On Thu, 12 Jul 2018 13:07:19 -0500, amdx <nojunk@knology.net> wrote:>On 7/12/2018 2:40 AM, tom wrote: >> "Tim Williams" <tiwill@seventransistorlabs.com> wrote in message >> news:pi6t93$a7g$1@dont-email.me... >>> FYI: >>> 1. Dropbox says it's a file, not an image, so it has to be downloaded. >>> 2. Dropbox? Really? >>> 3. It's 710x483 which is fine, but it's saved in the worst possible image >>> format, 24-bit PNG. It's literally a zipped bitmap. Use JPEG, usually >>> around 90-95 quality factor, and you'll see file size drop to maybe 50k. >>> Only use PNG for reduced-color line drawings. >>> 4. Try to set up square shots, especially for scope shots! Look for the >>> reflection of the camera off the screen/bezel, and center that on the >>> screen and in the camera viewfinder. Turn off ambient lights to eliminate >>> the reflection, then take the picture. Adjust exposure until the trace is >>> easily visible, not burned out -- automatic settings are usually poor on >>> high-contrast displays. The graticule intensity seems to have kept >>> contrast reasonable so that only a little trace is burned out (just >>> barely, around the top right), which works as well. >>> 5. And always focus the picture. (Probably fine on the present case -- >>> this is general advice.) Don't crowd the subject, that can only ever make >>> things worse. Preferably, take the picture from a distance and use >>> optical zoom to enlarge it -- this also reduces barrel/fisheye distortion, >>> and abberation of the lens. Some postprocessing may still be necessary to >>> correct for the spherical CRT face. All the more reason to move into the >>> 20th century with a digital scope -- even better, one with floppy drive >>> (if you're really old fashioned), serial or GPIB interface so you can save >>> a screenshot directly. >>> >>> Tim >>> >>> -- >>> Seven Transistor Labs, LLC >>> Electrical Engineering Consultation and Contract Design >>> Website: https://www.seventransistorlabs.com/ >>> >>> "amdx" <nojunk@knology.net> wrote in message >>> news:pi60di$can$1@dont-email.me... >>>> I ordered a built 74AC14 TDR square wave generator. >>>> It has overshoot and ringing, 2 or 3 cycles. >>>> Is there any way to tame it with out increasing rise time? >>>> I added a 33pf across scope side input, it helped but increased >>>> rise time. >>>> Before and after pictures, > >>>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>>> >>>> >>>> Not sure it matters, I would just like a nice rising edge to start with. >>>> >>>> >>>> >>>> Here's the TDR unit I bought, click through pictures to see layout >>>> of connectors. >>>>> https://www.ebay.com/itm/152587007700 >>>> Mikek >>>> >>> >> >> Good advice. And use the self timer with a tripod. >> >> >> >> > Ok, I'll try to give you better pictures next time. > I had to avoid a window that was reflecting off the screen, >That was some of the angle, I did turn down the intensity of both my >trace and the scale illumination. My camera has auto focus only. I'm not >sure my tripod will go high enough. >Here's a JPG, > >https://www.dropbox.com/s/48i8fmfp9mhy1o5/delayed%20sweep%20jpg.jpg?dl=0 > I'll go away and lick my wounds! > Mikek :-) > >I like to put a post-it in the image to remember what it is. If the scope doesn't have readout, the post-it can also note timebase and vertical scaling. https://www.dropbox.com/s/8lolk81giquvb8z/LM317L_ilim.JPG?raw=1 https://www.dropbox.com/s/n3z2huh4xnrhcg7/P400_Countdown.JPG?raw=1 -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
74AC14 TDR
Started by ●July 11, 2018
Reply by ●July 12, 20182018-07-12
Reply by ●July 12, 20182018-07-12
On Wednesday, July 11, 2018 at 6:30:13 PM UTC-4, amdx wrote:> I ordered a built 74AC14 TDR square wave generator. > It has overshoot and ringing, 2 or 3 cycles. > Is there any way to tame it with out increasing rise time? > I added a 33pf across scope side input, it helped but increased > rise time. > Before and after pictures, > > https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 > > > Not sure it matters, I would just like a nice rising edge to start with. > > > > Here's the TDR unit I bought, click through pictures to see layout > of connectors. > > https://www.ebay.com/itm/152587007700 > MikekAre you using a scope probe into the 1M scope input??? All you're C'ing is lead ringing. C'ing means you get a C on this project.
