Re: LF: Opera continuous changes

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

Dear Graham, LF Group,

> 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
I think partly this is due to the habit of  only transmitting partial 
callsigns - I am not sure why this is preferred to complete callsigns for 
beacon transmissions. But it is also true for, e.g. QRSS60 on 136kHz, that 
there will very often be one or more fades during the time it takes to 
transmit a full callsign, leading to loss of  some of the symbols. So, for 
an effective low-speed mode where the duration of the message is likely to 
be longer than the period between fades, the encoding scheme really has to 
include redundancy in order be able to cope with the loss of some of the 
data during fades. Over a much shorter period WSPR does this rather well; 
more than half the transmitted signal can be completely missing and the 
original message can still be fully recovered. WOLF also achieves this in a 
different way by integrating several repeated transmissions over a long 
period. You can do this "visually" with QRSS, etc, by looking at the 
received fragments of a repeated ID.  From what you say, I guess Opera must 
already include this sort of redundancy in some way, although it is 
obviously hard to comment without knowing anything about the encoding 
scheme...
Cheers, Jim Moritz
73 de M0BMU