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Message-ID: <3.0.1.16.20010126155050.21d74c42@mail.cc.kuleuven.ac.be>
Date: Fri, 26 Jan 2001 15:50:50
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: LF: Time efficient code
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If we want to develope a new 'code' for a time effecient mHz bandwidth
modulation first thing we should do is to make a list of requirements.
My list would be :

- suitable with non-linear amplifiers :
for sake of efficiency and simplicity of the amplifier

- be able to transmit at least 45 different 'characters' :

- if we want to use non-linear amps we can only transmit one 'tone' at a
time, so each character needs to be transitted a a sequence of 'tones'. The
more 'tones' you use the shorter the sequence per character will be but the
larger the required bandwidth, so we will have to find a compromize between
bandwidth and speed.
eg. 47 characters can be transmitted with 7 tones and 2 sequences per
character (49 posibilities) or as 4 tones and 3 sequences per character (64
posibilities).


An important question is : is it worth to make things that complicated ?
Assume the transmission speed is 60 seconds dotlength. In that case the
time needed to transmit 'CQ ON7YD K' would take :

114 minutes in QRSS
40 minutes in DFCW
30 minutes in '7 tone mode' if we have a space between characters
20 minutes in '7 tone mode' if we have no space between characters
40 minutes in '4 tone mode' if we have a space between characters
30 minutes in '4 tone mode' if we have no space between characters

>From the above is clear the step from QRSS to DFCW is significant (time
reduced to 35%), but the difference between DFCW and the 'multi tone modes'
is between nil and 50%, so we should have to go to a rather complicated
system (7 tones, no spacing) to have a significant gain.

Other opinions please ...

73, Rik  ON7YD