ACC-tender comes in aluminum enclosure and you are free to either lay it around your radio or mount it on top of it. Mounting positions other than radio's top are possible but never tested.
ACC-tender fits best at back end side on top of your K3. There are two mounting options for ACC-tender:
Once you decide ACC-tender's position, remove either leftmost and rightmost screws at the back row of K3 top cover for rear panel aligned installation or leftmost and rightmost screws on rear panel for front panel aligned installation.
Remove ACC-tender's top cover by removing 4 screws from left and right side and place the bottom in a way that mounting holes are over the holes that appeared after top screws removal.
Use the supplied #4-40 screws to fix ACC-tender bottom to K3 body through mounting holes. Please note that these screws are most probably longer than K3's original ones. This is to ensure that ACC-tender is properly fixed to K3 body. Keep the original screws at a safe place so you can put them back in case you decide to remove ACC-tender from your setup.
Check jumpers JP1-JP6 on ACC-tender PCB in order to ensure that their position is in line with your requirements for TX INHIBIT functionality.
Replace ACC-tenders top cover and tighten it with the provided screws.
Connect the DB15HD cable that comes out of ACC-tender box to K3's ACC.
Provide power to ACC-tender through supplied 2.5mm DC jack, preferably from 12VDC OUT RCA on K3's rear panel. If you use separate power supply for ACC-tender, please make sure that there is no voltage difference between its negative terminal and K3's negative one prior to connecting.
ACC-tender's ACC connectors are designed to behave as K3's ACC with one exception - K3 ON/TX INHibit.
Buffered ACC-tender outputs allow you to connect different types of devices on ACC1-3 and RCA connectors with no impact between them.
PTT buffering allows PTT switching of devices that utilize different positive voltages on their PTT input lines, e.g. +5V, +12V, +28V.
Output buffering also allows driving inputs that consume up to 10mA per pin, i.e. band decoders with opto-coupler isolated inputs.
ACC-tender inputs are connected in Y-cable style and have no separation between them.
ACC pin7 is a dual personality one and able to function as either input or output. This makes it difficult to implement a circuit able to cover use cases for both input and output directions. Since ACC-tender was born as contesting station add-on, TX INH function was the one to get focus.
Inside of ACC-tender there is a set of jumpers (JP2-JP6) that either enable or bypass the advanced TX INHibit circuit.
When TX INHibit circuit is in bypass mode, pin7 on ACC1-3 and TX INH RCA center pin are shortened and connected directly to K3 ACC pin7. This mode is the only to allow K3 ON signal out of ACC-tender but care should be taken in such situations because K3 ON signal on ACC-tender connectors is not buffered and goes directly to K3's ACC. In addition to that, since pins are shortened, it is not possible nor advisable to connect multiple devices that utilize K3 ON signal without protective circuitry.
When TX INHibit is in use, the default is to have the transceiver actively inhibited in Rx mode. If radio senses PTT input it sends PTT OUT signal to all peripherals, which in turn should assert their PTT OUTs (connected to radio's TX INH) low when ready, thus allowing the transceiver to transmit RF. When transceiver has single TX INH input, all inhibit-aware peripherals are daisy-chained and the time it takes to allow radio to go on air is the sum of all switching times of all peripherals along the TX INH path.
When TX INHibit circuit is enabled, pin7 on ACC1-3 and TX INH RCA are connected to a NOR gate through voltage level converters.
Level converters are in place to allow use of devices that source voltage towards TX INH inputs.
NOR gate makes it possible to connect up to 4 inhibit-aware peripherals to ACC-tender in parallel, thus reducing the allow-time to the switching time of the slowest peripheral. NOR gate is also the one to remove inhibit from K3 only when all TX INH inputs are asserted low. LEDs on ACC-tender front panel display status of each TX INH input. In case no inhibit-aware device is connected to particular input, it can be disabled (read forcefully asserted low) through DIP switch on the front panel.
JP1 in ACC-tender provides possibility to select HIGH or LOW active state of the inhibit circuit output towards K3. This is mostly cosmetic feature since K3 allows the same setting from its menus. If K3's TX INHibit setting menu is set to HI=INH ACC-tender can be configured to provide HIGH level through DIP switch on the front panel.