// CALCULATOR

PCM bit rate, frame rates and sample rates.

Describe a PCM format — word length, words per minor frame, minor frames per major frame — and give its bit rate or its minor frame rate. The calculator returns the other one, the sample rates of normal, supercommutated and subcommutated words, and where the format stands against the classes of IRIG 106 Chapter 4.

Runs in your browser. Nothing is sent.

YOUR VALUES

Minor frame

4 to 32 bits in Class I, up to 64 in Class II.

Count the sync pattern as the words it occupies: a 32-bit pattern in 16-bit words is 2 words.

Rate
Known value
Major frame and commutation

The range of the subframe counter (SFID): at most 256.

The slots a fast parameter holds in each minor frame.

Minor frames between two samples of a slow parameter: from 2 up to the major frame.

RESULTS

Bit rate

5 Mbit/s

8,192 bits per minor frame

Minor frame rate

610.35 frames/s

One minor frame every 1.638 ms

Details
Frames
Minor frame: 512 words of 16 bits 8,192 bits
Minor frame period 1.638 ms
Major frame: 32 minor frames 262,144 bits
Major frame rate 19.073 Hz · every 52.43 ms
Sample rate of a parameter
One word per minor frame 610.35 Hz · every 1.638 ms
Supercommutated, 8 words per minor frame 4,882.8 Hz · every 204.8 µs
Subcommutated, once every 32 minor frames 19.073 Hz · every 52.43 ms
Occupied bandwidth (99%)
PCM/FM, ≈ 1.16 × bit rate ≈ 5.8 MHz
SOQPSK-TG, ≈ 0.78 × bit rate ≈ 3.9 MHz

IRIG 106 Chapter 4

  • Bit rate

    Class I: from 10 bit/s to 10 Mbit/s.

  • Word length

    Class I: 16 bits, within 4 to 32.

  • Minor frame length

    Class I: 8,192 bits and 512 words, within 8,192 bits and 1,024 words.

  • Major frame

    32 minor frames, within the limit of 256.

  • Subcommutation

    Depth 32, within the major frame of 32 minor frames.

  • Supercommutation

    Evenly spaced: one sample every 64 words, as Class I requires.

HOW IT IS COMPUTED

Two lines of arithmetic; the rest is bookkeeping.

The frame rate is the bit rate divided by the minor frame length in bits. The sample rate of a parameter is the frame rate times the slots it holds in a minor frame, or divided by the depth of its subcommutation.

Minor frame length

L = word length × words per minor frame

In bits. The calculator assumes words of one length, the sync pattern counted in the words it occupies.

Bit rate and frame rate

Rb = L × f_minor ⇔ f_minor = Rb / L

Give one, the other follows. The default values are the worked example of the PCM telemetry article: 5 Mbit/s and 512 words of 16 bits, so 610 frames per second.

Major frame

f_major = f_minor / N

N minor frames, the range of the subframe counter, make one major frame: the complete format repeats at f_major.

Sample rates

f = f_minor · f = k × f_minor · f = f_minor / D

One word per minor frame is sampled at the frame rate; k evenly spaced words multiply it by k; a word subcommutated to depth D divides it by D. In the example: 610 Hz, 4,883 Hz and 19 Hz.

Occupied bandwidth

≈ 1.16 × Rb (PCM/FM) · ≈ 0.78 × Rb (SOQPSK-TG)

The 99% bandwidth from the modulation table of the PCM telemetry article: an order of magnitude to set against a frequency allocation.

The Chapter 4 checks use the limits summarised in our IRIG 106 Chapter 4 article. Class I is what every range can receive; anything Class II needs the range's agreement first.

Twice the highest frequency of interest is the theoretical floor of a sample rate, not a target: five to ten times gives time histories an engineer can read.

Further reading

Other online tools

Sizing a real installation?

Send us your parameter list or your link geometry: an engineer works through the numbers with you.

Write to an engineer  →