My article titled “The Regenerative Receiver” prompted a question. The question follows: “one question I have is – are the following principals basically the same – how do they differ? Heterodyne Regenerative and Super Regenerative. I want to try to answer that question here because I must have left something ambiguous in that article.
The word “heterodyne” is derived from two Greek words; “hetro” which means different and “dyne” meaning power. By combining the two words we see that it latterly means a different power. A heterodyne is a signal which is produced by mixing two or more signals in a non linear device or to say it another way heterodyning is the process of mixing two or more signal frequencies to produce a different frequency signal. When two frequencies are mixed they actually produce two new frequencies. So if a 7.100 MHz signal was mixed with another signal having a frequency of 6.645 MHz it would produce an output of 455 KHz and another of 13.745 (the sum and the difference of the two frequencies). In that case, considering 455 KHz is a very common IF frequency, the 455 KHz signal would probably be the one desired and the 13.745 MHz signal would be filtered out.
The technique of heterodyning was developed by a Canadian inventor and engineer named Reginald Fessenden.
After the process of heterodyning was developed and understood the superhetrodyne receiver could be developed. Prior to the superhetrodyne receiver and after amplification was possible receivers had a series of RF amplifiers ahead of the detector. Each of these amplifiers had to be retuned when the receiver frequency was changed. The superhetrodyne receiver eliminated the need to have a series of RF amplifiers that had to be tuned separately. Normally there is one RF amplifier ahead of the mixer though there can be more and sometimes the mixer is the first stage. The input to the mixer is tuned and the frequency of the local oscillator which produces the signal to be mixed with the incoming frequency can be variable (in some cases the local oscillator is crystal controlled) so the output frequency always remains the same. Each RF amplifier, which is actually called Intermediate Frequency (IF) amplifier, can be tuned to the same frequency no matter what the input frequency is. Using an IF frequency allows the construction of more selective circuits. Fixed frequency filters can be easily added to the IF giving a far greater selectivity then possible with simple LC circuits.
Ease of tuning, improved gain, and increased selectivity are three advantages of the Superhetrodyne receiver. An other advantage was provided by the fixed If frequency being fed into the detector is it allows the signal of the IF to be mixed with the signal produced by the beat frequency oscillator (BFO) which makes receiving CW and SSB much easier (the BFO heterodynes the IF frequency down to audio frequencies).
Regeneration is a process where by some of the output signal of an amplifier is sent back, in phase, to the input. When the output of an amplifier is sent back to the input it is called feedback. When a sufficient amount of the output signal is sent back to the input in phase the amplifier will sustain its own signal producing process called oscillation. Feed back can be regenerative (positive feedback or in phase feedback) and degenerative (negative feedback or out of phase feedback).
As the article I mentioned above describes, the regenerative receiver used a small amount of positive feedback to improve the receivers amplification and its selectivity so one tube acting as the RF amplifier and detector worked very efficiently. When the feedback was increased to the point where it started to oscillate a signal was being produced which would mix with the incoming signal to produce a tone so a CW signal could be read.
A super-regenerative receiver is a regenerative receiver which uses a quenching frequency to prevent oscillation. So I guess the answer to the question I was asked is heterodyne and regeneration are two different processes and regenerative and super-regenerative differ in that the latter uses a quenching frequency. The problem is that I was asked what the difference was between a Heterodyne Regenerative and a Super Regenerative receiver is and the only answer I have there is I have never heard of a Heterodyne Regenerative nor could I find any information when I researched this kind of receiver.