Choosing a radio band & a long range modem

We live in France.

We only have two choice, basically :

868Mhz or 433Mhz

433Mhz is jammed.. stays 868 with 500mW limitation, which should be enough

I found a 868Mhz modem long range :

http://www.y-lynx.com/index.php?option=com_content&view=article&catid=39:archives&id=82:y-lynx-releases-their-trm8053-500-868mhz-band-500mw-long-range-radio-modem&Itemid=78



It might be interesting to investigate a bit more in that direction..

Why is the choice of the GPS module so important?

Most of the GPS are compliant with what is called “COCOM Limits”. Here is the issue! 

Indeed, it refers to a limit placed to GPS tracking devices that should disable tracking when the device realizes itself to be moving faster than 1 200mph (1 900 km/h) at an altitude higher than 60,000 feet (18,000 m). In such situation, the GPS receiver continuously resets until the situation is cleared. 

The objective of such limitation was to avoid the use of GPS in intercontinental ballistic missile-like. applications. 

Some manufacturers apply this limit literally and disable the GPS tracking when both limits are reached when other manufacturers disable tracking only when one of the limit is reached (higher than 60 000 feet OR moving faster than 1 200mph). 

High-altitude balloons are released into the stratosphere, generally reaching between 60,000 to 120,000 feet (18 to 37 km). For such application, 1 200 mph speed limitation is not an issue but the altitude limit is one! 

Therefore, if you want to be able to track your balloon as we would like, you have to choose a GPS using an OR statement that would continue to function above 60 000 feet. 

This is the case of the uBlox MAX-6 we have chosen. Order placed this last weekend on HAB supplies website. 

Max altitude: 164 041 feet (50 km) 

Support temperatures down to –40°C. 

The case / payload.. getting to it, at last !!

After a great long time without working on the project (holidays, back to work and so on), I finally found some time to go on with the next steps. 

I've been working a bit more on the "case". As a matter of fact, I hadn't worked on the mechanism that would enable the case to rotate on itself. The electronic part is getting ready, but I had to find a way to garantee that once the gyroscope sends a message to the motor gear, it may rotate the case. 

So here we are. The case looks like this : 

As we can see, the "eye" is made in plexiglass, and there is a "plate" on top of the box. This is the surface to which we will be attaching the parachute. This plate is attached to the case using a lazy susan, a bit like the one below

Here we see clearly the gap between the plate and the case.

On that example, we see how the lazy susan and the motorized part are linked together

We can see that the lazy susan is attached both to the blue and the green plate

Also, there is an axis that goes throught the lazy susan, and that is attached below the blue plate.

Through the green plate, there is a ball bearing, (below in red) so that the axis turns freely.

Below, there is a structure that holds the gear motor and the two gears, as can be seen below.

We can also see a bearing, in blue, below one of the gear. Thanks to this mecanism, the axis can rotate firmly and yet freely. 

I didn't put the engine right below the axis so that it doesn't take the load directly. 

Also, there is no reduction factor because the gear motor was choosen to rotate at a maximum speed of 90rpm. I didn't want the engine to run slower for the rotationnal speed I expected. 

Also, the V sliders were thought as a plug that would fit in an identical structure attached to the case itself. It's a way to make the engine structure more rigid.

A big thanks to my brother in law Guillaume for the Catia making.

We'll be adding the electronic part & camera to the box in the next steps

Association

PY and I are are currently working on making an association, whose goal would be to make a good transport for working optical equipment in near space, to watch space itself, or to watch the earth with good camera equipments (partnerships and stuff).

Another way to stabilize the gopro

Available at fpv4ever for example : http://www.fpv4ever.com/fr/stabilisateur/457-stabilisateur-3-axes-fy-30a.html

Status - Work left to do (quite a lot !)

We're getting there..

Here's what's left to do :

• Get the DGAC authorization (we're getting in touch with local associations)
  
• Check that the GPS is able to retrieve position at 30km altitude
  
• Setup downlink communication from payload to ground 
• to receive GPS position on the ground (mavlink protocol) using either zigbee or the video link
• to send video on the ground - OK, i've got the transmitter but I need two antenna trackers and helicoidal antenas for a very directive antenna beam.

• Setup a uplink communication from ground to payload (mavlink protocol to send commands to control camera orientation)
• The best is to use ardupilot for that, and to plug a transmitter receiver such as zigbee
  
• Finalize the tilt roll stabilization (three options)
• use the stabilization from the ardupilot board but it seems that it is rather planned for use inside an aircraft (the stabilization isn't very responsive)
• Find a firmware that let me use the ardupilot as an IMU (I haven't found any at this point)
• Buy an IMU device (ardupilot or not) but in this case, I won't be able to control the orientation of the camera
• Make it all from RC equipment and use a heli gyro for stabilization (but that means I have to study the way it works..)
  
• Setup the pan rotation (waiting for order at servocity to arrive, received low temp grease from Molykote)

Optic 6 transmitter and Hobby King X-1000 head tracker

Here's the documentation of the Hobby King Head Tracker X-1000

(Image taken from hobbypartz.com)

I'm using an Hitec Optic 6 transmitter, and I was puzzled because it didn't work when I plugged it in, wherease it was said that it was plug and play.

I have to say that the package came without any notice, so it was quite difficult to find out about the configuration. But I ended up finding the documentation on hobby king's web site.

Well, talking about the connection, it is really plug n play for the optic 6!

But by default (that's the piece of information I didn't have), the HT is made to output the signal on the receiver on channel 7 and channel 8 ! So you have to use an 8 channel receiver to make it work. I was using a 6 channel receiver and was hopping to make it work on channel 5 + 6.

So.. it's possible, but it's not default configuration. You have to change the default configuration. The PDF shows how to do that, but in my case, I just changed the recevier for an 8 channel receiver and.. it worked !

Hope it can help anyone facing the same problem..

How to setup ChainLink 30Km UHF System

Rotation of the payload around its Z axis

This days I've been studying a little more in detail how to work on the rotation of the payload on itself, around the Z axis. The goal is to enable a rotation "in the air" in order to keep a steady heading (head lock).

Using Ardupilot Mega v2, it is possible to program a head lock using a software on the PC and using the mavlink protocol. So at this point, I am not too worried about programming a head lock.

The problem I was studying was rather : how to garanty that the servo is fast and robust enough to compensate a 60hz rotation during a 4 hours flight, while the payload is 2kg heavy.

The goal was to garanty that the servo wasn't the component undergoing the weight of the payload.

I came up with the idea of using a lazy susan that would be the connection between the balloon and and the payload (this is the piece thanks to which I have a free Z rotation non motorised)

Then, I need to have a rotation that can be controlled by the APMv2 board.

I found very interesting products on servocity. They have plenty of solutions for this kind of heavy duty activity. The schema below shows the whole mechanism.

Below is the a list of servos I am considering.

$60

$160

$60

All this equipments come from servocity. I still have to finalize my choice between the one that best fits my needs. 

I will be assembling it using the following lazy susan : 

It comes also from servocity (but can be found about anywhere on the web. At the time of writing, it's about $7

It's been a little while since I found some time to work on the project.

I've been working on two things :

* Stabilization of the gopro
* Fixing the XY rotation of the payload

I made a first try to stabilize the payload. Simulation of wind turbulences is made by my hand and arm, and I was very very strong in "turbulences"... I can't say that the result is as expected. Much work left to do..

You my jump to 1:16mn to see the gopro actually moving..

I will be talking a bit more about the XY rotation of the payload in the next post..

How to protect bearings against cold (-60°C)

I am using a ball bearing mechanism to allow an horizontal rotation of the payload around the z axis, to compensate the rotation due to the wind.

To protect the bearings against the cold (-60° at target altitude), I found a grease made for that purpose, that is financially accessible.

It's made by the company "Univars" and is cold : Molykote 33 Medium Extreme Low Temperature Bearing Grease, and cost £11.

