Here in my neck of the woods for me to play with this I would need to have
this fit into a 10khz Channel.
The baofeng radios (read: cheap $50 radios) are able to deal with NBFM
(11khz). So if we can fit it inside that BW (similar to the D-Star Systems
we have around here) that would be a help.
On Sat, Dec 13, 2014 at 9:07 PM, David Rowe <[email protected]> wrote:
>
> Hello Ross,
>
> Thanks for your comments,
>
> Re your MSK suggestion: I think a MSK signal at an audio carrier
> frequency of 1500Hz, sent over a FM radio, will have a wide RF bandwidth
> so have the same performance hit as FSK over FM.
>
> Cheers,
>
> David
>
> On 14/12/14 14:27, Ross Whenmouth wrote:
> > Hi,
> >
> > Audio over a standard NFM channel has the advantage of compatibility
> > with the huge installed base of transceivers that hams already have.
> > This enables amateurs with an NFM transceiver, a computer, and a basic
> > sound card <-> radio interface to experiment with digital speech (and
> > internet linked repeaters, "text" messaging, etc).
> > I think that if it is easy for hams to get their foot in the door so to
> > speak and experiment, that they will then be more likely to buy or build
> > new radio transceivers that are purpose built for digital modes.
> >
> >
> > May I suggest that something like 1200bps MSK (eg 1500 Hz carrier, +
> > pi/2 phase shift for a 1 and - pi/2 phase shift for a 0) which will fit
> > through the audio pass-band of a NFM voice transceiver and can be
> > coherently demodulated at the receiver.
> >
> > I also think that it would be a good idea for each frame (or
> > super-frame?) to include a synchronisation burst that has good
> > autocorrelation properties (eg a short maximal length sequence) - in
> > addition to robustly establishing frame sync, this known sequence could
> > be used by the receiver to correct linear distortion in the channel (eg
> > from pre- and de-emphasis audio filtering). This technique is used in
> > other radio systems, eg 2g-GSM and STANAG-4285.
> >
> >
> > Regarding the 7dB degradation in performance of FSK over NFM vs FSK over
> > RF (SSB), I wonder what effect would be had by increasing the bit rate
> > and using stronger forward error correction?
> > For example, dropping the requirement for compatibility with voice NFM
> > transceivers (but working with 9k6 FSK data transceivers) if say 9k6
> > baud GMSK with a r=1/8 convolutional code was used to carry 1200 bps
> > payload, how would the BER/SNR performance compare to 1200bps Bell202
> > AFSK over an NFM voice channel?
> >
> >
> > 73 ZL2WRW
> > Ross Whenmouth
> >
> >
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