RF Telemetry at BBWM
RF telemetry at BBWM had been implemented using Campbell Scientific Inc. (CSI) equipment.
There were five stations, all of which had CSI RF modems. At the time (circa 1987-88) the DC95 RF modem was used to move data from the CR21X dataloggers to Motorola HT90 hand transceivers.
The DC95 had two ports, one 10 pin port for a data ready radio (HT90 based in this case), the other a standard DB9 port for serial I/O. As I recall the serial I/O port was directly connected to a similar connector on the face of the CR21X.
Unlike when the CR21X loggers were installed, there are no CR1000 spares, and the Handar 436 was pretty much the only thing still being measured, other than outside air temperature. With no spares, that meant that the datalogger had to come back to the shop, so that the entire system could be checked.
The small silver box, partially obscured by the stepper motor mount, is a QD1 interface from CSI.
The QD1 interface is used to condition the signals coming from a device such as the Handar 436. The conditioned signals are then passed from the QD1 to a data logger.
The QD1 interface has an internal oscillator used as a clock. The clock frequency runs at about 2.5 KHz. The clock is used to turn the power on and off to the "Encoder +5" port. Along with the "Encoder +5" port the "S1", and "S2" ports are pulled high (+5 volts) through resistors. The duty cycle of the ON pulse is quite low. Presumably the low duty cycle is used to minimize power consumption. The idea being that there is no reason to power the encoder when there is no change to its inputs. This is a safe bet, since typical stage height changes are measured in minutes, and hours not milliseconds.