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RET-041 Instructions
95307-000-01 6/87
Fig. 8: Response of the First 10kHz Low-Pass Filter in the Passband and Stopband
Finally, all-pass delay corrector IC7b adds delay as necessary to make the delay of the second
filter more constant with frequency.
Fig. 9 shows the normal frequency response of the part of the second filter associated with
IC6b, while Fig. 10 shows the normal frequency response of the part of the second filter
associated with IC7a. Fig. 11 shows the overall frequency response of the second filter.
The normal frequency response of each all-pass delay corrector IC5b and IC7b) is flat,
although each has a frequency-dependent phase shift IClOb and associated components act
as a servo to eliminate DC offset at the output of IC9b.
Fig. 12 shows the normal power spectrum measured at OPTIMOD-AM ' s output with the
10kHz filter strapped in and bright program material applied to OPTIMOD-AM ' s input The
measurement made with an 801 -line FFT spectrum analyzer operated in " peak hold " mode
over a 20-minute observation period with OPTIMOD-AM controls at the normal recom
mended settings) verifies that NRSC power bandwidth specifications are met by the system.
The 10kHz filters can be strapped into the circuit with jumpers A and B. These jumpers
can also be configured to bypass all filters on Card #1F1O, retaining only the built-in 12kHz
filtering provided elsewhere in OPTIMOD-AM.
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