[GreenKeys] 66 WWPM ITTY

[boatanchor at martasystems.com]

In the late 1960's, my RTTY Elmer told me to remember the cigarette ad for
Lucky Strike "LSMFT". But in this case, it was "Lower Space Means Fine
Teletype". I was young then and didn't understand why, and now that I'm
old(er) I forget why...

Anyone ?




-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Ralph Mowery
Sent: Monday, February 07, 2011 10:49 PM
To: GreenKeys at mailman.qth.net
Subject: Re: [GreenKeys] 66 WWPM ITTY

The mark/space tones have been a problem for years.  I think the problem is
when the hams started feeding audio into the SSB transmitters.  Due to the
way it works, the tones are actually reversed when trnsmitted.  The usage
was that the mark tone was the higher frequency and shifted lower for space.
By putting the audio tone of 2125 into the ssb transmitter and then shifting
up to the higher space frequency (2295 or 2975) and using lower sideband,
the actual radio frequency would be shifted lower.
 
Difficult for me to explain in print.  However when just the audio is used
on the FM or AM transceivers the tones will be mark of 2125 and the space
will be a higher frequency.

Anyway, going from the way hams and much  comercial tones are sent, one is
usually reversed from the other.  Using the most common demodulators require
that you use lower sideband and normal for hams and upper sideband and
normal for comercial , or you can reverse the sidebands and also the normal
and reverse positions of the demodulator.  Slightly confusing isn't it ?





  ----- Original Message ----- 
  From: Martin 
  To: GreenKeys at mailman.qth.net 
  Sent: Monday, February 07, 2011 5:20 PM
  Subject: Re: [GreenKeys] 66 WWPM ITTY


  I sent this yesterday meaning it to go to the list but got it wrong again!


  PS Its not an issue, but am I wrong in thinking the mark and space 
  convention is supposed to be the other way around!

  Martin


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