Amtor FEC on LF]

[Andre Kesteloot]

Andy talbot wrote:

> is over 100 km away, so it does not
> > cause the same trouble you might have in areas such as the U.K. but helps
> > to fill the band at least with some signals  .... ;-)
> >
>
> > But scaled down Amtor (divide by 10 all round) might be useful
> >Stewart G3YSX
>
> It is far better to tailor a data modulation and coding sceme to the medium on
> which it is to be used rather than just cobble together an adaptation of
> another scheme.
>
> AMTOR is designed for HF which has the characteristics of short bursts of
>  interference mixed up with  fading and multipath - so has a short packet
> length (3 characters) and low baud rate to fit in between link disturbances.
>  High relative bandwidth is necessary at HF to counter multipath.
>
> 137k, on the other hand is characterised by a much more constant noise
> background and does not behave like HF divided by ten -  if fading is present,
> it covers a much longer period of tens of minutes or hours    These
> characteristics suggest a coding scheme that requires less error correction and
> can make use of narrower relative bandwidth to reduce noise.    We already have
> JASON for low speed work, albeit with no error correction, and PSK31 is ideal
> for keyboard typing speeds and includes a QPSK FEC mode, although the linear Tx
> requirement makes it difficult to use.    Link failures at LF will not be cured
> by ARQ (as in AMTOR) to the same extent as at HF due to the non burst nature of
> the noise.
>
> Andy  G4JNT
>
> -----Original Message-----
> From:   Stewart Bryant [SMTP:stewart.bryant@virgin.net]
> Sent:   2002/07/09 17:50
> To:     rsgb_lf_group@blacksheep.org
> Subject:        Re: LF: Amtor FEC on LF