[HSMS] HSMS Formules

Date: Tue, 4 Nov 1997 09:14:13 -0700
From:  Alf Green, NU8I 
To: hsms@tree.net
Subject: Re:  [HSMS] HSMS formulas

Andrew Flowers K0SM  enscribed:

    Several of you have asked for the formulas, and replying to the
    reflector is easier than keeping track of all of you, so here they are. 
    As always, check my math!

   The excel sheet has you enter the speed in LPM and the audio frequency
   you intend to inject into the transmitter.  From this it calculates the
   following:  (f = the audio frequency in Hz)

   WPM (speed in WPM)            = LPM * 5

   Actually,  WPM = LPM/5

   Typo, I expect, as it is correct on the spreadsheet.

   L   (length of a dot)         = 6/LPM
   Cycles/dot                    = L*f
   Corr (How 'good' the tone is) = sin(2pi*f*L)

   Corr is a number between -1 and 1.  The closer to zero the better the
   tone is and the less 'pop' there is after each CW element.  It is really
   a measure of how close to zero the sine wave is at the end of the
   element.  A 'one' would mean the element is stopping at the crest of the
   wave, a '-1' would mean the element is stopping at the trough--both are
   going to cause 'popping'.

   The sheet also calculates 'perfect tones' for the speed that you
   entered.  The perfect tones (in Hz) are any multiple of 1/(2*L).

Strictly speaking this only works if you can synchronize the audio to have the
zero-crossings at the keying edges. Even at the perfect tones, there will still be
'pops' if there is a phase error. 
Perhaps with the soundcard generators, this can be achieved, but I would think it 
rather difficult with an external keyed oscillator.
The principle is quite sound, however.

73,  Alf  NU8I
Scottsdale  AZ  DM43an
50 - 1296


Comments: Rein, W6/PA0ZN

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