On 7/24/26 23:29, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 23:17:16 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 20:56, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 19:51:18 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 19:07, Cursitor Doom wrote:
Gentlemen,
Does anyone here have a dedicated TDR? I'd previously assumed they >>>>>> were only good for 'distance to fault' applications, but was disabused >>>>>> of my ignorance during a recent read of Tom Lee's Planar Microwave >>>>>> Engineering, in which it was stated that they can also be used for >>>>>> identifying the value of caps and inductors by means of the shape of >>>>>> the reflection and doing a bit of integration to it.
A TDR is one of the vanishingly few items of test gear I do not
possess. I have a 50ps pulse generator which can be used with a fast >>>>>> 'scope to achieve a certain amount of functionality, but I was
wondering how much more useful and versatile a stand-alone TDR might >>>>>> be.
I use a VNA for determining the value of small caps and coils and find >>>>>> it hard to believe any TDR could give better results than that.
However, once again I could be wrong. Info, anyone?
I've done both frequency domain and time domain measurements
and you can easily use Fourier transforms to get from one to
the other after the fact. Invariably, I found that HP8753D VNA
measurements followed by an inverse Fourier transform were
superior in terms of S/N.
My TDR was a Tektronix S-6 sampler and an S-52 pulser, which
have a slight edge in terms of bandwidth. If I averaged >10k
measurments, the S/N approached that of the HP8753D, but a
lot of patience was needed.
In the end, sometimes one is better, sometimes the other.
Jeroen Belleman
To this I would add one comment:
VNAs have fairly narrow Receive and Video Bandwidths, often a few MHz, >>>> so the smallest discontinuity must be tens of meters long.
By contrast, a TDR has a bandwidth in the GHz, so far shorter
discontinuities may be detected.
Joe
No, no, it doesn't work like that. You use the VNA to acquire the
S11 frequency response over its full bandwidth. You then apply an
inverse Fourier transform to the complex S11 frequency data to
obtain the impulse response. Then you apply a time integration to
finally get the TDR plot with an equivalent bandwidth of the
full sweep of the VNA.
Note that the VNA has a directional coupler, so you'll get only
the reflection, not the incident *plus* the reflection like a
TDR. The nice thing is that with proper VNA calibration, the
reflection will start exactly at time zero and many setup
parasitics are suppressed.
I could resolve centimeter-sized discontinuities with ease with
S11 data from the HP8753D sweeping up to 6GHz.
Hmm. The people I was watching were not doing anything like the
above. How long does data collection take? TDRs are fast.
Joe
The VNA sweeps the whole range in a second or so. The HP5387D has
a wimpy CPU, so it takes a few seconds to do the transform. I also
did the transform after transferring the data to my PC, which is more >laborious, but the actual transform is then basically instantaneous.
(I did not time it.)
My TDR was a Tektronix 7904, with 7T11 and 7S11 plug-ins driven
by a VME DAC and read out with a VME ADC. That was pretty slow,
especially when I averaged measurements to improve the S/N.
Jeroen Belleman
On Sat, 25 Jul 2026 00:07:40 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 23:29, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 23:17:16 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 20:56, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 19:51:18 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 19:07, Cursitor Doom wrote:
Gentlemen,
Does anyone here have a dedicated TDR? I'd previously assumed they >>>>>>> were only good for 'distance to fault' applications, but was disabused >>>>>>> of my ignorance during a recent read of Tom Lee's Planar Microwave >>>>>>> Engineering, in which it was stated that they can also be used for >>>>>>> identifying the value of caps and inductors by means of the shape of >>>>>>> the reflection and doing a bit of integration to it.
A TDR is one of the vanishingly few items of test gear I do not
possess. I have a 50ps pulse generator which can be used with a fast >>>>>>> 'scope to achieve a certain amount of functionality, but I was
wondering how much more useful and versatile a stand-alone TDR might >>>>>>> be.
I use a VNA for determining the value of small caps and coils and find >>>>>>> it hard to believe any TDR could give better results than that.
However, once again I could be wrong. Info, anyone?
I've done both frequency domain and time domain measurements
and you can easily use Fourier transforms to get from one to
the other after the fact. Invariably, I found that HP8753D VNA
measurements followed by an inverse Fourier transform were
superior in terms of S/N.
