Several years ago I developed a Zero IF Direct Conversion HF receiver (Ref.1) to be used as a lab component of my HF Telecommunications course (Ref.2). The idea was to learn HF theory by Scicos simulation, electronic circuit design (schematic capture, pcb design, LTspice simulation, working with smd) and testing with a scope and spectrum analyzer. Figure 1 shows the RPiZonia schematic layout. The RPiZonia was designed to be controled and operated by the Raspberry Pi and fits on top of the GPIO.
Block & Level Testing
Figure 2 shows the Block & Level Diagram used for testing with the scope and spectrum Analyzer.
The first block to be tested is the Si514 VFO. The Si514 boots with a frequency of 10MHz. Figure 3 shows the spectrum of the Si514 output on Pin4. The level of the 10MHz is approx +16dBm (Spec analyzer has 20dB probe pad). Figure 4 shows the scope picture of the output showing the square wave from 0VDC to 3.3VDC. Since the output is a square wave, we have square wave Fourier components at 3x, 5x, 7x….and all odd multiples. Figure 5 shows the padded down input to the SA612 mixer on Pin6 of -3dBm (SA612 needs 200 – 300mP2P ext.osc input).
To test the receiver operation, a signal generator supplies an input signal at 10.01MHz through a 60dB pad. The input power to the Balun is shown in Figure 6 which is -55dBm. Figure 7 shows the SA612 mixer output of -47dBm at 10KHz on pin4. Figure 8 shows the OPA2134 baseband amplifier output of +6dBm at 10KHz on Pin7. Finally Figure 9 shows the LPF Max292 output on Pin5 of +5dBm at 10KHz.
Please send your comments, questions and suggestions to:
#1 – “RPiZonia HF Zero IF Direct Conversion Receiver”
#2. – “HF Telecommunications Learn by Simulation”,