# LOS One-way radio system, 4km with at least 1000bytes/s

In order to track skydivers/BASE-jumpers with flysight I am looking for a one-way radio system to transmit the location data. System needs the following specifications:

Frequency:          Not important, preferable legal (Europe)
Bandwidth           1000 bytes per second (at least)
Range:              4000 meters
Line of Sight       Yes
Latency             As little as possible
Mobile Coverage     Not available
Transmitter
- Location      Air
- Movement      Moving, up to 200 km/h horizontal groundspeed
vertical distance: closing towards receiver during operation
- Interface     USB or serial
- Weight        As little as possible
- Size          As small as possible
- Location      Ground
- Movement      Stationary during operation, movable by car
- Interface     Not important, what ever works
- Weight        Not important, movable by car
- Size          Not important, movable by car


Any suggestions?

• Commercial, or is amateur okay? Jun 5 '14 at 21:32
• It sounds like you would need a tiny PC of some sort to control the flysight and the transmitter, read data from one and send it to the other. There might be a rough hobby solution for a couple of amateur radio enthusiasts with licenses and time to prototype and experiment, but this looks more like you want a working plug and play solution.
– Paul
Jun 6 '14 at 3:01
• @PearsonArtPhoto Amateur is fine. Jun 6 '14 at 6:08
• @Paul Flysight uses a Atmel AT90USB646 chip and needs to be reprogrammed to push out the location data over USB. Have some Atmel chips on PCBs at my new work so have to learn that sooner or later anyways. Know some programming and have a fair understanding of electronics. It is the radio stuff I don't quite grasp. Jun 6 '14 at 6:09
• This question has about zero value to anyone but you, and makes me wish "too localized" was still a close option. What are the odds that someone else will need to find a solution to your very same requirements? It would be much better to ask about whatever difficulty you are having in finding the solution to these requirements yourself. For example, do you not understand how to estimate the range? Or is this just a shopping question? Jun 6 '14 at 12:54

There are a number of commercially available RF data modems that operate within the amateur radio spectrum for hobby use particularly with RC (remote controlled) hobby aircraft. However, I believe your specific ITU Region imposes additional output power limitations which will make this challenging at 4 km distance.

The RFD900 developed by an Australian company is sold in the USA by jDrones for hobby RC use and will support ranges up to 40km and data rates up to 250 kbps! However please note these specs are inversely related and subject to the limitations of your antenna system and the environment (more speed closer, slower data rate further away). Line of sight open air 4 km should be no problem at all with the data rates you are talking about.

This particular model outputs 1 watt in the 902 Mhz to 928 Mhz frequency range otherwise known as the 33cm band in ITU Region 2 (Americas). However, it appears this band is not allocated in Europe (ITU Region 1) and may exceed your maximum output power limits - so you may not be able to use this specific model of hobby radio modem in your location. This is simply the only one I know because I am in Canada.

For Europe you should look for a comparable model in the 70cm (433 Mhz) band such as the PipX (only 100 mw). However the additional limitation on output power may limit operational range.

In that case you may need to look into building an antenna tracker for use with a highly directional antenna such as a yagi. This involves transmitting the GPS co-ordinates down the link and having the antenna tracker point the antenna straight at the target. This may be somewhat experimental if you are moving at 200 km/h - I think you will need to custom build your antenna tracker, perhaps taking into account the average falling speed and any latency in the motor controller and anticipating the targets future position.

Eitherway, experimentation is part of the hobby of amateur radio! So if you do decide to take this on, publish your project progress somewhere for all to enjoy.

• A google search related to your answer led me to the copter.ardupilot.com/wiki/… Only a 100 bucks. Excellent. Jun 12 '14 at 21:19

Amateur radio doesn't have a convenient off the shelf solution for you. Typical packet radio modems support up to 9,600 bits per second, which, after overhead, will be less than 960 bytes per second. Even if you use a faster modem, typical off the shelf radios have limited channel bandwidth that would prevent your required data rate.

You should be able to find 2.4Ghz transmitters at will handle the data rate, and with a power a loftier and the proper use of antennas you should be able to have the distance and data rate needed. A lightweight, small, low power solution will require a good bit of investigation and integration, and you'll need a proper amateur radio license and will have to follow the regulations for the area you are using this in, but you should be able to do what you want.

Look for high altitude balloon projects for inspiration. Most of those are low data rate links, but some have experimented with high data rat links for images and video as well.

• I believe they get around the limited channel band-width with Frequency hopping spread spectrum (FHSS) technology. In the USA (and Canada, Australia, New Zealand) you are allowed to increase the power output of FHSS transmitters to 1 Watt because "The spread-spectrum signals add minimal noise to the narrow-frequency communications, and vice versa. As a result, bandwidth can be used more efficiently." I am not as knowledgeable as I'd like to be in this area, but understand this to be possible and legal in some regions. Jun 11 '14 at 23:58
• No, they actually increase the signal bandwidth for higher data rates. Check out figure 4.3 in the data sheet, the signal is between 200kHz and 750kHz depending on the chosen data rate. Jun 12 '14 at 12:08
• Thanks Adam, yes I see that now. A wonderful thing datasheets are. Should have read that in more detail. :-) Jun 12 '14 at 17:28