oscilloscope views inside a superheterodyne (shortwave) radio receiver скачать в хорошем качестве

oscilloscope views inside a superheterodyne (shortwave) radio receiver

A brief explanation about how a superheterodyne radio receiver (shortwave, middle wave, or whatever frequency band) handles the received radio station. It is received on the antenna, the mixer creates a new frequency (carrier wave from often 455 KHz, this refers b.t.w. to simple radio's) that is amplitude modulated by the received radio signal. After IF amplification the diode rectifies the amplituded modulated wave, the capacitor after the diode "drains" the carrier wave to ground and "removes" it. Now we have only the "modulation" left (= the audio, the sound). This appears as a varying voltage that we can send into an audio amplifier. Because the bandwidth from the IF filter is 7 KHz wide (= standard IF filter, there are filters with a smaller bandwidth), we look through a "window" of 7 KHz wide to the radio stations available on the antenna coil. The selectivity raises "dramatically" by this way of radio receiving. Please note that this is a simple radio. Sophisticated HAM receivers often use a much higher IF (e.g. 10 MHz or more) to avoid the problem that the radio station appears 2 (or even more) times on the tuning scale from the VFO. Or (another problem) that "whistles" can be heard when tuned to a certain radio station. Both problems happen because the VFO also produces harmonics, they can mix with the antenna frequency to products in the KHz range. And/or a frequency - (minus) 455 KHz from the antenna coil frequency also produces a (modulated) 455 KHz product. The radio is described in my book: "Shortwave receiver 2-10 MHz and 1 transistor VFO's", available on the Lulu website (author Ko Tilman).