Useful Information: Communications
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AMPLITUDE MODULATION

power in each sideband = (M^2)/4 * CW  (i.e. total power = 1+(M^2)/2)

  where M = modulation index (sinusoidal modulation)

         M^2
So/No = ----- * Si/Nm
        2+M^2

So/No = (M^2)/2 * C/Nm

  where Nm = noise in IF in modulation bandwidth (half the IF bandwidth)

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FREQUENCY MODULATION

If B is small (<0.1)

power in first order sidebands = (B/2)^2

  where B = delta_f/fm = modulation index (sinusoidal modulation)


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DIGITAL TRANSMISSION ERROR RATES

coherent BPSK, QPSK, OKQPSK, MSK

 Pe = 0.5*erfc(SQRT(Eb/No))                 (must be gray coded)

coherent FSK

 Pe = 0.5*erfc(SQRT(0.5*Eb/No))

where Eb = energy per bit
      No = noise in bit rate bandwidth

differentially encoded schemes have 2x error rate above

C/N = Eb/No*fb/Bw

  where fb = bit rate
        Bw = noise bandwidth


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DATA RATE AND CABLE LENGTH

For imperfectly terminated lines the data rate is limited by the round trip delay i.e. when the reflected wave arrives back at the driver.

Delay = 2*l/(v*c)

where:
 l = length
 v = velocity factor of cable
 c = speed of light

so maximum data rate = 0.5*v*c/l

As v is typically about 0.66, max data rate rule of thumb:

 bits/sec * length(m) < 10^8