การพัฒนาระบบฝังตัวสำหรับการมอนิเตอร์แถบคลื่นความถี่วิทยุระยะไกล

Abstract

A survey frequency monitoring contributes more helpful to NBTC frequency regulator. Therefore, this work introduces a low-cost embedded system that can monitor frequency band usage. The system is easy to be moved and installed in the remote area, yet in coverage area of cell phone to enable remotely control function via GPRS network. The system is designed to be attached with a commercial radio transceiver, ICOM-2200. It is composed of 3 eight-bit MCUs and a GPRS module. The 1st MCU traps signals between the radio transceiver’s panel and body to acquire frequency and signal strength of the operating channel. The strength is scaled into 3 levels corresponding to 3, 9 and 18 dBV that are calibrated with NBTC instrument. The second MCU emulates a signal to command the panel to change frequency channel ranging from 136 to 174 MHz. The last MCU controls the other MCU and also interfaces to the GPRS module in order to upload data and download parameters from a server. With this structure, the officer is allowed to remotely select parameters, i.e. start and stop frequency to be scanned, scanning period, and measuring interval. Various conditions are set in order to test the system. Among the conditions, the system can perform monitoring and uploading functions properly. For an example, a 5-watt fixed-frequency radio source is used to emit 60 times of one-second-long signal. The system can catch 13 times or 21.67% by averaged where is enough for evaluating channel occupancy. And the shortest period of uploading is about 23 seconds.