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Operating Instructions
760A / 760D / 760N
2–5
L indicates signal amplitude from the LEFT channel input.
R indicates signal amplitude from the RIGHT channel input.
L=R indicates monaural amplitudes and “in phase” left and right signal
amplitudes.
L=–R indicates “out of phase” left and right signals. A pattern display
oriented along this line is poorly suited for monaural reception.
Phase Marks and Phase Tangent Lines are used in conjunction with one another to
make system phase error measurements. This procedure is explained later in this
section. All other graticule markings are used for performance verification and
adjustments in SECTION 5, PERFORMANCE CHECK AND CALIBRATION.
LED BARS
The three 100–segment LED bars allow direct readout of the signal levels. Two
of the bars are dedicated to the left and right channels, while the third bar can be
switched to display
L+R
2
(sum), or
L–R
2
(difference) of the input voltages, or
to display the level of the AUXILIARY input. By dividing Left + Right by two,
the third bar will read the same as the left and right bars do, when the two
channels are of the same phase and amplitude.
The standard 760A, the 760D (DIN scale), and the 760N (Nordic scale) employ
different scales and resolutions for the LED bars, as described below:
760A The scale is dB linear between +8 and –20dB, with scale marks every 4 dB.
Below –20 dB the scale is progressively tapered to –45 dB with marks every 5
dB. Above –20 dB each LED segment represents a 0.4 dB increment. The LED
bars are green up to 0 dB, and red above that point. With the EXPAND SCALE
button depressed, the scale is expanded by a factor of four, and the resolution is
increased to 0.1 dB. The scale range is –5 dB to –11 dB while the EXPAND
SCALE button is being held in, as shown by the scale printed in blue. The
sensitivity for the standard 760A is jumper selectable (see SECTION 3, INSTALLA-
TION).
760D The 760D uses a DIN scale in accordance with DIN 45 406, with a range of
+5 to –50 dB. The scale is progressively compressed from top to bottom, having
a resolution of 0.25 dB from +5 to 0 dB, and tapering to 2 dB from –40 to
–50 dB. With the EXPAND SCALE button depressed, the resolution is increased to
0.125 dB and the scale range is –5 to –13 dB (shown in blue). The LED bars are
green up to 0 dB, and red above that point. A 1.55 V rms sinusoidal input
(+6 dBu) produces a reading of 0 dB, and there are arrows which indicate the
–9 dB test level.