HF Receiver Testing – Zero IF Direct Conversion_b

Introduction

In the previous post (Ref.1) I examined the signal flow through the RPiZonia Zero IF Direct Conversion Receiver by examining the Block & Level testing diagram. Figure 1 shows the schematic diagram. Figure 2 shows the Block & Level testing diagram.

Fig.1 RPiZonia DIP Receiver Schematic Layout

Fig.2 RPiZonia Block & Level Q Channel DIP

Reception SW Station 11.930MHz

In order to receive a shortwave station on 11.930MHz, the Si514 mixer is set at 10KHz below this frequency to 11.92MHz. To do this a Python program to write the Si514 is loaded into the Raspberry Pi Thony Python IDE as shown in Figure.3. The frequency is loaded into the variable FON.

Fig.3 Python Program si514_prog_write_34.py

The baseband output of the RPiZ LPF is fed into a simple USB sound card that plugs into the RPi3. In order to decode the baseband, I use the amateur radio program Quisk (Ref.2). I downloaded Quisk 4.1.15 from the RPi repository. I noticed that the default audio setting for Quisk was sound card hw:0. Adjusting the Quisk config settings over VNC viewer took time, so I used the procedure of Bastien Bourdon (Ref.3) to adjust the boot order of sound cards, so that the USB sound card is hw:0 if it is present. Otherwise the boot order remains the same. This involves using terminal to edit several config files, which was very well explained. Figure 4 shows the received baseband, with the SW station located in the middle at 10KHz. It is decoded using the Quisk AM selection. Figure 5 shows a check on the Si514 signal of 11.92MHz.

Fig.4 Quisk Baseband Showing Rx Signal at 10KHz
Fig.5 Si514 Unbalanced Pickup on Mixer Pin2
Fig.6 YouTube Video HF Receiver Testing – Zero IF Direct Conversion_b

Please send your comments, questions and suggestions to:
jclark@clarktelecommunications.com

YouTube Channel
YouTube Channel

References

#1. – “HF Receiver Testing – Zero IF Direct Conversion_a”,
https://jeremyclark.ca/wp/telecom/hf-receiver-testing-zero-if-direct-conversion/

#2. – “Quisk SDR Software”
http://james.ahlstrom.name/

#3. – “Quickly setup a USB sound card on a Raspberry Pi 3”,
https://bastienbourdon.com/2016/raspberrypi-usb-sound/

#4 – “RPiZonia HF Zero IF Direct Conversion Receiver”
https://www.clarktelecommunications.com/design.htm

#5. – “HF Telecommunications Learn by Simulation”,
https://www.clarktelecommunications.com/simulation.htm

By Jeremy Clark

Jeremy Clark is a Senior Telecommunications Engineer and Advanced Amateur Radio Operator VE3PKC. He is the author of E-Books on Telecommunications, Navigation & Electronics.