TRANSMIT SPECTRUM ISSUES by yurtgc548

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									TRANSMIT SPECTRUM
     ISSUES
 MANUFACTURERS MEETING AUGUST 2004
           Peter Woolner
          Mitretek Systems
        pwoolner@mitretek.org
           703-610-1724
  SOME CHANGE IS NEEDED
• The NTIA controls spectrum allocations and sets
  performance standards for ALL radio operations
  by ALL U.S. Government agencies. (See
  Preface to NTIA Manual.)
• The previous proposed change incorrectly cited
  ITU requirements that NTIA do not allow for
  transmissions at frequencies below 470 MHz.
• The correct performance standard that applies is
  NTIA subsection 5.2.2.2.

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       NTIA SPEC FOR 300 BPS
                                    Channel Allocation
                                         750 Hz                           Current 2nd
                                                                          Sideband limit
    Maximum                                                               is 15 dB below
     Possible     NTIA EMISSION MASK             225 Hz                   carrier
    Frequency
     Variance
     = 139 Hz             Filter
                         Roll-off                                 25 dB
                          65 Hz
                                                                               35 dB
                                                         450 Hz




                                Necessary Bandwidth
                                      300 Hz

Maximum Doppler                215 Hz         150 Hz
   Shift 11 Hz
                                                         375 Hz



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NTIA SPEC FOR 1200 BPS
                              Channel Allocation
                                  2250 Hz
            NTIA EMISSION MASK             900 Hz
 Maximum
  Possible          Filter
 Frequency         Roll-off
  Variance                                                   25 dB
                   260 Hz
  = 254 Hz                                                               35 dB
                                                   1800 Hz




                          Necessary Bandwidth
                                1200 Hz

Maximum Doppler          860 Hz         600 Hz
  Shift 11 Hz
                                            1125 Hz



                                                                     4
    DEMODULATOR FILTER
• NESDIS believes that the explicit transfer
  function used in the CDA receivers needs to be
  identified to provide DCPRS designers with a
  guide for spectral match.
• SRRC advantage is reduced adjacent channel
  interference and minimum ISI, its disadvantage
  is it has higher peak-to-average power ratio.
• Worse peak-to-average power ratio can be
  eliminated by reducing the maximum output
  power allowed from any DCPRS by 1 dB.
• Therefore a SRRC filter will be recommended for
  the CDA receivers.
                                         5
           DCPRS FILTER
• Narrow band and wide band attenuations
  must meet NTIA requirements
• PROPOSAL: Don’t require DCPRS use
  SRRC filter – leave it as a design decision




                                      6
DERIVATION OF REQUIREMENT
• NTIA require the mean power of any emission
  be compared to the mean power of the
  fundamental
• “Fundamental” and “any emission” are not
  defined but may be inferred from the basic
  (sin(x)/x) spectral distribution
• A spectrum analyzer could use any RBW small
  enough to resolve the actual sideband peaks
  and nulls
• The NTIA requirement could be reduced by 3 dB
  because the fundamental is at least twice the
  bandwidth of any other spectral lobe
                                       7
DERIVATION (Cont.)

NTIA EMISSION MASK         900 Hz
                        3 dB min

                                             25 dB
                                                         35 dB
                                   1800 Hz




             Necessary Bandwidth
                   1200 Hz




                                                     8
        PROPOSED NEW CS TEXT
4.5          DCPRS Transmit Spectrum
The DCPRS shall be designed to be received by the CDA stations, which will include a SRRC demodulator filter
with α = 1.0, using at least 100 taps [To Be Confirmed].
4.5.1        Narrow Band Transmit Spectrum
When modulated with a random data stream and measured on a spectrum analyzer using any convenient resolution
bandwidth of 1 Hz to 100 Hz, the peak response of the unwanted signals, relative to the peak response in the
necessary bandwidth, shall be equal to, or better than:
At any frequency removed from the assigned channel center frequency by more that 75% of the necessary
bandwidth, up to and including 150%, at least 22 dB attenuation.
At any frequency removed from the assigned channel center frequency by more that 150%, up to and including
300%, at least 32 dB attenuation.
The “necessary bandwidth” is 300 Hz for 300 bps and 1200 Hz for 1200 bps.
4.5.2        Wide Band Transmit Spectrum
The power in any sideband, harmonic, or spurious signal, that is more than 900 Hz from the assigned channel
center frequency (for 300 bps) or more than 3600 Hz from the assigned channel center frequency (for 1200 bps)
shall be at least 60 dB below the power in the unmodulated carrier.
If the power of the signal applied to the antenna transmission line is greater than 50 watts, the power in any of
these undesired emissions shall be not more than 50 microwatts.

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