[Fwd: LF: PSK Data modes]

Andre Kesteloot akestelo@bellatlantic.net
Thu, 23 Apr 1998 07:37:40 -0400



drassew2@interalpha.co.uk wrote:

> There has been some interest shown in the use of PSK data modes, in
> particular the PSK31 modes used for the contact between G3PLX and G4JNT last
> weekend.  The questions paraphrased from some asked by G3LDO......
>
> >> On Sunday 19/04/98 at 1150z  G3PLX and G4JNT made  what may be the first Two
> >> Way data communications QSO on 136.5kHz.  Using PSK31 in Binary PSK mode,
> >> copy was 100% each way at a speed that equates roughly to 60WPM in CW terms.
> >> The carrier from G3PLX was just about audible by ear in a 300 Hz bandwidth
> >> and CW would probably have been possible if I was any good at receiving it!
> >> In real engineering terms the carrier was around 30dB above noise in a 1 Hz
> >> bandwidth.
>
> > From the performance of the mode this would seem the way foward.
> >What are your opinions pressing for this mode to be the standard - or
> >are there better ones.
>
> Phase Shift Keying is certainly one of the better data modes around when
> compared with FSK etc. PSK31 is just one of  implementation and there are a
> few 'amateur' ones in existance.  One in particular in the VE2IQ 'Coherent'
> software, making use of either the Soundblaster or a separate interface
> (I've discovered that this can be a modified version of my PIC A/D design)
> This is what I used in the PSK tests on 73kHz with G4GVC a few months ago.
>
> PSK is optimised for narrow bandwidth and takes up just 15 Hz at the -60dB
> points.  (This theoretically makes it possible to have a QSO between the two
> tones of a standard 170Hz shift RTTY signal)
>
> The problem with the VE2IQ software is that, unlike PSK31, it uses hard
> keying of the transmit waveform and so does not control the bandwidth of the
> transmitted signal.  This can be filtered separately but then intersynbol
> interference is introduced with an attendant loss in bit error rate.  I
> believe that later versions using the Soundblaster make some attempt to
> solve this problem but I haven't investigated this version at all.
>
> >If PSK31 is to be the standard what equipment is required? I feel
> >sure that you have discussed it before but I am uncertain as where to start.
>
> PSK31 requires the use of a 56002EVM card, PC and SSB transmitter.  The 'EVM
> is a Motorola DSP evaluation kit available at around 150 from a number of
> suppliers.  The PSK31 code produced by G3PLX, which now includes a QPSK
> version using Viterbi error correction, is available for free, either direct
> or by download from a web site.  Once you have an EVM other software can be
> used on it.  Currently I use a spectrum analyser prog EVMSPEC, also by G3PLX
> and some d narrowband decimation and filtering routines for ultra narrow
> band reception.
>
> Andy  G4JNT