On Dec 15, 2013, at 7:31 PM, Ron Kolarik wrote:
> I noticed a few signals during last
> weekend having the same chirp.
Ron,
I had to go back to a personal email from David in March to find his
description of the start-up sequence used in 2Tone.
Historically, RTTY starts up in the Mark tone. Stay there for a short
duration, before it starts keying between Mark and Space (first non-Mark bit is
the start bit of the first character). We are accustomed to hearing this.
However, that is not how 2Tone starts up.
As described to me, 2Tone starts with the Space tone. It ramps up the
amplitude of the Space tone over one bit period, stays constant for one
character period, before switching to Mark, and then always sending the Baudot
LTRS or FIGS shift as the first transmitted character.
Could this amplitude ramp up Space-start sequence be causing you to hear
something that sounds like a chirp? I do not run Windows, so I can't look at
the AFSK waveform myself. If there really is a chirp (a linear FM change in
frequency), then you definitely should ask David to do something about it.
I had alluded to this starting sequence in an earlier thread:
http://lists.contesting.com/archives//html/RTTY/2013-10/msg00093.html
With FSK keying instead of AFSK keying, you will not get the benefit of the
soft amplitude ramp, of course. That is why on a waterfall, many FSK
transmissions start with a pretty wideband pulse that is cause by an abrupt
un-shaped carrier turning on.
73
Chen, W7AY
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