BBC VHF test tone transmissions and Engineering information about broadcast services.

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BBC VHF test tone transmissions

Transmission starts about 4 minutes after the end of Radio 3 programmes on Monday and Saturdays.

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Notes

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 pre-emphasis. 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 should be made on the crosstalk checks.

6. Adjustment of the balance control to produce equal loudness from the Land R loudspeakers is best carried out when listening to the announcements during a stereophonic transmis­ sion, 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.

Engineering information about broadcast services

Information about all BBC services as well as advice on how best to receive transmissions (including television) can be obtained from:

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Relevant engineering information, including information regarding newly appointed transmitters etc., is broadcast by the IBA every Tuesday at 9.15 a.m. and 12.15 p.m., on Channel4 television.

World time

Difference between local time and coordinated universal time The differences marked + indicate the number of hours ahead of UTC. Differences marked - indicate the number of hours behind UTC. Variations from summer time during part of the year are decided annually and may vary from year to year.

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International allocation of call signs

The first character or the first two characters of a call sign indicate the nationality of the station using it.

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