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However, though we liked Tracer, we found a couple of snags. First, the unit is available only in a 2xT1 configuration. Even with the additional T1 channel, Tracer's price is competitive with GWM's single-channel unit, but the bigger issue relates to bandwidth use. Unlike Lynx.sc, which provides six channels at 5.8 GHz (two of which are required to support full-duplex communication), Tracer supports only two channels at 2.4 GHz. The lack of alternate channels limits your ability to overcome interference, a problem that is more serious in the increasingly congested 2.4-GHz ISM band.

When we raised this issue with Adtran, company representatives provided us with a fairly detailed explanation of the benefits of 2.4-GHz systems. In comparison to 5.8 GHz, the officials said, 2.4-GHz systems exhibit lower attenuation, both in feeder cables as well as over the air, and they are less susceptible to rain-fade and multipath interference. In addition, their field experiences have resulted in very few instances of interference when high-gain directional antennas are used.

Having said all that, Adtran added that a 5.8-GHz product is in development, a clear acknowledgement of the benefits of the greater available bandwidth and reduced congestion associated with 5.8 GHz. Adtran's modular design should make it fairly easy to add this capability to the company's product line.

Tracer's configuration and monitoring capabilities are the best we saw in any of the products we tested. The cursor-addressable VT-100 interface provides clear status information related to link quality and error conditions. The menu interface is easy to navigate without slowing you down. Adtran delivers the best of both worlds by also providing full hardware configuration capabilities, with switches concealed behind a front-panel LED display that folds down for access. All configuration switches are clearly labeled.

Adtran also offers the most rugged outdoor RF unit of any product we tested. The Tracer features the same waterproof housing that other Adtran products use, many of which are mounted in underground manholes that are prone to periodic flooding. The rack-mount RF unit, which is less than two inches high, is powered from the modem unit using a short coax cable.

Tracer's performance was excellent: It achieved 99.8 percent of the data throughput of our crossover-cable T1 baseline.

Adtran provides the best warranty coverage of the bunch. Not only is its five-year warranty virtually unprecedented, it includes 24-hour advanced replacement coverage. If a component fails during the warranty period, the company says you'll get a replacement the next day.

Tracer, $8,095 rack mount, $8,595 mast mount, Adtran, (800) 9-ADTRAN, (256) 963-8000; fax (256) 963-8699. www.adtran.com