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Optical Transmitters
This is a new array of LEDS. The base for the array is a 6" x 8" perfboard purchased at Radio Shack.
There are 34 rows of LEDS in this array of 24 diodes each. Each diode was painstakingly removed form cable television remote controls, tested and incorporated
into this array. I had access to the remote controls as I was a CATV engineer at the time. Each row of 24 diodes is broken down further into a six diode segment
and a series resistor. The series resistor is employed to assure equal current into each six diode segment. Then the segments are paralleled into two 408 LED
groups.
Each 408 LED group has its own Power Mosfet that switches the current for the group. The gate signal for the 2 Power Mosfets originates from the same drive
circuit. The wavelength of the array is 940 Nanometers
This is a new array of LEDS. The base for the array is a 6" x 8" perfboard purchased at Radio Shack.
There are 34 rows of LEDS in this array of 24 diodes each. Each diode was painstakingly removed form cable television remote controls, tested and incorporated
into this array. I had access to the remote controls as I was a CATV engineer at the time. Each row of 24 diodes is broken down further into a six diode segment
and a series resistor. The series resistor is employed to assure equal current into each six diode segment. Then the segments are paralleled into two 408 LED
groups.
Each 408 LED group has its own Power Mosfet that switches the current for the group. The gate signal for the 2 Power Mosfets originates from the same drive
circuit. The wavelength of the array is 940 Nanometers
| Front view of the 816 LEDS array |
| Closeup view of the group of six LED clusters |
| Two 4" muffin fans "force" air into the plenum and out through the holes in the perfboard. |
| The aluminum chassis provides a convenient way of mounting the perfboard LED array while also providing a plenum for cooling. Duct tape is used to seal the box and to channel all of the air flow through the small holes in the perfboard, thus cooling the diodes. |
| Many years ago, sometime in the late 80's perhaps, I did some NON -LOS optical communications experiments. This is certainly old hat to folks now but at the time is was cutting edge to me. The pictures are terrible, but you can get the general idea of what was hoped to be accomplished. The recordings below are the actual data that from the night of the experiment. It was a great deal of fun. The path was a 3.5 mile cloud bounce path, but taking the cloud ceiling height at 10,000 feet into consideration, the distance was actually closer to 5 miles. Click on the files below to hear how it sounded. |
Optical Detectors
Optical detectors are just small solar panels, with an amplifier after it.
Factors effecting the performance of an optical receiver are:
application. A very low noise, high input impedance amplifier will need to follow it.
The smaller the detector area, the lower the internal noise. Smaller detectors usually have higher frequency response.
The detector used for my cloud bounce experiments is a unit from Digikey PDB - 715 - 100 ND, manufactured by Photonic Detectors, Inc.
Optical detectors are just small solar panels, with an amplifier after it.
Factors effecting the performance of an optical receiver are:
- Area of detector
- (NEP) Noise equivalent power of the detector
- 1st stage noise
- 1st stage input impedance
- Optical response of detector
application. A very low noise, high input impedance amplifier will need to follow it.
The smaller the detector area, the lower the internal noise. Smaller detectors usually have higher frequency response.
The detector used for my cloud bounce experiments is a unit from Digikey PDB - 715 - 100 ND, manufactured by Photonic Detectors, Inc.
Optical Antennas
The antenna in an optical receiver system can be either, concave mirror or convex lens. I chose lens, it was easier to mount and I happened to have a 5" lens available.
Several pictures of the original receiver assembly have been included here. A 5" lens is fitted into the end piece of an aluminum pipe. The pipe is lined with black felt.
The black felt is used to minimize internal reflections of light entering the tube off axis and mixing with the desired signal at the focal point of the lens. Flocking paper sold
by Edmund Scientific would have been a better choice but I had the felt on hand.
Insert the optical detector in the small hole located at the rear of the tube to locate the optimum focal point for different applications. Slide the optical electronics in or out
to maximize signal strength. All of the optical detectors are built into aluminum tubing that fit snugly into this opening. The aluminum tubing works great as a 60HZ main
shield
The antenna in an optical receiver system can be either, concave mirror or convex lens. I chose lens, it was easier to mount and I happened to have a 5" lens available.
Several pictures of the original receiver assembly have been included here. A 5" lens is fitted into the end piece of an aluminum pipe. The pipe is lined with black felt.
The black felt is used to minimize internal reflections of light entering the tube off axis and mixing with the desired signal at the focal point of the lens. Flocking paper sold
by Edmund Scientific would have been a better choice but I had the felt on hand.
Insert the optical detector in the small hole located at the rear of the tube to locate the optimum focal point for different applications. Slide the optical electronics in or out
to maximize signal strength. All of the optical detectors are built into aluminum tubing that fit snugly into this opening. The aluminum tubing works great as a 60HZ main
shield
Rescue Electronics Surplus
TO66 Package and Lens, another OpticalTransmitter
Here is a transmitter that uses projection TV lens as a collimator
It consists of a 36 diode configuration. The diodes are all mounted in a single TO66 package. The TO66 is mounted about 1 inch behind a television
projection lens. This arrangement results in a beamwidth of approximately 10 degrees. This transmitter runs approximately 15 watts of input power.
Here is a transmitter that uses projection TV lens as a collimator
It consists of a 36 diode configuration. The diodes are all mounted in a single TO66 package. The TO66 is mounted about 1 inch behind a television
projection lens. This arrangement results in a beamwidth of approximately 10 degrees. This transmitter runs approximately 15 watts of input power.
| NON-LOS Optical Communications |
| To be continued |
| Optical Cloud Bounce Audio The audio starts with approximately 30 seconds of key down of the carrier tone and begins to ID after that. Cool Edit was used to filter the audio |