Dave, Exactly.
Sent From iPhone > On Nov 25, 2014, at 7:34, Dave Martindale <dave.martind...@gmail.com> wrote: > > The 20 MHz output should be OK, since it is series-terminated with 50 ohms > at the source and the buffer can source enough current. The driver sees a > 100 ohm load (50 ohm resistor in series with 50 ohm coax impedance) for > that 32 ns round trip time, so it will increase power dissipation (as you > note). But the load at the far end of the coax should see a clean edge, > and the reflection should be absorbed when it returns to the source (due to > the source terminator). Just don't look at the signal half way along the > coax. > > The other outputs apparently don't have either the current drive or the > source terminator, so a long piece of coax is likely to do unpleasant > things to the edge. > > In either case, if you want to run any of the signals 10 feet it's likely > better to run a very short connection from the LTE-Lite to a proper 50 ohm > line driver. That gets the power dissipation off the board, and then you > can use drivers that give you whatever output swing you want, and which can > drive a 100 ohm load continuously so you can use parallel termination at > the far end. > > - Dave > > On Tue, Nov 25, 2014 at 12:23 AM, Hal Murray <hmur...@megapathdsl.net> > wrote: > >> >> Said Jackson said: >>> Correct, and thats why its all a bad trade off if you have to use 50 Ohms >>> termination. Either more heat or more PN, and more circuitry. >> >>> So driving 50 Ohms inputs is not optimal here, 1M inputs are much better >> for >>> this purpose. >> >> That only works if you have a (very) short connection to the next stage. >> >> Things get interesting if you have, say, 10 feet of unterminated coax. >> >> 10 MHz is 100 ns, or 50 ns between transitions. Coax is ballpark of 5/8 c >> so >> that's 16 ns one way or 32 ns round drip. That's 60% of the heat as well >> as >> lots of nasty reflections. >> >> (Somebody please check my numbers.) >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.