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Input impedance of if and rf amplifier

Discussion in 'Radio and Wireless' started by Joshi, Mar 1, 2020.

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  1. Joshi

    Joshi

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    Mar 1, 2020
    Why is the dynamic input impedance of an IF amplifier greatly affected by loading and detuning of it's tank circuit when a large resistor is placed in parallel across it, like a large resistive load. And why is it better to use a rf amplifier in this situation?
     
  2. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    Please post a schematic diagram of the IF amplifier you are concerned with. If IF transformers are involved, specify their parameters. Is this a solid-state IF amplifier or a vacuum tube IF amplifier? Virtually all IF amplifiers ARE rf amplifiers tuned to a specific "center frequency" (the intermediate frequency) with specific bandwidths. Adding a resistance load to a tank circuit affects its Q and, depending on the intermediate frequency, may also add parasitic inductance and parasitic capacitance that results in detuning.

    Please tell us what you are trying to DO and someone here may be able to help you. How much experience (if any) do you have working with radio frequency circuits, and at what radio frequencies do you have this experience?
     
    davenn likes this.
  3. Joshi

    Joshi

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    Mar 1, 2020
     

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  4. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    That was less than helpful. Is this homework? Your so-called schematic is incomplete. It appears to be part of a text book page explaining one method of inserting an Automatic Gain Control (AGC) into a receiver circuit.

    How does any of this relate to your original question concerning "dynamic impedance" and "loading and detuning" of tank circuits?

    Why haven't you answered or attempted to answer my question regarding your experience with circuits utilizing radio frequencies? Why haven't you explained what you are trying to DO? Don't you think you would be better served by trolling some other forum?
     
  5. davenn

    davenn Moderator

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    Sep 5, 2009
    since the OP wont answer questions posed

    thread is closed
    @Joshi --- if/when you are ready to answer the questions about what you are asking about
    message me and I will reopen the thread
     
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