On Tue, Jan 23, 2018 at 11:12 AM, Bill Gunshannon via cctalk <cctalk at classiccmp.org> wrote: I also have a tap drill somewhere, but it was a rescue from a clean-out. I've never installed any Thicknet... so far. I did pick up a bit of yellow 10mbit cable at VCF Midwest a couple years back, and a couple of taps. I wish I had one more to make it interesting. I do have some of the boxy transceivers but with 10Base2 BNCs on the mounting plate that can also take a vampire tap mounting plate. One of my long-term low-priority projects is to mount that Ethernet segment high up on a wall, display fashion, and have 2-3 stations and AUI cables hanging down to table height for interconnecting vintage networking gear. I do have 10BaseT hubs with AUI ports and even one or two AUI<->Fiber MAUs to make it all interesting. Something I have that may be of interest here is a small box of N-connector 50 Ohm terminators. I can't ever imagining needing more than 2 pair for my entire life, so if anyone wants to swap for vintage network hardware, let me know. Mostly, I really want one or two of the clamp-on vampire taps, the kind you could unscrew from the transceiver (so that you never had to disturb the tap but you could remove a station). The last time I knew I was using Etherhose was at the South Pole in 1996 - they had a long run of it before they switched all the building interconnects to fiber. It's probably still buried there. -ethan

On 01/23/2018 12:07 PM, Marc Verdiell via cctalk wrote: I really liked that video, and the entire Alto restoration series from CuriousMarc. I've got to say, I think David Boggs saying "?very simple off the shelf stuff, for people who want to know, it's RG-8. ? This is the 50 ? version of it." I can fairly clearly see the RG-8/U on the side of the cable that David is holding at 8:01. That's good enough for me. Sure, there was probably a better alternative that came along after, with better shielding and marking bands. But it sounds like RG-8/U is definitive acceptable to me. I'll assume that David meant quality RG-8. What I don't know is if RG-8/U was used for 3 Mbps and then something else was used for 10 Mbps. -- Grant. . . . unix || die

On 01/24/2018 10:52 AM, Al Kossow via cctalk wrote: Thank you for the pictures. I really like the idea of the BNC modification. I think that would make the transceivers slightly more usable. -- Grant. . . . unix || die

And if anyone has any of the early TCL transceivers, check the tantalums on the power supply input. I've had many failures of them. On 1/24/18 10:38 AM, Al Kossow via cctalk wrote:

On 01/23/2018 09:10 AM, Bill Gunshannon via cctalk wrote: It's my understanding that the marks (black bands or other markings on the sheath) were exactly one wavelength apart. Which from what I remember ~> understand from my ham radio days is quite important. -- Grant. . . . unix || die

"Transceivers should be installed only at precise 2.5-metre intervals. This distance was chosen to not correspond to the wavelength of the signal; this ensures that the reflections from multiple taps are not in phase. These suitable points are marked on the cable with black bands." It cites "IEEE Standard 802.3<https://en.wikipedia.org/wiki/802.3>-1985;-1985. IEEE<https://en.wikipedia.org/wiki/IEEE>EE>. p. 121." bill ________________________________ From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Pete Turnbull via cctalk <cctalk at classiccmp.org> Sent: Tuesday, January 23, 2018 1:54 PM To: cctalk at classiccmp.org Subject: Re: Ethernet cable (Was: Sun3 valuations?) On 23/01/2018 16:48, Grant Taylor via cctalk wrote: No, that's quite wrong. The marks are every 2.5m (8.2 feet) wich IIRC is 1/19th of a wavelength apart, the point being to try to minimise the likelihood of connections being made where they'd suffer constructive (additive) interference and to prevent transceivers being too close together. -- Pete Pete Turnbull

If you want a real hoot try reading what <https://books.google.com/books?id=tmbgBwAAQBAJ&pg=PA212&lpg=PA212&dq=what+was+the+purpose+of+the+black+bands+on+ethernet+cables?&source=bl&ots=DV53aRJc9P&sig=3GFr8Hz_uQjFELOrnXk8x8KjKVM&hl=en&sa=X&ved=0ahUKEwj-i_j_5u7YAhVD34MKHeSQC-wQ6AEIWzAG> "A System Administrator?s Guide to Sun Workstations"<https://books.google.com/books?id=tmbgBwAAQBAJ&pg… has to say about it. Google has it available for reading. bill ________________________________ From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Grant Taylor via cctalk <cctalk at classiccmp.org> Sent: Tuesday, January 23, 2018 2:13 PM To: cctalk at classiccmp.org Subject: Re: Ethernet cable (Was: Sun3 valuations?) On 01/23/2018 12:09 PM, Bill Gunshannon via cctalk wrote: Thank you for correcting ~> educating me. #learnSomethingEveryDay -- Grant. . . . unix || die

Yes, the purpose of the marks is to make the collision mechanism reliable. Ethernet does not have any critical timing; collisions do not depend on timing. The black stripes on official Ethernet cable exists for a different reason: to get you to place the taps at positions that are NOT round multiples of a quarter wavelength. The reason: a tap is a (small) impedance bump, which causes reflections on the cable. If you have a lot of taps and they are spaced multiples of a wavelength apart, those reflections will combine to produce a large reflection, which if you're unlucky will look like a collision. If you pick the correct spacing, the reflections from the various taps are spread out across time and don't combine, so none of them add up to a strong enough pulse to be seen as a collision. This is clearly stated in the Ethernet V2 spec, section 7.6.2: Reading between the lines, it's clear you could ignore those marks and get away with it in many cases. Low tap count, for example. Other positioning that meets the "non-alignment" intent. But for large installations, using the marks ensures that you stay out of trouble. The need to have a transmission line with controlled reflections is also why the cable is required to be terminated with accurate terminating resistors, at both end points (but not at any other point :-) ) and why splices are made with constant impedance connectors (N connector barrels). Apart from the marks, the 10Base5 cable is pretty ordinary. It's not exactly RG-8/U but it is not all that differen either, and if the diameter is close enough something like RG-8/U would make an acceptable substitute. The same sort of considerations could apply to 10Base2, but there things are not as strict because the cable is shorter and the station count is significantly lower (max of 30). So the spec simply states that stations should be at least 1/2 meter apart, and that there must not be a significant stub (more than a few centimeters) between the T connector and the transceiver electronics. If you build with transmission line design rules in mind, you can make Ethernet buses out of cable of your choice, so long as it's 50 ohms and good quality components are used throughout. You can, for example, splice 10Base5 to 10Base2 (with a barrel, not a T) if you follow the more restrictive of the two configuration rules. paul