Al Whaley writes:
>Xpress is sent over CNN. The frequency varies by cable company because
>CNN is on various different cable channels. The receiver is made by MACOM
>(of San Diego I think) which takes a 9600 baud serial signal straight off
>of some part of the CNN signal. I don't know if MACOM sells these receivers
>separately, but enough disgruntled customers are probably out there that a
>net news article mind find a used one.
Well... sort of correct. From what I understand Xpress is still
on CNN on the satellite, but that's not how it's delivered to the
typical cable subscriber. At your "friendly" local cable outfit's
head end, the data stream is stripped from the CNN (or whoever is
carrying it) signal and is used to FSK modulate a carrier at 9600
bps. This new signal is usually placed somewhere in the extra 4
MHz gap that exists between video channels 4 and 5. It can go
elsewhere, but this gap is the most commonly available. 73.000
MHz is what my system uses, but there are several others.
The big advantage to this scheme is that basic subscriber demodulators
are *cheap* (to manufacture). You can roll your own with one of
several RF chips available from Motorola, NSC, or Philips/Signetics.
Any scheme that uses the vertical interval signals or "in channel"
sub-carriers needs a significant amount of additional hardware.
In the 6 or 7 years I've had Xpress, CNN has changed channels
several times and my CATV system has upgraded from 300MHz to 450MHz
total bandwidth. The feed is still at 73.000 MHz and I'm using
the same hardware (although my decoder plug-in just died). There's
really no relation between CNN and Xpress, unless you have a dish.
>I wrote software to decode the signal on a Sun workstation but never did
>anything with it.
>
>The thing I dislike most about Xpress (outside of having to pay a monthly
>fee if I want the encrypted part) is the Copley news service which tends
>to dominate the news feed. It is in my own opinion a pretty raunchy excuse
>for a news company (including biased).
I agree, Copley is pretty second rate... I miss the UPI stuff that
used to be on XPress. The S&P stuff and Newswire are pretty good,
but it does cost (still less than service from other outfits that are
available in this area).
Regards,
-Tom Kloos, WS7S, Sequent Computer Systems, Inc., Beaverton, OR tk@sequent.com