The receiver in this scheme uses three vacuum tubes: 6A2 (frequency modulation), 6N2 (regenerative detector + first-stage low-frequency amplifier), and 6N1 (audio power amplifier). The results have been satisfactory in practice. Below is a video of the receiver in operation, for reference. I also hope to be able to discuss this with interested friends.
1. Monitor CW signals within a range of 600 km (using a 40-meter band).
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2. Monitor CW signals over 1200 km (40-meter band)
3. Monitor a 1600km CW signal. Received the World Championship 7023 CW signal from callsign E2WRTC.
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Here is a listening report for this device on March 11, 2023.
Time: 8:25 PM
Weather: Sunny
Temperature: 18°C
Location: Apartment, 6th floor, interior
Device: This unit
Antenna: Single cable (ordinary electrical wire) extending 5 meters inside the balcony.
Frequency: 14.023 MHz (with added beat frequency)
The weather is pretty good today! I don't have much time to wait for the signal. Although there is some background noise, the signal strength is still clear enough that I can identify it. However, due to the very high transmission speed and my own poor skills, I can only copy the characters in front, but lose track of the ones behind, leaving me completely confused! I'm ashamed! Later, I posted the video on a WeChat group for amateur radio enthusiasts, and with the help of their teachers, I was able to translate it: It is the Australian ham call sign: VK6T, calling a HAM in South Africa （SY）, but the signal cannot be identified. After searching on Baidu, the distance between us is approximately 6000-8000 kilometers.
Conclusion: The receiver's sensitivity to incoming signals is reasonably good, the circuit design is feasible, and the DIY results are effective.
Here is the link to the live video:
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