AP-1 AUDIO PROCESSOR BOARD

    The AP-1 is an audio processing board which performs low-pass filtering and adjustable audio compression (AGC). It's designed to be an add on option for the FM-6 stereo generator. This is recommended if no external filtering is used so that no energy appears in the vicinity of the 19 kHz pilot. This could cause problems in stereo locking of the FM receivers if the filtering were not used. Many satellite receiver audio outputs have significant energy above 15 kHz which needs to be removed for any stereo generator.
    The AP-1 has two adjustments to set the compression characteristics. A "knee" control sets the point at which the gain begins to be reduced. If the signal is below this level, no compression is applied. A "compression" control sets the slope of the input/output curve. A compression ration of 1:1 has no effect on the signal. For example; a 1dB change in the input results in a 1dB change in the output. If the compression ratio is set to 2:1, a 1dB change in the input results in a 0.5dB change in the output. A compression ratio of infinity puts it in an AGC mode. In this mode, if the input level is above the knee, the output level will remain constant.
    Standard 75 usec pre-emphasis (removable) (50usec available) is included. An audio presence detector (APD) output provides a low going signal if no audio is present for 30 seconds. This can be used to mute the translator if the audio feed is lost. LED indicates when unit is compressing.
 

Electrical Specifications:

Input Level	0 dBm balanced or unbalanced 600 Ohm or 10k Ohm, factory or field configurable.
Output Level	0dBm unbalanced (adjustable)
Power Requirements	13 to 24 VDC
Frequency Response	50-15,000 Hz
Compression Ratio Adjustment Range (adjustable by VR1)	1:1 (no compression) to infinity (AGC)
Knee (adjustable by VR2)	-40dBm to -l0dBm
Attack Settling Time to Within 3dB of Final Value with a 1kHz sinusoid (depends on step size)(set by fixed resistor and capacitor values)	l0dB step: 71 msec  30dB step: 93 msec
Decay Rate with a 1kHz sinusoid (set by capacitor value, 33uF)	20dB/sec
Electrical Interface:	All audio signals and APD signal are on a 10 pin SIP header (P 1).  Power is connected via 2 pin SIP header (P2).

 
Mechanical Specifications:
The PCB measures 3.5 by 2.6 inches with mounting holes appropriate for mounting on the FM-6 Stereo Generator Board (see drawing below).
 

Back Home