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How Do Superheterodyne Radios Work?

What is superheterodyne? How does superheterodyne work? What is IF frequency? What is an intermediate frequency? A radio amplifies and decodes a radio signal, in stages. When consumer radios were first introduced in the twenties, radios used TRF or tuned radio frequency tuning, and the signal had to be tuned by the user at every stage. That’s because vacuum tubes of the day performed well at the lower frequencies of the dial, but as frequencies increased, they couldn’t keep up. So, back in 1929, this guy had to use his left hand, right thumb, and right fingers to tune a radio station, just to find out that the stock market crashed. Guess he’s gonna have to sell that radio. And he may as well, because right about that time radios were being introduced featuring an improved superheterodyne circuit that required just one hand to tune. Physics is full of laws and one of them is that 1+1=4. Well, at least with waves. Super-heterodyning is the principle of taking two frequency waves, mixing them together, and getting four frequencies. The original two, the sum of the original two, and the difference between the original two. A superhet radio uses this law of physics to make tuning easier and improve performance. It takes the radio station carrier frequency, let’s say 530 kilocycles, and adds 986. This added frequency comes from the radio’s very own tiny radio transmitter called an oscillator. When the 530 and 986 kilocycle waves are added, it leaves the original 530 and 986, the sum of 1,516, and the difference of 456. And since radio stations encode an audio signal into the carrier wave, the audio wave is also added into the mix, showing up on each of the four waves. Tubes are more efficient at lower frequencies, so a superhet radio filters out the three higher frequency waves, and amplifies only the lowest frequency, which is called the intermediate frequency, or IF for short. To improve things further... A superhet ensures that the IF stays locked at the same frequency. In our radio, it’s locked at 456 kilohertz. To keep the IF locked, the oscillator frequency must be tuned at the same rate as the radio station frequency, so the difference, always equals 456 kilohertz. This is the job of the variable condenser which we’ll discuss in more detail in the next segment. It has a tuning section for the antenna, a tuning section for the oscillator, and both are directly connected by one shaft, so they can be tuned at the same rate, with just one knob. Superheterodyne radios like our Emerson were a vast improvement over TRF radios. The tubes are happy at the low, middle, and high ends of the band. And we only have one tuning knob, not three. #radiorepair #radio #electronicsrepair #restoration