Here is the product :

How to increase the battery of a gopro

I ran into a new problem today. While working on the whole system, I forgot to ask myself how would the gopro be able to stand an 8 hours flight. This is way longer than most flights ! but some flights can long such a long period.

Two problems :

• size of the video : no problem, a simple 32Go will do for no. It's a 4 hours recording, but it will be fine to begin with..

• battery autonomy : That's the real problem. For a native gopro battery pack, it's a lipo 1100mAh, and you can last a little over 2 hours. So I told myself that it should be possible to plug a ubec into the gopro in order to use one of my lipos to increase the time. I finally found a solution on a post of someone using the USB connectivy to power the gopro via external power. He is using a 2650 mah lipo and managed to make a 6 hour timelaps,and the lipo was only 40% empty. So.. nice result :)
  
  Here's the detail story :  http://fangin.com/blog/2011/08/25/gopro-hero-external-lipo-power/

Also, I didn't know it had become that cheap to use a usb battery such as this one : http://www.amazon.fr/TeckNet-batterie-T%C3%A9l%C3%A9phones-Incredible-Blackberry/dp/B001AH0ITA/ref=sr_1_1?ie=UTF8&qid=1338902485&sr=8-1

How to setup a transmitter to control ardupilot mega modes (mine is Optic 6)

For me, it was rather difficult to set up a switch on my transmitter to change mode on the APM.

I finally understood but I think it can be explained a little more in details. 

First of all, here's a list of link adressing the issue

• http://www.rcgroups.com/forums/showthread.php?t=1477169
• http://rangevideo.com/forum/showthread.php?1994-Auxiliary-channel-on-Hitec-Optic-6-radio-This-is-my-method
• http://code.google.com/p/arducopter/wiki/AC2_ModeSwitch

Rather use the helicopter ardupilot firmware than the ardupilot firmware

This post might be the exact same problem as I am facing..

http://diydrones.com/forum/topics/ardupilot-for-stabilize-3-axis-camera-gimball-possible

It recommands using the helicopter firmware : http://code.google.com/p/arducopter/wiki/APM2_Motor_order

Maintaining heading lock

I found a file for ardupilot mega, that was made for test purpose, but that fits perfectly my needs.

Here's the content of the file (with the link to the original post below)

[optional] Ground Testing with the FixedDirection ModeIf you want to test the autopilot further on the ground, we have included a special softwaremode to allow this. In previous version of the software, we had special "NorthEast" codethat would attempt to always steer the plane north-east for testing purposes. In version 2.2and above, this mode can be enabled with a simple settings change in the EasyStar.h (orwhatever airframe you're using) file:Set the following lines as per the below://9-1#define FAKE_BEARING 1 //If set to 1, will fake the bearing and willtry to go always head to the defined DESIRED_FAKE_BEARING//9-2#define DESIRED_FAKE_BEARING 45 //Will try to go NorthEast, you canchange that to 0 = NORTH, 90 = EAST, 180 = SOUTH, 270 = WEST orwhatever!//9-6#define WALK_AROUND 1 //Must be "0" to test the GPS and headingagainst the servo and "1" for normal operation[Walk-Around mode disables stabilization, turning ArduPilot into a navigation-only autopilot.This is also useful if you want to use ArduPilot in ground vehicles that don't requirestabalization, or if you want to use ArduPilot in an aircraft that already has its ownstabilization system, such as the FMA CoPilot]Save the file, then open the Arduino IDE, load the ArduPilot code and download it toArduPilot.Now walk outside with your plane (with all the RC stuff hooked up) and power up, waitinguntil you get a GPS lock (solid blue LED). Once you've got that, toggle the autopilot on andstart walking around at a brisk pace in big circles. You should see the rudder (assumingyou're using the EasyStar; ailerons if you you're using a plane with them) try to steer youso you're going NorthEast.When you're done with the ground testing, return the autpilot to its normal mode by editingthis line as follows and re-uploading the code to ArduPilot://9-1#define FAKE_BEARING 0 //If set to 1, will fake the bearing and willtry to go always head to the defined DESIRED_FAKE_BEARING

