Simple homebrew programming cable for Kenwood radios (TM-271)

I went to the South Milwaukee swap fest this weekend on the look out for another 2 meter rig I could possibly use in my car. I found a Kenwood TM-271 for a good price in mint condition. My ADI rig does not have the ability that I am aware of to program it with a PC. This Kenwood does. I did not want to purchase a programming cable for it as I am aware that most of these radios use some form of TTL serial port for its programming communications method. I think this should work on other Kenwood mobile rigs with the same mic connection scheme.

The Kenwood uses a standard RJ-45 jack for the Mic connection and uses this same jack for programming. You can use a standard Ethernet patch cable for this. Look below to verify your sacrificial Ethernet cable has the colors in normal patch cable order as shown below.

Ethernet patch cable pinout

Looking through the schematic of the service manual for the Kenwood I verified the proper wiring for the transmit pin, the receive pin and ground. I did this by just measuring the two ground pins to the chassis with no power then referenced these pins to the "8 volt" power out pin. If you follow the schematic you find that the HOOK and PTT are also the RX/TX respectively from the Kenwood radio.

For connecting the the Kenwood I found that the wire colors with regard to the standard Ethernet patch cable color code were as follows:

Ethernet Orange: RX from Kenwood (Kenwood Pin 2 HOOK/RXD)
Ethernet White/Blue: TX to Kenwood (Kenwood Pin 5 PTT)
Ethernet Green: GND (Kenwood Pin 6 GND)

Kenwood service manual snippet.

I used an FTDI breakout board which is a USB to serial TTL converter. I have this available for talking to microcontrollers I play around with. I left the levels set to 3.3 volts per the jumper on my breakout board I recommend doing the same. 

How this works:

• All you have to do is cut an Ethernet cable to the length you want (within reason, a couple feet should be fine). 
• Strip the orange, white/blue and green wires. 
• (Note: white/blue is one wire, white with a blue strip)
• (Optionally) Tin these wire ends with solder to make it easier to insert into a bread board. 
• (Optionally) You should also trim/tape off the wires not used to prevent them from shorting or causing issues.
• Using an FTDI breakout board connect as follows
• Orange to TX on FTDI
• White/Blue to RX on FTDI
• Green to GND on FTDI
• Connect your radio to a power source and plug in the USB cable for the FTDI.
• Plug the RJ-45 into your radio open Chirp or your favorite programming tool and away you go!
• I recommend to have a dummy load connected when doing this. The PTT is used as one of the programming pins. If something strange happens the radio could potentially go into transmit. Better to be safe then end up with a dead final.

This worked for me using Chirp software and is very easy. I can now easily change my frequency memory list when ever I want to go on trips.

Bread board with FTDI and cable wires. -AC9LF

Here is a link to a breakout board that should be usable for this type of thing:

https://www.amazon.com/Qunqi-FT232RL-Serial-Adapter-Arduino/dp/B014Y1IMNM/ref=sr_1_4?ie=UTF8&qid=1499692518&sr=8-4&keywords=ftdi&refinements=p_72%3A2661618011

If you are attempting to do this or anything presented on this blog I am not responsible if anything bad results. Sometimes being cheap can be expensive if you end up turning your fancy radio into a brick. You are responsible for your own actions.

Good luck!