This is our Basic 101 lesson on RC Airborne Video Downlinks for those who have little to no understanding about RF Microwave transmission with airborne aircraft.

Aircraft Size:

Lets first start off with the size of the aircraft and weight of the video transmitter, camera, and battery. If we start out with a 40 size trainer type airplane or 30 size helicopter we can carry about 16 ounces (1 pound) and have not problems flying the aircraft. The larger the airplane/helicopter the less we notice the extra weight and more aerobatic we can fly. The majority of the weight of the airborne video downlink is in the battery weight. You can reduce the battery weight quit a bit if you use Li-Po 3S batteries. We do offer light weight model transmitters which weigh in at 4 ounces for a 1-WATT transmitter with our TC Camera.

Installation:

Installing the airborne transmitter and our NI-MH battery packs into or onto the aircraft is done by our supplied Velcro method which as has been successfully used for 20 years. The cameras we offer vary as to how their are mounted depending on which camera you choose.

Cameras:

The camera you choose will determined how good the video quality will be. A misunderstanding most people have regarding the camera choice is selecting a low lux rated camera. The lower the lux is the more sensitive the camera is to light, when you fly you will be looking into the sun most all low lux cameras will loose the video picture due to overpowering the imager of the camera. This is not good when you are flying from the video. Our 4 cameras have been selected for light weight, size, durability, lines of resolution, current draw, and the ability to see directly into the sun with out loosening the video picture. We offer 2 CMOS and 2 CCD type cameras.

Transmitter / Receiver:

To better understand how microwave transmission works on 2.4GHz let me offer you this analogy, think of the transmitter RF output as a light bulb emitting light. We require a clear line of sight between the transmitter and the receiver just like you would need to see light. When we use a Omni type transmitter antenna it transmits much like a light bulb 360 degrees all the way around in all directions. If we were extend this analogy to night time and your eyes were the receiver the stronger the wattage (RF) of the light bulb was the brighter the light and the easier it would be to see the light. This would be a good example of how the transmitter works on the aircraft. Now let talk about the receiver, your eyes. If we had a low wattage light on the aircraft and you used just your normal eye sight to see it, the further it would travel out the weaker and harder the light would be to see. To increase the ability to see the light we need to either increase the light bulbs wattage (RF) or use binoculars to increase your eyes ability to see further out.

Now lets convert this example to what is really going on. We use FM Analog to transmit and receive the video. Think of the FM radio in your car compared to the AM radio, FM is much more reliably locking onto the channel and is not subjected to interference from outside sources such as high voltage near by. We will use the Omni transmitter antenna on the aircraft and use a low gain directional antenna on the receiver. The lower the gain is on the receiver the wider the beam width is of the directional antenna. The wider the beam width of the receiver antenna the better performance is when we fly back and forth over the runway left to right. The receiver has a sensitivity level which is vary important and is part of the formula that  determines how far we can transmit a signal. Once we add the type and gain of the transmitter antenna, the transmitter output power, the receiver antenna type and gain factor, than the sensitivity level of the receiver we can determined how far we can transmit.

To increase the range we need to either increase the RF output power of the transmitter and/or change the receiver antenna to a higher gain antenna. Now lets go back to the analogy with the light bulb. If we want to increase the brightness of the light bulb to see further away we need to increase the wattage (RF) which means we need more power to run the light bulb, larger battery capacity. There is a point were increasing the wattage (RF) of light bulb requires a larger battery power to power it up and the battery weight becomes to much to carry. If we use a 1-WATT light bulb and than use binoculars to see it we can increase the range more efficiently. When we use the binoculars we also reduce the field of view which is the same as using a higher gain receiver antenna we reduce the beam width and need to point the directional antenna towards the aircraft. So if we use a low power transmitter and low gain directional receiver antenna we can fly in front of the antenna without adjusting the receiver antenna and fly within a shorter distance (1.45 miles) from the receiver. If we want to increase the transmitter power to 1-WATT and use the low gain directional antenna we can fly further out (4 miles) and not have to adjust the receiver antenna. If you want to fly out even further (15 to 25 miles) we want to use the 1-WATT transmitter and use a higher gain receiver antenna and point it towards the direction of the airplane.

Helicopters Aerial Photography:

Helicopters use different types of main rotor blades, wood, fiber glass, and carbon fiber. The wooden and fiber glass blades are made of material which RF signals can pass right through as if they did not exist. Carbon Fiber main rotor blades are much different, they act like metal and as they rotate around they act like a large metal disc which reflects the transmitted signal back to the receiver and cause flicker or blinks. The flickers or blinks are when the receiver is receiving the main signal from the transmitter than also receives a second signal at the same time, since we are using FM modulation the end result is a flicker or blink in the video picture. When the helicopter is used for aerial photography it usually is hovering above or near the ground station. When we have a condition were the ground station is near metal such as cars, buildings etc the signal often reflects off of these items and causes reception problems. We have solved this problem using our "H" series transmitters which have a built in circular patch antenna. The matching receiver also has the same type of antenna, they way the system works is both antennas put a spin on the signal much like a signature. Each side is looking for that particular signature and ignores the the reflected signal. The transmitter is placed onto the helicopter with the antenna side pointed downwards transmitting a cone shape pattern, the matching receiver antenna is pointed towards the transmitter with the same type of cone shape pattern. The range is based more on altitude (height) than distance (horizontal) range.

When the helicopter is being flown off in the distance and using carbon fiber blades the Omni transmitter will work fine since it is not hovering above the ground station.

Helicopter Sport Flying:

Helicopters flying normal sport or 3D flying that use wooden or glass blade can use the Omni type transmitters with no problems, just remember to tie down the transmitter antenna so you do not cut it off in inverted flight!