From here : http://api.ning.com/files/8uesEX-AhXHtK*U594HwOxfrqYufSbIoQAlrDkdwsBdI5cy1IHpwN2fjM8j4uq-pgdgq-iHztCUjG3YBXUeL0vaetPJviF0U/ArduPilot_2_Manual.pdf

The config file is here :
http://ardupilot.googlecode.com/files/ArduPilotNE.zip

Projects than can help

Also I want to print out that my need is very specific and sometimes, because ardupilot mega and the software mission planner or so well made, well.. I fear to realize later than a feature that I needed was already in front of my nose but I didn't see it because I didn't understand it.. we'll see..


PROBLEM ONE : HEADING LOCK

• How to set up ardupilot mega for continuous servo rotation... I'm looking into arduTracker to identify a solution
• Also, I noticed there is a fonctino in the mission planer named "head lock" which would be exactly what I  would be looking for. But it doesn't seem to be working. I don't know yet if I'm doing something wrong or if it's just not made for that purpose

PROBLEM TWO : TILT PAN of my camera

There seem to be a number of things already in place for that problem :

• "stabilize" mode of the mission planer: I tried to use it to see how the APMv2 reacts. But the servo drive isn't in adequation with the movement of my board. I think the purpose isn't to make a full reverse compensation ( with the same angular speed) as my board, as would do a fully dedicated IMU
• Adding a camera on arduCopter : home made
• Stabilized camera mount : home made camera mount to manage tilt pan for a goPro
• Here is the description of some code that seems to work with APM1
• Here
• Here
• and here
• Another thread with onboard equipment from the APM manual
• Another lead using arducopter : 3 axis camera gimball
• http://code.google.com/p/ardupilot-mega/wiki/Tracking
• http://diydrones.com/forum/topics/anybody-getting-camera-servos-to-work-on-apm2?commentId=705844%3AComment%3A837026&xg_source=activity

Setting up ardupilot mega v2 / APMv2 setup

to come tonight

Ardupilot mega v2 setup / APMv2 setup

I will be making a video tonight or so, about how to setup APMv2 from scratch, for those of you who ain't programmer, and who don't know anything (yet) about arduino.

I found myself struggling about how to setup my RC equipment. Very basic stuff, but I lost a lot of time understanding simple things, just because I didn't want to make a mistake (misconnect some cable) and ruine the board.

Also, I found that it wasn't so easy as I thought to get the camera to point at a predefined heading. Ok, it's easy when you know how to program it in the code. But if you don't, then you have to rely on previous works or similar projects.

I will make two distinct posts to talk about setting up APMv2 for RC equipment and another one about the similar projects I have found.

Battery for GoPro - 20h continuous recording

It might become necessary for long time flights. Below is a link of such equipements

http://www.actioncameras.fr/batterie_drift_powerpack.html

quelques sujets intéressant à explorer

http://diydrones.com/page/uav-devboard
http://diydrones.com/forum/topics/wind-estimation-without-an
http://www.diydrones.com/forum/topics/maximum-safe-servo-pwm-pulse

Yes, understanding IMU is complexe !

Just a post to talk a bit about my recent attempts to get into Arduino and more specifically in Ardupilot Mega.

I was hopping to find a pre-programmed pde file (the firmware you upload into your arduino board) that would  be ready out of the box.

Why ? because Ardupilot Mega v2 (APMv2) includes already all the electrical components that you had to buy separatly before with APMv1 (that is : a gyroscope, a GPS, accelerometer, magnometer). When you buy the ArduPilot Mega v2 hardware, everything is intgrated and you don't have to buy the complementary arduIMU board you had to buy before with APM v1.

I looked into the manual of APMv2, I found a test program (IMU test) that prints out values in the command line interpreter/shell of Arduino.

But then what ? I'm having a hard time to understand the block diagram that describes the whole chain starting from "getting values from the sensors" to "servo moving in such or such direction to compensate".


