Modern military forces strive for agility and mobility, given the nature of modern threats. Current strategies plan on putting rapidly deployed small armed on the ground anywhere in the world within 96 hours. In support of such readiness, the US Navy's Command, Control, Communication, Computer, and Intelligence (C4I) system must be fully functional and working in concert with air support and sea vessels. One of the key instruments in maintaining this system is the compact Site Master cable and antenna analyzers and handheld spectrum analyzers from Anritsu Co., used by the Navy for service and performance diagnostics on their sophisticated C4I systems.
Although the Navy's measurement frequencies of interest are classified, the battery-powered Site Masters are designed with wideband measurement capabilities to cover a host of contingencies. Site Masters are currently offered with vector-network-analysis capabilities—with the ability to measure return loss and isolate faults in cable runs between a transmitter (Tx)/receiver (Rx) and an antenna—as well as with spectrum-analysis capabilities (in order to view traditional plots of signal amplitude as a function of frequency). For example, the recently announced S810C and S820C Microwave Site Masters are vector-analyzer-based instruments with frequency spans of 3.3 to 10.5 GHz and 3.3 to 20 GHz, respectively (see figure). Suitable for remote measurements of return loss and fault location, they feature a return-loss range of 0 to 54 dB with 0.01-dB resolution. These compact analyzers, which measure just 10 × 7 × 2.4 in. (25.4 × 17.78 × 60.96 cm) and weigh slightly more than 4 lbs. (1.8 kg), contain enough nonvolatile memory to store as many as 200 measurement traces.
In addition, model MS2711B is a portable spectrum analyzer with measurement range of 100 kHz to 3 GHz. It exhibits a noise level of better than −115 dBm and amplitude accuracy of ±2 dB. Weighing just under 5 lbs. (2.25 kg), the analyzer offers resolution-bandwidth filters of 10 kHz, 30 kHz, 100 kHz, and 1 MHz and video-bandwidth filters from 100 Hz to 300 kHz. The instrument has built-in amplitude-modulation (AM) and frequency-modulation (FM) demodulation capabilities, trace averaging, an RS-232C interface, and is well suited for both Tx and Rx measurements. Other Site Masters include the model S113C, with scalar-analysis capabilities from 2 to 1600 MHz, the model S114C, with spectrum-analysis capabilities over the same range, the model S331C, with scalar-analysis capabilities from 25 to 4000 MHz, and the model S332C, with spectrum-analyzer functions from 25 to 4000 MHz.
Although nominally developed for commercial wireless applications, these analyzers possess the traits and capabilities well suited for military wireless testing. Military testing, of course, is subject to potentially more severe environments that commercial situations. At sea, for example, salt water and sea spray can cause rapid corrosion, resulting in damaged connectors and weather seals. Salt water can also damage antennas. In addition, vibration from large guns can loosen cable connectors and waveguide, causing shorts or intermittent electrical contacts. In some cases, servicemen may accidentally paint over an antenna or damage waveguide while painting, leading to electrical problems that can be readily detected with a SiteMaster instrument.
Communications and electronic-warfare (EW) systems on fighter planes extend from the cockpit to wingtips. The cabling is in a fixed, confined space that is often inaccessible. Furthermore, these aircraft systems are exposed to wide discrepancies in temperature. For example, temperatures on an aircraft carrier can reach as high as +120°F during takeoff and −62°F when a plane is at cruising altitude. Vibration caused by weapon firing is another factor that can adversely affect the performance of communications systems.
Despite these obstacles, communications systems must maintain operation for any mission to be a success. The Site Master analyzers feature frequency-domain reflectometry (FDR) in contrast to time-domain reflectometry (TDR), analyzing RF signals in the frequency domain rather than DC pulses in the time domain to discern problems with an on-board military communications system. The FDR capability makes it possible to perform distance-to-fault (DTF) measurements to quickly detect the location of an impedance mismatch of break in a transmission line. DTF measurements are especially useful because they provide the clearest indication of trouble areas by revealing both the magnitude of signal reflection and the location of the signal anomaly. In addition, the analyzers provide 517 data points to enable identification of faults at more than twice the range of competitive offerings.
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This measurement capability serves as the foundation of all the Site Master analyzers, including those developed specifically for the military. Technicians are using Site Master analyzers to determine a cable and antenna system's health in just a few minutes. The analyzer can identify if there is water in the antenna, cable damage, a defective weather seal, or a loose connection. It can even determine if the antenna has been painted over or the waveguide has been damaged and its effect on signal transmission. All of these measurements can be made easily because the analyzer has an intuitive and menu-driven user interface that allows measurements to be made by servicemen who are literally in on-the-job training scenarios.
Another crucial benefit of the Site Master is the patented superior immunity to interference. The analyzers have interference immunity of +17 dBm, which allows technicians to conduct analysis in the most complex and RF rich environments. This is especially important on a warship, which is part of a vast command, control, computer, and information network. Moreover, a Navy ship topside consists of a sophisticated assortment of weapons, electromagnetic (EM) radiators, and other hardware. A large number of antennas, Txs, and Rxs are required to meet the radar, electronic and information warfare, and communication requirements. In fact, the number of radiating systems (antennas, arrays, and radar) on a ship can range from 50 to over 100, and the communication antennas operate over a wide range of frequencies, including high frequency (HF), very-high frequency (VHF), and ultra-high frequency (UHF).
The capability of the Site Master analyzers to store as many as 200 measurement traces is beneficial as part of the Navy's PMS (Plan Maintenance Schedule), which requires maintenance to be performed on a quarterly basis. A technician can recall previous measurements taken of specific antennas to determine if the performance has degraded—even to the slightest degree.
When testing aircraft EW systems, the Site Master gauges amplitude levels over a wide dynamic range, from insertion loss as low as −90 dB to gain as high as 50 dB (160-dB dynamic range) with 0.1-dB resolution. This analysis capability is used to ensure that new or replacement cables match the loss for loss sensitive application or phase in phase-sensitive application. It is also used to determine overall system loss.
The lightweight, small size, and battery operation of the Site Master and handheld spectrum analyzers are also proving invaluable out at sea. When a technician is dangling 20 feet in the air at the tail section of a fighter plane or climbing a vertical ladder between decks on a ship, the fact that the instruments weigh about 5 lbs. (2.25 kg) proves invaluable. Anritsu Co., 490 Jarvis Dr., Morgan Hill, CA 95037-2908; (408) 778-2000, FAX: (408) 778-0239, Internet: www.us.anritsu.com.