RLC circuits and tuning

Discussion in 'Wireless & RF Design' started by xiongyw, Jul 1, 2009.

  1. xiongyw

    Thread Starter New Member

    Jul 1, 2009
    I guess I understand your question, since I am also a newbie in this.

    It seems that some replies already answered part of your questions, that the "pick-outed" signal at resonance contains not only the desired the frequency (or range of frequencies), but also ALL the other undesired frequencies. The difference is the amplitude of desired and undesired are very different, i.e., bigger enough for the desired, and smaller enough for the undesired. I am not sure what's the quantative criteria to "bigger enough" or "small enough", but the basic idea should be that. The other difference among different frequencies after tuning, is the phase shift regarding the original signal flowing in the air, but this may not as important for this topic.

    It seems what you wanted, according to my own experience, is not just an answer like above, but an explanation (or understanding) on why. I must confess that I am not a qualified one to offer you explanation, since I am still in doubts of some points, but I would like to share what I have learnt so far on this, and you may judge if it helps, or contains faults, etc.

    I personally feel more comfortable (or more concrete) when viewing series circuits as voltage dividing circuits, and viewing all types of elements (R,L,C) as voltage dividors. I personalize the voltage as the work load, and R, L, and C as workers to carry out the work load altoghther, and their have different personalities in terms of how fast/long they tend to carry out the work load...

    My tentative summary related to this can be found here where I asked question related to RLC circuit:

    The attachment of the my 2nd post in that thread is a kind of summary, which also contains question marks. I guess gurus here can also help me on clarifying my doubts, particularly, I want to know in a tuning circuit of AM radio (e.g.), we usually pick out the signal from R, or L, or C, which to be coupled into the next stage?

  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Welcome to AAC.

    When you post into an old thread - http://forum.allaboutcircuits.com/showthread.php?t=23057&page=4 - it can be a bit confusing. The original poster has likely gone on, and nobody is quite sure who is in the discussion.

    Please always start a new question in a new thread if the topic changes of the date indicates some time has passes, as in this case.

    You might want to do some research into AM tuners. The more usual method was to vary C to tune the parallel tank circuit and local oscillator, but I have also seen L tuned oscillators.

    In any case, the signal is developed across the tuning tank, and is picked off between the antenna input and the tank. Here is the Wikipedia article - http://en.wikipedia.org/wiki/Tuner_(radio)