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What Is It?
The Model 404 is a hand-held combination T1 Digital, Datacom and Wideband Test Set for the telecom field technician. It is a digital, full function 1.544Mbps T1/Datacom Tester, as well as a full function analog transmission impairment tester. Uniquely designed with a touch screen graphical user interface for extreme ease of use. It is about the size of a small telephone book, weighs approximately 3-1/2 lbs. and is powered by an internal rechargeable NiMH battery pack with five to six hours of battery life. It comes standard with a 115/230 VAC adapter or an optional 12 VDC cigarette lighter adapter. Analog and DS0 tests meet IEEE standards.
How Does It Work?
The Model 404 is ideally suited for the field technician who must relate to all types of digital and analog circuits. Datacom testing provides for emulating either the DTE or the DCE while sending patterns and injecting errors. If the T1 line is driven by HDSL technology, the wire itself can be tested using wideband analog testing to 400 kHz, and the repeaters can be tested with the extensive BERT capabilities.
What Does It Do?
The digital test functionality of the Model 404 allows a wide range of bit error testing on framed or unframed 1.544Mbps T1 circuits, and Datacom circuits, including V.35, RS232 and EIA530. As an Analog Tester, the unit provides a wide variety of industry standard measurements to accomplish transmission impairment testing on 2- or 4-wire dedicated or dial-up analog circuits. With the Enhanced Digital option, a T1 telephone is added with dial, talk & listen capability on any user selected T1 voice channel. The 400kHz bandwidth of the instrument makes it ideal for qualifying metallic digital circuits which use an analog carrier such as ISDN BRI ("U" interface) and 4-Wire HDSL circuits. The unit, of course, is also ideal for qualifying voice circuits, which often will carry data modem and fax modem signals.
What Can It Test?
As a Digital Tester two TX/RX ports are provided in order to allow bi-directional drop and insert testing. The unit can terminate the line (simultaneous pattern generation and pattern measurement) or monitor the line for BERT patterns, ABCD bit status, and SLC 96 alarm maintenance and message decode. The Model 404 is compatible with unframed PCM, as well as D4 and ESF framing with B8ZS or AMI encoding.

As a Datacom Tester the extensive pattern generation and detection and the G.821 bit error rate reporting are available for V.35, V.36, RS232 and EIA530 interface testing. The Model 404 acts as a synchronous DTE or DCE device and uses either the DCE clock or its internal clock to generate and verify patterns at speeds ranging from 300 BP/S to 1.544Mbps.

The Enhanced Digital option provides VF testing of any user selected DS0 channel including voiceband level, frequency, noise and return loss. Real-time error counters are augmented by histograms so that the distribution of errors during a test can be studied. It also provides a graphical display of pulse shape with the standard mask or a user set mask.