Is the K3 capable of ESSB?

[Fred (FL)]

The SSB bandwidth 2007 realities, sound familiar.
In 1978 - max bandwith over telephonic modems,
and conditioned AT&T lines was like 6250 baud.
A "limit" everyone agreed.

Then some clever soul or group, came up with
quadrature modulation - and rather quietly,
modems into the hot-copper telephone lines
of 52kbaud became a reality.

Similiarly, perhaps HF comms SSB, needs to
rethink its SSB modulation approach, to allow wider
more naturally sounding voice comms, and still
not take up unnecessary bandwidth, beyone which
supposedly 2.7khz now consumes. (when do we
start talking about amplifiers?)

This topic, started as an attempt to learn
technically what ESSB was all about, in
its application to Amateur Radio.  Never
learned anything, except everyone is
against it.

PLEASE close this topic, and wait out our
K3 purchase.  I have no interest in bandwidth
debates or reasons, rather just what they
have been working on in SSB techniques.  I'm
sure the FCC, and ARRL will reign us in, if
we stray.

Fred
N3CSY


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[David Woolley (E.L)]

Fred (FL) wrote:
> The SSB bandwidth 2007 realities, sound familiar.

Yes, this sort of false reasoning is common in marketing.  They rely on
a perception that anything new to the market must be better, and that
the general public doesn't understand the true reasons for limitations.

> In 1978 - max bandwith over telephonic modems,
> and conditioned AT&T lines was like 6250 baud.

The maximum baud rate over telephone lines with the standard analogue
telephony bandwith is about 2400, and still is.

> A "limit" everyone agreed.
>
> Then some clever soul or group, came up with
> quadrature modulation - and rather quietly,

6250 bps is not possible without at least the use of quadrature
modulation.  I think the limit for that is 4800 (although it might just
be 2400).  I guess, if you pushed the bandwidth to the limit, you might
get 3125 baud, and therefore 6250 bps with quadrature modulation.

> modems into the hot-copper telephone lines

The limits were not set by the copper, but by the SSB carrier systems
used on the trunks between exchanges (central offices).  Their bandwidth
was set to the minimum needed for the general public to consider the
quality acceptable for speech.

> of 52kbaud became a reality.

What actually happened is that it became possible to  manufacture
digital signal processors cheaply enough to use them in telephone
modems, and that made it possible to use echo cancellation and advanced
equalisation algorithms.  In addition, it required that the transmission
path from the local office to the service provider be all digital.  The
modems now attempt to select every possible quantisation level in every
sample on the digital bearer - this relies on the remote end not having
an analogue connection (they are only acting as a modem over the local
loop in the downlink direction)!  The actual 56kbps limit is set by the
characteristics of the PCM network, including  US robbed bit signalling
and the need to avoid putting too much power into the equivalent
analogue signal, thus not achieving the absolute limit of 64kbps.  The
baud rate is actually 8k, but one gets away with that because the local
loop analogue connections are not bandwidth limited.

Actually, because PCM phone connections are companded, some of the steps
between quantisation levels are much smaller than others, so 56k modems
                  don't actually take full advantage of the signal to
noise ratio.  Assuming the telephone SNR and that equalisation doesn't
impose too much of a problem, an analogue radio channel should be able
to achieve a lot more than 56kbps in 2.7kHz.

Also, a considerable time before this sort of modem became possible
(and, I think, significantly before the enabling technology of PCM
bearers became common) it became possible to transmit  communications
quality speech over a 2400 bps connection.  That suggests that the true
technical advance would be the transmission of amateur radio speech in
about a thirtieth of the 2.7kHz, SSB, bandwidth, assuming landline
telephone signal to noise ratios.

By comparison, there is really no new technology at all in using laxer
SSB filters.


> rethink its SSB modulation approach, to allow wider
> more naturally sounding voice comms, and still
> not take up unnecessary bandwidth, beyone which
> supposedly 2.7khz now consumes. (when do we

It's the essence of SSB that it takes up the same bandwidth as the
baseband signal!  To get more natural speech in less bandwidth, you have
to basically treat the channel as being a digital one, and send a signal
that takes advantage of the actual nature of speech signals (generally
these use some sort of voice tract model).



--
David Woolley
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RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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[David Woolley (E.L)]

Fred (FL) wrote:
> In 1978 - max bandwith over telephonic modems,
> and conditioned AT&T lines was like 6250 baud.
> A "limit" everyone agreed.

Shannon's classic paper on communications theory was published in 1948,
so, for 30 years before 1978, anyone who knew the signal to noise ratio
and did the maths would have known that that was not the limit.  What
they were probably actually saying is that that was the limit for pure
quadrature phase modulation, or, maybe for economically realisable
hardware at the time.

Incidentally, there now is a hard limit, because the telphone network
core is digital, and you cannot exceed 64kbps (or in the USA, with
robbed bit signalling, slightly less than that).  At that time, the
limit would have depended on the signal to noise ratio.  SNR would
depend on the line.

(The telcos don't allow modems to run as fast as they could, because
that would compromise the analogue parts of the network, hence a 56,
rather than 64kbs, limit.)


--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.

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