On Wednesday, September 14, 2016 at 3:07:15 PM UTC-4, John Larkin wrote:> On Wed, 14 Sep 2016 10:26:07 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Wednesday, September 14, 2016 at 12:23:37 PM UTC-4, John Larkin wrote: > >> On Wed, 14 Sep 2016 08:46:25 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >On Wednesday, September 14, 2016 at 10:33:31 AM UTC-4, Phil Hobbs wrote: > >> >> >Is it typically done with steps or pulses? > >> >> >https://en.wikipedia.org/wiki/Time-domain_reflectometer > >> >> > >> >> >Silly question, Doesn't zero ohms, give -Vgen, 50 ohms = 0 and open = +Vgen? > >> >> > >> >> Yes, but sitting on top of the step, so it's 0, +Vgen, and +2Vgen. > >> >> > >> >> Cheers > >> >> > >> >> Phil Hobbs > >> > > >> >Got it, a step then... I should make one. (someday.) > >> >https://www.youtube.com/watch?v=9cP6w2odGUc > >> > > >> >Does the 74AC series have the fastest edges? (Without going ECL crazy.) > >> > > >> >George H. > >> > >> AC is usually sub-ns. Some of the Tiny Logic parts get to around 600 > >> ps. Parallel all three sections of a NL37WZ16 for a brutal step > >> generator. > >> > >> But ECL crazy is better, if you have a fast scope. > >> > >> I have a pcb layout for a fast, cheap, maybe 60 ps TDR, but I haven't > >> had time to build it. > > > >Well just sorta thinking of a product to sell for student use. > >Into a 'scope.. (say 100-200 Mhz) So ~1-2ns edges would be fast enough. > > > >Maybe put together sections (say ~6') of 50 ohm and 75 ohm coax and > >measure the different lengths. (As well as changing the termination.) > > > >AoE3 has a nice appendix on all this stuff... I was just reading it the > >other day. And yeah, I'd want to do both TDR and TDT. > > > >George H. > > A little box with a few connectors and a wall-wart could be a nice 1 > ns TDR/TDT. Maybe $5 worth of electronic components. I could work on > that with you, just for fun. >Thanks John, My boss would have a cow if I suggested it. But maybe I could do it in my "free" time, and then just present it. It would be nice if it did both a short pulse and a fast step. BNC connectors, the box would cost more than ~$5 so spending a bit more on electronics is no big deal. Getting the connections to bnc's inside the box such that it doesn't distort the fast edge is where I might need help. (The few times I've done something fast like that, I've just used little sections of coax to pipe signals around.) I've not done any controlled impedance traces. Could I do it with a double sided pcb? (That's sorta our standard, and I could piggy back a pcb onto some other project/ prototype.) Let me think more. George H.> > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Coax modelling question
Started by ●September 13, 2016
Reply by ●September 14, 20162016-09-14
Reply by ●September 14, 20162016-09-14
On Wed, 14 Sep 2016 12:43:37 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Wednesday, September 14, 2016 at 3:07:15 PM UTC-4, John Larkin wrote: >> On Wed, 14 Sep 2016 10:26:07 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >> >On Wednesday, September 14, 2016 at 12:23:37 PM UTC-4, John Larkin wrote: >> >> On Wed, 14 Sep 2016 08:46:25 -0700 (PDT), George Herold >> >> <gherold@teachspin.com> wrote: >> >> >> >> >On Wednesday, September 14, 2016 at 10:33:31 AM UTC-4, Phil Hobbs wrote: >> >> >> >Is it typically done with steps or pulses? � >> >> >> >https://en.wikipedia.org/wiki/Time-domain_reflectometer >> >> >> >> >> >> >Silly question, Doesn't zero ohms, give -Vgen, 50 ohms = 0 and open = +Vgen? >> >> >> >> >> >> Yes, but sitting on top of the step, so it's 0, +Vgen, and +2Vgen. >> >> >> >> >> >> Cheers >> >> >> >> >> >> Phil Hobbs >> >> > >> >> >Got it, a step then... I should make one. (someday.) >> >> >https://www.youtube.com/watch?v=9cP6w2odGUc >> >> > >> >> >Does the 74AC series have the fastest edges? (Without going ECL crazy.) >> >> > >> >> >George H. >> >> >> >> AC is usually sub-ns. Some of the Tiny Logic parts get to around 600 >> >> ps. Parallel all three sections of a NL37WZ16 for a brutal step >> >> generator. >> >> >> >> But ECL crazy is better, if you have a fast scope. >> >> >> >> I have a pcb layout for a fast, cheap, maybe 60 ps TDR, but I haven't >> >> had time to build it. >> > >> >Well just sorta thinking of a product to sell for student use. >> >Into a 'scope.. (say 100-200 Mhz) So ~1-2ns edges would be fast enough. >> > >> >Maybe put together sections (say ~6') of 50 ohm and 75 ohm coax and >> >measure the different lengths. (As well as changing the termination.) >> > >> >AoE3 has a nice appendix on all this stuff... I was just reading it the >> >other day. And yeah, I'd want to do both TDR and TDT. >> > >> >George H. >> >> A little box with a few connectors and a wall-wart could be a nice 1 >> ns TDR/TDT. Maybe $5 worth of electronic components. I could work on >> that with you, just for fun. >> >Thanks John, My boss would have a cow if I suggested it. But maybe >I could do it in my "free" time, and then just present it.Your boss needs more imagination.