Simple direct conversion receiver with dual diode mixer BAT85

I present a simple direct conversion radio receiver, with which you can receive radio stations with amplitude modulation, one sideband and telegraph. It works on short waves at the frequency to which you will have the input filter and generator tuned, I made it for the 80 meter range. You will need to connect a tunable generator to the receiver, this can be done on one transistor or connect a ready-made generator like I did. How does such a receiver work? The signal from the antenna goes to the filter L1 C2, which is tuned to a frequency range of approximately 3400-3700 kHz, this filter will suppress all other frequencies. The mixer is assembled on two Schottky diodes BAT85. The signal from the filter L1-C2 and the signal from the generator go to the mixer, and the frequency of the generator should be two times less than the received signal, since the mixer "multiplies" the frequency of the generator by two, I will describe its operation below. If one of the frequencies differs from the other by, say, 1000 Hz, you will hear these 1000 Hz in the speaker and this is called beating. There will be different signals at the mixer output, and 1000 Hz must be passed through the speaker and everything else must be filtered out. This is done by a two-link low-pass filter on two coils L2-L3 and three capacitors. It filters the high-frequency signals and passes the desired low-frequency signal. The sound signal is amplified by a preamplifier on a transistor. 2sc3198 and then goes to the low frequency amplifier.

The L1 coil is wound on a 6mm diameter frame with a ferrite core. It contains 46 turns of 0.12mm diameter wire with a tap from the 6th turn. I will tell you how to make a low-pass filter on L2-L3 in another article, but you can also make a single-link filter or another filter altogether from the circuits of other similar receivers. In the evening, with a 5-meter antenna, I received AM broadcasting stations and an SSB signal from amateurs. You can also receive AM signals at 2900 kHz; to do this, you need to adjust the ferrite in the coil and change the capacitance C2

Here's how the mixer works on these two diodes: when the generator voltage passes through zero, two diodes are closed. At the peaks of the negative or positive half-waves, one of the diodes opens and the L1-C2 filter is connected to the low-pass filter. The mixer closes and opens with a double generator frequency. At the generator frequency of one million Hertz, two diodes switch two million times. This is how the generator frequency is "multiplied". The diodes operate from the generator signal and its amplitude should be at least 1 Volt, I checked this in practice. But you can find the optimal generator voltage yourself, it also depends on the antenna. For good reception, turn off all sources of interference near the antenna and receiver. The signal from the generator must be shielded. I did not select the diodes. It can also work with a rectangular signal