5

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
Receiver
    - 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?

Kevin Reid AG6YO
  • 24,506
  • 7
  • 51
  • 103
wittrup
  • 153
  • 4
  • Commercial, or is amateur okay? – PearsonArtPhoto Jun 05 '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 06 '14 at 03:01
  • @PearsonArtPhoto Amateur is fine. – wittrup Jun 06 '14 at 06:08
  • @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. – wittrup Jun 06 '14 at 06:09
  • 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? – Phil Frost - W8II Jun 06 '14 at 12:54
  • @PhilFrost Let's say my words "It is the radio stuff I don't quite grasp." is an understatement. Except for some experience which learned me basic handling like how to grab a handset and communicate over radio, turn the knob to change the frequency, if the display says suspiciously low "SNR: 0" your car most likely lost your antenna etc. I know next to nothing about radio communication. I have a vague idea of attenuation, amplification, noise, jamming... To answer your question more directly: I do not know how to estimate the range. I basically do not know where to start in radio-world. – wittrup Jun 06 '14 at 15:50
  • @wittrup Sounds like a pretty broad problem...too broad to answer here. You might check out What is a link budget, and how do I make one? which addresses one facet of that problem. – Phil Frost - W8II Jun 06 '14 at 16:58
  • @wittrup It seems to me that the easiest and most legal way for you to solve this problem is to use a smart phone platform with a more high performance GPS, perhaps with an electronic barometric altimeter, instead of the consumer GPS in phones or the flysight device. After that it is an Android programming problem. Built-it-yourself cell phones do exist where you can add unique sensors, the name escapes me at the moment. Unfortunately, this is all off-topic on this amateur radio Q&A site. Try the Electronics SE site perhaps? – Paul Jun 07 '14 at 05:09
  • @Paul One of the key-features with Flysight is the real-time audio feedback to the jumper/flyer (that has to be reproduced with the phone platform), as well as the high-performance u-blox 6 based NEO-6 series of GPS module needed to provide accurate data at about 200 km/h. At default it is set with a 5Hz / 200ms refresh rate. I have stumbled upon a Digi XTend module that might work: http://www.digi.com/products/wireless-wired-embedded-solutions/zigbee-rf-modules/point-multipoint-rfmodules/xtend-module It costs though and seems troublesome to acquire outside North America. – wittrup Jun 07 '14 at 10:26
  • @wittrup Back before everyone became paranoid, I once pointed a hiking-quality GPS out a commercial aircraft window. It did fine at 500+ mph. I think, though, that to record acrobatic maneuvers for display on a computer screen, something better is needed. Also, voice will use up more than 1khz of bandwidth and amateur radio technologies combining voice and data are at a primtive level. Besides cell, I would also think the alternate band wireless internet 802.11(a) (@5.? Ghz) could work. Good luck with it. Cheers! – Paul Jun 07 '14 at 10:42
  • This question appears to be off-topic because it is about engineering a data link for commercial purposes, not amateur radio. – Paul Jun 07 '14 at 10:45
  • @Paul There is no voice or audio radio transfer involved. The real-time audio feedback goes from Flysight to jumpers ear with earplugs or similar 3,5mm jack speaker, all on the same helmet on flyers head. Flysight is designed to do this specific task as well as store log files that can be downloaded and reviewed on ground. There is nothing commercial about my project. – wittrup Jun 07 '14 at 12:16
  • This question appears to be off-topic because it is not about amateur radio in anything other than as a telemetry medium. – WPrecht Jun 20 '14 at 13:19

2 Answers2

4

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.

BenSwayne
  • 681
  • 1
  • 7
  • 14
  • A google search related to your answer led me to the http://copter.ardupilot.com/wiki/common-using-the-3dr-radio-for-telemetry-with-apm-and-px4/#What_range_can_I_expect Only a 100 bucks. Excellent. – wittrup Jun 12 '14 at 21:19
0

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.

Adam Davis
  • 12,125
  • 2
  • 47
  • 107
  • 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. – BenSwayne 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. – Adam Davis 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. :-) – BenSwayne Jun 12 '14 at 17:28