Hi Mike,
You wrote to Marco van den Bovenkamp:
MB> MB> Of course, anything within 10% tolerance will work without any
MB> MB> trouble.
I've got a copy of an Unapproved Draft of the "ARCNET Local Area
Network Standard" (Version 1.4) issued by the ARCNET Trade Association.
The only items that refer to the physical layer impedance are
(selective excerpts):
"7.3.1 Transmitted Signals
7.3.1.2 Signal level
 The minimum magnitude of the transmitted signal, measured at the MIC
 with a 93ohm resistive termination, is 15.4V, peak to peak."
and
"7.3.2 Received Signals
7.3.2.4 Receiver Impedance
 For Star-topology  systems, the receiver shall present an impedance of
 93 +/- 25 ohms."
My Note: MIC is the "Medium Interface Connector", which is specified in
section 7.5.1:
 "The MIC for use with coaxial cable is a conventional, 50 or 75 ohm,
 female BNC."
MB> MvdB> Make that 'for Arcnet, just about *anything* will work' :-).
MB>Well, that's true, too.  :)
And some vendors took advantage of it (Datapoint!).
I've got a copy of the Datapoint ARCNET Cabling Guide here, publication
No 51087, Edition 02, Copyright 1988, which may explain why some
participants in the thread have said RG-59/U is suitable.
Relevant excerpts:
Page 1-3:
"RG-62 (Belden #86262 or equivalent), as recommended for ARCNET
installation since 1977.
RG-59/U (Belden #89108 or equivalent), suitable for use with both ARCNET
and MINX real-time video teleconferencing systems."
They also say:
"RG-62 cable
  The key advantage of RG-62 coaxial cable is its high propagation
  velocity and low attenuation at ARCNET frequencies. This permits cable
  lengths of up to 2,000 feet between hubs and RIMs (or between hubs).
RG-59/U cable
  The key advantage of RG-59/U coaxial cable is the fact that it has the
  correct impedance and attenuation characteristics for carrying video,
  voice, and ARCNET data for the MINX product line over distances of up
  to 1,000 feet. This cable is also fully suitable for non-MINX ARCNET
  use over distances of up to 1,500 feet."
Page 1-5
"Peformance characteristics for ARCNET
  Cables that provide the following performance characteristics are
  considered adequate for the transmission of ARCNET LAN signals:
   Approximate impedance range of 75 to 93 ohms; cables outside this
   range are acceptable with appropriate baluns or other matching
   adaptors fitted to make the cable fit within the range
   Less than 11 dB total attenuation at 5 MHz over an uninterrupted
   length of cable"
Page 1-12
"RG-59/U or RG-62:
  Baluns and filters are not required to meet FCC Part 15 Class A
  standards when using the recommended RG-59/U or RG-62 coaxial cables.
  Substituting less expensive RG-59/U TV cable with less shield coverage
  may require filters to meet the emmisions standards and, for that
  reason, is not recommended. The less expensive RG-59/U variants have
  slower propagation and higher attenuation rates: they may not work at
  all."

I got all the technical data when I was looking at implementing
communication between our own design machines, and gave up and
implemented a system based on UARTS and our own line drivers
because of the uncertainty about the availability of (and difficulty
in sourcing) ARCNET interface components.
George
 * SLMR 2.1a * Shin - Device for finding furniture in the dark.
--- Maximus/2 3.01
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