On Wed, 14 Sep 2016 18:11:12 -0400, krw <krw@nowhere.com> wrote:>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. ;-)Almost all the cars here are grey or silver or white or black. Same as most cities in the world, according to Street View. Mine is highly visible in a parking lot. I wonder how other people can find their car. -- 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 14/09/16 21:22, Phil Hobbs 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.Is that fast? I belong to a club where 12 year olds go 0-40 in 4s and 0-60 in 5s. Then it is climbing with your feet higher than your head. And when they are 14 they can, if they are safe, do it solo. Visitors usually say something like "Oh my God" when they first see it, and are occasionally heard screaming when they first do it. The last one I heard do that finished with the usual inane grin on her face, and did it all again :) https://youtu.be/gIy8381lX3A?t=21 https://www.youtube.com/watch?v=-U0Np1Laxy4 https://www.youtube.com/watch?v=KKWuS_jLFHE
Reply by ●September 14, 20162016-09-14
On 14/09/16 23:26, Clifford Heath wrote:> 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?The faster the edge rate, the better. Some suggest Analog Device's fastest comparators, but I haven't seen any measurements on circuits. Three parallel (74LVC1G14+130ohms) is sub-nanosecond, but you have to pay attention the decoupling capacitors. Apart from that you just need a fast enough scope.
Reply by ●September 14, 20162016-09-14
On Thu, 15 Sep 2016 00:12:00 +0100, Tom Gardner <spamjunk@blueyonder.co.uk> wrote:>On 14/09/16 23:26, Clifford Heath wrote: >> 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? > >The faster the edge rate, the better. Some suggest >Analog Device's fastest comparators, but I haven't >seen any measurements on circuits. >ADCMP582 has diff ECL outputs with typ 37 ps edges. It's around $10.>Three parallel (74LVC1G14+130ohms) is sub-nanosecond, >but you have to pay attention the decoupling capacitors. > >Apart from that you just need a fast enough scope.Right. If you want to make a sub-100 ps TDR, the real problem is waveform digitizing. -- 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 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. > > > > > >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.comHi John, I've been wandering around my fields, (with 'cobber' me mum's dog, an Australian kelpie. herding dog... very active!) Anyway lotsa random thoughts and if anything works for you... there we go. Well first off I'm totally jazzed about making a tdr, mostly because I know nothing. Second this reminds me SPAD, cool physics, ~few dollar circuit. I thought it should have been sold as a kit. (for ~< $100. $99) We've sold 3... I've helped ~10 people with the circuit. 100 kits at $100 would have worked. So my third thought is could we make it a kit? A kit sounds like through hole, to me, at least the primitive version. Two kits? one through hole and another surface mount? Do people do surface mount kits? Fifth thought, can you do something else with fast edges/pulses. (Add functions) I only have one idea here, (maybe two things) and that is drive it from a random noise source. ~100 MHz noise source and pseudo shot noise generator (with the pulse) Pulses of charge are like big fat electrons and make more noise. How do you support a kit? I don't know... get someone else (the customers) to do it? Some forum? Adafruit, eevblog, ? George H.
