[RTTY] ARRL issues Official Reply: Re 2.8KHz HF digital BW

[Kok Chen]

> Does this comfort you?

As comforting to a CW op feels when I unleash 2.8 kHz wide digital signals down at 14.025 MHz, where I am authorized by the FCC to do.

Wide signals and narrow signals just don't mix (I still remember a quote by Henning Harmuth at an IEEE conference back in the 1970s regarding the use of Walsh Functions as radio carriers).

Keep 2.8 kHz signals above 14.125 MHz and it might make sense.

Otherwise change the existing symbol rate rules to limit bandwidth to 500 Hz.  Not 2.8 kHz.

Re: Harmuth.  Henning Harmuth had back in the 1960s proposed a different orthogonal basis instead of sine waves, and had developed an entire system (including how to phase antennas for Walsh carriers).  His orthogonal basis?  The Walsh Function.  And instead of Fourier Transforms and spectrum, you have Hadamard Transforms and Hadamard spectrum.

At one conference, someone pointedly asked (I paraphrase): "Prof. Harmuth, your system would just splatter all over our spectrum of carrier based signals, making the existing systems useless."  Harmuth's reply: "No, it is *your* carrier based systems that are creating wide splatters in *my* Hadamard spectrum and rendering my system useless."

Now imagine that the Hadamard stuff extends over 2.8 kHz.

Ivory Tower? Look up Walsh Functions and Hadamard transforms on the web and you might find that some of your favorite digital modes actually use them (but over a narrower bandwidth).

I still have Harmuth's "Non-sinusoidal Waves for Radar and Radio Communication" (1981, ISBN 0-12-014575-8) on my book shelf.  Fascinating read (stuff like how to construct bandpass filters for Walsh functions) if you like thinking out of the box.  There is even a section on "Bandwidth Required for Teletype and Data Links."

73
Chen, W7AY