Morse Expert 1.09

Morse Code Decoder for Android

Copyright © 2020 Alex Shovkoplyas VE3NEA

freeware







Overview

Morse Expert decodes Morse Code audio to text. Optimized for decoding weak, fading signals in the presence of interference, especially on the Amateur Radio bands. Optionally highlights Ham callsigns and keywords. The audio may come either from the built-in microphone or from another device, such as a radio, via an audio cable. Decoding is performed using the same algorithms as used in CW Skimmer.



Download

Download the program from Google Play by clicking on the button below:

Get it on Google Play



Discussion Group

Join the Morse Expert for Android Google group to discuss the program and request support.



Specifications

Waterfall Bandwidth: 200-1200 Hz
Decoded Frequencies: 300-1100 Hz
Keying Speeds: 12-45 WPM
CW Pitch: Auto



Text Selection Mode

A long-click on the decoded text switches the app to the text selection mode. Use the selection handles to adjust your selection, then use the Selection menu to copy, share or save selected text. Decoding is suspended in the selection mode, tap outside of your selection to resume decoding.

The Save command saves decoded text to the this folder on your phone:

Android/data/com.ve3nea.morse_expert/files/

To copy the file to your PC, connect the phone to your machine with a USB cable.



Frequency Lock Mode

By default, if there is more than one signal in the passband, the decoder switches automatically between the signals. A tap on the waterfall display locks the decoder frequency, and the green triangle changes its color to yellow , indicating the lock mode. A second tap on the waterfall disables the frequency lock.



Ham Radio Mode

The Settings screen allows you to switch between the default, General Text mode, and the Ham Radio QSO mode. In the latter mode, the app performs extra processing of the decoded text to improve word segmentation and highlight the callsigns and special words, as shown on this screenshot:



Reducing Echo

Morse Expert can decode audio from the microphone, but acoustic echo picked up by the mic may degrade decoding accuracy, or even completely destroy decoding.

I used the Morse Letters video uploaded by someone to YouTube to test the effect of the echo. The first screenshot was taken with the aduio played back via a speaker and picked up by the microphone, the second one was taken when the audio was fed to the smartphone through a cable, as described in the next section. The tails after every Morse element visible on the first screenshot made decoding impossible, while the audio fed via the cable was decoded perfectly.

I strongly recommend the use of a cable, but if this is not an option, try to place the phone's mic as close to the speaker as possible, to minimize the echo.



Audio Adapter

Many consumer electronic devices, as well as Amateur Radio equipment, output the Line-In level signas, about 600 mV r.m.s. Such signals need to be attenuated to the Microphone level (a few mV) before they are fed to a smartphone. DC decoupling is also often required, in particular, because Android devices apply DC to the Mic pins to detect the presence of an external audio source. I used the circuit shown below to feed the audio from my shortwave transceiver to the phone, with excellent results.

To build the attenuator, I used resistors salvaged from an old TV, and the 4-contact audio connector was cut from the broken earbuds. Such earbuds are sold for less than $1 on Ebay. Ironically, the connector alone costs several times more.

I put the components on a tiny PC board, as shown below, and protected the circuit with a heat-shrink tube.


Ground Loop

It is not recommended to connect the audio and USB cables to the phone at the same time since noise pickup may increase greatly due to a ground loop formed by the two cables. Check the input signal level shown on the status bar above the decoded text, and make sure that it is within -50..-20 dBFS. Higher levels (-20..-1 dBFS) indicate insufficient signal attenuation, ground-loop noise, or other problems.

If you need to have both cables connected, e.g., to keep your smartphone charged, use an isolating transformer to break the ground loop. I have discovered that the ground loop is eliminated completely usingng the "Audio Aux Noise Filter Ground Loop Isolator" that I bought on eBay for $5:



Using Morse Expert With a Radio

The best way to connect your phone to the radio is via the ACC connector on the rear panel of the transceiver or receiver. Another option is the Headphones jack on the front panel - this also works, though it is less convenient.

To fix the phone on top of my radio, I use a smartphone holder made from a paper clip. I was very proud of my invention until I discovered that it was a well-known trick :)




My emailMy other software