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Some notes on interfacing to the Kenwood TKR-720 and TKR-820 tabletop repeaters By Mike Morris WA6ILQ

This is a "quickie" page that was put together to share two pages of handwritten notes from my file cabinet that cover interfacing a TKR-n20 repeater to an external repeater controller (where "n" is 7 for VHF or 8 for UHF). The second pass a few months later added the TS-64 notes.
Please don't email me asking for any other info as I no longer have access to the TKR-n20s or the book, and everything in that project file folder is here.

This web page is not pretty but it works. If someone has a TKR-n20 repeater and wants to create a photo article he is free to use the tables below and I'll be happpy to replace this page with his article.

Information I don't have: (can somone provide them?)
1) Closeup photo of the acccessory connector (without anything plugged into it)
2) DigiKey or Mouser part number(s) for the mating connector body and pins that go on the cable that plugs into the TKR (i.e. what part numbers to order)
3) Schematic of the circuitry around the accessory connector
4) Info on TKR-n20 programming and any relevant notes (maybe some computer screenshots?)

TKR-n20 Accessory connector
Pin Layout: The connector is five rows of three pins across in this format: 1     2     3 4     5     6 7     8     9 10   11   12 13   14   15
Pin	Description and Notes
1	Jumper to pin 11 (ground) - grounding this pin tells the TKR to disable the internal controller and use an external controller
2	Audio ground
3	Transmitter modulator in (used as external CTCSS tone encoder injection input - don't use for anything else). If you are using shielded cable - recommended - tie the shield to pin 2.
4	Receiver discriminator out (hook the audio input of any external CTCSS tone decoder(s) here, otherwise don't use). Use pin 2 as the ground for any shielded wire.
5	Transmitter audio in (i.e. repeat audio from the external controller). If you are using shielded cable - recommended - tie the shield to pin 2.
6	External speaker ground (see pin 12) (jumper this pin to pin 11)
7	+12vDC out of the TKR.   This pin will source up to 1 amp so you can power an external controller from this pin.   My old notes don't mention if this pin is fused inside the TKR (or if it's fused separately from the radio), so don't short it to ground accidentally. You don't want to melt a trace or the harness.
8	PTT input (ground to xmit) (see note 1)
9	Internal speaker (jumper to pin 12 to enable)
10	De-emphasized receiver audio (i.e. repeat audio out to the external controller). If you are using shielded cable - recommended - tie the shield to pin 2.
11	Ground
12	Internal speaker audio out (jumper to pin 9 to enable)
13	RUS out (see note 2)
14	Empty hole in the connector body (see note 3)
15	Empty hole in the connector body (see note 3)

Table notes:

1. If you trust your external controller you will want to disable the TKRs internal timeout timer.
2. Pin 13 is Receiver UnSquelched (RUS), a signal that is either carrier driven or tone driven depending on how the receiver is programmed. This signal is about 3.5 volts with the receiver muted/squelch closed/no tone, and about a quarter of a volt with the receiver unmuted/squelch open/with tone, which is enough to drive an open collector driver transistor just fine.
3. Pin 14 and Pin 15 are empty holes in the Molex plug (i.e. are not used in stock units). My personal preference is to leave the connections on pins 1-13 stock and to do any mods/additions by adding pins into the holes in positions 14 and 15. I suggest that you leave some kind of paperwork inside the cabinet for the next guy so he knows that it's not stock on those two pins, and what you've done...

If you want a system that is remotely switchable between carrier and tone (which is very handy when you are trying to figure out what the grunge is) you need to do one of three things:

1. Program the unit for tone, and use a digital output from the controller to manipulate the changeover line that is attached to the front panel "Monitor" switch (maybe run a wire to pin 15).
2. Program the unit for carrier squelch even if you run a toned repeater, and use an external tone decoder or DPL decoder. Run the RUS lead to the controller COR input, and run the output of the external decoder to the controller PL/DPL decoder input (maybe on pin 14). There is plenty of room inside the cabinet for an external tone decoder.
3. A variation on (a) and on (b) is to use a external TS-64 tone decoder and use a digital output from the controller to ground or unground the TS-64 violet wire. The white wire and the violet wire can be connected to pins 14 and 15.

Notes on the Com-Spec TS-64 tone decoder
Wire Color	Signal Description and Notes
Red	+ DC power in
Black	Ground
Green	AUDIO INPUT. Hook this to the receiver discriminator
Violet	This is the HANGUP input. Ground this pin. When it's floating the decoder is disabled. When it's grounded the tone must be present.
White	MUTE - This is the actual tone decoder output signal. It is an active high open collector output, and it requires a pullup resistor. If you need active low install jumper JP7 to cause the signal to go to ground on decode.
Yellow	This is the ENCODE Output. This audio is connected to the transmitter modulator.
Orange	PTT input. Ground this to switch the tone encoder on. When ground is removed the encoder phase is shifted (i.e. reverse burst), and the encoder stops when the 160ms is over. In our application the repeater controller PTT output goes to this pin.
Grey	PTT Output. This signal goes low when the orange wire is grounded and stays low for the duration of the grounded input plus the reverse burst timing. In normal radio usage the PTT lead from the microphone would be disconnected from the radio and be connected to the orange wire, and the grey wire be connected to the point in the radio where the microphone PTT lead was. In our appliction this pin goes to the transmitter PTT input.
Blue	FILTERED RECEIVE AUDIO OUT. The path from the green wire (in) and the blue wire (out) has a high pass / low cut audio filter in line, designed to remove the subaudible tone from the user audio. This is an installers choice - You can feed the blue wire back into the receve audio connection. This type of radio surgery is very radio dependent and cannot be covered here. Many radios have a tone removing high pass filter in them from the factory and in that case you can simply tape off the blue wire and ignore it.