> >It would be nice if it did both a short pulse and a fast step. >BNC connectors, the box would cost more than ~$5 so spending >a bit more on electronics is no big deal.Pulse and step would be easy.> >Getting the connections to bnc's inside the box such that >it doesn't distort the fast edge is where I might need help. >(The few times I've done something fast like that, I've just used >little sections of coax to pipe signals around.) >1 ns is practically audio! Things get harder around 100 ps.>I've not done any controlled impedance traces. >Could I do it with a double sided pcb? (That's sorta our standard, >and I could piggy back a pcb onto some other project/ prototype.)It might be done double-sided, but 4 layer would be much better. Probably 1 ns on 2 layers would work.> >Let me think more.OK, let me know if you want to play with this. I do have a simple deconvolution algorithm that can beautify an ugly step waveform. Suck a waveform out of the scope into a PC and pass it through an adaptive FIR filter to pretty it up. That might make the product more interesting; add some signals+systems math. https://dl.dropboxusercontent.com/u/53724080/TDR/TDR_Decon_demo.jpg -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 14, 20162016-09-14
On Wed, 14 Sep 2016 15:21:47 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 09/14/2016 03:11 PM, John Larkin wrote: >> On Wed, 14 Sep 2016 13:06:27 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 09/14/2016 11:59 AM, John Larkin wrote: >>>> On Wed, 14 Sep 2016 07:10:42 -0700 (PDT), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Tuesday, September 13, 2016 at 10:27:32 PM UTC-4, John Larkin wrote: >>>>>> On Tue, 13 Sep 2016 18:01:06 -0700 (PDT), George Herold >>>>>> <gherold@teachspin.com> wrote: >>>>>> >>>>>>> On Tuesday, September 13, 2016 at 4:07:30 PM UTC-4, John Larkin wrote: >>>>>>>> On Tue, 13 Sep 2016 12:49:27 -0700 (PDT), George Herold >>>>>>>> <gherold@teachspin.com> wrote: >>>>>>>> >>>>>>>>> On Tuesday, September 13, 2016 at 3:34:35 PM UTC-4, John Larkin wrote: >>>>>>>>>> On Tue, 13 Sep 2016 17:34:56 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> On 13/09/2016 16:34, John Larkin wrote: >>>>>>>>>>>> On Tue, 13 Sep 2016 09:51:04 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> I can model a coax cable in LT spice using the inbuilt model or a lumped >>>>>>>>>>>>> collection of R C and L. >>>>>>>>>>>>> >>>>>>>>>>>>> But the cable I want to model has no overall screen insulation, and >>>>>>>>>>>>> somewhere between most and hardly any of it is very tightly wound onto a >>>>>>>>>>>>> drum, so the outer on the drum is all 'shorted' together. The outer is >>>>>>>>>>>>> steel and has the same order of resistance as the copper inner. >>>>>>>>>>>>> >>>>>>>>>>>>> That means there is part of the cable which looks like, I suppose, a >>>>>>>>>>>>> mass of steel with an embedded coil. >>>>>>>>>>>>> >>>>>>>>>>>>> I don't have a cable to hand. >>>>>>>>>>>>> >>>>>>>>>>>>> How would you go about modelling this? I suppose that for the wound >>>>>>>>>>>>> section, the R reduces, the C remains the same, but I'm not sure what to >>>>>>>>>>>>> think about the L. >>>>>>>>>>>>> >>>>>>>>>>>>> Cheers >>>>>>>>>>>> >>>>>>>>>>>> Are you talking about a spool of insulated wire inside a metal bucket? >>>>>>>>>>> >>>>>>>>>>> I suppose a loosley wound spool of insulated wire in a cylinder of >>>>>>>>>>> mercury might approximate. >>>>>>>>>>> >>>>>>>>>>>> That would have various amounts of wire-wire coupling, which will >>>>>>>>>>>> cause all sorts of nasty effects. >>>>>>>>>>>> >>>>>>>>>>>> A sketch would help. >>>>>>>>>>> >>>>>>>>>>> Just take some coax, strip off the outer insulation and wind it on a drum. >>>>>>>>>>>> >>>>>>>>>>>> "somewhere between most and hardly any" makes modeling difficult. >>>>>>>>>>> >>>>>>>>>>> Yes, but that's the reality. >>>>>>>>>>> >>>>>>>>>>>> What is this for? >>>>>>>>>>> >>>>>>>>>>> A long cable (a wireline) for use in boreholes. The outer is steel >>>>>>>>>>> armour for strength and has no insulation covering it. The inner is >>>>>>>>>>> copper and there's a dielectric, probably PTFE. It's partly on and >>>>>>>>>>> partly off a winch drum. Instruments at the bottom of the hole send >>>>>>>>>>> signals to equipment at the top, sometimes vice-versa. >>>>>>>>>>> >>>>>>>>>>> I'm not sure what happens to the inductance of the part on the drum >>>>>>>>>>> compared the the