TRANSMIT SPECTRUM ISSUES

MANUFACTURERS MEETING AUGUST 2004Peter Woolner

Mitretek Systemspwoolner@mitretek.org

703-610-1724

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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

150 Hz

225 Hz

Channel Allocation750 Hz

Maximum DopplerShift 11 Hz

375 Hz

MaximumPossible

FrequencyVariance= 139 Hz Filter

Roll-off65 Hz

450 Hz

25 dB35 dB

215 Hz

NTIA EMISSION MASK

Necessary Bandwidth300 Hz

Current 2ndSideband limitis 15 dB belowcarrier

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NTIA SPEC FOR 1200 BPS

600 Hz

900 Hz

Channel Allocation2250 Hz

Maximum DopplerShift 11 Hz

1125 Hz

MaximumPossible

FrequencyVariance= 254 Hz

FilterRoll-off260 Hz

25 dB

35 dB

860 Hz

NTIA EMISSION MASK

Necessary Bandwidth1200 Hz

1800 Hz

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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.

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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

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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

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DERIVATION (Cont.)

900 Hz

25 dB

35 dB

NTIA EMISSION MASK

Necessary Bandwidth1200 Hz

1800 Hz

3 dB min

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PROPOSED NEW CS TEXT4.5 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.