Reply by ●July 12, 20182018-07-12
On 07/12/2018 02:13 PM, amdx wrote:> On 7/12/2018 1:03 PM, bitrex wrote: >> On 07/11/2018 06:30 PM, amdx wrote: >>> I ordered a built 74AC14 TDR square wave generator. >>> It has overshoot and ringing, 2 or 3 cycles. >>> Is there any way to tame it with out increasing rise time? >>> I added a 33pf across scope side input, it helped but increased >>> rise time. >>> Before and after pictures, > >>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>> >>> >>> Not sure it matters, I would just like a nice rising edge to start >>> with. >>> >>> >>> >>> Here's the TDR unit I bought, click through pictures to see layout >>> of connectors. >>>> https://www.ebay.com/itm/152587007700 >>> Mikek >>> >> >> Does "No quibble returns" mean you can return it for any reason and >> they won't quibble or they won't accept returns based on "quibbles"? > > I'm have no desire to send it back, it works. > What do you want it to do? > Mikek >idk the phrasing is just a bit ambiguous. Note to self when selling things make return policy unambiguous and clear for even English-speakers with limited skill (unless one likes losing customers.)
Reply by ●July 12, 20182018-07-12
On Thu, 12 Jul 2018 20:53:33 +0200, Gerhard Hoffmann <ghf@hoffmann-hochfrequenz.de> wrote:>Am 12.07.2018 um 04:15 schrieb John Larkin: >> On Wed, 11 Jul 2018 16:45:58 -0700, mike <ham789@netzero.net> wrote: >> >>> On 7/11/2018 3:30 PM, amdx wrote: >>>> I ordered a built 74AC14 TDR square wave generator. >>>> It has overshoot and ringing, 2 or 3 cycles. >>>> Is there any way to tame it with out increasing rise time? >>>> I added a 33pf across scope side input, it helped but increased >>>> rise time. >>>> Before and after pictures, > >>>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>>> >>>> >>>> Not sure it matters, I would just like a nice rising edge to start with. >>>> >>>> >>>> >>>> Here's the TDR unit I bought, click through pictures to see layout >>>> of connectors. >>>>> https://www.ebay.com/itm/152587007700 >>>> Mikek >>>> >>> >>> Looks like you got just about what the website promised. >>> You should be able to determine the advertised parameters >>> for cables longer than the ring time. >>> >>> Some things to think about... >>> That's likely a T-connection where three things >>> (unknown, sense, stimulus) come together. >>> Everything needs to be properly terminated in both >>> directions. That's hard do with that configuration. >>> Most anything you do makes it worse. >>> >>> What's the transient response of your scope with >>> a real calibration generator? >>> >>> What's the input impedance of your scope? >>> If it's 1M in parallel with some pF, you've already >>> shot yourself in the foot. Put some QUALITY cable in between >>> the scope and the TDR. Use a 10X 50 ohm attenuator >>> (an expensive/good one) >>> and a terminator on the scope too...or select 50 ohm >>> input if available. >> >> No. This kind of generator is a 50 ohm voltage source. Adding a 50 ohm >> scope in parallel makes it 25 ohms. A 50 ohm TDR should be a 50 ohm >> step generator and a hi-Z scope. >> >> Or a 50 ohm scope and a current step, which is how most classic TDR >> scope heads worked. > >When we get to a bandwidth that is outside the children toy league, >there is no such thing as a hi-Z scope. > >The proper way is a splitter and 50 Ohm devices. See Fig. 11 in >< https://kh6htv.files.wordpress.com/2015/11/an-05c-10ps-tdr.pdf > > >When the generator/scope side is not perfectly matched, everything >after the first large reflection is just dirt. And you usually do not >have a long enough precision air delay line. Maybe in the VNA cal kit. > >cheers, Gerhard > >Well, you could also do gates--100r--BNC--50r--------coax------50r scope But we're talking $18 TDR boards here, not shock-line step generators and 50 GHz scopes. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●July 12, 20182018-07-12