length in the borehole. You'll have the effect of the >>>>>>>>>>> shorted outer, which must reduce overall inductance and resistance, and >>>>>>>>>>> then the fact that the inner is making a big coil, with possibly many >>>>>>>>>>> hundreds of turns on a 1 or 2 metre diameter. >>>>>>>>>>> >>>>>>>>>>> So does the inductance increase or decrease with winding? >>>>>>>>>>> >>>>>>>>>>> Cheers >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> I'm guessing (free, no charge) that it will behave just like a >>>>>>>>>> straight coax. Winding it on the drum should have no effect beyond any >>>>>>>>>> mechanical distortion, and a little resistance change as the shield >>>>>>>>>> turns scrape. >>>>>>>>>> >>>>>>>>>> If the signal is balanced (no sneaky ground currents) the coax behaves >>>>>>>>>> like a N-ohm transmission line, where N can be calculated from the >>>>>>>>>> standard coax equation (or use Appcad.) There should be no additional >>>>>>>>>> inductance. >>>>>>>>>> >>>>>>>>> This may not be practical for Syd, but I was thinking it would be nice to have data. >>>>>>>>> Hit the big coax with a pulse or step, with the end open or shorted and see what >>>>>>>>> the reflection looks like in both cases. (wound on spool and unwound.) >>>>>>>> >>>>>>>> That's TDR, which can be done with a pulse generator and a scope for >>>>>>>> longish runs. That could be mocked up pretty easily, with some >>>>>>>> stripped coax. >>>>>>>> >>>>>>> OK I've only done it with a big spool (~100') of coax. >>>>>>> The great thing about hitting it with a nice >>>>>>> sharp edge is you get all the frequencies at one shot. >>>>>>> (The hard part, (I'm guessing) is figuring out what it means.) >>>>>>> But looking for difference's is easy enough. >>>>>>> >>>>>>> George H. >>>>>> >>>>>> TDR is approximately a graph of impedance vs distance. The vertical >>>>>> scale is actually reflection coefficient, from 0 ohms to infinite ohms >>>>>> over the span of 0 volts to Vgen. >>>>> >>>>> Yeah I get it "in theory", I've never done it "in practice". It would be >>>>> a nice technique to put in my bag of tricks. >>>>> Is it typically done with steps or pulses? >>>>> https://en.wikipedia.org/wiki/Time-domain_reflectometer >>>> >>>> Electrical is usually steps, optical is usually a narrow pulse. >>> >>> I recently got a chance to try out an OTDR, for an expert witness case. >>> They're fun. The main difference from electrical is that you get a >>> pretty strong Rayleigh backscatter signal that allows a direct >>> measurement of the fibre loss. >>> >>> (Also just put in an offer on a _brand new_ 2012 Mustang convertible >>> with a 6-speed manual. They're even more fun.) >>> >>> Cheers >>> >>> Phil Hobbs >> >> Mo and I rented a red convertible Mustang in Massechusetts a few years >> back. We hated it. It was an immense struggle to get the top up or >> down. The instruments were basically invisible. I thought everything >> felt tacky. >> >> >The old ones were horrible, I agree, especially the V6. However, they >changed it completely for the 2011 model year, and it's pretty nice, >actually. The V6 is faster than the 5-litre 2010 GT. It also doesn't >have the GT's super-fascist traction control software--in those things >you have to have the wheel pointed dead straight or it won't give you >full power. All the budding Mario Andrettis with mid-life crises have >to be protected from themselves, I suppose. > >It's amusing to drive a 5-year-old car with 150 miles on the odo. > >Cheers > >Phil "Too old for a mid-life crisis" HobbsWhen I got the flaming red 156-MPH Audi, I had to explain to Mo that it's just a red car. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●September 14, 20162016-09-14
On Wed, 14 Sep 2016 13:06:27 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 09/14/2016 11:59 AM, John Larkin wrote: >> On Wed, 14 Sep 2016 07:10:42 -0700 (PDT), George Herold >> <gherold@teachspin.com> wrote: >> >>> On Tuesday, September 13, 2016 at 10:27:32 PM UTC-4, John Larkin wrote: >>>> On Tue, 13 Sep 2016 18:01:06 -0700 (PDT), George Herold >>>> <gherold@teachspin.com> wrote: >>>> >>>>> On Tuesday, September 13, 2016 at 4:07:30 PM UTC-4, John Larkin wrote: >>>>>> On Tue, 13 Sep 2016 12:49:27 -0700 (PDT), George Herold >>>>>> <gherold@teachspin.com> wrote: >>>>>> >>>>>>> On Tuesday, September 13, 2016 at 3:34:35 PM UTC-4, John Larkin wrote: >>>>>>>> On Tue, 13 Sep 2016 17:34:56 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>> wrote: >>>>>>>> >>>>>>>>> On 13/09/2016 16:34, John Larkin wrote: >>>>>>>>>> On Tue, 13 Sep 2016 09:51:04 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>> wrote: >>>>>>>>>> >>>>>>>>>>> I can model a coax cable in LT spice using the inbuilt model or a lumped >>>>>>>>>>> collection of R C and L. >>>>>>>>>>> >>>>>>>>>>> But the cable I want to model has no overall screen insulation, and >>>>>>>>>>> somewhere between most and hardly any of it is very tightly wound onto a >>>>>>>>>>> drum, so the outer on the drum is all 'shorted' together. The outer is >>>>>>>>>>> steel and has the same order of resistance as the copper inner. >>>>>>>>>>> >>>>>>>>>>> That means there is part of the cable which looks like, I suppose, a >>>>>>>>>>> mass of steel with an embedded coil. >>>>>>>>>>> >>>>>>>>>>> I don't have a cable to hand. >>>>>>>>>>> >>>>>>>>>>> How would you go about modelling this? I suppose that for the wound >>>>>>>>>>> section, the R reduces, the C remains the same, but I'm not sure what to >>>>>>>>>>> think about the L. >>>>>>>>>>> >>>>>>>>>>> Cheers >>>>>>>>>> >>>>>>>>>> Are you talking about a spool of insulated wire inside a metal bucket? >>>>>>>>> >>>>>>>>> I suppose a loosley wound spool of insulated wire in a cylinder of >>>>>>>>> mercury might approximate. >>>>>>>>> >>>>>>>>>> That would have various amounts of wire-wire coupling, which will >>>>>>>>>> cause all sorts of nasty effects. >>>>>>>>>> >>>>>>>>>> A sketch would help. >>>>>>>>> >>>>>>>>> Just take some coax, strip off the outer insulation and wind it on a drum. >>>>>>>>>> >>>>>>>>>> "somewhere between most and hardly any" makes modeling difficult. >>>>>>>>> >>>>>>>>> Yes, but that's the reality. >>>>>>>>> >>>>>>>>>> What is this for? >>>>>>>>> >>>>>>>>> A long cable (a wireline) for use in boreholes. The outer is steel >>>>>>>>> armour for strength and has no insulation covering it. The inner is >>>>>>>>> copper and there's a dielectric, probably PTFE. It's partly on and >>>>>>>>> partly off a winch drum. Instruments at the bottom of the hole send >>>>>>>>> signals to equipment at the top, sometimes vice-versa. >>>>>>>>> >>>>>>>>> I'm not sure what happens to the inductance of the part on the drum >>>>>>>>> compared the the length in the borehole. You'll have the effect of the >>>>>>>>> shorted outer, which must reduce overall inductance and resistance, and >>>>>>>>> then the fact that the inner is making a big coil, with possibly many >>>>>>>>> hundreds of turns on a 1 or 2 metre diameter. >>>>>>>>> >>>>>>>>> So does the inductance increase or decrease with winding? >>>>>>>>> >>>>>>>>> Cheers >>>>>>>> >>>>>>>> >>>>>>>> I'm guessing (free, no charge) that it will behave just like a >>>>>>>> straight coax. Winding it on the drum should have no effect beyond any >>>>>>>> mechanical distortion, and a little resistance change as the shield >>>>>>>> turns scrape. >>>>>>>> >>>>>>>> If the signal is balanced (no sneaky ground currents) the coax behaves >>>>>>>> like a N-ohm transmission line, where N can be calculated from the >>>>>>>> standard coax equation (or use Appcad.) There should be no additional >>>>>>>> inductance. >>>>>>>> >>>>>>> This may not be practical for Syd, but I was thinking it would be nice to have data. >>>>>>> Hit the big coax with a pulse or step, with the end open or shorted and see what >>>>>>> the reflection looks like in both cases. (wound on spool and unwound.) >>>>>> >>>>>> That's TDR, which can be done with a pulse generator and a scope for >>>>>> longish runs. That could be mocked up pretty easily, with some >>>>>> stripped coax. >>>>>> >>>>> OK I've only done it with a big spool (~100') of coax. >>>>> The great thing about hitting it with a nice >>>>> sharp edge is you get all the frequencies at one shot. >>>>> (The hard part, (I'm guessing) is figuring out what it means.) >>>>> But looking for difference's is easy enough. >>>>> >>>>> George H. >>>> >>>> TDR is approximately a graph of impedance vs distance. The vertical >>>> scale is actually reflection coefficient, from 0 ohms to infinite ohms >>>> over the span of 0 volts to Vgen. >>> >>> Yeah I get it "in theory", I've never done it "in practice". It would be >>> a nice technique to put in my bag of tricks. >>> Is it typically done with steps or pulses? >>> https://en.wikipedia.org/wiki/Time-domain_reflectometer >> >> Electrical is usually steps, optical is usually a narrow pulse. > >I recently got a chance to try out an OTDR, for an expert witness case. >They're fun. The main difference from electrical is that you get a >pretty strong Rayleigh backscatter signal that allows a direct >measurement of the fibre loss. > >(Also just put in an offer on a _brand new_ 2012 Mustang convertible >with a 6-speed manual. They're even more fun.) > >Cheers > >Phil HobbsWanna drag ?>:-} ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | STV, Queen Creek, AZ 85142 Skype: skypeanalog | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I'm looking for work... see my website.
