HP 4935A, Руководство по эксплуатации и обслуживанию

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Model
Operation
To obtain loss deviations relative to 1004 Hz, the button is pressed during reception
of the I reference signal. The received power level is stored (in and simultaneously displayed as
readings taken at other frequencies are compared to the 1004 Hz reference and displayed in
The reference will not have to be subtrartrd from levels at other frequencies to obtain
readings.
According to telephone industry convention, attenuation is defined as a change in loss of a
telephone circuit, compared to the loss of a nominal 1000 Hz signal on that circuit. For example, a circuit
with 6 more loss at 2800 Hz would have an attenuation distortion of
3-30. SF SKIP
Skip (single frequency skip) automatically prevents the from transmitting frequencies in
Hz to 2750 Hz range. This feature is used when transmitting over a dial-up network with single
frequency signaling units. Any skipped frequency can be programmed using the STORE capability of the
Figure
3-32. MESSAGE CIRCUIT NOISE MEASUREMENTS
The message circuit noise measurements determine the effects of background noise and tones.
illustrates the basic setup for these measurements.
( Q U I E T T E R M I N A T I O N )
TELEPHONECIRCUIT
T
TRMT
I
RCV
LINE
M O N I T O R
Figure 3-5. Message Circuit Noise Measurements
message circuit measurement is obtained by measuring the noise present on a line with a quiet
termination on one end (supplied by the transmitting and a weighted measuring device on the other
end (receiving
The C-message filter measures noise signals that annoy the typical telephone service subscriber.
weighting is also used to evaluate the effects of noise on voice-grade data circuits. C-weighting is
valid for data transmission since the response characteristic is relatively flat over most of the frequency
range for data transmission (600 to 3000 Hz, see Figure
The flat filter has a response that provides much less attenuation to the low frequencies (60
Hz to 500 Hz) than the C-message filter. By comparing a flat noise measurement to a C-message noise
measurement, the relative influence of low frequency noise (60 Hz commercial power, 20 Hz ringing, etc.)
can he determined (see Figure