800m transmitter circuit using SAW resonator

There are many forms of wireless transmission circuits using SAW resonators. Here is another circuit. I made this circuit three years ago by referring to an article in the Electronics Newspaper and combining it with the actual sample of the module introduced in the article. After mass production, some parameters have been improved. Now this product is really good. However, there are too many imitation products of this thing now, and the quality varies greatly. However, because it is relatively simple, I think it is still necessary to make it available to everyone. I have also found many similar circuit diagrams on the Internet, but some of them have traps. I hope everyone will pay attention to learn to identify some bugs by themselves.

I have not tested the absolute power of wireless transmission of this module, but we drove the car on the road to pull the distance, it cooperated with the ordinary 315M super regenerative receiving module, can reach 800 meters, although my circuit only needs to reduce the value of the 8050 base resistance, the communication distance will increase to 1200 meters or even farther, but after a lot of experiments, it has been proved that it is not very reliable. I am not very clear about the reason. There may be two reasons. One is that when R2 is small, 8050 is slightly turned on, resulting in the failure of rapid termination of transmission. Another is that R2 is very small, and the current of 8050 is relatively large, which may be a disturbance to the power supply and fail to meet the oscillation requirements. I once doubted whether my circuit was well matched, so I bought a lot of similar modules claiming to have a range of 1500 meters, and found that they also had the same unreliability, which was generally manifested as occasional failure to oscillate or the baud rate being less than 2K. Later, I increased the R2 resistor. When it was greater than 15K, the transmission was always normal, and the distance was similar to that of 27K, so now I use this resistor. For L1L2 here, I use 0.8mm paint-free enameled wire and wrap it around a 3mm drill bit for 4 semi-debonded turns.