On Thu, 12 Jul 2018 12:10:45 -0700 (PDT), bloggs.fredbloggs.fred@gmail.com wrote:>On Wednesday, July 11, 2018 at 6:30:13 PM UTC-4, amdx wrote: >> I ordered a built 74AC14 TDR square wave generator. >> It has overshoot and ringing, 2 or 3 cycles. >> Is there any way to tame it with out increasing rise time? >> I added a 33pf across scope side input, it helped but increased >> rise time. >> Before and after pictures, > >> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >> >> >> Not sure it matters, I would just like a nice rising edge to start with. >> >> >> >> Here's the TDR unit I bought, click through pictures to see layout >> of connectors. >> > https://www.ebay.com/itm/152587007700 >> Mikek > >Are you using a scope probe into the 1M scope input??? All you're C'ing is lead ringing. C'ing means you get a C on this project.The ebay TDR board is shown hanging directly off the scope's BNC input connector. The ringing is probably ground bounce in the DIP gate, and bad board layout. Lots of digital scopes ring a bit, too. Some people have no shame. One could interface to a digital scope, suck out the ugly step waveform, and apply some FIR filter math to make the step perfect. https://www.dropbox.com/s/iqpldbkq2awdeml/TDR_Decon_demo.jpg?raw=1 A modest risetime improvement is possible too. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●July 12, 20182018-07-12
On 7/12/2018 1:53 PM, Gerhard Hoffmann wrote:> Am 12.07.2018 um 04:15 schrieb John Larkin: >> On Wed, 11 Jul 2018 16:45:58 -0700, mike <ham789@netzero.net> wrote: >> >>> On 7/11/2018 3:30 PM, amdx wrote: >>>> I ordered a built 74AC14 TDR square wave generator. >>>> It has overshoot and ringing, 2 or 3 cycles. >>>> Is there any way to tame it with out increasing rise time? >>>> I added a 33pf across scope side input, it helped but increased >>>> rise time. >>>> Before and after pictures, > >>>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>>> >>>> >>>> Not sure it matters, I would just like a nice rising edge to >>>> start with. >>>> >>>> >>>> >>>> Here's the TDR unit I bought, click through pictures to see layout >>>> of connectors. >>>>> https://www.ebay.com/itm/152587007700 >>>> Mikek >>>> >>> >>> Looks like you got just about what the website promised. >>> You should be able to determine the advertised parameters >>> for cables longer than the ring time. >>> >>> Some things to think about... >>> That's likely a T-connection where three things >>> (unknown, sense, stimulus) come together. >>> Everything needs to be properly terminated in both >>> directions. That's hard do with that configuration. >>> Most anything you do makes it worse. >>> >>> What's the transient response of your scope with >>> a real calibration generator? >>> >>> What's the input impedance of your scope? >>> If it's 1M in parallel with some pF, you've already >>> shot yourself in the foot. Put some QUALITY cable in between >>> the scope and the TDR. Use a 10X 50 ohm attenuator >>> (an expensive/good one) >>> and a terminator on the scope too...or select 50 ohm >>> input if available. >> >> No. This kind of generator is a 50 ohm voltage source. Adding a 50 ohm >> scope in parallel makes it 25 ohms. A 50 ohm TDR should be a 50 ohm >> step generator and a hi-Z scope. >> >> Or a 50 ohm scope and a current step, which is how most classic TDR >> scope heads worked. > > When we get to a bandwidth that is outside the children toy league, > there is no such thing as a hi-Z scope. > > The proper way is a splitter and 50 Ohm devices. See Fig. 11 in > < https://kh6htv.files.wordpress.com/2015/11/an-05c-10ps-tdr.pdf > > > When the generator/scope side is not perfectly matched, everything > after the first large reflection is just dirt. And you usually do not > have a long enough precision air delay line. Maybe in the VNA cal kit. > > cheers, Gerhard > > >Is that what is known as a humble-brag? Mikek I bought the Fast Edge Pulse Generator to find the Characteristic impedance of 253ft of wire laying on the ground. I can do that by adjusting the termination at the far end until I don't have any step in the square wave. Also, with it unterminated, I can find out the VF of the wire, knowing the length. I hope to reduce the VF down to around 0.55 using several coils along the length of the wire. Here is a very short video showing how the wire on ground is directional. The problem, this is about as low in frequency as the antenna goes before losing directionality. I hope with coils inserted in the wire I can reduce the VF making the antenna seem longer. I just wanted to have some measurements as a starting point to see how the characteristics were changing as I made the physical changes. Just having fun. I gave up on the camera, the auto focus, goes through focusing, but then stops at the wrong place. Wife dropped her phone in the water, so I don't have my phone to take any pictures, They may be better.
