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  Some notes on interfacing to the Kenwood TKR-720 and TKR-820 tabletop repeaters
By Mike Morris WA6ILQ
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This is a "quickie" page that was put together in late January 2008 as there was a converation on the repeater-builder mailing list that asked some questions. I provided some info from my notes and thought that publishing them might help. So I pulled the two pages of handwritten notes from my file cabinet that cover interfacing a TKR-n20 repeater to an external repeater controller and made a web page from them. The second pass a few months later added the TS-64 notes.
Please don't email me asking for any other info as everything in that project file folder is here and I no longer have access to those TKR-n20s.

This web page is not pretty but it works. If someone has a TKR-n20 repeater and wants to add some info to this page just email me at (mycall) at repeater-builder dot com. If anyone wants to write an additional article just let me know.

The TKR720 (VHF) and TKR-820 (UHF) are tabletop or rack-shelf-mount repeaters and were derived from the TK-720 and TK-820 mobile radios. The VHF and UHF TKRs interface the same. If Kenwood sticks to its numbering plan a low band unit would be a TKR-620 if they make one. In this writeup I'm going to use the format of TKR-n20 just to keep things generic.

Note that the TKB-n20s are the base station version and has totally different pin numbers on the accessory socket.

While the KSG-4500 is basically a TKR-820 with a 100 watt continuous duty amplifier and power supply built in (and fits in 4 rack units!), the interfacing is not the same. First, the KSG uses a DB-15 accessory connector where the TKR uses a Molex 15 pin, second the pinout is completely different, and third you have to go chasing internal changes - such as finding a soldered jumper the on the "Repeat" button (locking it in repeat). There are PDFs of a TKR service manual and a preliminary manual on the KSG on the Kenwood page at this web site.

Again, this page is a collection of NOTES, not a step-by step procedure. You may have to play with some of the connections to make them work, as I took the notes as I did the work, and I may have missed writing something down. I also used the internal decoder on one TKR and a TS-32 decoder on another, and my old notes are not clear as to what was different between the two. If anybody wants to take what is here and write a real article from it, feel free to. And things change in Kenwood's production - for example, the earliest TKR-n20s didn't bring out tone decode to the accessory connector - the repeater might be programmed for tone, but the COS pin was a carrier indicator, not a receiver unsquelched indicator.
So these notes are accurate as of the date I did the work described below, and there is no guarantee that later units will work the same.

The square at the bottom right is the microphone jack.

The connector under the middle of the gold heat sink is for an external 12v backup battery.

Bandsplit information:
On both the TKR units and the KSG units just look for the FCC ID number on the serial number tag.

Anyone have the similar information for VHF?

Output power:
    Keep in mind that the TKR-n20 is rated for 100% duty cycle at only 5 watts and below, and 50% duty cycle at 20 watts. Power is set by VR1 on the PA assembly. There is a properly placed hole in the sheet metal for a non-metallic screwdriver to adjust it. Resist the temptation to put a fan on it and run it at a higher power... fans fail and you will discover that burnt up PA decks are expensive. You will be much, much happier if you run it at 5 watts or less and put an external continuous duty amplifier behind it.

These cunits an be found with an internal duplexer, but it's a flat-pack notch-only duplexer which is NOT appropriate for a busy site. The quick test is to look on the rear and if you see one coax jack then you have an internal duplexer or if you see two coax connectors (separate transmit and receive) then there is no duplexer option. Finding a VHF unit (a TR-720) with an internal duplexer is RARE, and when you do, it's one with a multi-megahertz offset.

Repeater Features:
In short, very little in the way of bells and whistles. It has a carrier delay (hang-in) timer, a time out timer, and does not have an IDer. It has CTCSS and DCS encoding and decoding built in. The tone encoder doesn't generate true reverse burst. Just like many other manufacturers the TKR tone encoder tone is shut off a very short time before the transmitter carrier drops.

RF Frequency Programming:

Presently there are three ways to program a TKR-n20:

  1. Using the Kenwood KPT-20, which operates standalone (with its own keyboard and screen).
  2. Using the Kenwood KPT-50, which can operate standalone (with its own keyboard and screen), or using a PC with KPG-21D software (the required Kenwood software package - much easier).
  3. Using some math and the techniques used in this article by Matt Krick K3MK.
The KPT-50 and the PC software is MUCH easier to use than the KPT-50 by itself, and that is much easier than a KPT-20.

The K3MK method involves carefully unsoldering the 9346 chip that holds the RF frequency information and installing a 8-pin DIP socket where the chip was. Then the chip is programmed per the instructions in the article using a common chip programmer, and then plugging the reprogrammed chip into the new socket. The same is done for the PL Tone / DPL Code chip (also a 9346), but that one is already socketed from the factory. If you remove the PL Tone / DPL Code chip from the socket then your reepater drops into carrier squelch mode.