The compensation movement a sensor must make is dependant on the structure you're playing with. If you're playing with a multicopter, the compensation (variation of engines speed) will be different that if you're playing with an aircraft (motion compensation is produced by ailerons/rudder/pitch compensation, thus servo motion.

You have to imagine how complexe it is to program the variation of engines speed in order to maintain heading/altitude or in order to maintain stability.

Also, in an aircraft problem is a little easier, because the axis you want to compensate is well defined : yaw, pitch, roll

In my case, it's about the same : I have pitch and roll of the camera inside the basket, and yaw outside the basket


Anyway, at this point, I still need to understand how to route the values acquired by the DCM to servos, but I really have this crazy feeling that I'm trying to do stuff that is already programmed somewhere.

I will be writing a post specifically on my understanding of IMU problems



Some documentation
http://www.youtube.com/watch?v=bWDXsKlHvIs
http://www.youtube.com/watch?v=yAVCZstkORY&feature=related

A tutorial on kalman filter
http://www.youtube.com/watch?v=37ZoeVqouc8&feature=channel&list=UL
http://www.youtube.com/watch?v=8R0Ny1l1o1Q&feature=related

A description of DCM algorithm


A code understandable to create stabilization : http://ardupilot.googlecode.com/svn/trunk/Ardupilot_25/attitude.pde
http://ardupilot-kit.googlecode.com/svn-history/r9/trunk/ArduPilotSIM_2_6/attitude.pde

Compass test
http://code.google.com/p/ardupilot-mega/source/browse/libraries/AP_Compass/examples/AP_Compass_test/AP_Compass_test.pde?r=cefe1a07bc82c346bb5f99a7e1425de3a9298229


Some information about understanding how a servo is put into rotation :
http://arduino.cc/fr/Main/LibrairieServo


Here's a test about driving a servo into rotation :
http://api.ning.com/files/XwPN7URDsnkplTraVMr-7sjgFznrv7VhulKe60zoO95*kYBeXvrIoTiax7I8S-9lynBUKK940lFTo0Ghyw5HO6XsaelWJZqR/RCTest.pde

Using Ardupilot to answer the needs

Questions I am working on : 

* How do I change from a flight mode to another in ardupilot mega, if I plan on sending commands from my PC on the ground ?

* How do I define which channel is used for auto stabilization of tilt & roll ?

* How do I specify what kind of movement is required on the servo to stabilize my camera gimball ?

* How do I setup headlock and how do I define servo movement associated to Z axis ? (must support continuous rotation)

According to this article : http://code.google.com/p/arducopter/wiki/AC2_Camera, if I load a arducopter firmware,

By default, quad and hex mutlicopters have stabilization turned on. APM's Out 5 and Out 6 pins will drive tilt/roll servos to auto-stabilize a camera. Out 5 is pitch and Out 6 is roll.

The default is that you can also control the pitch of your camera (but not the roll) with your RC transmitter. 

You can reverse the direction of either servo in the Mission Planner by changing the MAVLink parameters for that channel  

According to the description of the arducopter main page (arducopter.com), it seems that all needed is available under the arducopter firmware :

ArduCopter Platform Feature List

• 6 Degree of Freedom IMU stabilized control

• Gyro stabilized flight mode enabling acrobatics (loops and barrel rolls)

• GPS for position hold

• Magnetometer for heading determination

• What is a sketch file ? what is a PDE file ?
  
• A sketch is the name that Arduino uses for a program. It's the unit of code that is uploaded to and run on an Arduino board.
• pde is the extension of a sketch file

• How do I modify the behavior of arducopter ?
  
• According to this tutorial, I have to modify the arducopteur.pde  file.

My first test :

I want to move my APM around the Z axis clockwise, and have a unique servo go counterclockwise, at the same angular speed.

Playing with Arduino (ardupilot mega v2)

After a while of thinking and preparing the electronic part, here I come again to write about our needs for AHRS : altitude and heading reference system

As explained before, the payload will be stabilized so that the images that we film do not suffer from turbulences.

