we would most likely want to operate our transmitters under is called the "Low Interference Potential Devices" (LIPD) class licence. I have attached the LIPD class licence frequency list to this email, sorted by frequency. In the LIPD class licence, there are many possible frequencies that we will be able to legally operate on, subject to power and other constraints. The majority of cheap consumer radio equipment, however, is in the following bands: 433MHz band (433.05-434.79MHz in the LIPD) 472MHz band (472.0125-472.1125MHz in the LIPD) 900 MHz band (915-928MHz in the LIPD) 2.4GHz band (2400-2483.5MHz in the LIPD) 5.8GHz band (Around 5500-5875MHz in the LIPD) When viewing the specs of or purchasing transmitters: 1. The conformity to a class licence must be taken into account. This is because it is a requirement for the UAV challenge. 2. Any claim to distance that is made in the spec sheet will be assuming a certain power, transmitter/receiver antenna gain and receiver sensitivity. I have made and attached an excel spreadsheet that calculates theoretical maximum distance of a comms link. 3. Know that the easiest links to find an adequate transmitter for are ( the digital telemetry links ). This is because they are relatively low bandwidth when compared to the video link, and therefore can be fairly low power and can be bought cheaply off the shelf. To put this in perspective, a telemetry or command link might require 10kbps (10-50kHz of bandwidth), whereas a video link (analogue or digital) requires about 6MHz (6000kHz) or more. Increased bandwidth means you have to increase the power to support the bandwidth, otherwise your power spectral density won't be enough to literally go the distance. This is where we will start coming up against ACMA power limits - for the video link. -o0o-
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