🚀 go-pugleaf

nagle@netcom.com (John Nagle) writes:

>scottcr@wkuvx1.bitnet writes:
>>I am designing a custom 9600 baud link using a voice channel
>>with the following specs: BW: 100-5Khz  S/N = 35+ dB.
>>Are there any "rules of thumb" about choice of carrier
>>freq 2K ?  3k ?  What about FSK deviation?  With this
>>type of system how does modulation index affect performance?

>        I'd suggest getting the current Rockwell modem data products
>book.  There's probably an off-the-shelf single-chip solution to your problem.
>Try Rockwell Semiconductor Products at 1-714-833-4655.  Other
>manufacturers offer similar solutions.  Using a 9600 baud FAX modem
>part is probably the simplest way to go.  The channel you have is
>good enough.  FAX modems are half-duplex (one way at a time), so
>assuming you want a simplex channel (one way), this is the way to go.
>You avoid the complex bidirectional cancelling schemes used to push
>data in both directions simultaneously over two wires that are used to
>make 9600 baud data modems work.  Those modems won't work over a one-way
>link.

>					John Nagle

I used a Rockwell Fax chip a couple of years ago in a radio modem design, it
worked well and was easy to control, unfortunately before each transmission
of data it had to send a "training sequence" to get transmitter and reciever
into synch. This training sequence took almost a second, longer than the 512
byte packet that followed it and considerably longer than the returning 
"Ack" packet, thereby considerably reducing data throughput.

Looking through the data sheets, Rockwell do now have several 9600 Baud modem
chips which just need a few peripheral components to make a complete modem.

Pete Dunster

pdunster@cc.uow.edu.au