dya@unc-c.UUCP (10/11/83)
I just finished testing Universal Data Systems {Mototrola} 9600 baud
synchronous modems, half-duplex, over dial up lines on the Scum of the
Earth telephone system, Yadkin Valley Telephone Cooperative. This is the
phone system where, if you want to call Advance, N.C. from Advance, N.C.,
the call makes an 85 mile round trip through North Wilkesboro, N.C.
They worked beautifully, once the various equalisations are set.
My suggestion would be to get two BROADCAST GRADE phone lines between
your VAXen, (be SURE that they understand each end will originate one of
them) and operate your modem in the 4 wire mode instead of 2 wire mode.
While working in Richmond, VA, we were able to get 30-15 kHz between our
studios on Broad Street and transmitter at Highland Springs, which is 11
miles away.
Since, when you order these circuits, frequency equalisation costs
not one penny more, you can give those adaptive filters a rest inside
your modem. In addition, their phase characteristics aren't so bad;
certainly better than dial-up.
If you MUST have 19.2 kb, and have an extra 10,000 buckos, Racal-Vadic
makes a data concentrator which supposedly doubles the data rate. 10,000
can buy about 100 months of line rent. When we uftp from mcnc over 9600,
the delay isn't so bad.
Be sure to ask to talk to the "radio shop" when you order equalised
circuits. Most 'customer service representatives' don't know diddly
squat about equalised phone lines.
If the distance is really short, how about current loop ?
--David {....duke!mcnc!unc-c!dya}
cc: dya mcnc!unc!duke!pkb@omsvax.UUCPmsc@qubix.UUCP (Mark Callow) (10/12/83)
Noooooo! Don't use FFT as an abbreviation for Fast File Transfer.
FFT is so widely used as an abbreviation for Fast Fourier Transform that mass
confusion will result.
--
Mark Callow, Saratoga, CA.
...{decvax,ucbvax,ihnp4}!decwrl!
...{ittvax,amd70}!qubix!msc
decwrl!qubix!msc@Berkeley.ARPA