Video Link Payload


The payload includes the following major subsystems.

Controller Board  The controller handles commands from the UHF cross payload receiver, sends commands to the camera controller, and controls the operation of the PA.

SMA Attenuator  An in-line SMA attenuator is use between the modulator and the PA.  This reduces the power level from the modulator as well as improving the impedance match between the devices.  The in-line devices allow for ease in adjusting power levels.

Final PA  The final Power Amplifier is housed in a solid aluminum block for shielding and as a heat sink.  The device dissipates almost 1 watt of power in the form of heat.  This is still efficient for a class-C amplifier operating in the S-Band.  Because the payload operates in the thin atmosphere of near space, a large heat sink must be utilized to draw heat away from the device.  Thanks to Louis, W7LMW, for his efforts in machining the heat sink from a solid block of aluminum.

Attachment Cord  The payload is mounted in the payload train using a 4 corner harness.  4 attachment points on the top and bottom of the payload are connected to the main payload string.  The aluminum, 90° channel enclosure provides high strength and rigidity.

Li-Ion Battery Pack  This is the first payload designed to utilize a non-primary (rechargeable) battery pack.  Complete information on these cells is available in the Power Sources section.

quadrifilar Antenna  A quadrifilar helix antenna provides a spherical, omni-directional pattern well suited for high altitude flights.  Because of the antenna's low gain (<2 dBi) and radiation pattern, nulls for fading are minimized.  The antenna was a custom built unit from Directive Systems.  Although it is possible to build your quadrifilar helix, it takes a lot of experience to build and tune it for a broad band application such as a video link.  The cost of the antenna (around $225) is very reasonable.  Although Directive Systems provide descent quality hardware, customer service is very poor.  Expect long lead times, unasnwered e-mail, and frequent toll calls to check delivery status.

Block Camera  The block camera is an OEM device that provides basic camera functions in a bare bones device.  Typically, these devices are rated for operation at -20°C to +60°C and require minimal power.  This unit is a Sony FCB-IX47 that includes S-video output, video overlay, RS-232 command port, and special video feature.  The video features include freeze-frame, 0-lux operation (night vision), 16:9 wide screen, and full remote zoom/focus/white balance control.  With commanding, the camera can be placed in a mode suitable for a balloon flight.  For example, the white balance can be fixed for outdoor use and the auto focus can be disable to prevent "hunting" when pointed at a low contrast horizon.  The camera also utilizes a 37mm screw mount to accept wide angle or filter lens.  For high altitude use, a Tiffen circular polarized filter was used.  The filter greatly reduces UV light and glare.  When mounting the lens, care should be taken to ensure moisture or debris isn't trapped behind the filter that may obscure the image or cause condensation in the cold, dry air of the upper atmosphere.  Thanks to Ralph, W0RPK, for providing the camera.