The proper way to align the front end is to use the internal sample port, but rough guess tuning by most seems to work ok. I really suggest getting a manual (or downloading the service manual file from this web site) and read the tuning section.

Interfacing the TKR-n20 units:
15-Pin Accessory Connector Info
  Molex Part Numbers Digikey Part Numbers Mouser Part Numbers
Housing: 03-06-2152 WM1228-ND 538-03-06-2152
Pins: 02-06-2103 WM1000-ND 538-02-06-2103

Information I don't have: (can somone provide them?)
1) a photo of the connector inside the TKR where the KPT programmer plugs in.
2) Connector info and amp-hour sizing info for the backup battery.
3) Some computer screenshots of the Kenwood software used with the KPT-50, plus any relevant notes.

The TKR-n20 Accessory connector
Pin Layout:   (looking at the rear of the unit)
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
Note that the connector in the TKR is a male body with female pins! You need to purchase a female socket and male pins. Radio Shack used to carry these a long time ago, and maybe can still get them. Unless you have a good electronics store close by you will probably have to order from Mouser or DigiKey.
Pin Description and Notes
1 Internal Controller disable - Jumper to pin 11 (ground) - grounding this pin tells the TKR to disable the internal controller completely and use an external controller, except the PL encoder / decoder is still operational. Set the "tone" number in the programming to zero for carrier squelch, otherwise set it for the tone you want.
2 Audio ground.
3 Transmitter modulator in (used as external CTCSS tone encoder injection input - don't use this pin for anything else). If you are using shielded cable - recommended - tie the shield to pin 2.
4 Receiver discriminator out (connect this to the audio input of any external CTCSS or DCS decoder(s) here, otherwise don't use). If you are using shielded cable - recommended - tie the shield to pin 2.
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 electronics), so until you check be careful that you don't short it to ground accidentally. You don't want to melt a trace or a wire in 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)
Do not use this pin as a source of repeat audio. This is monitor audio only.
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 can disable the internal timeout timer in the TKR.
  2. Pin 13 is Receiver UnSquelched (RUS), a logic signal that is either carrier driven or tone driven depending on how the receiver is programmed. This signal is about 3.8 to 3.9 volts with the receiver muted/squelch closed/no tone, and about a 0.25 to 0.4 volt with the receiver unmuted/squelch open/with tone, which is enough to drive most external repeater controllers, or an open collector driver transistor (i.e. a buffer circuit) just fine.
    It's easy to damage the chip that is the source of this signal, so be careful, or use a buffer circuit here.
  3. Pin 14 and Pin 15 are empty holes in the chassis mounted connector (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...

Using the above information, the Repeat, Monitor and Take-over buttons on the front panel will be in the "out" position.

If you want a system that is remotely switchable between carrier and tone (which I do on every repeater I build, and 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 mount a tone decoder or DPL decoder (or both) inside the unit. Run the RUS lead to the controller COR input, and run the output of the add-on decoder to the controller PL/DPL decoder input (maybe using pin 14 to bring it out of the TKR). There is plenty of room inside the cabinet for an add-on decoder board.
  3. A variation on (1) and on (2) is to mount a TS32 or TS-64 tone decoder inside and use a digital output from the controller to ground or unground the hookswitch lead (the violet wire on the TS-64). The decode output and the hookswitch lead can be connected to pins 14 and 15.

Notes on the Com-Spec TS-64 tone decoder
Signal Description and Notes
Red + DC power in
Black Ground
Green AUDIO INPUT. Hook this to the receiver discriminator
Violet HANGUP input. Ground this pin to make it active. When it's floating the tone 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 (1K works fine). If the signal is upside down from what you need then install jumper JP7 to get an active low signal (it will go to ground on decode).
Yellow ENCODER output. This audio output 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 we connected the PTT output of the external repeater controller 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 application this pin went 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.

All of the above TS-64 information is in the Instruction Sheet that is packed with the TS-64 itself. In addition it can be downloaded from the Com-Spec web site, or from the TS-64 page at this web site.

I included the TS-64 info above instead of the TS-32 as it's a current product, and easier to use. If you take the above info, a TS-64 data sheet and a TS-32 data sheet and compare them you can figure out the hookup of a TS-32.

Contact Information:

The author can be contacted at: his-callsign // at // repeater-builder // dot // com.

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This page originally posted on 28-Jan-2008

Article text and hand-coded HTML © Copyright 2008 by Mike Morris WA6ILQ

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.