We use an arduino plateforme named Ardupilot Mega (I bought the latest version APMv2), which comes with gyroscopes and magnometer, so that I am able to program the main heading, and so that the plateform maintain it's heading in gusty winds (usually causing the payload to spin around the axis of the parachute).

Need :

• To manage different modes of heading and autonomous modes, pre programmed before launch and selectable by sending a remote command.
• Mode 1 shoud consist in programming a fixed heading
• Mode 2 shoud consist in programming an autonomous rotation of 45° heading every minute
• Mode 3 shoud consist in programming an autonomous rotation of 45° heading every 15 secondes
• Mode 4 shoud consist in programming a rotation of 180° heading

• At any time, I should be able to change the heading using my transmitter (or by sending manually a value as a new heading)
• The plateform should be gyrostabilized, meaning that if the wind generates an angular speed of 5°/seconde, the servo should apply a rotation of -5°/seconde. The only axis concerned is the Z axis.
• The two other axis are stabilized only to compensate gusty wind meaning a relatively slow degree of motion (and no need of 360° rotation)

That's it

Now, I will be looking deeper into the manual of ardupilot mega in order to find out more about how to answer those needs. Next post is about that.

How to launch the balloon in regard to real aircraft traffic

We plan on declaring our launch to the DGAC (french FAA), but an idea could be to add ADS-B to the balloon in order to make it known and declared on the radar, like a transponder.

Here's the description from Wikipedia :


Automatic Dependent Surveillance-Broadcast (ADS-B) is a surveillance technology for tracking aircraft as part of theNext Generation Air Transportation System (NextGen).^[1] The United States will require the majority of aircraft operating within its airspace to be equipped with some form of ADS-B Out by January 1, 2020.

In French with more details :

L'Automatic dependent surveillance-broadcast (ADS-B) est un nouveau système de surveillance coopératif pour le contrôle du trafic aérien et d'autres applications connexes. Un avion équipé de l'ADS-B détermine sa position par un système de positionnement par satellite (GNSS) et envoie périodiquement cette position et d'autres informations aux stations sol et aux autres appareils équipés de l'ADS-B évoluant dans la zone.

http://www.coaa.co.uk/planeplotter.htm

This program shows the following digital signals : ACARS, ADS-B and HFDL

There is already a DIY ADB-S receiver existing. As stated on DIYdrones.com, it would be great to have an arduino based project that enable the HAB community to broadcast the position of a balloon.


In order to monitor air traffic control, you can use PlanePlotter, that is an implementation of the protocol, plotting on a map live air traffic control.

Download in english here

Telecharger en français ici

Testing the gopro gimball in different modes

Here's a view from the balloon basket. We are testing the different modes of the gopro, in order to determine what mode is the best.

We like the "medium" angle of view best.

Test gopro gimball for space launch

We have been building the basket in the past month. 

Here is a collection of pictures and video tests that we made. 

We are using a gopro for the camera, that will be placed in the middle of a half sphere in plexiglass.

The gopro has the ability to move on a 180° angle in every direction of the sphere.

Here's a video of the gopro in rotation

It will be placed on a gyroscopic plateforme so that the camera is stabilized

Wiki for HAB community and people involved in the same idea

I feel like I just found the right community tonight..

There is a place at last for people trying to work on arduHAB ! It seems new, as the topic is dated January 2012.

Here are the different links I have found :

• The topic on DIYDrones
• Daniel Nugent 's forum :  has already investigated the possibility of a glider in autopilote mode, returning home, with the gravity problems, lack of air density etc..
• Cuddy has already some background about GPS lock at such high altitudes
• tuckerobie seems to know about people on the forum working on the plane concept
• Ken seems to know about NMEA and different configuration of GPS
• Art Whaley knows how to configure ardupilot along with standard NMEA GPS
• Monroe seems to be working on rocket guidance, and has been working with HAB
• balloomerang project as part of the iHAB project : "a long terme effort to design and build a HAB vehicule/payload with autonomous flight capabilities".

