Morse code on paper tape: how telegraph registers printed it
The first telegraph receivers did not make a sound for the operator to read. They wrote. A register pulled a strip of paper past a marking point at a steady speed, and while current flowed in the line, an electromagnet pressed the point onto the paper. A short burst of current left a short mark, a dot; a longer one left a dash; no current left blank paper. The operator read the strip afterwards, much as you would read a line of print.
Paper tape was how Morse code began. It did not last long as the main way to receive it, and the reasons why still shape how the code is learned today.
Inside a register
A register combined three things: a way to move paper, a magnet and something to make a mark.
- The paper drive. A clockwork drive turned a pair of rollers that pulled a narrow strip of paper off a reel at an even speed.
- The magnet. The same electromagnet and armature found in every telegraph receiver. Current in the line pulled the armature down; when it stopped, a spring pulled it back.
- The marker. On the earliest registers, the armature lever pressed a point into the paper, embossing a line you could see and feel. Later registers inked the marks instead, which made them easier to read.
The even speed matters more than it seems. On a tape, time turns into distance. If a dash lasts three times as long as a dot, it leaves a mark three times as long, and a long pause leaves a long stretch of blank paper. The register did not understand the code at all. It simply drew a picture of the timing, and the operator did the reading.
How to read a Morse tape by hand
Because a tape is just timing drawn as length, you read it the same way you would decode Morse written out in pencil. The difference is that nothing tells you where the letters end. You work it out from the gaps.
- Sort the marks. Each mark is either short or long. Do not measure them with a ruler; compare them with the other marks on the same tape. How long a dot looks depends on the paper speed and the sending speed, so a dot is simply “the short one on this tape”.
- Sort the gaps. There are three sizes. The gap inside a letter is about as long as a dot. The gap between letters is about as long as a dash. The gap between words is more than twice that.
- Mark the boundaries. Draw a line at every letter gap and a bigger one at every word gap.
- Look up each group. Write each letter’s pattern down and read it off a chart, or from memory.
A tape of the distress signal shows why the gaps matter. The prosign SOS, ...---..., is nine marks with only the short gaps between them, one continuous character. The three letters S, O and S, ... --- ..., show the same nine marks broken by two wider gaps. On paper the difference is plain to see, which makes a tape a good way to understand what a prosign is.
Hand-sent tapes are rarely tidy. Dots wander in length and gaps shrink when the sender hurries. When a group will not decode, try splitting it or joining it at the nearest gap. A tape that shows ..- might be U, or it might be I and T, .. -, with the letter gap squeezed too short. How to decode Morse code by hand, step by step has more on working through a message this way.
A tape of American Morse, the code used on American landlines, is harder still. Some of its characters (C, O, R, Y, Z and the ampersand) have spaces inside them, and L and the figure 0 use extra-long dashes, so a gap on the tape does not always mean a new letter. American Morse code vs International Morse code sets the two codes side by side.
Why operators switched from tape to sound
A register’s armature clicked as it worked. Operators heard those clicks all day, and they soon found they could read the message from the rhythm alone, without looking at the paper. Reading by ear turned out to be faster and simpler, and on most lines the sounder, an instrument built only to click, replaced the register.
The advantages were practical:
- One step instead of two. An operator reading by ear could write the message down as it arrived. With a tape, the message had to be received first and read afterwards.
- Eyes and hands free. A listening operator could keep their eyes on the message form and their hands on the pen.
- A simpler instrument. A sounder has no clockwork to wind, no paper to load and no ink to refill.
That switch is a large part of why Morse is taught by ear. A pattern you have learned to see on paper does not help much when the same pattern goes past as sound at speed. If you are learning now, Learn Morse code by sound, not from a chart explains how to build that skill from the start.
Where paper tape carried on
Tape did not disappear. It found other jobs.
Some busy lines later used automatic sending. Messages were punched into paper tape as rows of holes ahead of time, then fed through a transmitter that keyed the line faster than any hand could, and at the far end a receiver inked the dots and dashes on tape for an operator to read and write out.
The paper ribbons that came out of stock tickers were a different thing altogether. A ticker printed letters and figures, not dots and dashes, so ticker tape is not Morse tape, whatever it looks like in old photographs.
Make your own tape with a pencil
You can draw a correctly timed Morse tape on squared paper, which is a good way to see the rhythm of the code and makes a fine classroom exercise.
Let one square be one unit. Fill 1 square for a dit and 3 for a dah. Leave 1 blank square between the elements of a letter, 3 between letters and 7 between words. A strip cut from a sheet of squared paper, or a length of receipt paper ruled into squares, works well.
| What you draw | Morse | Squares |
|---|---|---|
| E | . |
1 |
| T | - |
3 |
| A | .- |
5 |
| S | ... |
5 |
| O | --- |
11 |
| HI | .... .. |
13 |
| SOS as one prosign | ...---... |
23 |
| S O S as three letters | ... --- ... |
27 |
Check one by counting: HI is four dits and three short gaps for H (7 squares), a letter gap (3) and two dits with one gap for I (3), which makes 13. SOS as one prosign is 15 squares of marks and 8 one-square gaps, 23; as three letters, the two letter gaps add 4 more, 27. Then swap tapes with a friend and decode each other’s messages using the steps above.
Dot & Dash prints its own tape as a nod to the register: on its machine, a message prints in dots and dashes on an on-screen paper tape as the tone plays, whether you type it and press Send or key it yourself. You can share any message as a tape image, a PNG of its printed tape, which stays free along with the machine after the trial. Send a Morse code message as an image people can decode covers making one that reads clearly.
Questions
Did the telegraph print Morse code on paper?
At first, yes. The earliest receivers, called registers, marked dots and dashes on a moving strip of paper, but operators soon learned to read the clicks by ear and the sounder replaced the register on most lines.
How do you read Morse code on a paper tape?
Sort the marks into short and long, then sort the gaps into three sizes: inside a letter, between letters and between words. Split the tape at the letter and word gaps and look up each group.
Is ticker tape the same as Morse tape?
No. A stock ticker printed letters and figures on its tape, while a telegraph register marked dots and dashes that someone still had to decode.
Why did operators stop reading Morse from tape?
Reading by ear let an operator write the message as it arrived, with no tape to read afterwards, and a sounder was simpler than a register. On most lines it soon took over.