jwk@SCRIPPS.EDU ("Two Sheds" Kupec) (10/21/89)
Hi, I've got an thick-wire Ethernet that may be running over the max length restriction (500m = 1640ft). I've asked the local networking gurus the following and have not gotten the cut and dried answer I seek: 1. An N-type barrel connector equals how many feet of thick coax? 2. A tranceiver tap equals how many feet of thick coax? To ask it another way: What is the effective length of a 400' section of coax with n barrels and x taps? TIA, jwk@scripps.edu
c11234@D1.DARTMOUTH.EDU (Stan Dunten) (10/24/89)
We have a Time Domain Reflectometer (TDR). I use that to measure the total loss of a coax segment, connectors, tranceivers, and all. The spec says that the total loss should be less than 6 DB. If you get your hands on a TDR be aware that it may send a positive pulse which drives the tranceivers out of their linear range. We use a transformer to invert the pulse. Remember that I check a segment for total loss but recall seeing about -15 DB returns from tranceivers and -30 DB returns from connectors. Used an Excel spreadsheet to convert DB returns to feet of cable: Loss/Ft from enet spec = -6DB/(500M*3.28) = -0.0037 DB/Ft Ref DB -10 -15 -20 -25 -30 Ref Power 10^(R2C/10) 0.100 0.032 0.010 0.003 0.001 For Power 1-R3C 0.900 0.968 0.990 0.997 0.999 For Loss DB 10*LOG10(R4C) -0.458 -0.140 -0.044 -0.014 -0.004 Len Feet R5C/-0.0037 125 38 12 4 1 So a tranceiver is good for 40' and a connector for 1'. Disclamer: I wouldn't trust these numbers to within a factor of two. We use 75 ohm low loss CATV coax ($.30/ft and about half the loss). Have run segments of 3400'. With 50 ohm coax the impact of a tranceiver would be less and a connector more.