R80T2

Title of work: 1420MHz tuner

Introduction of works:

This design uses the TPS7A4701 ultra-low noise linear power supply chip from Texas Instruments. In previous projects, the received signal quality was poor due to power supply issues; this chip supports wide voltage input, with the input voltage ranging from +3V to +36V. The output is extremely low, and the ripple cannot be seen using an oscilloscope, and the maximum output current can reach 1A, which is sufficient for the previously designed low-noise amplifier. This work also features programmable output voltage.

This design uses R820T as the main component. The chip has built-in low-noise amplifier, mixer, automatic gain, phase-locked loop, etc. This chip can be used to downconvert radio frequency signals from 25MHz to 1700MHz to an intermediate frequency of 3.57MHz. Conveniently use low sampling rate analog-to-digital converters to collect RF signals.

Physical picture display:

PCB display:

3D renderings:

Welding completed physical display

Test renderings:

Use an RF signal source to generate a 300MHz RF signal with a Vpp of 100mVpp. (Pass: The input is too large and the output waveform has been distorted. The main reason is that I set the gain of the R820T2 low-noise amplifier to the maximum. You can configure it according to your needs during the test. )

At the output end, you can see that the IF signal is 3.57MHz. Although the signal is distorted, the effect has been achieved. This module will heat up seriously after working for a long time and needs to be well dissipated. Otherwise, the PLL inside the chip will cause the output frequency to be unstable due to temperature changes.

The internal principle of the chip is as follows. The intermediate frequency is 3.57MHz, which is consistent with the effect measured by the oscilloscope. Since the chip output is the IQ component output, I used a balun to convert the signal from double-ended to single-ended. Convenient for oscilloscope measurement.

There are still many shortcomings in this experiment. The main reason is that several of the chips I bought have problems, which makes it impossible to read the ID number of the chip when using the microcontroller to control. After many experiments, I have learned from good A good chip was removed from the device for testing, and the final effect was achieved. Finally, weld the chip back into the device and complete this experiment using the computer. The computer can directly write the tuned frequency, which is much more convenient than using a microcontroller to control.