[RTTY] If you care about CW and RTTY - time is of the essence

[Kok Chen]

> On Aug 17, 2016, at 7:20 AM, Al Kozakiewicz <akozak at hourglass.com> wrote:
> 
> In an all analog world, it makes some sense to regulate transmissions based on content. In a digital world, it does not. There is no syntactic difference between text, image, an Excel file or any other non-streaming data source.  It is all data.

Please allow me to play the pedant for a moment, then follow with less off-topic comments below.

What we have on HF *is* an all analog world.  This is why we need modems that allow us to take discrete data and convert them to analog waveforms which then make use of the “analog” mechanism of data transfer.

One exception is perhaps Henning Harmuth’s work on directly transmitting “square waves.”  The basis of his “waveforms” are based on the Walsh functions instead of sinusoids.  

Harmuth's “spectrum” consists of coefficients of the Hadamard transforms, rather than the Fourier transforms that we usually associate with a “spectrum.” (In mathematics, a spectrum is a pretty general animal.)

Harmuth’s “carrier,” being a Walsh function, would spread from DC to infinity in the Fourier space.  By the same token, a sinusoidal carrier would spread from DC to infinity in the Hadamard transform space.  The two will never coexist peacefully, and Harmuth has said as much.

This part of Harmuth’s work was published in an Academic Press book in the series “Advances in Electronics and Electron Physics,” Supplement 14, “Nonsinusoidal Wavesform Radar and Radio Communications,” ISBN 0-12-014575-8, and even included chapters on antennas for this type of waveforms.

That being said, what we have in the all-modem (a.k.a. digital) world has equally bad consequences when you mix narrow and wide band signals.  

The extreme example are spread spectrum (Hedy Lamarr’s invention, bless her soul) and something like RTTY or CW, and is a reason why spread spectrum is still not allowed for amateurs below 29 MHz.  

At least in the case of spread spectrum and CW or RTTY, the damages are lowered performance, and not complete incompatibility — spread spectrum will appear to a CW or RTTY op as a raised noise floor, and narrow CW will appear to a spread spectrum signal as errors that are correctable by FEC.

It is actually a less extreme case where the problem is possibly greater.  

A wideband digital signal is not spread evenly in the spectrum (they won’t dare claim to be spread spectrum for fear of being banned by the FCC) to simply appear as a raised noise floor to a narrow band RTTY signal.  The wideband signal has spectrum structures that will (not “may”) cause harm to RTTY, especially since RTTY has no error correction.  Take it from someone who has occasionally dabbled in RTTY modem techniques, a wide “digital" signal will cause harm to RTTY, and vice versa, if the two are allowed to intermingle.

Sure we can add FEC to RTTY, but we are a *hobby*, folks.  We (the royal “we," since I haven’t even used keyboard CW in a decade :-) still use CW, and that is as inefficient a mode to transfer discrete information (OOK) as you can get.   Many aspects of amateur radio is not about efficiency (which ARRL lawyers appear to keep harping on) but about enjoyment and love of operating.  

Now show me an HF email user who enjoys “operating.”

73
Chen, W7AY