[RTTY] 2Tone

[Ron Kolarik]

Thanks Chen. I'll see if I can stretch this out in the time domain and get a look
at what's going on in there. It probably won't hurt anything but it is annoying and
it will cost precious milliseconds :)

73,
Ron
K0IDT

----- Original Message ----- 
From: "Kok Chen" <chen at mac.com>
To: "Ron Kolarik" <rkolarik at neb.rr.com>
Cc: "RTTY" <rtty at contesting.com>
Sent: Sunday, December 15, 2013 11:08 PM
Subject: Re: [RTTY] 2Tone



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