Why Use a Carbon Cradle?

Or

How I Was Able To Get RDAS Telemetry & GPS To Work
by

Arnold Roquerre

2008 _©

The primary reason I chose an all carbon cradle was the inability to get GPS and the 900 MHz telemetry to work in tandem. This is a problem others have had using similar units produced by other vendors. Inexpensive electronics not shielded or configured to work with all the components in close proximity to each other definitely has problems when there is a telemetry transmission and GPS receiver and antenna in close proximity. Carbon attenuates radio frequency much like a ferrite core. Grounding and shielding become non-concerns, but energy absorption is one that has to be watched. Fortunately, since the radio transmitter is very low power (less than 50 mW) and the entire electronics package uses less than 1 amp of current the cradle would not be adversely affected by radio frequency energy leaking from the operation of the RDAS components.  Carbon makes it possible to get the maximum out of inexpensive electronics that are not shielded. Properly shielded electronics to protect the functionality of each and every possible component combination would make the units prohibitively expensive. The use of a carbon cradle solved all the radio frequency problems that lead to the failure of the GPS unit to secure a lock or to regain lock after launch.

It is important to keep the cables against the carbon cradle and the cable that wraps around the cradle frame to the other side were it is attached to the transmitter should be tapped against the frame at both ends of the bend. A coax cable runs from the transmitter to a half duplex 900 MHz antenna setting above the electronics shielded by the carbon cradle. Below the telemetry antenna is a ground plane with a patch GPS antenna attached parallel to the 900 MHz antenna above it. (See figure below for details).