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Sunday, April 25, 2021

An Inexpensive Interface Cable for Baofeng Transceivers


Much less expensive than the individual components 

I know many of us have Baofeng and Wouxon transceivers. I recently came across this tip to cannibalize an inexpensive mic for the cable, which can then be easily interfaced to a TNC or other digital device.

The Baofeng UV-5R and similar radios are extremely inexpensive dual band (2m/70cm) HT's that are widely used for FM voice communication. But what about using them on packet radio? Yes, this is possible, but a number of people have had problems with either home made cables are some that were bought commercially. The major problem is that the radio keys, but does not unkey. It seems to be a grounding problem because when you bring your hand close to the radio, it then unkeys. More information on how to fix this momentarily. 


One way to overcome this is to make your own radio/TNC cable using a speaker/microphone that is designed for the Baofeng radio. You then cut off the microphone and just use the cable and connector. This may sound expensive, but as it turns out, speaker/mics are available for the Baofeng on line in the US$5 range. Do a search on Amazon for "Baofeng Speaker" and you will find them. You will also need a 5 pin DIN or 9 pin serial plug for the other end of the cable. 

You can buy these DIN Plugs on the TNC-X web site for $2 and serial plugs are universally available. Locally Lee’s Electronics is my choice for supplier.


Here is the Baofeng Speaker/Mic purchased from Amazon.The pin out for the plug is:

  • TX Audio: Ring on big plug
  • Ground: Sleeve on small plug 
  • PTT: Sleeve on big plug 
  • RX Audio: Tip on small plug

In the photo above, the 3 screws that hold the microphone rear plate in place have been removed and it is opened up. You can see that the wires are labelled on the printed circuit board, which makes it easy to figure out which wire is which. On this microphone the connections are as follows:

  • Red = TXAudio
  • White = Ground
  • Black = PTT
  • Green = RXAudio

NOTE 1: Some of these mics have the M- (ground) and SP+ (RXAudio) wires reversed. Since these wires are connected to the speaker, this doesn't matter for the operation of the speaker/mic, but it does matter for TNC connections. Typically the white wire is ground and the green wire is RXAudio. To be certain, clip the microphone off the cord and check the continuity between the white wire and the sleeve on the small plug. 

NOTE 2: A few Baofeng speaker/mics don't work.  It is suggested that before you cut the cable, make sure the speaker/mic works with your Baofeng HT.  If it does not work, the cable probably won't work either. 

The next step is to strip the wires and tin them with solder. Notice that the black wire is significantly shorter than the other wires. 

Solder a 2.2K resistor onto the pin where the PTT (black) wire is going to be attached. (This will solve the problem of the TNC getting stuck in transmit. Use as small a resistor as will fit, wattage is not important. Next solder the connector on to the remaining wires. 

Here's the completed cable, ready to go! As you can see it is not a difficult assembly process. However, if you would like to buy one already built, they are available for $20 plus shipping from https://www.tnc-x.com/ This company also sells TNC kits.

 ~ John VE7TI 

   19-02

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