DRA-SR H1 and H2 Header Explanation:

Note - These headers are not present or required on REV2 and higher circuit boards.

Headers H1 and H2 are the interface for installation of an optional audio filter.  
While these 4-pin headers can be used for multiple functions, their main purpose is for easy 
interfacing of the FL-10 filter board.  When the FL-10 is not installed, a simple 2-pin header 
jumper "shunt" or "short" is installed onto the center two pins of the header completing the 
audio path between the CM119A and the LM386 audio amplifier ICs.  

To use the optional FL-10 filters, simply remove the shorting bar "shunt" and install the FL-10 
observing polarity.  The ground connection is nearest the silkscreen markings "H1" and "H2".


See the DRA-SR-DIN6 or DRA-SR-RJ45 Pinout Documents for detail on the other headers and jumpers.