Re: [rcpilot-devs] 9k6 packet modem

[Val P. <val...@ya...>]

Thanks Mark,

How important is the filtering step?
> > 	- Get the analog samples from a mapped sin table or 

My understanding is that it is done to reduce bandwidth of the modem
output within narrow FM band spec. Do you think I can skip it? I am
planning to operate the modem in 20 Khz wide bandwidth of audio
subcarrier of video transmtiter.

Val.



--- Mark <ma...@cp...> wrote:
> 
> 	I forgot to mention the first step, that is the HDLC bit-stuffing.
> 
> 	Mark Jordan, PY3SS
> 
> On 8 Mar 2004 at 12:16, Mark wrote:
> 
> > 	Well, for the start, the whole TX process is this:
> > 
> > 	- Convert the TX bytes from NRZ to NRZI.
> > 	- Pass them through a scrambler X0+X12+X17.
> > 	- Get the analog samples from a mapped sin table or 
> > 	- Calculate them from a FIR coefficient table.
> > 	- Send the samples to a DAC (R2R).
> > 	- Use a hardware anti-aliasing low-pass filter.
> > 
> > 	Mark Jordan, PY3SS
> > 
> 
> 
> 
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