4-Wire Testing With Responder - AMERITECH AM5 Instruction Manual

AM5(e) Classic Instruction Manual
SND pair which travels to the RCV pair at the far end. At the far end the
loopback connection joins the incoming RCV pair to the outgoing SND pair and
the signal is returned to the near end.
The AM5(e) Classic receives the signal (into the RX jack) from the near-end RCV
pair and measurements are made on the incoming signal. By comparing SEND
levels with MEASured levels, line degradation can be measured.
NOTE: A loopback test cannot be done on 2-Wire circuits because signals can not
be sent and measured simultaneously on the same pair.
The advantage of loopback testing is that only one AM5(e) Classic and one
operator is needed at the test site.
Though loopback testing is more convenient and less costly than end-to-end
testing, it is also less reliable. The disadvantage is that it does not identify
transmission impairments in each direction. In fact, a satisfactory loopback
measurement could actually hide impairments in each direction which cancel
each other out.
To perform a loopback test with a Western Electric Model 829 at the far end and
an AM5 Classic at the near end test site:
1. Connect the TX/2W jack to the SND pair of a 4-Wire circuit, and connect the
RX jack to the RCV pair. Ground the sleeves (or ground terminal) to the CO
ground if Noise-to-Ground tests are required.
2. Turn off SF SKIP, if lighted, then send a brief 2713 Hz tone from the AM5
Classic. (If a different loopback frequency is required, set the QUIET mode
parameter for F4 to that frequency before sending the tone.) This will activate
loopback in the distant Model 829.
(To send the tone, repeatedly press the right SEND key until F4 is flashing.
Then press and hold the right SEND key for over three seconds until F4 is
lighted steady. After about five seconds, press the key again briefly to stop the
tone.)
3. As required, SEND the required test signals and make the desired
measurements on the looped back test signal. (If frequency sweeps are made,
be sure SF SKIP is ON to avoid false commands to the Model 829.)
4. To end the test, repeat step 2 to deactivate loopback in the distant Model 829.
5.4.3 4-Wire Testing with Responder: Most of the advantages of both end-to-end and
loopback testing can be achieved if multifunction responders, such as Ameritec's
AM3-4A (4-Wire DTMF Commandable V.F Responder) or AM3-2 (2-Wire DTMF
Commandable V.F. Responder), are located at the far end of circuits which may
require testing.
Like 4-Wire loopback testing, the use of a responder eliminates the need for
another AM5(e) Classic and operator at the far end. In addition to loopback tests,
the responder can generate tones which can be measured by the AM5(e) Classic;
therefore, one-way impairments from far-to-near and near-to-far end can also be
measured. Figure 5-5 shows a typical 4-wire test configuration using an AM3-4A
November 19, 1997
(18-0047)
Page 5-9
LINE FUNCTIONS