THREE (3) WAYS TO DETECT INFO IN A RADIO WAVE.

July 30, 2018

     Two more days and it will Ghost Month, August.

Good morning to ALL.

Well, please see the topic. I wrote about this last week but it did not get saved , so I lost it. I say 3 but not only 3 ways. This is just observations from research and projects.


1. Diode Detector

     Probably the oldest and also most used in a long time. Crystal set and superhets. They use diode to "detect" the sound. See AM radio. The RF which is DC is rectified to DC.Since the modulation was amplitude, the DC fluctuates in accordance with the sound.


2. Current Sense

     I coined this description. It is called regenerative but actually, it a low power oscillator as a receiver.
Toy walkie talikie is a fine example. One tranny is made to oscillate very low power. A dropping resistor is used to lower the rail voltage, usually 9 volts. Any radio signal of the same frequency suppresses the oscillation and the current draw from the battery changes. The resistor acts like a ballast. The current changes reflects the amplitude change of the received signal. Thus, the audio is heard.


3. Direct Conversion.

     The Crystal set radio can be described a  DC radio since it dos know go to converting the RF before the diode. In a superhet, an intermediate frequency is created. In a regular commercial AM radio set, a ocal oscillator provides a frequency 455 Khz above the incoming signal. Mixing the frequencies results to leaving the IF 455 Khz which is amplified then detected.

    In a DCR (Direct Conversion Receiver), no diode is used. a mixer down-verts the frequency to the audio range. So, it converts RF to AF directly by mixing.