IRIG 106-99  CHAPTER 3 - FREQUENCY DIVISION MULTIPLEXING TELEMETRY STANDARDS
3.1 General
3.2 FM Subcarrier Characteristics
3.3 FM Subcarrier Channel Characteristics
3.4 Tape Speed Control and Flutter Compensation
Footnotes




CHAPTER 3

FREQUENCY DIVISION MULTIPLEXING TELEMETRY STANDARDS



3.1 General

In frequency division multiplexing, each data channel makes use of a separate subcarrier which occupies a defined position and bandwidth in the modulation baseband of the RF carrier. Two types of frequency modulation (FM) subcarrier formats may be used. The data bandwidth of one format type is proportional to the subcarrier center frequency, while the data bandwidth of the other type is constant, regardless of subcarrier frequency.


3.2 FM Subcarrier Characteristics

In these systems, one or more subcarrier signals, each at a different frequency, are employed to frequency modulate (FM) or phase modulate (PM) a transmitter in accordance with the RF conditions specified in chapter 2. The following subparagraphs set forth the standards for utilization of FM frequency division multiplexing.

3.2.1  Each of the subcarriers conveys measurement data in FM form. The number of data channels may be increased by modulating one or more of the subcarriers with a time-division multiplex format such as pulse-code modulation (PCM).

3.2.2  The selecting and grouping of subcarrier channels depend upon the data bandwidth requirements of the application at hand and upon the necessity to ensure adequate guard bands between channels. Combinations of both proportional-bandwidth channels and constant-bandwidth channels may be used.


3.3 FM Subcarrier Channel Characteristics
    3.3.1 Proportional-Bandwidth FM Subcarrier Channel Characteristics
    3.3.2 Constant-Bandwidth FM Subcarrier Channel Characteristics

The following subparagraphs describe the characteristics of proportional-bandwidth and constant-bandwidth FM subcarrier channels.

3.3.1 Proportional-Bandwidth FM Subcarrier Channel Characteristics.
Table 3-1 lists the standard proportional-bandwidth FM subcarrier channels. The channels identified with letters permit 15 or 30 percent subcarrier deviation rather than 7.5 percent deviation but use the same frequencies as the 12 highest channels. The channels shall be used within the limits of maximum subcarrier deviation. See appendix B for expected performance tradeoffs at selected combinations of deviation and modulating frequency.

TABLE 3-1.     PROPORTIONAL-BANDWIDTH FM SUBCARRIER CHANNELS

7.5% CHANNELS
Channel
Center Frequencies (Hz)
Lower Deviation Limit (Hz)
Upper Deviation Limit (Hz)
Nominal Frequency Response (Hz)
Nominal Rise Time (ms)
Maximum Frequency Response (Hz)
Minimum Rise Time (ms)
1
2
3
400 
560 
730 
370 
518 
675 
430 
602 
785 


11 
58      
44      
32      
30 
42 
55 
11.7     
8.33   
6.40   
4
5
6
960 
1300 
1700 
888 
1202 
1572 
1032 
1398 
1828 
14 
20 
25 
25      
18      
14      
72 
98 
128 
4.86   
3.60   
2.74   
7
8
9
2300 
3000 
3900 
2127 
2775 
3607 
2473 
3225 
4193 
35 
45 
59 
10      
7.8   
6.0   
173 
225 
293 
2.03   
1.56   
1.20   
10
11
12
5400 
7350 
10 500 
4995 
6799 
9712 
5805 
7901 
11 288 
81 
110 
160 
4.3   
3.2   
2.2   
405 
551 
788 
.864 
.635 
.444 
13
14
15
14 500 
22 000 
30 000 
13 412 
20 350 
27 750 
15 588 
23 650 
32 250 
220 
330 
450 
1.6   
1.1   
.78 
1088 
1650 
2250 
.322 
.212 
.156 
16
17
18
40 000 
52 500 
70 000 
37 000 
48 562 
64 750 
43 000 
56 438 
75 250 
600 
788 
1050 
.58 
.44 
.33 
3000 
3938 
5250 
.117 
.089 
.06   
19
20
21
93 000 
124 000 
165 000 
86 025 
114 700 
152 625 
99 975 
133 300 
177 375 
1395 
1860 
2475 
.25 
.19 
.14 
6975 
9300 
12 375 
.050 
.038 
.029 
22
23
24
25
225 000 
300 000 
400 000 
560 000 
208 125 
277 500 
370 000 
518 000 
241 875 
322 500 
430 000 
602 000 
3375 
4500 
6000 
8400 
.10 
.08 
.06 
.04 
16 875 
22 500 
30 000 
42 000 
.021 
.016 
.012 
.008 
TABLE 3-1 (CONT'D).     PROPORTIONAL-BANDWIDTH FM
SUBCARRIER CHANNELS