Reply by ●September 14, 20162016-09-14
>Wanna drag ?>:-}Nah, never was my style except in boats. I'm getting the 6-sec zero-to-sixty model and no the 4-sec model. That's lots fast enough for grins. Now all I need is a box of ball caps in the back seat, for when the one I'm wearing blows off in the wind. ;) Cheers Phil Hobbs
Reply by ●September 14, 20162016-09-14
On Wednesday, September 14, 2016 at 4:04:19 PM UTC-4, John Larkin wrote:> On Wed, 14 Sep 2016 12:43:37 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: > > >On Wednesday, September 14, 2016 at 3:07:15 PM UTC-4, John Larkin wrote: > >> On Wed, 14 Sep 2016 10:26:07 -0700 (PDT), George Herold > >> <gherold@teachspin.com> wrote: > >> > >> >On Wednesday, September 14, 2016 at 12:23:37 PM UTC-4, John Larkin wrote: > >> >> On Wed, 14 Sep 2016 08:46:25 -0700 (PDT), George Herold > >> >> <gherold@teachspin.com> wrote: > >> >> > >> >> >On Wednesday, September 14, 2016 at 10:33:31 AM UTC-4, Phil Hobbs wrote: > >> >> >> >Is it typically done with steps or pulses? > >> >> >> >https://en.wikipedia.org/wiki/Time-domain_reflectometer > >> >> >> > >> >> >> >Silly question, Doesn't zero ohms, give -Vgen, 50 ohms = 0 and open = +Vgen? > >> >> >> > >> >> >> Yes, but sitting on top of the step, so it's 0, +Vgen, and +2Vgen. > >> >> >> > >> >> >> Cheers > >> >> >> > >> >> >> Phil Hobbs > >> >> > > >> >> >Got it, a step then... I should make one. (someday.) > >> >> >https://www.youtube.com/watch?v=9cP6w2odGUc > >> >> > > >> >> >Does the 74AC series have the fastest edges? (Without going ECL crazy.) > >> >> > > >> >> >George H. > >> >> > >> >> AC is usually sub-ns. Some of the Tiny Logic parts get to around 600 > >> >> ps. Parallel all three sections of a NL37WZ16 for a brutal step > >> >> generator. > >> >> > >> >> But ECL crazy is better, if you have a fast scope. > >> >> > >> >> I have a pcb layout for a fast, cheap, maybe 60 ps TDR, but I haven't > >> >> had time to build it. > >> > > >> >Well just sorta thinking of a product to sell for student use. > >> >Into a 'scope.. (say 100-200 Mhz) So ~1-2ns edges would be fast enough. > >> > > >> >Maybe put together sections (say ~6') of 50 ohm and 75 ohm coax and > >> >measure the different lengths. (As well as changing the termination.) > >> > > >> >AoE3 has a nice appendix on all this stuff... I was just reading it the > >> >other day. And yeah, I'd want to do both TDR and TDT. > >> > > >> >George H. > >> > >> A little box with a few connectors and a wall-wart could be a nice 1 > >> ns TDR/TDT. Maybe $5 worth of electronic components. I could work on > >> that with you, just for fun. > >> > >Thanks John, My boss would have a cow if I suggested it. But maybe > >I could do it in my "free" time, and then just present it. > > Your boss needs more imagination.Well that's a discussion that would take at least two beers.> > > > > >It would be nice if it did both a short pulse and a fast step. > >BNC connectors, the box would cost more than ~$5 so spending > >a bit more on electronics is no big deal. > > Pulse and step would be easy.That's what I figured, say a 10 -20 ns pulse. I think students would understand the pulse more easily.> > > > >Getting the connections to bnc's inside the box such that > >it doesn't distort the fast edge is where I might need help. > >(The few times I've done something fast like that, I've just used > >little sections of coax to pipe signals around.) > > > > 1 ns is practically audio! Things get harder around 100 ps. > > > >I've not done any controlled impedance traces. > >Could I do it with a double sided pcb? (That's sorta our standard, > >and I could piggy back a pcb onto some other project/ prototype.) > > It might be done double-sided, but 4 layer would be much better. > Probably 1 ns on 2 layers would work. > > > > > >Let me think more. > > OK, let me know if you want to play with this.Yeah I'll get some 74AC somethings and make some edges.. see what things look like on various 'scopes. We've got no fast 'scopes (200 MHz max)> > I do have a simple deconvolution algorithm that can beautify an ugly > step waveform. Suck a waveform out of the scope into a PC and pass it > through an adaptive FIR filter to pretty it up. That might make the > product more interesting; add some signals+systems math. > > https://dl.dropboxusercontent.com/u/53724080/TDR/TDR_Decon_demo.jpgYeah that would be kinda fun too... The big issue is that making little ~$100-200 dollar boxes (even $500) and selling 10 - 20 of them a year just does not make enough money to pay for development and such. We've never sold to much more than physics departments. And I'm not sure how many of them will have any interest. We could sell only 10 units total! Anyway don't hold your breathe. George H.> > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
Reply by ●September 14, 20162016-09-14
