Function Reference
BTSC Sound
5
5-55
Select among:
1. Single tone mode
Stereo ON, L = 0.3 kHz, 1 kHz, or 3 kHz, R = 0
2. Double tone mode
Stereo ON, for example, L = 3 kHz, R = 1 kHz
3. Double tone mode (L = 300 Hz, R = 3.1 kHz) using Test 1,
which is especially useful for Philips BTSC Decoder circuit TDA 9855 but may be
useful also for other decoders.
•
SAP level adjustment of BTSC decoders.
To adapt the SAP output level of a BTSC decoder to the corresponding level of the
Mono signal (volume), Test 3 generates L+R and SAP with 100%.
•
Further performance measurements concerning harmonic distortion, frequency
response, and bandwidth are possible.
Recommendations
Because the BTSC receiver is sensitive to the signal level and to interfering frequency
components, there are several sources of decreasing performance. Any of the following
can cause loss in stereo channel separation.
•
Bandwidth reduction within the IF or intercarrier filters of receivers or excessive
group delay ripple.
•
Frequency response of FM demodulators.
•
Interfering components from the video modulation, mainly n x fH.
To reduce problems during alignments or measurements of BTSC sound, it is recom-
mended that you turn off the video modulation of the 54200 with BTSC sound (Video
Extern mode).
For stereo separation alignments, it is also helpful to select a stereo signal with a lower
and a higher frequency component. As long as the stereo signals are high enough this
leads to a masking of interfering components.
For example:
L = 3 kHz and R = 1 kHz, or Test 1, or Test 2.
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