And there youtube channel : http://www.youtube.com/user/SAIDiasMobile?feature=watch

• Larry Grater also works on GPS stuffs
• Another page dealing with the same kind of information (CONOPS)
• http://www.ukhas.org.uk/  : A wiki page for us
• A similar german project :  http://vexredus.de/

Two first launches configurations

After many month of search and comparison of previous projects, technology, and reading back my telco undergraduate books, here's at last the definition of the two first launch about to take place :




First launch main goals: 

• Send and receive telemetry data using an arduino board
• Record videos from the onboard gopro on an onboard sdcard
• Stabilize camera recording using an onboard gyroscopic plateform built on ardupilot
• Ssend servo commands to the arduino board so that the gopro (on a pan/tilt mechanism) moves as I move my joystick on the ground
• Communication distance targeted : 33km LOS
• Frequency used : 868Mhz using Zigbee pro protocol (or alternative if more suitable, but at the time being, the best identifed.. there are a number of problems with this protocol.. I am aware of it.. )
• Reception and live monitoring of position, angle of incidence, speed, external and internal temperature on a ground station using HK Ground Station

Second Launch main goal :

• live transmission of HD video on the ground using digital COFDM modems and a gopro as video camera

You are a growing number of people reading this blog. Please don't hesitate do drop a comment.

Recommandation of 900Mhz & 1.2Ghz equipment for long range flight

A page giving all kind of advice for long range video transmittion : http://www.terranova.net/~winger/RCVideoStore/DragonLink/Flying/VideoSystem/VideoSystem.htm

The writer ackwonledges that many of the transmitters on the market have a real power output much lower than that indicated by the manufacturer (125mW instead of 500mW). Also, from what he tells, transmitter can get hot because of bad impedance match between antenna & the load.

He recommends using this kind of equipment available from hobbywireless.com in the 900Mhz :

900Mhz is also a frequency where receivers are kinda old, and not very sensitive, compared to 1.2Ghz for example.

• Transmitter :  T905 Transmitter 900 MHz 500 mW (above)

• Receiver : R900 - 900MHz High Sensitvity Receiver Standard  (above)

• 5dbi antenna :  AN905 HIGH GAIN WHIP ANTENNA 900Mhz 5dBi

1.2Ghz

http://hobbywireless.com/cart/index.php?main_page=product_info&cPath=10&products_id=100&zenid=7ad59c8ec255d0d65eee7473f5daa55f

http://hobbywireless.com/cart/index.php?main_page=product_info&cPath=9&products_id=102&zenid=7ad59c8ec255d0d65eee7473f5daa55f

http://www.lightinthebox.com/Brand-New-1-2GHz-Outdoor-High-Gain-Yagi-Antenna-with-15dB-Cable-15dB-Max-Gain--ES500-_p118587.html

http://www.l-com.com/item.aspx?id=20248

digital and analog video downlink provider

The best product I found :

http://www.rotoconcept.com/products/digitalrfvideotransmitters/rq3highpowernlosvideolink/

http://navtech.newcomweb.demon.com/downloads/index.htm

Technology from 2005. Probably expensive compared to today's standards.

Still interesting to see how digital downlink is achieved.. here, it seems they are using COFDM modulation and they provide receiver and transmitter. But I beleive it must be very heavy....

Other provider of COFDM receiver/transmitter :
http://www.alibaba.com/showroom/uav-transmitter.html
http://www.alibaba.com/product-gs/513686401/Cute_Mini_COFDM_Transmitter_and_Receiver.html
http://www.alibaba.com/product-gs/261883052/MV2025TTSE_Mini_Wireless_COFDM_Transmitter.html
http://www.alibaba.com/product-gs/379850065/COFDM_Wireless_Digital_Transmitter_for_UAV.html


Great provider all in one and compact :

http://www.discover-cctv.com.sg/professional-cctv/digital-wireless-transmission

Specifications: 

