Thanks' Jim
Looking at the spec-plots for long haul DX on 136 , the peak signal
levels do not appear to support the full call sign when using the
very long qrss periods , the ref is often pinged with post asking as
to who xx is or zyz etc , so it followed that to capture a full
call using OP , then a decode capability , matching these, xx zyz
times would present a viable alternative ?
To decode over longer periods would require a signal over the
threshold for 66% of the transmission ? ... however ...
Tnx G.
--------------------------------------------------
From: "James Moritz" <james.moritz@btopenworld.com>
Sent: Tuesday, January 17, 2012 10:58 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF: Opera continuous changes
Dear Graham, LF Group,
It was felt the Op50 /64 was perhaps too long a capture period
for 136Khz
with max 33% data loss this was still 40mins , which , was
possibly
a little too long.
OP32 , will reduce to 20 mins capture window and is perhaps more
realistic?
As currently implemented, Opera is purely a beacon mode; as far as I am
aware, it transmits only the station ID. It is quite normal to transmit
beacon signals using QRSS60 or even slower signalling. At 60s per dot, it
takes of the order of 60 minutes to transmit a typical callsign, so quite
a similar rate to "Op50" or "Op64". Most people run their beacon
transmitters and/or receivers for hours at a time. If complete station IDs
with some sort of signal level assesment can be obtained within that
period, I guess most would think one such detection per hour is a
satisfactory result and slowness would not be a problem. A very slow
beacon signal, accompanied with the information that the SNR is only just
adequate for decoding, or good enough to try a faster mode, is certainly
more useful than a faster mode that can't be detected!
For a communications mode, it would be pointlessly slow of course. But
with beacon signals we are often trying simply to see if anything can be
detected at all with the combination of radiated power, propagation path
and RX noise level that is available, and if so, how much. I'm sure if
there were Op128 or Op256 modes, people would be happy to try using them
too... A nice feature of the current Opera is that the receiver can detect
signals at whichever speed happens to be in use, so there is nothing to
stop people altering their transmission mode to see what will work,
without having to re-arrange the test.
Cheers, Jim Moritz
73 de M0BMU
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