DIY SDR radio with ESP32 and Si5351

The radio receiver can receive all MW and SW bandwidth, and can also be used as an SDR receiver, so we can decode many different types of signals by means of PC and appropriate software. It consists of several parts: At the input, we start from 1 k ohm potentiometer, it is an RF attenuator. The next circuit is a pre-selector that can be switched to the MW and SW range. The tuning of the preselector is accomplished by the potentiometer. The tuning voltage is stabilized by 4 LEDs, but you can of course use 6.8 V or 8.2 V Zener diodes. The RF amplifiers of the two transistors increase sensitivity and prevent local oscillator signals from mixer from leakage to antenna input. This will cause a lot of buzz. The mixer is a well-known NE612 (or NE602, SA602, SA612). Now, more details on local oscillators. This VFO is actually the reason I decided to build this receiver. It creates a virtual Analog rotary dial on the Color TFT screen based on the Genius idea of ​​T. UEBO / JF3HZB. When preparing this section, an ESP32 microcontroller, a Si5351A I2C signal generator module board and a 1.8-inch 128x160 TFT LCD with ST7735 chip are used. The rotary encoder is used to change the frequency. You can download the code from the following, you can download code directly from the AUTR page: https: //tj-lab.org/2019/02/17/VFO5/. You can easily modify the code so that we can change the scale and background color, the scale shape, the direction of rotation, and the rotational speed. You can also change the offset and carrier frequencies, and minimum frequencies change steps and other parameters. In the picture below, you can see some visual modifications to the scale feet. I am in this case the code modification is: -Char f_rev = 1; // Rotation direction change -VTH = 0.2 // acceleration -RACC = 0.02 // -Rdec = 0.2 / / speed change faster The next step is the intermediate frequency amplifier and decoder. I tried several types of integrated circuit TCA440, TDA1072, but I was challenged to use the IF transformer to complete this part in a good future method. Setting it really requires a lot of patience, but the effect is very good. Now, the signal is transmitted to a pre-amplifier based on 741 IC, and finally the AlieXpress's D class amplifier board with PAM8403. Finally, it is emphasized that the sensitivity and selectivity of the receiver is excellent.

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