Reply by ●September 14, 20162016-09-14
On Wednesday, September 14, 2016 at 8:05:13 PM UTC-4, George Herold wrote:> 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. > > > > > > > > > >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 > > Hi John, I've been wandering around my fields, > (with 'cobber' me mum's dog, an Australian kelpie. > herding dog... very active!) > > Anyway lotsa random thoughts and if anything works > for you... there we go. > > Well first off I'm totally jazzed about making a tdr, > mostly because I know nothing. > > Second this reminds me SPAD, cool physics, > ~few dollar circuit. I thought it should > have been sold as a kit. (for ~< $100. $99) > We've sold 3... I've helped ~10 people with the circuit. > 100 kits at $100 would have worked. > > So my third thought is could we make it a kit? > A kit sounds like through hole, to me, at least > the primitive version. Two kits? one through hole > and another surface mount? Do people do > surface mount kits? > > Fifth thought, can you do something else with fast edges/pulses. > (Add functions) > I only have one idea here, (maybe two things) and that is > drive it from a random noise source. ~100 MHz noise source > and pseudo shot noise generator (with the pulse) > Pulses of charge are like big fat electrons and > make more noise. > > How do you support a kit? I don't know... > get someone else (the customers) to do it? > Some forum? Adafruit, eevblog, ? > > George H.Oh, seventh thought, TDR should be marketed first to electronics geeks... there's lot's more of those than there are physics majors. GH
Reply by ●September 14, 20162016-09-14
On 15/09/16 09:41, John Larkin wrote:> On Thu, 15 Sep 2016 00:12:00 +0100, Tom Gardner > <spamjunk@blueyonder.co.uk> wrote: > >> On 14/09/16 23:26, Clifford Heath wrote: >>> 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? >> >> The faster the edge rate, the better. Some suggest >> Analog Device's fastest comparators, but I haven't >> seen any measurements on circuits. >> > > ADCMP582 has diff ECL outputs with typ 37 ps edges. It's around $10.Thanks, that's the kind of info I was looking for. A good deal faster than I could build a sampler for...>> Three parallel (74LVC1G14+130ohms) is sub-nanosecond, >> but you have to pay attention the decoupling capacitors. >> >> Apart from that you just need a fast enough scope. > Right. If you want to make a sub-100 ps TDR, the real problem is > waveform digitizing.I'd put a sampler on the same board, using a voltage-controlled delay like what Win showed recently using an LVDS receiver, pulsing a pair of microwave diodes. Sweep the delay with enough pulses for averaging and you don't need a fast scope. Drive the whole thing from an Arduino and you have a geek TDR kit. Clifford Heath.
Reply by ●September 14, 20162016-09-14
On 09/14/2016 06:12 PM, krw wrote:> 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. ;-) >No, that's where I'm _from_, not where I live. The weather here suits me very well--much sunnier than Vancouver and nicer than Palo Alto. (I got so sick of _brown_ living in CA. Westchester County is a really nice place. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●September 14, 20162016-09-14
On Thursday, September 15, 2016 at 2:23:37 AM UTC+10, 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.If you want bigger-than ECL voltage swings, using ECL to drive broad-band transistors - BFR92 is NPN 5GHz, BFT93 PNP 5GHz complement - is pretty straight forward. Both offer peak bandwidth at 14mA, which gives you 0.7V into 50R - +/-0.7V with complementary drive. There are bigger cheap broad-band transistors, good for perhaps 60mA. We used the NPN BFR96. A similar PNP part showed up a bit later, too late for me to use. Back in the 1980's we used BFR92s to drive HP RF transistors to get 7.5V swings into 50R with a roughly 300psec 10% to 90% transition time. As John points out, transmission lines are do-able on a double-sided board but a four-layer board make the job a lot easier. It might be worth making the outer layers of the board with one of the Rogers microwave substrates http://www.rogerscorp.com/documents/776/acm/High-Frequency-Laminates---Product-Selector-Guide.aspx Talk to you printed circuit supplier to see if they keep any of them in stock - Rogers seems to sell the stuff in large sheets, which are expensive. E-mail me if you do decide to go ahead. I've done this kind of stuff (and used step-recovery diodes to get fast edges) and I'd be happy to help. -- Bill Sloman, Sydney
Reply by ●September 14, 20162016-09-14
On 9/14/2016 3:21 PM, Phil Hobbs 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: >>[...]>>> >>> (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" HobbsAfter postponing my mid-life crisis for a couple of decades, I retired my Taurus wagon and went shopping for something that "went like stink". Ended up with a Camaro 1LE - track suspension and brakes, different gearing, fat tires, oil coolers, but an otherwise normal 430HP V8. I was a little concerned that mileage would suck but the rest of the package suited. Turns out that I get 27-30 mpg on a leisurely highway trip and somewhere around 23-24 on a commute into the big city. I leave the traction control in the "performance mode" - no traction control so it won't fight me if I want to get frisky but it will add a little "torque vectoring" should the direction the car is going not match the direction I'm requesting by a significant amount - I can steer with the throttle up to a point but it'll assert itself when I request turn-in and slipping a bit more than the front wheels can overcome without howling in protest. I'm OK with that. -- Grizzly H.
