On 13-Oct-99 Fred Finster wrote:
> Having worked with PCTEL using a soft modem for 56K baud for handhelds, I
> noticed that it took like 40-60 seconds for the line condition to be
> characterized (echo cancellation and phase shift) before any data could be
> transmitted. So think about this, can the transmission techniques in the
> software for AX.25 (or other format) support half-duplex with a 50 second
> turnaround? Well at least at 1200 baud the turn around time (sync up to
> the sound) is in the few hundred millisecond range.
That is because the installed software modulation scheme used for POTS needs
to spend all this time testing and probing the line charactistics to optimise
the likely transfer speed. Because you are connected by telephone it is
reckoned that you will be prepared to wait to get the best possible speed.
The issue here is whether it is possible to obtain the information from the
chip manufacturers of one of these modern modems to enable us to use it
effectively as a cheap DSP engine to do our own thing which is radio related.
I don't think anyone is suggesting that we use them with the firmware
provided but, having said that, there is no obvious reason why we could not
get similar speeds out of these devices (given programming info) using other
algorithms, greater bandwidths and wirelesses.
Dirk G1TLH
--
Dirk-Jan Koopman, Tobit Computer Co Ltd
At the source of every error which is blamed on the computer you will find
at least two human errors, including the error of blaming it on the computer.
