From: John Miles (jmiles@pop.removethistomailme.net) Message 4 in thread Subject: Re: Wireless ethernet?? Newsgroups: rec.radio.amateur.digital.misc Date: 1999/06/10 View complete thread (4 articles) Mikael Östh wrote: > > How about building your own transmitter and reciever for the ethernet > protocoll!!?? > > Is that possible ? > suggestions?? > > Regards > Mike > osth.teknik@telia.com This message was sent via a homebrew 10-megabit Ethernet link that's been running for about 2 weeks now, so yes, it is possible. :) One approach, by Fredrik Oberg, is described at http://w1.911.telia.com/~u91105482/indexeng.html. Fredrik's circuit has a few problems as detailed, but the last I heard from him, he was achieving at least some limited success at 10 megabits. With any luck I'll have a good description of my design up on http://www.qsl.net/ke5fx within a couple of weeks, complete with schematics and .JPGs. It'll depend on how much time I have over the next couple of weekends to take everything back apart and draw the schematics. Ralph Stirling, KC3F, has graciously volunteered to translate my back-of-the-napkin schematics into a legible CAD format, but at the moment the bottleneck is entirely on my end. I will drop an announcement here when the web page is functional. In the meantime, some general hints: - The N6GN 2-megabit link at http://www.tapr.org/~n6gn/uwavelink/uwv.html (see also the 1993 ARRL Handbook) is the usual starting point for those who are interested in 10-megabit work. Substitution of the faster MC13155 for the MC13055 used in Glenn's design is the obvious first step on the road to 10-megabit compatibility. There have been various efforts to "underclock" 10-megabit Ethernet cards down to 2 megabits for direct compatibility with Glenn's circuit, but I am not sure if people are having any luck with this approach. - The 10 GHz Gunnplexers sold at http://www.shfmicro.com are great for this purpose. They have built-in varactors with good modulation characteristics for wideband FSK (as opposed to the technique of voltage-modulating the Gunn diode directly in the original N6GN design). The 10-milliwatt Gunn diodes can be upgraded to 100 milliwatts if necessary. - Watch out for DC level-shifting issues! It is NOT a good idea to feed an FSK signal at +/- 2V or so to a +8V-biased varactor through a large coupling capacitor. The coupling time constant will mangle some or all of your packet traffic. An amp such as the OPA603 can be used to apply the desired DC offset to your varactor drive signal without any AC coupling at all. I spent way too much time ignoring this type of problem. - Further to that, in my experience it's best to treat the link's entire signal chain as an analog, rather than a digital one. Your Ethernet hardware (NIC, hub, whatever) has a very broad tolerance for out-of-spec signalling levels, waveshapes, and the like. It's unnecessary to use comparators, ECL line drivers, and the like in your transceiver units. (In fact, use of two-state comparators adds an extra dimension of polarity sensitivity to the problem.) - In any dual-Gunnplexer design, you will need to use the AUI (Attachment Unit Interface) port on your network hardware. The immediate temptation is to use 10BaseT directly, but the local echo generated by the Gunnplexers will be interpreted as a collision on every outgoing packet under 10BaseT. - Contrary to often-stated dogma from the Ethernet gurus, collision detection is not worth losing sleep over in the real world. If separation of two busy collision domains is required, simply use bridges or switching hubs to calm things down. A two-station point-to-point link will end up looking like an AUI crossover cable, which is an illegitimate but perfectly-functional hack. The collision pairs on the AUI ports are left unconnected. More later, hopefully. -- jm KE5FX ------------------------------------------------------ Note: My E-mail address has been altered to avoid spam ------------------------------------------------------