Re: LF: Opera continuous changes

["James Moritz" <james.moritz@btopenworld.com>]

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