Has anyone ever figured out why the RC96 does NOT mute RX audio when the receiver is inactive?
Looking at the schematic it appears that the rx audio mux switch pin of IC9 (4053) should, in theory (according to the schematic), control the audio gating. The switch control pin is tied to the "select 1" line, which is driven by the cpu (indirectly). However, when monitoring the switch pin of the 4053 for the rx audio path, the pin's logic state never changes. I have an application where I want to use unsquelched audio into the RC96. When using a 96 with the audio delay option board, as can be seen by reviewing the schematics, ACC uses a 4077 NOR gate to combine the SELECT 1 line with the rx COS signal to allow either function to control this audio gate, which by virtue of the delay board installation process gets moved up onto the daughterboard. For now I simply lifted the 4053's switch control pin from the ic socket and wired it to the rx COS pin by way of a transistor and pull- up resistor to Vcc of the chip, and this works great. However, as a purist, this has one caveat, in that if the repeater is in PL mode, any noise bursts which open the squelch (and result in COS going active) will allow rx audio to pass thru to the TX during hang time or IDs. Does anyone know why the processor is NOT controlling the rx audio gate? It would be nice if it did, so that the audio would only switch on when the rx is active, regardless of mode. Did ACC just never get around to implementing control of the SELECT 1 logic line in the firmware? I have confirmed this in more than one 96, so it's not a bad component. Eric KE2D
