more on RS-232/RS-422 networks

[Bob Fabry--N6EK]

George Cutsogeorge, W2VJN, gcutso@mcimail.com, mentions that flat 4
conductor telephone wire is available for $0.02/foot as part number 630-0630
from MECI at (800)344-4465.

R. E. Smith, Inc. at (513)874-4796 has volunteered to provide two pairs of
their RS-232 to RS-422 converters for evaluation on the Easter Island and
Heard Island expeditions.  We will try to run between tents with RS-232, but
if we get in trouble we can switch to RS-422.  Ron has been VERY supportive.

Fred Lucas, K1EFI, Fred_Lucas/Marketing/GDC/US.GDC@noteshub.gdc.com, who is
the chairman of the Telecommunications Industry Association (TIA) standards
committee TR-30.2 which is responsible for DTE/DCE interfaces including
RS-232 which is now officially called EIA/TIA-232-E reports:

>Your reference to 50 feet is an old misconception on the limit for 232.  In 
>early version of 232, up through 232-C, the distance was specified as
operating 
>up to 20 kbps over a cable capacitance of 2500 pf, typically 50 feet.  Many 
>users of 232 took this to mean 50 maximum when,  at the time of that writing, 
>it was typical.  Since the -C version, we removed all reference to any typical 
>distance.  The present version of the standard, EIA/TIA-232-E, provides some 
>guidance as to how to determine maximum cable length based upon cable 
>capacitance.  In today's world, cable with 10 - 12 pf per foot is common so 
>operation at 200 - 250 feet at 20 kbps is very reasonable.  As with any 
>standard, it has to be written for worst case applications.  I have seen very 
>successful operation of 232 installations at much greater distances,
especially 
>at lower data rates.


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