On Wed, 14 Sep 2016 15:28:21 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 09/14/2016 03:21 PM, krw wrote: >> On Wed, 14 Sep 2016 15:14:04 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 09/14/2016 02:53 PM, krw wrote: >>>> On Wed, 14 Sep 2016 13:06:27 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>>> >>>>> On 09/14/2016 11:59 AM, John Larkin wrote: >>>>>> On Wed, 14 Sep 2016 07:10:42 -0700 (PDT), George Herold >>>>>> <gherold@teachspin.com> wrote: >>>>>> >>>>>>> On Tuesday, September 13, 2016 at 10:27:32 PM UTC-4, John Larkin wrote: >>>>>>>> On Tue, 13 Sep 2016 18:01:06 -0700 (PDT), George Herold >>>>>>>> <gherold@teachspin.com> wrote: >>>>>>>> >>>>>>>>> On Tuesday, September 13, 2016 at 4:07:30 PM UTC-4, John Larkin wrote: >>>>>>>>>> On Tue, 13 Sep 2016 12:49:27 -0700 (PDT), George Herold >>>>>>>>>> <gherold@teachspin.com> wrote: >>>>>>>>>> >>>>>>>>>>> On Tuesday, September 13, 2016 at 3:34:35 PM UTC-4, John Larkin wrote: >>>>>>>>>>>> On Tue, 13 Sep 2016 17:34:56 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>>>> wrote: >>>>>>>>>>>> >>>>>>>>>>>>> On 13/09/2016 16:34, John Larkin wrote: >>>>>>>>>>>>>> On Tue, 13 Sep 2016 09:51:04 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>>>>>> wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>>> I can model a coax cable in LT spice using the inbuilt model or a lumped >>>>>>>>>>>>>>> collection of R C and L. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> But the cable I want to model has no overall screen insulation, and >>>>>>>>>>>>>>> somewhere between most and hardly any of it is very tightly wound onto a >>>>>>>>>>>>>>> drum, so the outer on the drum is all 'shorted' together. The outer is >>>>>>>>>>>>>>> steel and has the same order of resistance as the copper inner. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> That means there is part of the cable which looks like, I suppose, a >>>>>>>>>>>>>>> mass of steel with an embedded coil. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> I don't have a cable to hand. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> How would you go about modelling this? I suppose that for the wound >>>>>>>>>>>>>>> section, the R reduces, the C remains the same, but I'm not sure what to >>>>>>>>>>>>>>> think about the L. >>>>>>>>>>>>>>> >>>>>>>>>>>>>>> Cheers >>>>>>>>>>>>>> >>>>>>>>>>>>>> Are you talking about a spool of insulated wire inside a metal bucket? >>>>>>>>>>>>> >>>>>>>>>>>>> I suppose a loosley wound spool of insulated wire in a cylinder of >>>>>>>>>>>>> mercury might approximate. >>>>>>>>>>>>> >>>>>>>>>>>>>> That would have various amounts of wire-wire coupling, which will >>>>>>>>>>>>>> cause all sorts of nasty effects. >>>>>>>>>>>>>> >>>>>>>>>>>>>> A sketch would help. >>>>>>>>>>>>> >>>>>>>>>>>>> Just take some coax, strip off the outer insulation and wind it on a drum. >>>>>>>>>>>>>> >>>>>>>>>>>>>> "somewhere between most and hardly any" makes modeling difficult. >>>>>>>>>>>>> >>>>>>>>>>>>> Yes, but that's the reality. >>>>>>>>>>>>> >>>>>>>>>>>>>> What is this for? >>>>>>>>>>>>> >>>>>>>>>>>>> A long cable (a wireline) for use in boreholes. The outer is steel >>>>>>>>>>>>> armour for strength and has no insulation covering it. The inner is >>>>>>>>>>>>> copper and there's a dielectric, probably PTFE. It's partly on and >>>>>>>>>>>>> partly off a winch drum. Instruments at the bottom of the hole send >>>>>>>>>>>>> signals to equipment at the top, sometimes vice-versa. >>>>>>>>>>>>> >>>>>>>>>>>>> I'm not sure what happens to the inductance of the part on the drum >>>>>>>>>>>>> compared the the length in the borehole. You'll have the effect of the >>>>>>>>>>>>> shorted outer, which must reduce overall inductance and resistance, and >>>>>>>>>>>>> then the fact that the inner is making a big coil, with possibly many >>>>>>>>>>>>> hundreds of turns on a 1 or 2 metre diameter. >>>>>>>>>>>>> >>>>>>>>>>>>> So does the inductance increase or decrease with winding? >>>>>>>>>>>>> >>>>>>>>>>>>> Cheers >>>>>>>>>>>> >>>>>>>>>>>> >>>>>>>>>>>> I'm guessing (free, no charge) that it will behave just like a >>>>>>>>>>>> straight coax. Winding it on the drum should have no effect beyond any >>>>>>>>>>>> mechanical distortion, and a little resistance change as the shield >>>>>>>>>>>> turns scrape. >>>>>>>>>>>> >>>>>>>>>>>> If the signal is balanced (no sneaky ground currents) the coax behaves >>>>>>>>>>>> like a N-ohm transmission line, where N can be calculated from the >>>>>>>>>>>> standard coax equation (or use Appcad.) There should be no additional >>>>>>>>>>>> inductance. >>>>>>>>>>>> >>>>>>>>>>> This may not be practical for Syd, but I was thinking it would be nice to have data. >>>>>>>>>>> Hit the big coax with a pulse or step, with the end open or shorted and see what >>>>>>>>>>> the reflection looks like in both cases. (wound on spool and unwound.) >>>>>>>>>> >>>>>>>>>> That's TDR, which can be done with a pulse generator and a scope for >>>>>>>>>> longish runs. That could be mocked up pretty easily, with some >>>>>>>>>> stripped coax. >>>>>>>>>> >>>>>>>>> OK I've only done it with a big spool (~100') of coax. >>>>>>>>> The great thing about hitting it with a nice >>>>>>>>> sharp edge is you get all the frequencies at one shot. >>>>>>>>> (The hard part, (I'm guessing) is figuring out what it means.) >>>>>>>>> But looking for difference's is easy enough. >>>>>>>>> >>>>>>>>> George H. >>>>>>>> >>>>>>>> TDR is approximately a graph of impedance vs distance. The vertical >>>>>>>> scale is actually reflection coefficient, from 0 ohms to infinite ohms >>>>>>>> over the span of 0 volts to