PocketMorse

v1.3

Introduction

PocketMorse is a utility for decoding Morse Code audio signals. It runs on Windows desktop systems (equipped with a soundcard) or Pocket PC devices with the Pocket PC 2003 operating system (please contact us if you require a Pocket PC 2002 version). The Morse Code signal is either taken from the microphone input on the desktop/PocketPC or from a Line input (desktop).

PocketMorse can decode Morse when the signal is reasonably clear, and sent at a usual rate. If the signal is very noisy, faint, or sent very slowly (less than about 5 WPM) or very quickly (more than about 25 WPM) then the results from PocketMorse are unreliable.

Windows Desktop Version Installation Instructions

Simply put the WinPocketMorse.exe file into a convenient place on your hard disk e.g. C:\PocketMorse. To run it, double click the file, or create a shortcut to it on your desktop, and click that.

Pocket PC Version Installation Instructions

The PocketMorse.exe file should be copied to the \Windows\Start Menu directory on your Pocket PC. Do not try to execute the .exe on your desktop PC: it wont work!

Feature Overview

The main features of the display are described in the diagram above. The Scrolling Decoder Window shows a complete history of the Morse Code received, and how the characters have been converted to text. Each Morse character in the Window is delimited by a vertical bar "|". When a word is complete, a new line is started.

The Text Output Ticker shows the most recent decoded text stream (without the Morse). As more text is received, the text is moved to the left.

The Statistics and Information Window shows some useful data about how the decoder is functioning:

S/N: The Signal to Noise ratio is a dB measurement of the loudest detected audio level against the lowest detected audio level. The decoder will not attempt to extract Morse from a signal having S/N < 10dB. If the signal is below this level, then the text in the Statistics and Information Window will turn red.
D: The currently measured length of a Morse "dot", in samples. PocketMorse records at the rate of 8000 samples/second. So a dot length of 800 samples corresponds to a time length of 800/8000 i.e. one tenth of a second. As the decoder detects Morse, it adjusts the dot length according to the sent rate. From the dot length the Words Per Minute value is calculated (see WPM, below).
I: The currently measured time between Morse words, in samples. For 1:3:7 Morse code, this should be 7 times the dot length. It can (and does) vary considerably from this in practice.
T: The sensitivity threshold. This number can be varied between 0.1 and 0.9 (see Sensitivity below). Its default is 0.5, corresponding to average sensitivity. The sensitivity effectively determines the threshold above which the audio signal is said to be sending a dot or a dash.
WPM: This indicates the currently measured Words Per Minute send rate, and is simply computed as 1.2 divided by the dot length (in seconds).

The Raw Audio Signal is shown as a green trace: this is a plot of the audio samples as picked up by the microphone.

The Smoothed Input Signal is shown as a red trace. To smooth the raw signal a DSP filter that applies an exponential decay with a time constant of 125 milliseconds is applied. This has the effect of making random noise fluctuations affect the decoder less than if the raw samples were used.

(You can also have a bandpass filter applied to the signal: see below for details.)

Cutting across the smoothed signal from left to right is a dashed yellow line that shows the current setting of the Threshold value. Any part of the red curve above the yellow line is decoded as a dot or a dash. The results of the decoding are shown by a series of "*" and "-" symbols at the top of the signal window.

Starting PocketMorse

Place your PocketPC near to your radio's loudspeaker: the closer the PocketPC is to the audio, the better the Morse Code recognizer will work. (If you are running the desktop version, WinPocketMorse, you could also feed the radio's audio signal into the PC's soundcard Line In socket, and adjust the Windows Mixer settings to select that input.)

When PocketMorse is started, it spends some time calibrating what it hears from the microphone (or Line In). The following display is seen:

Once calibration has finished, then PocketMorse starts to display some results of decoding any Morse code. Generally it takes some time (30 seconds or more) for the decoder to "lock on" to the correct settings, so don't be discouraged if all you see initially is gobbledygook!

If no Morse code is being heard, or there is silence, or the Morse is being sent at an unusually slow or high rate, then PocketMorse may produce some odd-looking results. In these cases, or in cases where the Morse send rate has changed significantly, it may be necessary to re-Calibrate. Here is what can happen when a re-Calibration is required:

Calibration

You can re-Calibrate at any time by selecting "Calibrate" in the "Control" menu. This has the effect of re-setting the Morse "dot" length to a nominal value, and to re-start averaging the detected signal.

Sensitivity

Other options in the "Control" menu include an "Increase Sensitivity" and "Decrease Sensitivity" control. These adjust the signal Threshold, described above. If you see that the yellow line is cutting across the smoothed red signal curve too high (and therefore some "dots" and "dashes" are being missed) then you would want to increase the sensitivity. Conversely, if you are getting a lot of isolated "dots" (and thus decoded "E"s), you might want to decrease the sensitivity.

Filters

A set of bandpass filters are provided which can help with isolating the Morse Code signal. These can be selected using the “Filters” menu. Filters at 250Hz, 500Hz and 1kHz are provided.

Saving a Log File

You can save the complete text that has been decoded by PocketMorse into a Log File. To do this, select "Save Logfile" in the control menu. Then enter a name for the Log File in the screen shown below and click "OK".

The file written is prepended with the current date and time.

Clearing the Log

You can clear the contents of the text window using the Clear Log option in the Control menu.

Start/Stop

You may want to stop PocketMorse from recording/decoding while you scroll back and look at the decoded text. To do this, select the "Start/Stop" item from the "Control" menu. To re-start recording/decoding, simply select "Start/Stop" again.

Please don't hesitate to report bugs, errors or suggestions for improvements.

J.J.Bunn

Armchair Applications