Modulation Necessary BW (DD Form 1494)
PCM/FM 1.16*(OTA bit rate)
SOQPSK-TG 0.78*(OTA bit rate)
ARTM CPM 0.56*(OTA bit rate)
Five numbers and one letter can be used to express the emission designator’s necessary BW portion. For AMT waveforms, three numbers and one letter are sufficient. The letter occupies the decimal point position and represents the BW unit (“H” for hertz, “K” for kilohertz, “M” for megahertz, “G” for gigahertz).
For AMT systems, the emission designator for block 8 in the DD Form 1494 for each modulation scheme is specified at the maximum OTA bit rate.
An alternate method is to specify the emission designator for block 8 in the DD Form 1494 for each modulation scheme at a reference bit rate of 1 Mbps.
The necessary BW for each waveform at the link’s maximum capability can be found using Table A-3. For example, if the AMT system can operate at 20 Mbps for PCM/FM, 40 Mbps for SOQPSK-TG, and ARTM CPM, the resulting emission designators follow.
• PCM/FM - 23M2F1DBN
• SOQPSK-TG - 31M2G1DDN
• ARTM CPM - 22M4G1DDN
Table A-3. Modulation/Coding Multiplier
Modulation/Coding Multiplier n
PCM/FM/SOQPSK/ARTM CPM 1
SOQPSK-STC 26/25
LDPC Code Rate R=4/5 21/16
LDPC Code Rate R=2/3 25/16
LDPC Code Rate R=1/2 33/16
SOQPSK-STC/LDPC R=4/5 273/200
SOQPSK-STC/LDPC R=2/3 13/8
SOQPSK-STC/LDPC R=1/2 429/200
For an input bit rate of 1 Mbps, resulting emission designators are presented in this list.
• PCM/FM - 1M16F1DBN
• SOQPSK-TG - 780KG1DDN
• ARTM CPM - 560KG1DDN
The input bit rate must be known to determine any emission designator. Using the input bit rate, Table A-3, and Figure A-7, the OTA bit rate and necessary BW can be
calculated. As an example, if the input bit rate is 5 Mbps (R=5 Mbps), OTA bit rate nR = 5 Mbps (in this case the multiplier n in Table A-3 is 1) resulting in the necessary BW of 5M80, 3M90, and 2M80 respectively for each modulation scheme. These new numbers are then coupled with the emission classification for the appropriate waveform arriving at the new emission designator.
Figure A-7. OTA Bit Rate Determination
If coding is applied to the link, the OTA bit rate changes, which in turn requires a new calculation for necessary BW. A multiplier n can be applied to the input bit rate R to find the OTA bit rate as shown in Figure A-7. This new OTA bit rate is then used with Table
A-3 for the appropriate modulation mode to calculate the new necessary BW. Table A-3 specifies the multiplier n to be used based on all available combinations of coding. This new necessary BW is then used with the emission classification for the waveform to arrive at the new emission designator.
In addition, a note will be added in block 25 remarks explaining the emission designators for AMT links and how to arrive at a new necessary BW and thus a new emission
designator. An example of two versions of this note is below. The WP-21-001 white paper should be provided as an attachment explaining the rationale and this process.
(1) Emission designators for using the TM system’s maximum OTA bit rate capability.
These designators are for each modulation scheme (PCM/FM, SOQPSK-TG, ARTM CPM respectively) at an uncoded OTA bit rate. Enter the maximum OTA bit rates for each modulation scheme in this field. Refer Table A-3 and Figure A-7 for the multiplier “n” to be applied to the uncoded bit rate associated with each combination of modulation scheme and coding selected. This new OTA bit rate is multiplied with the IRIG-106 necessary bandwidth factor to create the new emission designator. See RCC WP-21-001 for further information.
(2) Emission Designators for a reference bit rate of 1 Mbps. These designators are for each modulation scheme (PCM/FM, SOQPSK-TG, ARTM CPM respectively) at an uncoded OTA bit rate of 1 Mbps. Refer to Table A-3 and Figure A-7 and chart for the multiplier “n” to be applied to the uncoded bit rate associated with each combination of modulation scheme and coding selected. This new OTA bit rate is multiplied with the IRIG-106 necessary bandwidth factor to create the new emission designator. See RCC WP-21-001 for further information.
g. Block 9 Frequency Tolerance. This is an important parameter as it is a contributor to carrier frequency error, which eventually needs to be compensated for in the receiver.
The value requested is in parts per million (ppm), meaning the absolute frequency tolerance will change within each AMT band. Typical value for this block for AMT transmitters can span ±1 to 20 ppm depending on the type of transmitter, digital versus analog. If available this parameter should be specified over temperature and age (time).
h. Block 10 Filter Employed. This block asks for information on any filtering in the transmitter. The NTIA is very interested in the technical details of this block since it affects out-of-band emissions. The information in this block is manufacturer-specific, which may require the vender to supply the information. Any filtering details are added to block 25 remarks if further explanation is required. An example on the type of
information that may go into block 25 is provided in the sample DD Form 1494. If a filter is employed
YES should be checked.Filtering is applied in three steps:
• Digital premodulation filtering, scaled automatically with the bit rate.
• Multiple stages of discrete component and stripline filtering in the upconversion circuits.
• 7-pole Butterworth low-pass filter after the final output stage.
i. Block 11 Spread Spectrum. The AMT systems are not spread spectrum system so this block should be checked as
NO.j. Block 12 Emission BW. Block 12 is for providing the modulated waveform’s emission BW, which is defined as that emission appearing at the antenna terminals and includes any significant attenuation contributed by filtering in the output circuit or transmission lines. Values of emission BW specified should be indicated as calculated or measured by marking the appropriate box. Be sure to indicate units used (e.g., Hz, kHz or MHz).
Measurements or calculations are made at the −3 dB/−20 dB/−40 dB/−60 dB points of the modulated waveform. For AMT applications, these measurements are referenced to the peak of the modulated waveform using the RBW and VBW settings for the spectrum analyzer as recommended within IRIG 106, which are RBW=30 kHz and VBW=300 Hz.
The span should be selected to capture the entire waveform. A good rule of thumb is for the span to be four to six times the OTA bit rate. See Figure A-8 for an example. In addition, block 12 also requires OBW be input. The OBW for AMT waveforms is directly addressed in IRIG 106, chapter 2, Appendix 2-A.
For AMT waveforms the terms “occupied BW” and “necessary BW” are interchangeable.
Figure A-8. Emission BW Example for AMT Waveforms
As is the case with the emission designator, emission BW and OBW varies with input bit rate, modulation mode, and coding selections. This results in endless combinations of required waveform measurements. To account for this, the same strategy is employed as the emission designator (i.e., the emission BW) at each measurement point (−3 dB/−20 dB/−40 dB/−60 dB/OBW) is given for each modulation scheme at a reference bit rate of 1 Mbps. These numbers for ideally generated waveforms are given in Table A-4. Note, these numbers should be verified with the actual transmitter. The PCM/FM generated via analog means can vary widely depending on the deviation ratio, data filtering type, and transmitter. It is recommended that, for this type of transmitter, these values be
determined by measurement. The numbers are in the Table A-4 scale if the maximum OTA bit rates are used.