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How does super regen receiver work -- simple explanation

Discussion in 'General Electronics Discussion' started by dietermoreno, May 3, 2013.

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  1. dietermoreno


    Dec 30, 2012
    How does super regen receiver work, in lay man's terms?

    We could get fancy and write down derivatives and integrals and solve differential equations, but I think that's making it harder than it needs to be and I'm not good at solving differential equations.

    The only coherent explanations of super regen receiver I found on the internet were pretty much black and white, either only the schematic with no explanation, or at the other extreme 10 pages of solving differential equations.

    Except I found one website that explained how it worked in only a few paragraphs in lay man's terms with no calculus required.

    The website I was looking at was the "Progressive crystal receiver to regenerative receiver" website that has the few paragraph layman's explanation of super regen receiver.

    The explanation was (in my own words):

    A problem the regen receiver has is that the user has to adjust the gain of the regeneration control for every station received since the regen detector is most sensitive right below oscillation. In addition, another problem is that any guitarist will know without any calculus that an amp overdriven left to its own means will over drive more and more infinitely (found that out the hard way when I went shopping for half an hour and my friends infinitely over drove the tube amp with feedback from 2 mics too close to each other until it started smoking when I returned), so the more time before lowering the gain means the more feedback squeal and clipping.

    While this is a strength of the regen receiver in its simplicity for receiving CW (compared to the super heterodyne receiver needs a beat frequency oscillator to receive CW) since CW reception is just increasing the gain until it squeals just like a guitar amp feedback, this isn't so good for receiving stations that aren't CW. (In fact, remember my post where I said I got an overdriven audio mixer feedbacking itself connected to my overdriven guitar amp to pick up an O'hare beacon
      _ _ _      . _ .       _ . .    
    since I live near O'hare). A regen receiver has 1,000 times more RF gain than a crystal set, but not necessarily better audio quality for stations that are nearby. The audio quality of a regen receiver is okay for broadcast AM band, but is unacceptable for music. So regen receiver is not used for FM, even though it theoretically could be used, it would sound terrible, not to mention another consideration.

    Another consideration for FM is that if you are using slope detection consisting of two taps on an inductor, the 2 different frequencies would feedback with each other infinitely when connected to a regen circuit, so regen receiver doesn't work with FM, except if the bandwidth is restricted to be narrow enough for the 2 different frequencies to not feedback infinitely. So regen receiver only works for narrow band FM, not the wide band FM used by the FM broadcast band.

    So in order to eliminate the problems of (1) having to constantly adjust the gain of the regen control, (2) infinte feedback causing poor audio quality, and (3) the feedback makes regen detector not work for wide band FM; the simple solution devised by Edwin Armstrong was to add an ultra sonic frequency oscillator where the regeneration control is on the standard regen set. The ultra sonic frequency oscillator is simply one capacitor and one resistor, as RC oscillators work for audio frequencies and ultra sonic frequencies. The ultra sonic frequency oscillator simply interupts the gain of the regen detector at an ultra sonic frequency. The frequency is ultra sonic so that it is not able to be heard by humans. A resistor network of a couple more resistors creates the interuptor circuit for charge to flow in the path of least resistance and the path of resistance is too great for charge to flow until the gain is increased high enough which the gain is oscillating at the frequency of the ultra sonic frequency oscillator.

    Only 1 more capacitor and 3 more resistors are needed to mod the standard regen circuit into the super regen circuit. Nothing more, nothing less. Its that simple.

    So in summary, if you want your crystal set to pick up farther away MW 50KW stations, you want to pick up SW amateurs, and you want to pick up CW from either amateurs or aviation band, build a regen set; if you want your crystal set to pick up farther away VHF Wideband FM 50KW stations, build a super regen set.
    Last edited: May 3, 2013
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