Wiring up the BITX40

The brown wire from Raduino goes to the black wire from the BITX DDS
The red wire from Raduino goes to the brown wire from the BITX DDS
The BNC antenna connector must be not more than 2 inches way from the antenna connector on the board
The box should have enough head room to allow the heatsink. The heatsink is not at ground potential. It should’nt touch any metal
Use a well regulated 12 volts, 2 amps linear power supply for best performance
Keep all the leads short

Below is the connection diagram.

This diagram is all you need to know to hook you your BITX40. You may want to follow the steps below to hook it up.

Step 1: The Antenna Connector

Mount the board and the BNC antenna connector close to each other
Mount the BNC connector on the transceiver box with the ground lug
Use a 2 pin connector between the antenna connector on the board and the BNC connector
The Black wire goes to the ground lug of the BNC, the brown to the central conductor
Keep the antenna wire to be less than 3 inches

Step 2: DC Power Connections

The DC power from the socket goes to the board through the on/off switch on the volume control. From the ON/OFF switch, route the power a parallel connection also goes to the transmitter power amplifier. This is kept as a separate connection on the board so that you can feed the power amp with a higher voltage.

Use a two-wire connector as shown in the diagram’s upper right side to supply +12v power to the board.
The brown wire should go to +12V line from the power supply and the black wire should go to ground line of the power supply.
The supplied DC socket can be hooked to the DC power lines. The large pin on the DC socket is the postive line (see the picture below
You may route the positive power line through the ON/OFF switch on the volume control
Use another PA POWER line to feed power to the Power Amplifier. This is shown on the top-left part of the wiring diagram

Step 3: Wireup the Raduino

Take the LCD display apart from the Raduino and mount it on the front-panel. Now, plug-in the Raduino behind it. Carefully note that all the 16 pins of the display are properly slipped into the Raduino connector.

Connect the tuning pot

Connect the 8-pin connector to the top side of the Raduino
Solder the violet (left most) wire of the 8-pin connector to the middle of the tuning control
Solder the green (3rd from the left) wire of the 8-pin connector to the left of the tuning control
Solder the yellow (4th from the left) wire of the 8-pin connector to the right of the tuning control
Solder the 0.1uF disc ceramic (marked as 104) between the yellow and violet wires on the tuning pot

Connect to the DDS connector of the BITX

Connect the 5-pin connector to the bottom side of the Raduino
Solder the black wire to the DC power socket
Solder the orange wire to the DC power switch on the volume control
Connect a 2-pin connector to the DDS poin on the BITX board
Solder the brown wire of the Raduino’s 5 pin connector to the black wire of the BITX’s DDS connector
Solder the red wire of the Raduino’s 5 pin connector to the brown wire of the BITX’s DDS connector

The brown wire of the Raduino’s 5 pin connector does NOT connect to the brown wire of the BITX’s DDS conenctor!

Step 4: Volume Control

Connect a 3-pin connector to the volume connector on the board
Solder the red wire of the 3-pin connector to left lug of the volume control
Solder the brown wire of the 3-pin connector to the middle lug of the volume control
Solder the black wire of the 3-pin connector to the right lug of of the volume control

Step 5: Speaker

Connect a 2-pin connector to the speaker connector on the board
Solder the two ends to the speaker lugs on
Use only an 8-ohms speaker or earphones. Lower impedance speaker may result in howling sound from audio oscillations

Step 6: Wiring up the microphone and Push to Talk

Use a 2-pin wire connector for the mic.
There are two solder pads behind the electret mic. The solder pad with small tracks to the case is connected to the ground (black) wire from the mic connector.
The brown wire from the mic connector goes to the other solder pad on the mic
Use another 2-pin wire connector for the the Push-To-Transmit connection. You may use the supplied push button switch to control transmit/receive.

Note:
Don’t solder the ground (black) wire of the speaker to the ground. It should only connect to the speaker or the earphone jack.
You may optionaly route the audio through the supplied stereo earphone jack to the speaker such that if you plug in the earphones/headset the speaker will disconnect. This is left as an exercise to you.

Step 8: Operate!

Always use the BITX40 with a properly tuned antenna or a dummy load.

Insert an amp meter capable of measuring upto 5 amps into transceiver’s DC power line
Switch on the transceiver. There should be a soft hiss from the speaker. The transceiver should draw 150-140 mA in receive mode
Connect the antenna, loud band noise should be audible
Tune around, listen to the sweet sound of an all analog receiver!
Push the PTT and the current should now be between 300-350 mA
Say ‘HAAAALOOO’ and the current should jump to 1 Amp

Are you still reading? Go and work some DX!

Alignment of the BITX40

The BITX40 comes pre-aligned out of the box. However, it may go out of alignment for some reason and here are the steps to align it. Keep the circuit handy while you do it. If you can’t understand what it means to ‘insert the ammeter into the power line’ ask someone for help.

Attach a dummy load to the antenna
Insert a ammeter (you may use your VOM meter in high amps range) into the PA power supply’s positive line
Keep the PA BIAS preset (RV1) to fully clockwise position. Now when you press the PTT button, the ammeter should read about zero.
Increase PA BIAS without speaking into the mic until the PA current shows 100 ma
Give a loud and long HAAAALLLOOWW into the mic and the current should jump to slightly over 1 amp
Adjust the RV136 to increase the PA drive if the current doesn’t jump all the way to 1A
Keep monitoring your signal on a nearby receiver.

<>Note: You may use the RV136 to reduce the output power to drive an external linear or go QRPp.

Calibrating the Raduino

Due to variations in the frequency of the crystals used, the frequencies generated by the Raduino may be off by a few hundred hertz. You can easily calibrate like this :

Attach a switch between the RED wire of the the 8-pin Raduino connector and the ground.
Tune in an SSB signal of a known frequency. For instance, you can ask your friend to transmit on 7100.0 KHz
Set the tuning pot such that it reads the actual frequency of the signal (ex: 7100 KHz). At this time the signal may not sound proper
Now short the RED wire of the Raduino to ground. This puts the Raduino into calibration mode.
Now carefully tune the signal to sound best
Remove the RED wire’s short to save the calibration

Be sure to keep the RED wire from shorting to the ground again unless you want to recalibrate the Raduino.