I would like to introduce you to a new radio modem that we developed for very long range datalinks!
Some of the key features of the RFD900 are as follows:
- Multi point and point to point link capability.
- Long range >40km depending on antennas and GCS setup.
- 2 x RP-SMA RF connectors, diversity switched.
- 1 Watt (+30dBm) transmit power.
- Transmit low pass filter.
- > 20dB Low noise amplifier.
- RX SAW filter.
- Passive front end band pass filter.
- Open source firmware / tools, field upgradeable, easy to configure.
- Small (30 x 57 x 13 mm), light weight (14.5g).
- Compatible with 3DR / Hope-RF radio modules.
- License free use in Australia, Canada, USA, NZ.
These modems are designed to support long range applications, while being easy to use and affordable.
These modems have been flying in various platforms and have demonstrated excellent performance in real applications.
RFD900 modems are now available at: http://store.rfdesign.com.au
Support within APM planner and the radio configurator from Michael Oborne is already available.
It works seamlessly with APM planner, all radio Mavlink parameters are available.
Update, December 2014: The RFD900+ with improved specifications is available now at:
I was thinking about using a helium ballon thus basically an endless flight time for the high flyer.
we are thinking of something slow and efficient for the the high flyer that could easily outlast the low flyers endurance. balloons do not allow us to repostion the high flyer as the low flyer grid searches. the biggest issue i think i haven't figured out is the recovery (landing) of both the high and low flyer vehicles. my current plan is to find a place near the command center but that involves a little cross country which is wasted battery time for both. we could hand launch both near the search scene after packing them in with a team if we wanted but that hike takes time - batteries are cheap and easy to replace so we just need to manage our energy very well. i would like an emergency chute system on both vehicles (HF and LF) but that just adds weight. a locater beacon will also be mandatory so we can find the beasts when they crash in the middle of the forest.
for initial search we intend to use fixed wing assets for both HF and LF. once we spot the target of the search we might want to send in a multi-rotor with a radio or medical supplies. a multi-rotor would also allow an up close and personal look at the scene from the air to assist planners on the extraction. we could airdrop stuff from a fixed wing as well. this applications has all sorts of issues (possibilities).....
I have done this successfully using FPV video. I think this would be more useful for you. What is so important about telemetry once the mission is underway. You really want to see where you are going so you can assure obstacle clearance. I used a 5.8Ghz link airborne on a Bixler since the Rx is so light, and a 1.3Ghz on the ground. The 433Mhz DragonLink did well enough "around the corner" so I didnt need to relay that signal. However it is very easy to relay a PPM signal too. I would use something with a lighter Tx than the DragonLink, like OpenTx. Just connect it to the CPPM output of a little 2.4Ghz Rx and you have a control relay to over-ride the flight plan when you see the mountain getting too big in your goggles.
I view telemetry as a nice to have luxury since I only trust what I can see. Especially in the mountains where the google maps are less accurate.
I want to be able to interact with the vehicle as it does the grid search. i want to be able to RTL or orbit a point that wasn't part of the mission planned grid search. i would like to be able to modify the mission based on new info without returning to base and uploading that info. Seeing and avoiding large trees would also be nice. Once I lose line of sight with the vehicle after launch my rc control is lost and i hope to be able to use the MavLink to control the vehicle using a joystick connected to my ground control station computer - crude control, but still some control. ideally i would want to hand off the rc control from whoever launched the craft from the command center to someone in the search area that has line of sight with the low flyer - i cannot do that because of the pairing issues with today's rc systems. I am not really too interested in the telemetry data but it would be nice to have in case things start going weird....
Using RC you can RTL or Loiter, but you can not modify the auto mission without mavlink control.
You can hand off RC control using DragonLink using a specialized version of the firmware that they provide. It allows 2 transmitters to control the same Rx, you just need to coordinate one operator turning off their Tx when the other turns his on.
i am not the RC guy - i am the data guy. i will pass this on to the "pilot" and that will really make a nice change in the concept of ops for the design. i really appreciate your input. i knew we could change the flight mode using the RC to a couple of pre-planned settings - we do that all the time with the quadcopters. i like the flexibility of being able to communicate with the autopilot from the GCS if i can keep that link up - that's my real goal for the TM now that the field folks will be able to RC control the low flyer.
i am working on an application for search and rescue which will involve using a low flying search vehicle, a high flying TM relay vehicle, and a pair of ground control stations for both vehicles. The need for the TM relay vehicle is because of the terrain of the search areas and need for a takeoff and landing strip that would support launch and recovery of the searching assets. i have a couple of questions regarding the RFD900+ and the TM distribution board that are part of my conceptual design.
1. has anyone ever tried what i am doing - i hate to learn everything the hard way so if someone has experience i would love to hear about their experiences
2. i see that the RFD900+ can be used on one end of a link with a 3dr (or compatible?) modem at the other. i don't really intend to do that but would that work with the TM distribution board in the loop.
3. am i right to assume that i need two TM distribution boards - one to combine the serial streams on the transmit end and one to break them back apart on the receiving end. also, does anyone have any experience they would like to share regarding the use of the TM distribution boards?
i am looking forward to any help i might receive.
Flying a repeater is not a good idea. You'll get better performance from ground based repeaters. You simply can't compete with large ground based antennas and antenna trackers.
Still won't make up for a good ground station vs. whatever you can shoehorn onto a aerial repeater.
Even if you want to fly illegally, way out of VLOS, like suggested your best bet is still a ground repeater.