15% CHANNELS
Channel
Center Frequencies (Hz)
Lower Deviation Limit (Hz)
Upper Deviation Limit (Hz)
Nominal Frequency Response (Hz)
Nominal Rise Time (ms)
Maximum Frequency Response (Hz)
Minimum Rise Time (ms)
A
B
C
22 000 
30 000 
40 000 
18 700 
25 500 
34 000 
25 300 
34 500 
46 000 
660 
900 
1200 
.53 
.39 
.29 
3300 
4500 
6000 
.106 
.078 
.058 
D
E
F
52 500 
70 000 
93 000 
44 625 
59 500 
79 050 
60 375 
80 500 
106 950 
1575 
2100 
2790 
.22 
.17 
.13 
7875 
10 500 
13 950 
.044 
.033 
.025 
G
H
I
124 000 
165 000 
225 000 
105 400 
140 250 
191 250 
142 600 
189 750 
258 750 
3720 
4950 
6750 
.09 
.07 
.05 
18 600 
24 750 
33 750 
.018 
.014 
.010 
J
K
L
300 000 
400 000 
560 000 
255 000 
340 000 
476 000 
345 000 
460 000 
644 000 
9000 
12 000 
16 800 
.04 
.03 
.02 
45 000 
60 000 
84 000 
.008 
.006 
.004 
TABLE 3-1 (CONT'D).     PROPORTIONAL-BANDWIDTH FM
SUBCARRIER CHANNELS

30% CHANNELS
Channel
Center Frequencies (Hz)
Lower Deviation Limit (Hz)
Upper Deviation Limit (Hz)
Nominal Frequency Response (Hz)
Nominal Rise Time (ms)
Maximum Frequency Response (Hz)
Minimum Rise Time (ms)
AA
BB
CC
22 000 
30 000 
40 000 
15 400 
21 000 
28 000 
28 600 
39 000 
52 000 
1320 
1800 
2400 
.265 
.194 
.146 
6600 
9000 
12 000 
.053 
.038 
.029 
DD
EE
FF
52 500 
70 000 
93 000 
36 750 
49 000 
65 100 
68 250 
91 000 
120 900 
3150 
4200 
5580 
.111 
.083 
.063 
15 750 
21 000 
27 900 
.022 
.016 
.012 
GG
HH
II
124 000 
165 000 
225 000 
86 800 
115 500 
157 500 
161 200 
214 500 
292 500 
7440 
9900 
13 500 
.047 
.035 
.026 
37 000 
49 500 
67 500 
.009 
.007 
.005 
JJ
KK
LL
300 000 
400 000 
560 000 
210 000 
280 000 
392 000 
390 000 
520 000 
728 000 
18 000 
24 000 
33 600 
.019 
.015 
.010 
90 000 
120 000 
168 000 
.004 
.003 
.002 
Round off to nearest Hz.

The indicated maximum data frequency response and minimum rise time is based on the maximum theoretical response that can be obtained in a bandwidth between the upper and lower frequency limits specified for the channels. See appendix B, paragraph 3.0 for determining possible accuracy versus response tradeoffs.

Channels A through L may be used by omitting adjacent lettered and numbered channels. Channels 13 and A may be used together with some increase in adjacent channel interference.

Channels AA through LL may be used by omitting every four adjacent double lettered and lettered channels and every three adjacent numbered channels. Channels AA through LL may be used by omitting every three adjacent double lettered and lettered channels and every two adjacent numbered channels with some increase in adjacent channel interference.


3.3.2 Constant-Bandwidth FM Subcarrier Channel Characteristics. Table 3-2 lists the standard constant-bandwidth FM subcarrier channels. The letters A, B, C, D, E, F, G, and H identify the channels for use with maximum subcarrier deviations of 2, 4, 8, 16, 32, 64, 128, and 256 kHz, along with maximum frequency responses of 2, 4, 8, 16, 32, 64, 128, and 256 kHz. The channels shall be used within the limits of maximum subcarrier deviation. See appendix B for expected performance tradeoffs at selected combinations of deviation and modulating frequencies.

TABLE 3-2. CONSTANT-BANDWIDTH FM SUBCARRIER CHANNELS
Click here to view Table 3-2



3.4 Tape Speed Control and Flutter Compensation

Tape speed control and flutter compensation for FM/FM formats may be accomplished as indicated in subparagraph 6.8.4, chapter 6. The standard reference frequency used shall be in accordance with the criteria in table 3-3 when the reference signal is mixed with data.

TABLE 3-3.  REFERENCE SIGNAL USAGE
Reference Frequencies for Tape
Speed and Flutter Compensation

Reference Frequency (kHz 0.01%)

  960 12
 480 1
 240 1
200
100
  50
  25
     12.5
         6.25
            3.125


If the reference signal is recorded on a separate tape track, any of the listed reference frequencies may be used provided the requirements for compensation rate of change are satisfied.

If the reference signal is mixed with the data signal, consideration must be given to possible problems with intermodulation sum and difference frequencies. Also, sufficient guard band must be allowed between the reference frequency and any adjacent data subcarrier.


Chapter 3  Footnotes

12. These frequencies are for flutter compensation only and not for capstan servo speed control. In addition, the 240 kHz reference signal may be used as a detranslation frequency in a constant-bandwidth format.


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