regading noise figure

Discussion in 'Wireless & RF Design' started by EXCodeX, Jun 20, 2012.

  1. EXCodeX

    Thread Starter New Member

    Jun 18, 2012
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    pls help me 2 solve this problem....

    The block diagram of a wireless receiver frond-end circuit is shown in below. A noise source with a power of -70 dBm is applied to the receiver input. The physical temperature of the system is 270 K. The operating frequency band is 1850-1860 MHz.
    (please take a look at the attached file...)
    a) What is the equivalent noise temperature of the source over the operating bandwidth?

    b) What is the overall noise figure of the receiver?

    c) What is the equivalent noise temperature of the overall system?

    d) What is the total power output (in mW) of the receiver?

     
  2. t_n_k

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    Mar 6, 2009
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  3. EXCodeX

    Thread Starter New Member

    Jun 18, 2012
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    hi... can you plz tel me what is the meaning of Ff and Ff in bandpass filter? also how can we find noise factor of the receiver(to find noise temp ) without knowing SNR?
     
    Last edited: Jun 20, 2012
  4. EXCodeX

    Thread Starter New Member

    Jun 18, 2012
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    hi... can you plz tel me what is the meaning of Ff and Lf in bandpass filter? also how can we find noise factor of the receiver(to find noise temp ) without knowing SNR?
     
  5. EXCodeX

    Thread Starter New Member

    Jun 18, 2012
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    If we try to find it using P/B = Kb .T ,{ENG} then the temperature value become very high. Is this correct?
     
  6. t_n_k

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    Lf would be the insertion loss [in dB] for the filter
    Ff would be the noise figure [in dB] for the filter.

    The LNA noise temp [Ta] is shown as 200K. The conventional relationship between noise figure and noise temp is usually stated as

    T_{noise}=290\(10^{\frac{NF}{10}}-1\)

    So if Ta = Amplifier noise temp = 200K then the amplifier noise figure would be ...

    NF_{amp}=10log\( \frac{270}{290}+1\)=10log(1.931)=2.858 \ dB

    Woops! that should be


    NF_{amp}=10log\( \frac{200}{290}+1\)=10log(1.69)=2.278 \ dB

    See these links as well

    http://www.satellite-calculations.com/Satellite/noisefigure.htm

    http://www.rfcafe.com/references/calculators/noise-figure-temperature-calculator.htm
     
    Last edited: Jun 21, 2012
  7. t_n_k

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    It does seem extraordinarily high - perhaps the noise source should be -170dBm rather than -70dBm ....??? Are you sure of the value?

    Another useful link ....

    http://www.rfcafe.com/references/electrical/noise-power.htm
     
    Last edited: Jun 21, 2012
  8. t_n_k

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    Over several years I've used an application called AppCAD [originally from Agilent] which can be downloaded free off the web. I recollected that this included a noise analysis module - "Noise Calc". It's particularly relevant to your problem since you can configure a multistage analysis - effectively as many stages as you wish.

    If you are going to be doing more of these types of problems it might be worth downloading the application.
     
  9. EXCodeX

    Thread Starter New Member

    Jun 18, 2012
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    hi...... t_N_K . many thanks for your replies... I wll download the software u hv mentioned. It will help me alot for my futher studies.. -70dBm is given in a book. Dont knw wether is a printing mistake :confused: ..
     
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