channel
– 250 Hz at zero level
2 900 Hz at
+7dB
6 900 Hz at +7dB
7 900 Hz at
+7dB
8 No modulation
9 Tone sequence at −4dB: 40 Hz
6·3kHz
100 Hz
10 kHz
500 Hz
12.5 kHz 1000 Hz 14 kHz
This
sequence is repeated
channel
440 Hz at zero level
900 Hz at
+7dB,
antiphase to left channel
900 Hz +7dB, in phase
with left
channel
900 Hz at
+7dB
No modulation PurposeIdentification of left and right channels and
setting of reference level
Adjustment of phase of regenerated subcarrier (see Note 4) and check of distortion with L–R signal only
Check of distortion with L + R signal only
Check of R to L cross-talk
Check of L-channel
frequency response and L to R cross-talk at high and low frequencies
Tone sequence as for left channel
Check of R-channel
frequency response and R to L cross-talk at high and low frequencies
14 20 No modulation No modulation
15 20 End of test transmissions
Notes:
PurposeCheck of noise level in the presence of pilot
1. This schedule is subject to variation or cancellation to accord with programme requirements and essential transmission tests.
2. The zero level reference corresponds to 40% of the maximum level of modulation applied to either stereophonic channel before preemphasis. All tests are transmitted with pre-emphasis.
3. Periods of tone lasting several minutes are interrupted momentarily at one-minute intervals.
4. With receivers having separate controls of subcarrier phase and crosstalk, the correct order of alignment is to adjust first the subcarrier phase to produce maximum output from either the L or the R channel and then to adjust the crosstalk (or ‘separation’) control for minimum crosstalk between channels.
5. With receivers in which the only control of crosstalk is by adjustment of subcarrier phase, this adjustment of subcarrier phase, this adjustment should be made on the crosstalk checks.
6. Adjustment of the balance control to produce equal loudness from the L and R loudspeakers is best carried out when listening to the announcements during a stereophonic transmission, which are made from a centre-stage position. If this adjustment is attempted during the tone transmissions, the results may be confused because of the occurrence of standing-wave patterns in the listening room.
7. The outputs of most receivers include significant levels of the 19-kHz tone and its harmonics, which may affect signal-level meters. It is important, therefore, to provide filters with adequate loss at these frequencies if instruments are to be used for the above tests.