[Lowfer] " XR " HSCW experiment tonite on 186.100 KHz

[jrusgrove at comcast.net]

JD

Good explanation. This is not meteor scatter where signals are often astonishingly strong during the 
short bursts.

Jay

----- Original Message ----- 
From: "JD" <listread at oswegoblade.com>
To: "Discussion of the Lowfer (US, European, &amp;UK) and MedFer bands" <lowfer at mailman.qth.net>
Sent: Monday, January 10, 2011 1:21 AM
Subject: Re: [Lowfer] " XR " HSCW experiment tonite on 186.100 KHz


>>>>Curiousity has me wondering just how much information could
>>>>be conveyed at the rate of 1200 wpm when a lowFER signal
>>>>peaks above the noise ??
>
> In principle, almost none outside the immediate neighborhood.  In practice,
> even less.
>
> Remember, Andy, "the noise" is not some quantity that's the same for every
> mode.  The higher the data rate, the broader the transmission bandwidth;
> thus, the broader the receive noise bandwidth will have to be also, and the
> harder it is for a miniscule LowFER signal to ever peak above it at all!
> The statistical chances of overcoming the noise grow smaller and the time
> intervals during which it can happen grow shorter.  Even at conventional CW
> speeds, one is already well into the area of diminishing returns so far as
> data throughput per day is concerned (compared to lower speed, narrow band
> modes).  Over any substantial distance, you have to wait a very long time
> for a good enough opening to occur to copy anything at all.
>
> That's one limitation in principle.  In practice, there's another, and it's
> a biggie: if your LF antenna has any efficiency at all, it is too limited in
> bandwidth to transmit a signal that wide in the first place.  That's why I
> said the chances in practice are even less than "almost" none.
>
> Consider 12 wpm Morse.  A continuous string of dits would comprise a 10 Hz
> square wave imposing itself as 100% amplitude modulation on your carrier.
> To maintain anything resembling a square shape to the envelope (required for
> distinct detection of the on/off states) it is necessary to transmit the
> first few odd harmonics of the 10 Hz fundamental frequency.  The third and
> fifth are sufficient--but that still means crucial sidebands exist as far as
> + and - 50 Hz from the carrier, which is why 100 Hz is a reasonable
> bandwidth specification for a carefully shaped 12 wpm CW signal.  Multiply
> the data rate times 100, and your signal will be 10 kHz wide!  It wouldn't
> make it through your antenna without serious envelope distortion and group
> delay problems...not to mention, you might need to move down in frequency a
> bit to keep sideband products within the band if you somehow did broaden the
> antenna response enough. :)
>
> As a rough approximation of what high speed CW would do to your coverage
> area, imagine transmitting music in AM mode over your LowFER and seeing just
> how far away you can decipher unfamiliar lyrics on an AM radio.  The range
> will be a tiny fraction of what you achieve with CW, let alone QRSS.
> Antenna bandwidth is the main reason spread spectrum techniques have never
> caught on among LowFERs, too.
>
> John
>
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