Modifying a Baofeng UV82
The Baofeng UV-82 is a dual band 144/440 1W or 5W radio. It is typically available for less than $30 from many retailers. It makes a nice Allstar node radio which is a little easier to modify and better quality than the Baofeng 888 and it gives you the ability to use either the 2 meter or 3/4 meter bands.
There are very few parts required for this modification. Three resistors, a FET, a connector and shell, and wire is all that is required. The board does not need to be removed from the frame and connections are easy to make
Here are the connection points on the UV-82 circuit board
and the wires after connection. Note the COS line is fed through a 10K resistor located in the yellow heatshrink. This can be a 1/4 or preferably a 1/8W resistor. Wire colors are not important as long as you standardize at both ends. Shown here the Red is PTT, Green is RX audio, Black is TX audio, White is COS with small black on the other side of the resistor to the board, and the small black is ground.
This is a view of the DB25 connector end wired to plug into a DMK/URI or similarly wire mate. The 4.7K resistors and the 2N7000 FET are mounted at the connector end
Here is the pinout diagram of the DB25 connector. The source pin of the 2N7000 goes to ground, the drain goes to the COS pin 8, and the gate goes back to the radio to the 10K resistor.
For those wishing to see where the COS connection is in the radio here is a portion of the schematic that shows the connection. It is connected at the collector of Q19. This results in a low going level on RX at the drain output of the 2N7000 FET. This is desireable as this allows the use of cosfrom=usbinvert (carrierfrom=usbinvert) in simpleusb.conf.
and here is a photo of the completed assembled radio ready to play. It is highly recommended and often necessary that an external antenna (removed from the radio) be used to keep RF away from the radio.
Powering the UV82
The UV-82 being a handheld is normally powered by a battery but as a node radio you would need a steady fixed source of power. The 12V battery eliminator adapter for the UV-82 is one way to do this but the commercial adapters are not well designed electrically. They use an inefficient three terminal regulator and an inadequate heatsink. This quickly heats up and would destroy itself in short order. The answer is to open the car adapter, remove the original regulator, and install an efficient replacement regulator. Here is what the adapter looks like before removing the original parts.
The replacement regulator board is available from Ebay and is very inexpensive. It has a pot to adjust the output to the 7.5 volts required for the UV-82.
Battery Eliminator Adapter
DC-DC BUCK Adjustable Step Down Module
Here are photos showing the module installed in the car adapter. Input voltage is about 9-24V but typically this would be run at 12-14 volts from a DC supply source. A 12V "wall wart" rated at least 2 amps would work and for portale use a larger 12V battery or car electrical system would work fine.
The easiest way to program your UV-82 is using a programming cable and Chirp. Front panel programming of a Baofeng is a chore but can be done. You also need to disable the voice prompts so they do not go out over the node. Once programmed you can change the channel on the radio. The BOTTOM display is what is received and transmitted. In simpleusb you would use rxboost=1, cosfrom (carrierfrom) =usbinvert, and the audio levels would need to be set. A good starting point is RX level = 550, and TX level = 750 but these could vary greatly depending on the FOB type you are using and the radio you are using to talk to your node. The volume on the UV82 has no bearing on Allstar levels. It should normally be turned all the way down but you can raise it to monitor the input signal to your node. A dummy plug should be inserted in the larger remote mic jack on the UV-82 to disable the internal microphone when using the radio as an Allstar node. A standard unconnected stereo miniature plug can be used or preferably a plastic dummy plug cut from a stylus pen like this:
Plastic dummy plug
Cut off the pen but leave the string to pull it out when needed.
CAUTION! Do NOT run this radio on high power on a busy Allstar channel. It will most definitely overheat. Handhelds are not designed for continuous TX operation at high power. It should run fine on low power.
Purchasing a UV82
Probably the easiest place to buy is Amazon but there are other sources. Goggle "buy uv82"
Amazon UV82 Free Shipping
External dual band antenna (recommended)
There is a now discontinued UV-82x that is dual band 144/222. If you happen to have one or you acquire one it could be modified in the same way as this radio. The Baofeng UV5 series of radios although physically different uses the same electrical connections. We are planning to mod a tri-band UV5 and when we do we will do a howto on it.
The radio shown was modified by WB3DZZ who sells modified radios, FOBS, and other accessories. He can be reached at his QRZ email address.
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