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Understanding of Bandwidth was that it is the Range of Frequencies

  1. Jul 5, 2008 #1
    Ok I seem to have a serious problem.

    My understanding of Bandwidth was that it is the Range of Frequencies that a Radio Receiver can let through its RLC Circuit (or known as the Bandpass Filter). I thought that The set of frequencies are such that they are larger than half the total power???

    Now Quality Factor is Inversly proportional to Bandwidth. As I see it, increasing the Bandwidth would lower the Amplitude of the Resonant Frequency - hence the received quality is low?????

    So we started on AM & FM in School. The general idea was that Large Bandwidth meant more information (fair enough). They went on to say that increasing the Bandwidth of AM would lead to more quality. This is where I got Stumped. Now I am confused

    Does Bandwidth have multiple meanings or is my prior knowledge EXTREMELY Faulty??
  2. jcsd
  3. Jul 5, 2008 #2
    Re: Bandwidth

    Bandwidth means how much wide of a range of frequencies a given circuit will pass. The audio bandwidth in commercial AM is 0 to 5 Khz. So the upper and lower sidebands never get more than 5 Khz away from the carrier for a total bandwidth of 10 Khz. Increasing the bandwidth would mean that higher frequencies than 5 Khz are allowed through. The audio quality would most certainly increase since now more frequencies are being passed that have a role in recreating the original signal. I suspect you are simply confusing the 'Q' of a circuit with something that we arbitrarily are calling 'quality'.
  4. Jul 5, 2008 #3
    Re: Bandwidth

    Well perhaps...

    However, I managed to show myself that as the Bandwidth increases, the Resonant peak Amplitude decreases. Hence in order to maintain good signal strength more Power is required. Am I once again wrong??
  5. Jul 6, 2008 #4
    Re: Bandwidth

    You have totally missed the point. Re read my post. Can you not agree that letting more frequencies in the audio passband through increases fidelity and the 'quality' of the program being broadcast? Like I said, you are confusing the 'Q' of the circuit with what someone calls the 'quality' of the program they are listening to.
    You are correct, widening out the bandwidth decreases the peak of the passband. This is a tradeoff. It has alot to do with circuit 'Q' and very little to do with the quality of the end result since at times it is necessary to have a narrow bandwidth in order to receive the signal at all when the received signal has a low strength to begin with.
  6. Jul 6, 2008 #5
    Re: Bandwidth


    That is all I needed/wanted to Clarify...
  7. Jul 17, 2008 #6
    Re: Bandwidth

    There is no point in increasing the selectivity of a receiver (bandwidth is not really the right term..might refer more to the transmission) if the transmission doesn't carry the higher modulation frequencies. If fact you might make things worse by allowing more ajacent channel interference and introduce more noise.

    The main filtering in receivers is done at the Intermediate Frequency and will be taylored to the transmission. Ceramic or (in better receivers) crystal filters are used.

    Wider receivers do require higher power transmissions to maintain the signal to noise ratio.
  8. Jul 17, 2008 #7
    Re: Bandwidth

    I don't think the OP meant widening the bandwidth of JUST the receiver. I think what was meant was widening the bandwidth of the AM broadcast standard.
  9. Jul 18, 2008 #8
    Re: Bandwidth

    Increasing the max audio frequency and widening the receiver passband would improve the quality but you do lose signal to noise ratio. You would need more transmitter power to compensate.

    The most effective form of AM which requires far less power because the bandwidth is less and there is no carrier (which carries no information) is SSB.. Single Side Band.

    Simple morse (on-off keying) is very effective and can be received on receivers with bandwidths as low as a few Hz.
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