Reply by ●July 12, 20182018-07-12
On 7/12/2018 3:41 PM, amdx wrote:> On 7/12/2018 1:53 PM, Gerhard Hoffmann wrote: >> Am 12.07.2018 um 04:15 schrieb John Larkin: >>> On Wed, 11 Jul 2018 16:45:58 -0700, mike <ham789@netzero.net> wrote: >>> >>>> On 7/11/2018 3:30 PM, amdx wrote: >>>>> I ordered a built 74AC14 TDR square wave generator. >>>>> It has overshoot and ringing, 2 or 3 cycles. >>>>> Is there any way to tame it with out increasing rise time? >>>>> I added a 33pf across scope side input, it helped but increased >>>>> rise time. >>>>> Before and after pictures, > >>>>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>>>> >>>>> >>>>> Not sure it matters, I would just like a nice rising edge to >>>>> start with. >>>>> >>>>> >>>>> >>>>> Here's the TDR unit I bought, click through pictures to see layout >>>>> of connectors. >>>>>> https://www.ebay.com/itm/152587007700 >>>>> Mikek >>>>> >>>> >>>> Looks like you got just about what the website promised. >>>> You should be able to determine the advertised parameters >>>> for cables longer than the ring time. >>>> >>>> Some things to think about... >>>> That's likely a T-connection where three things >>>> (unknown, sense, stimulus) come together. >>>> Everything needs to be properly terminated in both >>>> directions. That's hard do with that configuration. >>>> Most anything you do makes it worse. >>>> >>>> What's the transient response of your scope with >>>> a real calibration generator? >>>> >>>> What's the input impedance of your scope? >>>> If it's 1M in parallel with some pF, you've already >>>> shot yourself in the foot. Put some QUALITY cable in between >>>> the scope and the TDR. Use a 10X 50 ohm attenuator >>>> (an expensive/good one) >>>> and a terminator on the scope too...or select 50 ohm >>>> input if available. >>> >>> No. This kind of generator is a 50 ohm voltage source. Adding a 50 ohm >>> scope in parallel makes it 25 ohms. A 50 ohm TDR should be a 50 ohm >>> step generator and a hi-Z scope. >>> >>> Or a 50 ohm scope and a current step, which is how most classic TDR >>> scope heads worked. >> >> When we get to a bandwidth that is outside the children toy league, >> there is no such thing as a hi-Z scope. >> >> The proper way is a splitter and 50 Ohm devices. See Fig. 11 in >> < https://kh6htv.files.wordpress.com/2015/11/an-05c-10ps-tdr.pdf > >> >> When the generator/scope side is not perfectly matched, everything >> after the first large reflection is just dirt. And you usually do not >> have a long enough precision air delay line. Maybe in the VNA cal kit. >> >> cheers, Gerhard >> >> >> > Is that what is known as a humble-brag? > Mikek > > I bought the Fast Edge Pulse Generator to find the Characteristic > impedance of 253ft of wire laying on the ground. I can do that by > adjusting the termination at the far end until I don't have any step > in the square wave. Also, with it unterminated, I can find out the VF > of the wire, knowing the length. I hope to reduce the VF down to around > 0.55 using several coils along the length of the wire. > Here is a very short video showing how the wire on ground is > directional.The Link,> https://www.youtube.com/watch?v=q8rBb2v13tgThe problem, this is about as low in frequency as the> antenna goes before losing directionality. I hope with coils inserted in > the wire I can reduce the VF making the antenna seem longer. > I just wanted to have some measurements as a starting point to see > how the characteristics were changing as I made the physical changes. > Just having fun. > I gave up on the camera, the auto focus, goes through focusing, but > then stops at the wrong place. > Wife dropped her phone in the water, so I don't have my phone to take > any pictures, They may be better. >
