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Practical Communication: Sending, Receiving and Operating

In Morse code a dot lasts 1 unit and a dash 3 units; letters are patterns of both. To send, you key the transmitter on and off; to receive, you listen or watch and write down the pattern. Good operating follows a fixed order (call sign, "this is", message, "over"), uses clear spelling with the phonetic alphabet, keeps distress calls on the proper channel and records every contact in a log.

🎬 Step-by-step story

  1. Two radio stations. One sends and one listens. A message must go from the left box to the right box.
  2. Morse code uses two signals. A dot lasts 1 unit. A dash lasts 3 units. Compare the small block and the long block.
  3. Build a letter. Press Dot and Dash. The code shows below, and the letter it makes is shown in the readout.
  4. Press the key and the carrier turns on and off. Yellow pulses travel across. The lamp at the receiver blinks the same pattern: dot, dash for the letter A.
  5. Good operators follow an order: say who you call, say who you are, say the message, then say "over" to give the other side a turn.
  6. Your turn. Build any letter from dots and dashes and press Send. Watch the receiver show the letter.

Tip: drag the 3D scene to turn it. Use two fingers to zoom.

🤔 Common doubts, cleared

Why do we need two different lengths?

With only on and off, the length of the "on" is the only thing that can change. Short and long give a code.

How do I know where a letter ends?

A longer gap (3 units) comes after each letter. Inside a letter the gap is 1 unit.

What travels from sender to receiver?

The carrier wave switched on and off. The receiver hears or sees the same on-off pattern.

Why say "over"?

On one channel only one station can speak at a time. "Over" tells the other station it is their turn.

What if I make a wrong letter?

Press Clear and start again. Real operators send a run of dots as an error sign.

Practical transmission and reception

Morse code turns letters into dots and dashes. Timing rules: dot = 1 unit, dash = 3 units, gap inside a letter = 1 unit, gap between letters = 3 units, gap between words = 7 units. Examples: E = ·, T = −, A = ·−, S = ···, O = −−−. So SOS is ··· −−− ···.

Sending: key the transmitter on for the right time, keep an even rhythm, speak slowly at first. Receiving: tune the receiver to the right frequency, reduce noise with the volume and filter, write each pattern as you hear it, and decode after the letter ends.

For voice, use clear speech: speak slowly, keep the mouth near the microphone, and spell hard words with the phonetic alphabet (Alfa, Bravo, Charlie…).

Communication operations

Rules for operating make sure the right station gets the message.

Emergencies: Mayday (said three times) means life in danger; Pan-pan means urgent but no immediate danger; Securite is a safety warning. On marine VHF the distress and calling channel is channel 16. Never use a distress call as a joke.

Try it

1. In the 3D, send E, then T, then A. Which letter is longest in time? 2. Write your own name in Morse on paper, then send two letters in the 3D to check. 3. With a friend, practise "Call, Me, Message, Over" using two paper cups or the phone speaker.

Key formulas and definitions

Worked examples

1. How many units does the letter A (·−) take, counting the 1-unit gap inside it?

Dot 1 + gap 1 + dash 3 = 5 units.

2. How many units does S (···) take?

Three dots = 3 units, two gaps = 2 units. Total 5 units.

3. Write SOS in Morse and give the number of units of the signal parts (ignore gaps between letters).

··· −−− ··· : 3 dots (3) + 3 dashes (9) + 3 dots (3) = 15 units of signal, plus the gaps inside letters.

4. Put these in correct order: "over", the message, your call sign, the other station.

Other station, your call sign, the message, over.

5. A boat takes in water and the crew fears for their lives. Which call and which channel?

Mayday (three times) on VHF channel 16.

Common mistakes

Practice quiz

1. A dash lasts:
2. SOS in Morse is:
3. "Over" means:
4. The usual marine VHF distress channel is:
5. A log book records:

Practice: answer these yourself

Type or choose your answer, then press Check. Use a hint if you are stuck; the full solution appears after you answer.

Frequently asked questions

How long is a dash compared with a dot?

A dash lasts 3 units; a dot lasts 1 unit.

What do "Mayday" and "Pan-pan" mean?

Mayday means life in danger and needs help at once. Pan-pan means an urgent message with no immediate danger.

Why keep a radio log?

It is a record of who called whom, when, on which frequency and what was said, useful for safety and checking later.

Where this is taught

Japan高校（専門学科）1〜3年Marine Communication Technology

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