can be used in place of the TS-2669/GCM. Both test sets furnish variable
carrier frequencies, accurate modulation rates, and digital readouts of
frequency. There are, however, several significant differences.
(1) The Model 340B is simpler to operate and calibrate than the TS-
2669/GCM.
(2) The 340B weighs much less, and is considerably smaller in size.
These features are brought about by incorporating solid-state devices
(transistors) in the equipment design.
(3) The readout of delay in the 340B indicates directly in
microseconds, while the delay meter of the TS-2669/GCM gives the delay in
milliseconds.
Since the delay parameters are stated in microseconds, the
340B eliminates the necessity of constantly converting from milliseconds to
microseconds (usec).
When using the TS-2669/GCM, the conversion of meter
reading involves moving the decimal point three places because 1 microsecond
is 10-3 millisecond.
Conversely, 1 millisecond is 103 microseconds.
For
example, if the meter measures 1.5 ms, the 340B readout should show 1,500
microseconds.
(4) The TS-2669/GCM has automatic phasing capability.
That is, in
measuring envelope delay the operator at the receiving station merely
presses a SYNC phasing button.
When the 340B is used, the operator must
manually phase his set to the incoming line signal.
2-2. Amplitude-Frequency Response.
One factor that can degrade signal
quality in a voice circuit is the unequal attenuation of different
frequencies.
In a nonloaded cable, for example, the high frequencies are
attenuated more than the lower ones. This variation in loss across the band
of interest can be compensated for by equalizing.
The equalizing process
consists of inserting into the circuit additional loss which varies with
frequency in exact opposite relationship to the line loss. Sufficient loss
is added at each frequency to bring the frequency response across the band
within a specified limit. However, before any equalization adjustments are
made, the technician must determine the characteristics of the unequalized
circuit at all frequencies specified, and plot the results on graph paper.
After analyzing the graphed results and comparing them with the parameter
dictated by the Telecommunications Service Order (TSO), the technician
decides whether the circuit must be equalized. If the telephone line meets
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