Reply by ●July 12, 20182018-07-12
torsdag den 12. juli 2018 kl. 22.41.23 UTC+2 skrev John Larkin:> On Thu, 12 Jul 2018 12:10:45 -0700 (PDT), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Wednesday, July 11, 2018 at 6:30:13 PM UTC-4, amdx wrote: > >> I ordered a built 74AC14 TDR square wave generator. > >> It has overshoot and ringing, 2 or 3 cycles. > >> Is there any way to tame it with out increasing rise time? > >> I added a 33pf across scope side input, it helped but increased > >> rise time. > >> Before and after pictures, > > >> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 > >> > >> > >> Not sure it matters, I would just like a nice rising edge to start with. > >> > >> > >> > >> Here's the TDR unit I bought, click through pictures to see layout > >> of connectors. > >> > https://www.ebay.com/itm/152587007700 > >> Mikek > > > >Are you using a scope probe into the 1M scope input??? All you're C'ing is lead ringing. C'ing means you get a C on this project. > > The ebay TDR board is shown hanging directly off the scope's BNC input > connector. > > The ringing is probably ground bounce in the DIP gate, and bad board > layout. >the deadbug version has a very similar waveform, https://youtu.be/9cP6w2odGUc?t=4m55s
Reply by ●July 12, 20182018-07-12
On 7/12/2018 3:56 PM, Lasse Langwadt Christensen wrote:> torsdag den 12. juli 2018 kl. 22.41.23 UTC+2 skrev John Larkin: >> On Thu, 12 Jul 2018 12:10:45 -0700 (PDT), >> bloggs.fredbloggs.fred@gmail.com wrote: >> >>> On Wednesday, July 11, 2018 at 6:30:13 PM UTC-4, amdx wrote: >>>> I ordered a built 74AC14 TDR square wave generator. >>>> It has overshoot and ringing, 2 or 3 cycles. >>>> Is there any way to tame it with out increasing rise time? >>>> I added a 33pf across scope side input, it helped but increased >>>> rise time. >>>> Before and after pictures, > >>>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>>> >>>> >>>> Not sure it matters, I would just like a nice rising edge to start with. >>>> >>>> >>>> >>>> Here's the TDR unit I bought, click through pictures to see layout >>>> of connectors. >>>>> https://www.ebay.com/itm/152587007700 >>>> Mikek >>> >>> Are you using a scope probe into the 1M scope input??? All you're C'ing is lead ringing. C'ing means you get a C on this project. >> >> The ebay TDR board is shown hanging directly off the scope's BNC input >> connector. >> >> The ringing is probably ground bounce in the DIP gate, and bad board >> layout. >> > > the deadbug version has a very similar waveform, > > https://youtu.be/9cP6w2odGUc?t=4m55s >Yes, the bug is called a feature, rightly so. Mikek
Reply by ●July 12, 20182018-07-12
On 7/12/2018 3:42 PM, amdx wrote:> On 7/12/2018 3:41 PM, amdx wrote: >> On 7/12/2018 1:53 PM, Gerhard Hoffmann wrote: >>> Am 12.07.2018 um 04:15 schrieb John Larkin: >>>> On Wed, 11 Jul 2018 16:45:58 -0700, mike <ham789@netzero.net> wrote: >>>> >>>>> On 7/11/2018 3:30 PM, amdx wrote: >>>>>> I ordered a built 74AC14 TDR square wave generator. >>>>>> It has overshoot and ringing, 2 or 3 cycles. >>>>>> Is there any way to tame it with out increasing rise time? >>>>>> I added a 33pf across scope side input, it helped but increased >>>>>> rise time. >>>>>> Before