The Uniden UH-040XR sold for $AUD99 per unit from Dick Smith in
Australia in 2001. It is a 0.5W 40 channel UHF CB transceiver.
MIC and EAR connections
Task: determine how to connect a TNC to the transceiver.
Solution: connect TNC to MIC input via 4.7uF polyester
capacitor, connect PTT to MIC input such that a 1k-10k resistance to
ground is in effect when the TNC wants to transmit. From a workshop
supervisor, care of Peter Illmayer, 4th March 2002.
In July 2001, Uniden declined to provide a schematic of the optional
headset with PTT switch.
Relevant aspects of the design:
Conclusion: transmitter is keyed by connecting a microphone through a
PTT switch to the MIC input socket.
- the MIC connection is a standard 2.5mm mono socket,
- the outer conductor connects to a diode visible on the PCB with
cathode to the socket, and anode to ground. The diode is a reverse
polarity protection diode. Further connections are hidden under the
- the inner conductor connects to transceiver ground.
- the EAR connection is a standard 3.5mm mono socket,
- the outer conductor connects to an SMT capacitor to transceiver
- the inner conductor connection is hidden under the LCD.
- the charger terminates to a 2.5mm mono plug,
- the rating is 70mA at 7V.
- floating voltage without load is 12V.
- plug is wired centre negative.
- the PTT switch is grounded on one side, and on the other has an
SMT capacitor to ground before the trace continues under the LCD.
- the transceiver can operate in receive mode while connected to the
charger, but pressing the PTT button yields no transmission. Without
batteries in the case, 6.25V is found on the battery terminals. The
circuitry includes a charging function.
- the transceiver PTT switch functions fine if the charger is
connected but not powered.
- the transceiver transmits for a short time when the charger plug
is inserted. A slow insertion yields a long transmission, apparently
as the pins are shorted.
- inserting a multimeter probe into the MIC socket to short the pins
causes transmission of silence.
- connecting stereo headphones to the EAR socket gives the receive
signal in the left headphone, and the PTT switch continues to work.
Therefore the MIC connection is non-essential.
The following picture shows the connections, the capacitors, and the
reverse polarity protection diode.
Figure 4, Close-Up of MIC and EAR connections
You will need a static protected workplace, and a Philips Head #1
(PH1) screwdriver. A PH1 electric screwdriver bit is probably not
long enough to reach down to two of the screws.
Note: there are case clips at top right and top left of the unit. See
the following pictures.
- remove battery cover,
- remove batteries,
- disconnect any cables,
- unscrew and remove the belt clip,
- unscrew the four screws in the battery compartment,
- lever the case apart.
Figure 1, Location of
Figure 2, Right Case
Figure 3, Left Case
Figure 5, Main Board, Rear Face
Figure 6, RF Board, Rear Face
How to drive the unit from Quozl's pump
controller, or other microcontroller based system.
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