DIY HF SSB Receiver 20M with AD9850 DDS tune and Active Hula Loop Antenna
The receiver is a simple syperheterodyne type with quartz crystal filter. The circuit is based on two NE612 mixer IC’s and one audio amplifier LM386. The electrical circuit as it described below in the manual is intended for 14.000MHz – 14.350MHz upper single side band receiving of amateur radio transmissions. However, the PCB allows modifying it for all others amateur SSB radio bands, or making it 2 bands receiver if required.
If you are beginner it’s strongly recommended to ask someone from your local radio club to help you with components selecting and receiver assembling. The syperhet calibration requires you to have an oscilloscope, DDS HF signal generator, LC Meter, multimeter and soldering tools. Moreover, it requires some basic knowledge of “how it works” for correct pre-set of the board. That’s why I recommend to ask help of someone experienced if you get trouble with receiver calibration.
The circuit is designed for 20M receiver. Some components has critical value, please check carefully the part list of the project: You need LC Meter to check precision values of C2, C4, C5, L1, L2 and also compare the inductance of L3 and L4 coils with circuit value.
AD9850 Digital Tuning Option:
The PCB design and the circuit allows you to use digital tuning with DDS module. Connect AD9850 module output to pin#6 of NE612 IC1 through 10nF cap. If you connect DDS then following components are not used: C14, C17, C9, C10, C15, C16, C6, C8, C11, IC4, R4, R3, R1, L4, CD1. Adding the DDS require a microcontroller to set the frequency. For my final project I decided to use it with 3.3V 16x2 LCD, encoder and PIC18F2550 controller.
I used lithium battery with Sparkfun charger and 9V Pololu step-up module to power the receiver.
DDS AD9850 Module and controller are powered through 3.3V regulator. Here you can download PCB layout and controller firmware for 20M SSB receiver. PCB layout has clear marking for connecting 3.3V LCD and encoder pins. To get battery voltage measurement connect battery output through divider to RA0 port of the processor. Divider is not shown on the PCB layout, but probably you'll need to use a potentiometer to get precision readings of the battery voltage. I used 1K-3K divider and you can use 5K potentiometer instead.
The receiver can work with Long-Wire antenna, however an Active Loop Antenna with rotating mechanism performs better for 20M band. I used loop antenna with high impedance differential op-amp across the loop. You can find Loop Antenna Amplifier DIY kit on the website store here: