What is the correct modulation rate and...

Question 1 / 27070

Question 1 of 27070Mm7TsW8aMLP0gFyw6PAC

What is the correct modulation rate and index of modulation for VHF-DSC?

Question 1 of 27070

What is the correct modulation rate and index of modulation for VHF-DSC?

🔍 Key Concepts

• VHF-DSC (Digital Selective Calling) uses a standardized ITU waveform for all GMDSS VHF sets • The modulation rate is measured in baud and is tied to how many symbols per second are sent • The index of modulation in this context is a small number (around 2–3) with a specified tolerance percentage

💭 Think About

• Think about what standard digital rate is commonly associated with marine DSC on VHF, MF, and HF systems • Consider whether DSC needs a relatively low, robust symbol rate or a very high one to work reliably in noisy distress conditions • Ask yourself which combination of baud rate and modulation index (with its tolerance) is most frequently quoted in GMDSS equipment specs and exam references

✅ Before You Answer

• Check which baud rate you have seen linked to DSC calls on Ch 70 (distress/safety calling): 800, 1200, 1500, or 1800? • Verify which index of modulation value (around 2–3) is normally associated with this DSC waveform and whether the tolerance is ±5% or ±10% • Eliminate any option where either the baud rate or the modulation index (or its tolerance) does NOT match what you recall from GMDSS / ITU-R DSC standards