> >> From: John Wilson > > > >> I chose the digital version of EE as my major precisely because I knew > >> I'd flunk Fields and Waves. Transmission lines are black magic as far > >> as I'm concerned!
I really do fail to see how you can possibly understand or design digital systems without understanding analogue electronics, in particular transmission lines. FWIW the Motorola ECL databooks were pretty good at giving an introduction to this, simpy because with ECL you have to design just about every interconnection as a transmission line. Do it right and the design works, and unlike some other logic families where you hope for the best with the interconnections, ECL stays working. > I still have a photo copied out of the 1980s magazine RSTS Professional, > which claimed to show how to convert > thick to thin Ethernet. The simple answer is “with a coax connector adapter” > since both are 50 ohm coax. The Err, yes :-). The BNC-N adapter is very useful :-). More seriously, I've seen thickwire transceivers that had a pair of N connectors (not a beesting tap) fitted with BNC-N adapters and ues on thinwire. Technically that is wrong, there is a minor difference in the transceiver spec (I forget what, but the data sheet for at least one of the transceiver ICs pointed it out), but in will work. > article instead used a thinwire T connector, with the terminator still on it. > As Tony points out, terminators go at ARGH! Ethernet is more touchhy than most as IIRC the transmitter is a current source, the receiver effectively senses the voltage across the terminator. A collision is too high a voltage. So ethernet can't work with incorrect termination. That's why DEC had you put 2 terminators on a T piece on the ethernet BNC connector of a VAXstation (or whatever) to get it to pass diagnostics. WIth a network that short you are not going to get detectable reflection problems, but if you only had one terminator, every transmission would be a collision. -tony