and after pictures, > >>>>>> https://www.dropbox.com/s/t5y0jfrmbxaqs0o/risetime.png?dl=0 >>>>>> >>>>>> >>>>>> Not sure it matters, I would just like a nice rising edge to >>>>>> start with. >>>>>> >>>>>> >>>>>> >>>>>> Here's the TDR unit I bought, click through pictures to see layout >>>>>> of connectors. >>>>>>> https://www.ebay.com/itm/152587007700 >>>>>> Mikek >>>>>> >>>>> >>>>> Looks like you got just about what the website promised. >>>>> You should be able to determine the advertised parameters >>>>> for cables longer than the ring time. >>>>> >>>>> Some things to think about... >>>>> That's likely a T-connection where three things >>>>> (unknown, sense, stimulus) come together. >>>>> Everything needs to be properly terminated in both >>>>> directions. That's hard do with that configuration. >>>>> Most anything you do makes it worse. >>>>> >>>>> What's the transient response of your scope with >>>>> a real calibration generator? >>>>> >>>>> What's the input impedance of your scope? >>>>> If it's 1M in parallel with some pF, you've already >>>>> shot yourself in the foot. Put some QUALITY cable in between >>>>> the scope and the TDR. Use a 10X 50 ohm attenuator >>>>> (an expensive/good one) >>>>> and a terminator on the scope too...or select 50 ohm >>>>> input if available. >>>> >>>> No. This kind of generator is a 50 ohm voltage source. Adding a 50 ohm >>>> scope in parallel makes it 25 ohms. A 50 ohm TDR should be a 50 ohm >>>> step generator and a hi-Z scope. >>>> >>>> Or a 50 ohm scope and a current step, which is how most classic TDR >>>> scope heads worked. >>> >>> When we get to a bandwidth that is outside the children toy league, >>> there is no such thing as a hi-Z scope. >>> >>> The proper way is a splitter and 50 Ohm devices. See Fig. 11 in >>> < https://kh6htv.files.wordpress.com/2015/11/an-05c-10ps-tdr.pdf > >>> >>> When the generator/scope side is not perfectly matched, everything >>> after the first large reflection is just dirt. And you usually do not >>> have a long enough precision air delay line. Maybe in the VNA cal kit. >>> >>> cheers, Gerhard >>> >>> >>> >> Is that what is known as a humble-brag? >> Mikek >> >> I bought the Fast Edge Pulse Generator to find the Characteristic >> impedance of 253ft of wire laying on the ground. I can do that by >> adjusting the termination at the far end until I don't have any step >> in the square wave. Also, with it unterminated, I can find out the VF >> of the wire, knowing the length. I hope to reduce the VF down to >> around 0.55 using several coils along the length of the wire. >> Here is a very short video showing how the wire on ground is >> directional. > > > The Link, > >> https://www.youtube.com/watch?v=q8rBb2v13tg > > > > The problem, this is about as low in frequency as the >> antenna goes before losing directionality. I hope with coils inserted >> in the wire I can reduce the VF making the antenna seem longer. >> I just wanted to have some measurements as a starting point to see >> how the characteristics were changing as I made the physical changes. >> Just having fun. >> I gave up on the camera, the auto focus, goes through focusing, but >> then stops at the wrong place. >> Wife dropped her phone in the water, so I don't have my phone to >> take any pictures, They may be better. >> >Also, when I get the characteristic impedance, properly terminated, I will add an additional ground rod at each end to see if that reduces my ground resistance.
