Briefly, this is what my idea is. Rather than standard 2-frequencies (low for space, high for tone) QRSS3 (3 seconds per dot), I eliminate the need for pauses between dots by using 3 frequencies (low for a space between letters, medium for dot, high for dash). The following images compare my call sign (AJ4VD) being sent with the old method, and the vdFSK method.

Traditional QRSS:

Again, both of these images say the same thing: AJ4VD, (.- .— ….- …- -..). However, note that the above image has greater than a 3 second dot, so it’s unfairly long if you look at the time scale. Until I get a more fairly representative image, just appreciate it graphically. It’s obviously faster to send 3 frequencies rather than two. In my case, it’s over 200% faster.

vdFSK method:

This is the code to generate audio files converting a string of text into vdFSK audio, saving the output as a WAV file. Spectrographs can be created from these WAV files.

### generate_audio.py ###
# converts a string into vdFSK audio saved as a WAV file

import numpy
import wave
from morse import *

def makeTone(freq,duration=1,samplerate=5000,shape=True):
    signal = numpy.arange(duration*samplerate)/float(samplerate)*float(freq)*3.14*2
    signal = numpy.sin(signal)*16384
    if shape==True: #soften edges
        for i in range(100):
            signal[i]=signal[i]*(i/100.0)
            signal[-i]=signal[-i]*(i/100.0)
    ssignal=''
    for i in range(len(signal)): #make it binary
        ssignal += wave.struct.pack('h',signal[i])
    return ssignal

def text2tone(msg,base=800,sep=5):
    audio=''
    mult=3 #secs per beep
    msg=" "+msg+" "
    for char in msg.lower():
        morse=lookup[char]
        print char, morse
        audio+=makeTone(base,mult)
        for step in lookup[char]:
            if step[0]==".":
                audio+=makeTone(base+sep,int(step[1])*mult)
            if step[0]=="-":
                audio+=makeTone(base+sep*2,int(step[1])*mult)
            if step[0]=="|":
                audio+=makeTone(base,3*mult)
    return audio

msg="aj4vd"
file=wave.open('test.wav', 'wb')
file.setparams((1, 2, 5000, 5000*4, 'NONE', 'noncompressed'))
file.writeframes(text2tone(msg))
file.close()

print 'file written'

And the other file needed…

### morse.py ###
# library for converting between text and Morse code
raw_lookup="""
a.- b-... c-.-. d-.. e. f..-. g--. h.... i.. j.--- k-- l.-.. m--
n-. o--- p.--. q--.- r.-. s... t- u.- v...- w.-- x-..- y-.-- z--..
0----- 1.---- 2..--- 3...-- 4....- 5..... 6-.... 7--... 8---.. 9----.
..-.-.- =-...- :---... ,--..-- /-..-. --....-
""".replace("\n","").split(" ")

lookup={}
lookup[" "]=["|1"]
for char in raw_lookup:
    """This is a silly way to do it, but it works."""
    char,code=char[0],char[1:]
    code=code.replace("-----","x15 ")
    code=code.replace("----","x14 ")
    code=code.replace("---","x13 ")
    code=code.replace("--","x12 ")
    code=code.replace("-","x11 ")
    code=code.replace(".....","x05 ")
    code=code.replace("....","x04 ")
    code=code.replace("...","x03 ")
    code=code.replace("..","x02 ")
    code=code.replace(".","x01 ")
    code=code.replace("x0",'.')
    code=code.replace("x1",'-')
    code=code.split(" ")[:-1]
    #print char,code
    lookup[char]=code

Automated decoding is trivial. The image above was analyzed, turned into the image below, and the string (AJ4VD) was extracted:

The code to do this:

### decode.py ###
# given an image, it finds peaks and pulls data out
from PIL import Image
from PIL import ImageDraw
import pylab
import numpy

pixelSeek=10
pixelShift=15

def findPeak(data):
	maxVal=0
	maxX=0
	for x in range(len(data)):
		if data[x]>maxVal:
			maxVal,maxX=data[x],x
	return maxX

def peaks2morse(peaks):
	baseFreq=peaks[0]
	lastSignal=peaks[0]
	lastChange=0
	directions=[]
	for i in range(len(peaks)):
		if abs(peaks[i]-baseFreq)<pixelSeek:
			baseFreq=peaks[i]
		if abs(peaks[i]-lastSignal)<pixelSeek and i<len(peaks)-1:
			lastChange+=1
		else:
			if abs(baseFreq-lastSignal)<pixelSeek:c=" "
			if abs(baseFreq-lastSignal)<pixelSeek:c=" "
			if abs(baseFreq-lastSignal)<pixelSeek:c=" "
			directions.append([lastSignal,lastChange,baseFreq,baseFreq-lastSignal])
			lastChange=0
		lastSignal=peaks[i]
	return directions

def morse2image(directions):
	im=Image.new("L",(300,100),0)
	draw = ImageDraw.Draw(im)
	lastx=0
	for d in directions:
		print d
		draw.line((lastx,d[0],lastx+d[1],d[0]), width=5,fill=255)
		lastx=lastx+d[1]
	im.show()

im=Image.open('raw.png')
pix=im.load()
data=numpy.zeros(im.size)
for x in range(im.size[0]):
	for y in range(im.size[1]):
		data[x][y]=pix[x,y]

peaks=[]
for i in range(im.size[0]):
	peaks.append(findPeak(data[i]))

morse=peaks2morse(peaks)
morse2image(morse)
print morse

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