[RTTY] 2Tone

[Kok Chen]

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