Transcript
Antenna System Monitoring
ASM Series Many modern base station repeaters provide measurement capabilities, but the use of combining and/or isolators in the RF path from the base station transmitter output to the antenna isolates the repeater from problems within the antenna systems. The use of an Antenna System Monitor in these instances facilitates the measurement of transmitter forward and reverse power, transmit-to-receive antenna isolation and receive signal level measurements.
Overview The Antenna System Monitor can be used to monitor the performance of: transmitter forward and reverse power transmit-to-receive antenna isolation receive signal level measurements This can be carried out on single repeaters or multi-repeater communications sites.
ASM Series ANTENNA SYSTEM MONITOR The inherent inaccuracies of using in-line watt meters to measure forward or reverse power on multicarrier systems can also be overcome by using the Antenna System Monitor product.
Many modern base station repeaters provide measurement capabilities, but the use of combining and/or isolators in the RF path from the base station transmitter output to the antenna isolates the repeater from problems within the antenna system(s). The inherent inaccuracies of using in-line wattmeters to measure forward or reverse power on multi-carrier systems can also be overcome by using the Antenna System Monitor product. An Antenna System Monitor is installed in the RF path between the repeater’s duplexer (or the site’s combining) and the antennas, and allows the measurement of these performance parameters by using channelised selectivity and carrier detection measurement techniques.
TRANSMITTER ANTENNA MEASUREMENTS The transmitter forward and reverse connections of the Antenna System Monitor are connected in-line with the transmit antenna using a directional coupler. The value of this coupler is determined by the transmit power levels that are to be measured, but a 30dB coupler is a typical value to use. The coupling value of coupler, in both the forward and reverse direction, is programmed into the Antenna System Monitor and these programmed values are added to the measured levels so that corrected “actual” values are reported. Individual transmit frequencies are programmed into the unit, along with a “minimum signal threshold” value. The Antenna System Monitor automatically “scans” through the frequency list, stopping on each frequency and looking to see if a carrier is currently present that is above the threshold level. If there is, then the unit measures the forward and reverse power of that carrier and records it in a “measurement table” stored in its memory. If no carrier is detected during that measurement cycle then the unit continues on to the next frequency in the list. In this way, the unit doesn’t record a “zero power” reading if any transmitter is not keyed at the time of the measurement. This is particularly important for low duty cycle or telemetry channels that have sporadic transmissions.
A channelised, high-selectivity measurement circuit ensures that the forward and reverse power that is sampled represents that of one frequency each time. This allows the Antenna System Monitor to measure the forward and reverse power of each individual frequency that may be present on a multi-carrier antenna feeder – unlike typical thru-line wattmeters or communications test sets. There are four (4) separate sets of forward and reverse inputs on the Antenna System Monitor, allowing up to four transmit antenna systems to be monitored in one installation. TRANSMIT TO RECEIVE ISOLATION MEASUREMENTS By connecting a spare receiver multicoupler port to the Rx test port of the Antenna System Monitor, it is possible to measure the transmitter-receive isolation performance of the site.
ISOLATION
If the test frequency programmed into the unit is in the “transmit” portion of the frequency band, then the measurement includes the transmit-to-receive isolation that exists on the tower, the rejection of the receive preselector, and the “nett” performance of the overall system - including cabling losses and receiver multicoupler gain. If the test frequency is programmed into the “receive” portion of the frequency band, then the measurement includes the transmit-to-receive isolation that exists on the tower, the “nett” performance of the overall system - including cabling losses, the insertion loss of the receiver preselector, and receiver multicoupler gain. These “receiver measurements” are made and recorded in the same measurement table as the transmitter measurements. Note: As the “isolation” measurement is also determined by the shape and interaction of the transmit and receive antenna pattern(s), this test is a thorough and reliable analysis of the performance of the respective antennas on the site. RECEIVE SIGNAL LEVEL MEASUREMENTS It is also possible to sample receive signal levels using a spare receiver multicoupler port connected to the Rx test port of the Antenna System Monitor. The level of a received signal from a fixed transmitter at a known location (such as the radio workshops) can be measured, recorded and reported to confirm the site’s inbound receive performance. Periodic measurement of this signal can provide an indication of any degradation or failure of the site’s inbound receive path and/or receiver multicoupler system.
MEASUREMENT REPORTING AND ALARMING If the performance value of the antenna system(s) on the site are measured as part of the initial commissioning activities, then the Antenna System Monitor can be configured to continue to monitor these parameters automatically into the future – recording measured values and reporting measurements continually, or as on-event or polled reports if values exceed programmed trigger levels. This allows the actual performance of the antenna system (and even the output of the transmitter combiners) to be monitored as all of these tests confirm the correct operation of the transmitters, transmit antenna(s), transmit-to-receive antenna isolation and receiver antenna system performance – including the receiver preselector and receiver multicoupler. Connection to Antenna System Monitor units can be provided via dial-up, radio or cellular modems or dedicated landline or backbone circuits. A PC-based alarm management tool is also available to collect and display messages from units located on communications sites. RFI PRODUCTS, SERVICES AND SUPPORT RFI offers a comprehensive suite of products and services to support communications systems. Our products include antennas, cables and connectors, grounding and lightning protection, AC and DC power systems including batteries and solar power products, and racking. We also provide RF system enhancement products including channelised and broadband bi-directional amplifiers and AM/FM/VHF/UHF/Cellular rebroadcast repeaters, antenna system monitors, RF amplifiers, RF signal filtering, duplexers and combiners and systems components including hybrid and directional couplers, power dividers, attenuators, terminations, etc. Coupled with this diverse range of products, RFI offers professional engineering and support services. These include site surveys, RF system design, installation, integration, commissioning, combiner retuning, testing and maintenance, coverage performance testing, documentation, training and project management activities for Distributed Antenna System (DAS), Radio Rebroadcast Systems and other projects - all provided to assist our customers in the deployment and ongoing use of our products. For further information on RFI’s products and services, please contact your nearest RFI sales office.
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