Vgen. >>>>>>> >>>>>>> Yeah I get it "in theory", I've never done it "in practice". It would be >>>>>>> a nice technique to put in my bag of tricks. >>>>>>> Is it typically done with steps or pulses? >>>>>>> https://en.wikipedia.org/wiki/Time-domain_reflectometer >>>>>> >>>>>> Electrical is usually steps, optical is usually a narrow pulse. >>>>> >>>>> I recently got a chance to try out an OTDR, for an expert witness case. >>>>> They're fun. The main difference from electrical is that you get a >>>>> pretty strong Rayleigh backscatter signal that allows a direct >>>>> measurement of the fibre loss. >>>>> >>>>> (Also just put in an offer on a _brand new_ 2012 Mustang convertible >>>>> with a 6-speed manual. They're even more fun.) >>>> >>>> My wife drives a '14 ruby red convertible, though it's an automatic >>>> 6-cyl. The '15s and '16s are better cars, though I think they look >>>> too much like a Beamer. >>> >>> I don't like the look of the new body style, though, and the IoT-style >>> spying is all over the new ones. Plus the dealer has had this one >>> sitting around for five years and is, shall we say, motivated. ;) >> >> I don't much like the Beamer look, either. Of all the body tweaks >> since '05, I like the '13-'14 body style the best. >> >> Not sure I'd like it sitting around for five years, though. >> >>> >>> Now to get it painted electric blue. >> >> Nice color. What color is it? Top? > >Currently white with a black top and black leather interior. The exact >colour scheme of my Mum's old Dodge Dart.Kinda plain but not an outrageously ugly combination. It's surprising that it didn't sell.> >Gotta get the dickey spoiler off the trunk lid, too.They're useless but I don't find them objectionable. I wouldn't want to patch holes, just to get rid of it.> >Soft tops last better in the NE than down your way, I expect, and for >the price difference, I can buy a lot of soft tops.We get a lot more use out of them down this way, too. ;-) My wife drives with her top down half the year. ;-)
Reply by ●September 14, 20162016-09-14
On Wed, 14 Sep 2016 13:07:33 -0700, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On Wed, 14 Sep 2016 15:21:47 -0400, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote: > >>On 09/14/2016 03:11 PM, John Larkin wrote: >>> On Wed, 14 Sep 2016 13:06:27 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 09/14/2016 11:59 AM, John Larkin wrote: >>>>> On Wed, 14 Sep 2016 07:10:42 -0700 (PDT), George Herold >>>>> <gherold@teachspin.com> wrote: >>>>> >>>>>> On Tuesday, September 13, 2016 at 10:27:32 PM UTC-4, John Larkin wrote: >>>>>>> On Tue, 13 Sep 2016 18:01:06 -0700 (PDT), George Herold >>>>>>> <gherold@teachspin.com> wrote: >>>>>>> >>>>>>>> On Tuesday, September 13, 2016 at 4:07:30 PM UTC-4, John Larkin wrote: >>>>>>>>> On Tue, 13 Sep 2016 12:49:27 -0700 (PDT), George Herold >>>>>>>>> <gherold@teachspin.com> wrote: >>>>>>>>> >>>>>>>>>> On Tuesday, September 13, 2016 at 3:34:35 PM UTC-4, John Larkin wrote: >>>>>>>>>>> On Tue, 13 Sep 2016 17:34:56 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>>> wrote: >>>>>>>>>>> >>>>>>>>>>>> On 13/09/2016 16:34, John Larkin wrote: >>>>>>>>>>>>> On Tue, 13 Sep 2016 09:51:04 +0100, Syd Rumpo <usenet@nononono.co.uk> >>>>>>>>>>>>> wrote: >>>>>>>>>>>>> >>>>>>>>>>>>>> I can model a coax cable in LT spice using the inbuilt model or a lumped >>>>>>>>>>>>>> collection of R C and L. >>>>>>>>>>>>>> >>>>>>>>>>>>>> But the cable I want to model has no overall screen insulation, and >>>>>>>>>>>>>> somewhere between most and hardly any of it is very tightly wound onto a >>>>>>>>>>>>>> drum, so the outer on the drum is all 'shorted' together. The outer is >>>>>>>>>>>>>> steel and has the same order of resistance as the copper inner. >>>>>>>>>>>>>> >>>>>>>>>>>>>> That means there is part of the cable which looks like, I suppose, a >>>>>>>>>>>>>> mass of steel with an embedded coil. >>>>>>>>>>>>>> >>>>>>>>>>>>>> I don't have a cable to hand. >>>>>>>>>>>>>> >>>>>>>>>>>>>> How would you go about modelling this? I suppose that for the wound >>>>>>>>>>>>>> section, the R reduces, the C remains the same, but I'm not sure what to >>>>>>>>>>>>>> think about the L. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Cheers >>>>>>>>>>>>> >>>>>>>>>>>>> Are you talking about a spool of insulated wire inside a metal bucket? >>>>>>>>>>>> >>>>>>>>>>>> I suppose a loosley wound spool of insulated wire in a cylinder of >>>>>>>>>>>> mercury might approximate. >>>>>>>>>>>> >>>>>>>>>>>>> That would have various amounts of wire-wire coupling, which will >>>>>>>>>>>>> cause all sorts of nasty effects. >>>>>>>>>>>>> >>>>>>>>>>>>> A sketch would help. >>>>>>>>>>>> >>>>>>>>>>>> Just take some coax, strip off the outer insulation and wind it on a drum. >>>>>>>>>>>>> >>>>>>>>>>>>> "somewhere between most and hardly any" makes modeling difficult. >>>>>>>>>>>> >>>>>>>>>>>> Yes, but that's the reality. >>>>>>>>>>>> >>>>>>>>>>>>> What is this for? >>>>>>>>>>>> >>>>>>>>>>>> A long cable (a wireline) for use in boreholes. The outer is steel >>>>>>>>>>>> armour for strength and has no insulation covering it. The inner is >>>>>>>>>>>> copper and there's a dielectric, probably PTFE. It's partly on and >>>>>>>>>>>> partly