A walk in the park
New hand-held analyzers make field testing easier and more convenient with their decreased size and combination of functions.
In the race to offer customers wireless services, carriers continue to add cell sites, both on the hills in the suburbs and on the rooftops of city buildings. Field technicians responsible for maintaining the performance of these cell sites have had to do more testing as a result of this commercial explosion, lugging so-called “portable” instruments to each location. New hand-held test instruments, however, are changing the way technicians look at signals and making analysis easier and less strenuous.
Carriers are expanding services by installing multichannel, multipoint distribution services (MMDS), local multipoint distribution services (LMDS) (currently known as BWA), wireless local area networks (WLAN) and other point-to-multipoint sites throughout the country, some close to existing cellular, PCS and microwave base stations. Although these services operate at different frequencies, interference occurs often because of the growing number of tower sites. Field technicians are being dispatched to quickly determine the cause of such noise.
Determining if there is a fault, interference or a cell coverage problem at a site adds another task for a single technician, who may already be responsible for as many as 50 cell sites. Worse, the field technician, who receives less training than in the past, may still carry a spectrum analyzer and a vector network analyzer (VNA) to the site. Although both instruments are considered “portable,” they are not lightweight-especially after the tenth stop. Most portable lab instruments are not user-friendly by field standards and are tailored to a user who is willing to browse through a thick operating manual to operate the instrument.
Since spring, field technicians for some of the nation’s largest carriers have implemented Anritsu’s newest Sitemaster analyzers, the S114B and S332B, to solve portability and operational challenges. Both instruments incorporate the testing capability of a spectrum analyzer and a VNA in one unit weighing only four pounds. The units were designed to perform tests much faster and more accurately by providing the spectrum analysis and vector measurement features in a single hand-held instrument.
Spectrum analysis capability is especially important in point-to-point signal analysis because it can be used as an initial test to get a quick review of signal strength. Using spectrum analysis, technicians can determine if there is a hole by checking if signal strength is below the threshold.
The new instruments also address multipath problems. The technician simply walks around the cell site’s area with either analyzer to make sure the signal remains above the threshold. It is much more difficult to do this with a “portable” spectrum analyzer weighing more than 35 pounds.
Portability is also useful when deploying a WLAN or WPBX system inside an office building. In such a scenario, signal holes may not be easily simulated by some site simulation programs because of modeling complexity. A portable analyzer allows a technician to measure the site and to report back to confirm or notify site coverage that differs from the computer prediction.
Technicians are also using the spectrum analysis feature to deploy a point-to-multipoint site. Most new RF radio designs specify a single outdoor unit (ODU) in which the RF circuitry is integrated with the antenna enclosure. The analyzers are being used to align the customer receiver antennas to the base station transmitter antenna and to ensure no interference signals are present that will impede the radio receiver performance. By connecting an analyzer to the IF output cable from the ODU, the technician can monitor the IF signal strength. Maximum signal level usually indicates the best alignment path. While in this configuration, the IF cable’s quality can also be determined.
Technicians can also assess the performance of a transmitter with the portable analyzers because the spectrum analysis function provides occupied frequency bandwidth measurement capability. Channel power and adjacent-channel leakage power of the radio transmitter can also be determined. The analyzer’s 10kHz resolution allows examination of TDMA and CDMA signals from cellular or PCS sites, further aiding technicians as they travel from site to site.
Because field technicians need to perform much more than spectrum analysis these days, the analyzers have been designed with more measuring capability. The units have better than a 285dBm noise floor to help technicians quickly determine if there is signal interference. They can conduct all the other measurements that are required in the field, including return loss (VSWR), RF signal output power, cable loss, and distance-to-fault. All these tests are performed at laboratory-quality tolerances.
An RF power monitor option is also being used by technicians. With the option, broadband power can be measured from 120 to 245 dBm with <61dB accuracy. Power can be measured in watts, in absolute decibels above 1mW (dBm), in relative power difference expressed as decibels (dBr), or as a percentage.
In addition to having multiple testing features in a lightweight housing, which inherently saves time, field technicians can conduct the tests rapidly because an intuitive and simple user interface guides technicians through the testing process. A menu-driven display requires the technician to make only a few keystrokes to conduct any of the standard tests. Results can easily be read under any conditions, even on cloudy days or at dusk, because the analyzers feature a large, backlit, VGA LCD.
The analyzers are also helping technicians back at the office. All traces can be downloaded to a database for data management or directly to a PC screen. The data can be exported as a metafile for reporting on-site deployment or maintenance. Data can also be downloaded into a spreadsheet for further analysis.
Today’s field technicians have had the gauntlet passed to them for installing and maintaining cell sites. With additional sites to monitor and fewer technicians to do it, bulky multiple instruments are no longer sufficient. By using analyzers with spectrum analysis capability, the technicians can now meet the demands of the market: timely analysis on as many cell sites as possible.
Lau is with the marketing department of the Mircowave Measurement Division of Anritsu, Morgan Hill, CA.
