Data acquisitionin a conventional radio environment
Linking acquisition and computer hardware creates a record of activity, transmission lengths and airtime used in a conventional radio system.
Data acquisition in an 800MHz trunking environment is an easy task that is built into the system controllers, but for those of us in a conventional radio system, it could be an almost impossible task. Justification data to add more conventional talk paths and more personnel takes a lot of work and, in some cases, is not practical because of the manpower and time involved.
I installed a computerized data acquisition system into the conventional radio network of the Palm Beach County Sheriff’s Office. This stand-alone system has many applications. It logs into a data file the push-to-talks, minimum and maximum lengths of the transmissions, and the total airtime used in both 15-minute and 60-minute intervals. This information is retrieved on a weekly basis and converted using Microsoft Excel spreadsheets to produce valuable data that is compared with computer-assisted dispatch-generated reports that show manpower statistics.
The acquisition hardware consists of a 486 PC running Windows 3.1 with a Keithley Metrabyte model 1202 16-port data acquisition module. The software was custom-written by Intech in Melbourne, FL, and consists of Visual Basic 4.0, combined with a custom graphical user interface and “Visual Test Extensions” VTX by Keithley Metrabyte. This package simplifies the process of data acquisition and custom report generation.
The tie points of the system required transitions from non-TTL levels to TTL levels for the module to accept. The high-voltage keying in the Motorola Centra-Com console in our application required the use of an opto-isolator and voltage pull-up resistors, which control an input channel on the data acquisition module. The voted bus line in the Motorola Spectra-TAC voter needed a voltage divider to bring the level down to +5V and 0V levels and then hooked to another input channel. These two applications were reproduced to sense five of our wide-area voice channels and our mobile data system. (See Fig. 1 on page 36.)
Installation options of this unit are versatile, depending on the type of system. I chose not to use it as an off-the-air unit. There is the possibility that erroneous data would be collected because of repeater hang time of other co-channel users, and there is the inability to separate the dispatcher and voted data. However, this is always an option to the system manager.
Captured data as of this time have shown the activity to be, on average, 40% to 45% on a normal day and then increasing to 90% to 95% during periods of high activity or a large number of users on the system. (See Table 1 on page 38.)
The Palm Beach County Sheriff’s Office is a 36-site voted communication system spanning 2,200 square miles with seven wide-area repeaters in VHF and five local coverage systems. It is tied together by 12 hops of 6GHz microwave, five hops of 960MHz microwave and leased telephone circuits.
Filla is radio system manager for the Palm Beach County Sheriff’s office in Southeast Florida. He is GROL-licensed, amateur radio Extra class KS4VT and has an associate’s degree in electronics technology.