Model Number	DIS-W1100/PN5	DIS-W1100/CN5	DIS-W1100/AN5
CPU	Atheros MIPS 24KC, 400MHz
EMS memory	32MB		64MB
Flash memory	8MB
Working frequency	5.470GHz~5.825GHz (IEEE802.11a/n)	5.150GHz~5.825GHz (IEEE802.11a/n)	5.470GHz~5.825GHz (IEEE802.11a/n)
Antenna connector	N type, Male (connect to the antenna directly)	-	2 x RP-SMA
Transmitting power output	Max. 400mW	Max. 500mW	Max. 500mW
Transmitting distance (LOS)	>50km	>15km	>50km
Transmitting speed	Max. 100Mbps TCP/IP	Max. 150Mbps TCP/IP
Channel bandwidth	40MHz, 20MHz, 10MHz & 5MHz (adjustable by PC program)
Network connector	1 x 10/100M Ethernet (RJ-45)	2 x 10/100M Ethernet (RJ-45)	1 x 10/100M Ethernet (RJ-45)
Appearance	Industrial grade outdoors type UV
Antenna	External	Integrated 2x2 MIMO dual-polarized intelligent antenna	External
Shell structure	Anti-corrosive, waterproof & sun-proof
Shell strength	ETSI300-019-1.4
Power	24V, Power-over-Internet (PoE)	15V, Power-over-Internet (PoE)	24V, Power-over-Internet (PoE)
Power consumption	6W	8W	6W
Working temperature	-40°C ~ 80°C	-30°C ~ 80°C
Working humidity	5% ~ 95% (non-condensing)
Dimension	15.2 x 3.1 x 3.7cm	29.4 x 8 x 3cm	16 x 8 x 3cm
Weight	0.18kg	0.4kg	0.5kg
Standard Certification	FCC Part 15.247, IC RS210, CE
RoHS	Compliant

Ordering Information: 

Please refers to above Specifications' Model Number

Autre solution :

http://wirelessvideocameras.com/my-cart.html?page=shop.product_details&flypage=flypage.tpl&product_id=7&category_id=53

5.8GHz 1 Watt Airborne Video Downlink (No Camera)

Includes:

5.8Ghz 1 Watt Transmitter with 12VDC to 24VDC input

5.8Ghz Receiver with 9VDC to 12VDC input

1  "rubber duck type" Omni-Directional Antenna for TX

1  Patch Directional Antenna for TX

1  9dBi High Gain Omni-Directional Antenna for TX for extended range and signal strength

1  High Gain 23dBi Directional Antenna Enclosure with Integrated 5.8Ghz Receiver & 30ft. cables

AC/12VDC power supply for RX and Instructions

Features:

Transmitter Weight only 4 ounces (113 grams)

Plug & Play system just add any composite video camera for TX and any TV for RX
High Quality Real-Time Wireless Video up to 25mile Clear-Line-of-Sight Range
Great for all types of Airborne RC & UAV applications, Airplanes, Helicopters, Blimps & more

5.8Ghz will not interfere with 2.4Ghz RC radio-control units

SMA connectors for TX & RX for use of Omni-Directional or Directional Antennas

23dBi High Gain Directional Antenna Enclosure with Integrated 5.8ghz Receiver & 30ft. Video, Audio & Power cables

11 degree Horizontal and 11 degree Verticle Antenna Signal Beamwidth for the Receiver Anetnna

Pole Mount bracket for Receiver Antenna Enclosure to raise off the ground for increased range

One-Year Warranty

Life-Time Free Technical Support to original purchasing customer

Solutions en COFDM

WVC-SD Digital COFDM Mini Transmitter System

COFDM Digital Wireless Video Mini Transmitter with True Diversity Receiver - Excellent choice for UAV and Body Worn applications - Credit Card sized Mini COFDM Transmitter
[Product Details...]

Our Price: Call for Pricing

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WVC-SD Digital COFDM Wireless Video System

COFDM Digital Wireless Video Transmitter & True Diversity Receiver - Available for Long Range Line-of-Sight and Urban Non-Line-of-Sight applications
[Product Details...]

Our Price: Call for Pricing