Radios sold as DSC CLASS-D radios must have their DSC transmitter and receiver performance tested and found in compliance with IEC Standard 62238, "Maritime navigation and radiocommunication equipment and systems - VHF radiotelephone equipment incorporating Class "D" Digital Selective Calling (DSC) - Methods of testing and required test results." In obtaining certification for a radio, the manufacturer often includes results of extensive testing as conducted by an independent laboratory according to the specified procedures. In many of the tests, the performance must be maintained while the temperature and supply voltage is varied over a specified range. The suite of tests include:
- 7 Environmental tests
7.3 Performance check
7.4 Vibration test
7.5 Temperature tests
8.1 Frequency error
8.2 Carrier power
8.3 Frequency deviation
8.4 Sensitivity of the modulator, including microphone
8.5 Audiofrequency response
8.6 Audiofrequency harmonic distortion of the emission
8.7 Adjacent channel power
8.8 Conducted spurious emissions conveyed to the antenna
8.9 Transient frequency behaviour of the transmitter
8.10 Residual modulation of the transmitter
8.11 Frequency error (DSC signal)
8.12 Modulation index for DSC
8.13 Modulation rate for DSC
8.14 Testing of generated call sequences
9 Radiotelephone receiver
9.1 Harmonic distortion and rated audiofrequency output power
9.2 Audiofrequency response
9.3 Maximum usable sensitivity
9.4 Co-channel rejection
9.5 Adjacent channel selectivity
9.6 Spurious response rejection
9.7 Intermodulation response
9.8 Blocking or desensitization
9.9 Spurious emissions
9.10 Receiver residual noise level
9.11 Squelch operation
9.12S quelch hysteresis
9.13 Multiple watch characteristic
10 Receiver for DSC decoder
10.1 Maximum usable sensitivity
10.2 Co-channel rejection
10.3 Adjacent channel selectivity
10.4 Spurious response and blocking immunity
10.5 Intermodulation response
10.6 Dynamic range
10.7 Spurious emissions
10.8 Verification of correct decoding of various types of DSC calls
10.9 Reaction to VTS and AIS channel management DSC transmissions
10.10 Simultaneous reception
The test specification establishes all relevant signals, signal levels, signal quality or purity, and required radio behavior. A brief explanation of a few of the DSC-specific test will be given.
8.14 Testing of generated call sequences--tests the DSC transmitter for ability to correctly format and transmit calls of the following categories: Distress, All Ships Urgency, All Ships Safety, Individual Routine, and Group Routine. These calls are generated by the transmitter under test and the response from a certified receiver and decoder are observed for compliance.
9.13 Multiple watch characteristic--the test examines three scanning characteristics: scanning period, dwell time (priority channel); and dwell time (additional channel). The receiver is tested on both simplex and duplex channels. To meet the specification, the scanning time must be less than two seconds; that is, the radio tune to the check the priority channel at least once every two seconds. The dwell time is the time the scanning radio will spend sampling a channel for a signal. For the priority channel the dwell time must not be greater than 150-milliseconds. For all additional non-priority channels being scanned, the total dwell time must be between 850-millisecond and 2 seconds.
10.3 Adjacent channel selectivity--tests the ability of the DSC receiver to be able to copy with a bit error rate of zero (BER =0) a desired signal on the DSC channel (156.525-MHz) in the presence of other signals on adjacent channels that are +25-kHz or -25-kHz
10.5 Intermodulation response--tests tests the ability of the DSC receiver to be able to copy with a bit error rate of 0.01 (one-percent) a desired signal on the DSC channel (156.525-MHz) in the presence of other signals on adjacent channels that are +50 and + 100 kHz or -50 and -100 kHz.
10.7 Spurious emissions--tests to confirm the operation of the DSC receiver does produce any spurious emissions that could affect other receivers nearby.
10.8 Verification of correct decoding of various types of DSC calls --test the ability of the DSC receiver to receive and properly decode a variety of DSC calls; tested call categories are: Distress, All Ships Distress Ack(nowledge), All Ships Relay, All Ships Urgency, All Ships Safety, Individual Urgency, Individual Safety, Individual Routine, and Group Routine. A certified encoder and transmitter sends to the receiver under test, and the receiver reaction and output is observed for compliance with ITU-R Recommendation M.493-11 regarding message composition and content. Also the decoded output sent from the receiver on its digital interface ("terminal") are examined for proper technical format including error-check characters, and for correspondence with the display indication on the receiver.
10.9 Reaction to VTS and AIS channel management DSC transmissions --test the DSC receiver for appropriate lack of response to certain DSC message not intended to elicit any change in a CLASS-D device. In particular, the CLASS-D device, when receiving the specified signals must: not sound an alarm, not display a message, not transmit a response, not suggest a transmitted response, not lock up, and not require operator intervention. This test verifies the radio will be immune to VTS and AIS Channel Management messages sent on the DSC channel.
10.10 Simultaneous reception--tests the ability of the DSC receiver to decode a desired DSC signal with a bit error rate of 0.01 while also receiving a voice transmission with the voice receiver.