https://en.wikipedia.org/wiki/Velocity_factor
On Sun, Dec 27, 2020 at 10:05 PM Paul Andrews <[email protected]> wrote: > Hmm. My recollection from high school physics was that the speed of > propagation along a wave guide was around 90% the speed of light - > presumably limited by the dielectric. Signals along a plain old wire, on > the other hand, were more like 1/3 the speed of light. Now I'm going to > have to double-check that for the first time in over 40 years! > > On Sunday, December 27, 2020 at 2:20:06 PM UTC-5 Chuck wrote: > >> A handy way I use, to remember the approximate speed of light, which is >> also the approximate >> >> speed at which an electrical signal travels in a wire is just to think of >> it >> >> as 1 nanosecond per foot. Approximately. >> >> >> ---- Original Message ---- >> From: "gregebert" <[email protected]> >> Sent: 12/27/2020 12:32:41 AM >> To: "neonixie-l" <[email protected]> >> Subject: Re: [neonixie-l] How close together do a controller and crystal >> need to be? >> >> I'm assuming you are routing the output signal of an oscillator, not the >> crystal signals themselves. >> >> The rise- & fall-times of the clock signal will determine how long the >> trace can be without termination. Faster edge-rates, say in the 2-3nsec >> range, will limit your trace to around 1 inch. >> Signals propagate around 150psec/inch, and if the rise/fall times are >> about 10x (or larger) longer than the flight-time, then reflections should >> not have sufficient amplitude to cause false clocking. >> >> In the example above, 1 inch of trace has a round-trip flight-time of >> 300psec. If the rise and fall delays are 3nsec or larger, you can safely >> use 1 inch of trace without using termination networks or >> controlled-impedance traces. >> >> SPICE simulations are very helpful when deciding how to design clock >> lines when you cant satisfy the above rule. >> On Saturday, December 26, 2020 at 4:06:26 PM UTC-8 Bill van Dijk wrote: >> >>> As long as there is not something very noisy on the other side of the >>> board you’ll be just fine. >>> >>> >>> >>> Bill >>> >>> >>> >>> >>> >>> *From:* [email protected] [mailto:[email protected]] *On >>> Behalf Of *Erick Anderson >>> *Sent:* Saturday, December 26, 2020 6:53 PM >>> *To:* neonixie-l <[email protected]> >>> *Subject:* [neonixie-l] How close together do a controller and crystal >>> need to be? >>> >>> >>> >>> >>> I designed a board for the 6-digit All Spectrum controller, which uses >>> the Dallas TCXO chip. That's what goes in the DIP-14 socket in the picture. >>> Right now they're as close to each other as possible. I'm thinking about >>> redesigning the board to be a bit shorter, and moving the socket into the >>> empty space at the right of the board would help. This would make the clock >>> signal trace much longer, but is that actually a problem? >>> >>> -- >>> You received this message because you are subscribed to the Google >>> Groups "neonixie-l" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> To view this discussion on the web, visit >>> https://groups.google.com/d/msgid/neonixie-l/1bbc978e-4883-4b0e-920f-d5f3ff4c4c2cn%40googlegroups.com >>> <https://groups.google.com/d/msgid/neonixie-l/1bbc978e-4883-4b0e-920f-d5f3ff4c4c2cn%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> -- >> You received this message because you are subscribed to the Google Groups >> "neonixie-l" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> >> To view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/bbe8ae0a-bb3c-4f4a-98f6-9f56bc1e1805n%40googlegroups.com >> <https://groups.google.com/d/msgid/neonixie-l/bbe8ae0a-bb3c-4f4a-98f6-9f56bc1e1805n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/480dcaf7-ce2b-45be-b8cc-bb1ee79bc5a2n%40googlegroups.com > <https://groups.google.com/d/msgid/neonixie-l/480dcaf7-ce2b-45be-b8cc-bb1ee79bc5a2n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/CALiMYruP%2BG1MwK5ivp-_SXgFPXO6AfnFPRAXNYpc68uFohPHmg%40mail.gmail.com.