off a winch drum. Instruments at the bottom of the hole send >>>>>>>>>>>> signals to equipment at the top, sometimes vice-versa. >>>>>>>>>>>> >>>>>>>>>>>> I'm not sure what happens to the inductance of the part on the drum >>>>>>>>>>>> compared the the length in the borehole. You'll have the effect of the >>>>>>>>>>>> shorted outer, which must reduce overall inductance and resistance, and >>>>>>>>>>>> then the fact that the inner is making a big coil, with possibly many >>>>>>>>>>>> hundreds of turns on a 1 or 2 metre diameter. >>>>>>>>>>>> >>>>>>>>>>>> So does the inductance increase or decrease with winding? >>>>>>>>>>>> >>>>>>>>>>>> Cheers >>>>>>>>>>> >>>>>>>>>>> >>>>>>>>>>> I'm guessing (free, no charge) that it will behave just like a >>>>>>>>>>> straight coax. Winding it on the drum should have no effect beyond any >>>>>>>>>>> mechanical distortion, and a little resistance change as the shield >>>>>>>>>>> turns scrape. >>>>>>>>>>> >>>>>>>>>>> If the signal is balanced (no sneaky ground currents) the coax behaves >>>>>>>>>>> like a N-ohm transmission line, where N can be calculated from the >>>>>>>>>>> standard coax equation (or use Appcad.) There should be no additional >>>>>>>>>>> inductance. >>>>>>>>>>> >>>>>>>>>> This may not be practical for Syd, but I was thinking it would be nice to have data. >>>>>>>>>> Hit the big coax with a pulse or step, with the end open or shorted and see what >>>>>>>>>> the reflection looks like in both cases. (wound on spool and unwound.) >>>>>>>>> >>>>>>>>> That's TDR, which can be done with a pulse generator and a scope for >>>>>>>>> longish runs. That could be mocked up pretty easily, with some >>>>>>>>> stripped coax. >>>>>>>>> >>>>>>>> OK I've only done it with a big spool (~100') of coax. >>>>>>>> The great thing about hitting it with a nice >>>>>>>> sharp edge is you get all the frequencies at one shot. >>>>>>>> (The hard part, (I'm guessing) is figuring out what it means.) >>>>>>>> But looking for difference's is easy enough. >>>>>>>> >>>>>>>> George H. >>>>>>> >>>>>>> TDR is approximately a graph of impedance vs distance. The vertical >>>>>>> scale is actually reflection coefficient, from 0 ohms to infinite ohms >>>>>>> over the span of 0 volts to Vgen. >>>>>> >>>>>> Yeah I get it "in theory", I've never done it "in practice". It would be >>>>>> a nice technique to put in my bag of tricks. >>>>>> Is it typically done with steps or pulses? >>>>>> https://en.wikipedia.org/wiki/Time-domain_reflectometer >>>>> >>>>> Electrical is usually steps, optical is usually a narrow pulse. >>>> >>>> I recently got a chance to try out an OTDR, for an expert witness case. >>>> They're fun. The main difference from electrical is that you get a >>>> pretty strong Rayleigh backscatter signal that allows a direct >>>> measurement of the fibre loss. >>>> >>>> (Also just put in an offer on a _brand new_ 2012 Mustang convertible >>>> with a 6-speed manual. They're even more fun.) >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Mo and I rented a red convertible Mustang in Massechusetts a few years >>> back. We hated it. It was an immense struggle to get the top up or >>> down. The instruments were basically invisible. I thought everything >>> felt tacky. >>> >>> >>The old ones were horrible, I agree, especially the V6. However, they >>changed it completely for the 2011 model year, and it's pretty nice, >>actually. The V6 is faster than the 5-litre 2010 GT. It also doesn't >>have the GT's super-fascist traction control software--in those things >>you have to have the wheel pointed dead straight or it won't give you >>full power. All the budding Mario Andrettis with mid-life crises have >>to be protected from themselves, I suppose. >> >>It's amusing to drive a 5-year-old car with 150 miles on the odo. >> >>Cheers >> >>Phil "Too old for a mid-life crisis" Hobbs > >When I got the flaming red 156-MPH Audi, I had to explain to Mo that >it's just a red car.Well, in SF, it figures you drive a flamer. ;-)
Reply by ●September 14, 20162016-09-14
On Wed, 14 Sep 2016 13:22:20 -0700 (PDT), Phil Hobbs <pcdhobbs@gmail.com> wrote:>>Wanna drag ?>:-} > >Nah, never was my style except in boats. I'm getting the 6-sec zero-to-sixty model and no the 4-sec model. That's lots fast enough for grins. > >Now all I need is a box of ball caps in the back seat, for when the one I'm wearing blows off in the wind. ;)I was going to suggest one with a brim all the way around to protect the ears and neck, too, but then remembered that you live were there is no sun. ;-)
Reply by ●September 14, 20162016-09-14
On 15/09/16 02:23, John Larkin wrote:> On Wed, 14 Sep 2016 08:46:25 -0700 (PDT), George Herold > <gherold@teachspin.com> wrote: >> Does the 74AC series have the fastest edges? (Without going ECL crazy.) > AC is usually sub-ns. Some of the Tiny Logic parts get to around 600 > ps. Parallel all three sections of a NL37WZ16 for a brutal step > generator. > But ECL crazy is better, if you have a fast scope. > I have a pcb layout for a fast, cheap, maybe 60 ps TDR, but I haven't > had time to build it.I've wanted to build a TDR for my own amusement. Would you mind giving some more pointers about your circuit or the ECL parts you'd use? Clifford Heath.
