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Date: Wed, 1 Feb 2012 10:40:46 +0000
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: OPERA and QRS
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Ah, now you're into the realms of soft decision decoding.   How does
the brain interpret a faulty QRSS symbol?   Or a faulty callsign?  Do
you see the callsign of a well know LF operator if the gap between
those two dots were filled in - or could it be a newcomer with a
coincidental callsign?  If you're expecting one of a few well known
stations, that becomes a code-book detection - and opens up all sorts
of worm cans.   The error detection capabilities of the human brain
are both remarkably powerful, and very prone to making gross
systematic faults based on what you are expecting.

I think, the comparison of time to send a given amount of data is
valid. ie One QRSS transmission vs one Opera / WSPR Tx.    If you want
to overlay QRSS periods, then you must consider, pro-rata, slower
Opera speeds to get the same time for the source data.

Has anyone really come to a decision on what S/N Ratio is OK for QRSS,
using either the FFT bin size or the reciprocal of the dot period as a
bandwidth reference?    My feeling is that a value of +3 to +6dB of
the bin bandwidth, which is about 0 to 3dB above a typical dot period
seems about right.   And probably not coincidently, is roughly about
the same S/N for audible morse it its dot-period bandwidth.

Andy
'jnt


On 1 February 2012 10:20, qrss <qrss@talktalk.net> wrote:
> We all seem to have agreed to compare OPERA with a QRS speed which takes =
the
> same time to send a call sign, correct or not?
> A QRS beacon can send the call continuously all day and successive period=
s
> are often used to establish the information.
>
> How about comparing like for like in the timing of Data Bits, OPERA uses
> digital techniques and no doubt repeats the data in =A0the 4 minute perio=
d of
> OP4. In this case we would need to be comparing it with QRS1 or QRS1.025 =
if
> you like.
>
> I feed a coding session coming on.
>
> 73 Eddie G3ZJO
>
>