If I ready it right, I think that Joes original point was that this could
turn into a step which would allow an easier path for commercial or
unregulated use of the bands. While bandwidth vs. mode as tech progresses,
in the ham community the commercial encroachment is the bigger worry - and
that all makes perfect sense to me. Guys will try to get away whatever they
can and if it looks like the FCC is taking a step back from a tight
overwatch, it will be exploited.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message-----
From: Kai
Sent: Thursday, July 25, 2013 4:07 PM
To: Kok Chen ; RTTY
Subject: Re: [RTTY] ARRL issues Official Reply: Re 2.8KHz HF digital BW
Hi Chen
The Henning Harmuth story was really interesting. I've run into his works
during
my tenure with Ultra Wideband and IEEE802 standards work. And folks worry
here
about 2.8 kHz BW signals! Thanks for the nice recollections.
We must remember that when radio started it was all wide band (spark) and
was
called "wireless". Eventually spark was abolished, and wireless became
narrow
band and was called "radio". Then came Armstrong who challenged "the
narrowband
mantra" to give us the audio quality of wide band FM. Later, Qualcomm
introduced
wide band digital spread spectrum, challenging the narrow band mantra once
more.
Well, we have wide band (up to 40 MHz BW) CDMA now (in dedicated bands), and
"radio" has again become "wireless"!
Henning was right: wide and narrow don't mix very well, but remember that
2.8
kHz ain't really wide! Many already legally do around 2 kHz digital at HF
with
currently authorized emissions (Pactor, Amtor) at HF. The proposal just ups
that
to 2.8, and more importantly, gets rid of the baud rate limitations.
My CW will always get through, and we'll always have 170shift 45.45 baud
ham-RTTY.
Thanks again, and 73
Kai, KE4PT
On 7/25/2013 4:20 PM, Kok Chen wrote:
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
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