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:[email protected]]
Sent: 2002/07/09 17:50
To: [email protected]
Subject: Re: LF: Amtor FEC on LF
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