My TDR was a Tektronix S-6 sampler and an S-52 pulser, which
have a slight edge in terms of bandwidth. If I averaged >10k
measurments, the S/N approached that of the HP8753D, but a
lot of patience was needed.
In the end, sometimes one is better, sometimes the other.
Jeroen Belleman
To this I would add one comment:
VNAs have fairly narrow Receive and Video Bandwidths, often a few MHz, >>>>> so the smallest discontinuity must be tens of meters long.
By contrast, a TDR has a bandwidth in the GHz, so far shorter
discontinuities may be detected.
Joe
No, no, it doesn't work like that. You use the VNA to acquire the
S11 frequency response over its full bandwidth. You then apply an
inverse Fourier transform to the complex S11 frequency data to
obtain the impulse response. Then you apply a time integration to
finally get the TDR plot with an equivalent bandwidth of the
full sweep of the VNA.
Note that the VNA has a directional coupler, so you'll get only
the reflection, not the incident *plus* the reflection like a
TDR. The nice thing is that with proper VNA calibration, the
reflection will start exactly at time zero and many setup
parasitics are suppressed.
I could resolve centimeter-sized discontinuities with ease with
S11 data from the HP8753D sweeping up to 6GHz.
Hmm. The people I was watching were not doing anything like the
above. How long does data collection take? TDRs are fast.
Joe
The VNA sweeps the whole range in a second or so. The HP5387D has
a wimpy CPU, so it takes a few seconds to do the transform. I also
did the transform after transferring the data to my PC, which is more
laborious, but the actual transform is then basically instantaneous.
(I did not time it.)
My TDR was a Tektronix 7904, with 7T11 and 7S11 plug-ins driven
by a VME DAC and read out with a VME ADC. That was pretty slow,
especially when I averaged measurements to improve the S/N.
Jeroen Belleman
Interesting. I have the 'C' suffix version of your VNA. Can you tell
me whereabouts the fourier transforms options are to be found buried
in the menu options? I've never come across them. Might not be in
exactly the same place, but shouldn't be too far removed....
On 7/26/26 10:04, Cursitor Doom wrote:
On Sat, 25 Jul 2026 00:07:40 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 23:29, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 23:17:16 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 20:56, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 19:51:18 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 19:07, Cursitor Doom wrote:
Gentlemen,
Does anyone here have a dedicated TDR? I'd previously assumed
they were only good for 'distance to fault' applications, but was >>>>>>>> disabused of my ignorance during a recent read of Tom Lee's
Planar Microwave Engineering, in which it was stated that they >>>>>>>> can also be used for identifying the value of caps and inductors >>>>>>>> by means of the shape of the reflection and doing a bit of
integration to it.
A TDR is one of the vanishingly few items of test gear I do not >>>>>>>> possess. I have a 50ps pulse generator which can be used with a >>>>>>>> fast 'scope to achieve a certain amount of functionality, but I >>>>>>>> was wondering how much more useful and versatile a stand-alone >>>>>>>> TDR might be.
I use a VNA for determining the value of small caps and coils and >>>>>>>> find it hard to believe any TDR could give better results than >>>>>>>> that. However, once again I could be wrong. Info, anyone?
I've done both frequency domain and time domain measurements and >>>>>>> you can easily use Fourier transforms to get from one to the other >>>>>>> after the fact. Invariably, I found that HP8753D VNA measurements >>>>>>> followed by an inverse Fourier transform were superior in terms of >>>>>>> S/N.
My TDR was a Tektronix S-6 sampler and an S-52 pulser, which have >>>>>>> a slight edge in terms of bandwidth. If I averaged >10k
measurments, the S/N approached that of the HP8753D, but a lot of >>>>>>> patience was needed.
In the end, sometimes one is better, sometimes the other.
Jeroen Belleman
To this I would add one comment:
VNAs have fairly narrow Receive and Video Bandwidths, often a few
MHz,
so the smallest discontinuity must be tens of meters long.
By contrast, a TDR has a bandwidth in the GHz, so far shorter
discontinuities may be detected.
Joe
No, no, it doesn't work like that. You use the VNA to acquire the
S11 frequency response over its full bandwidth. You then apply an
inverse Fourier transform to the complex S11 frequency data to
obtain the impulse response. Then you apply a time integration to
finally get the TDR plot with an equivalent bandwidth of the full
sweep of the VNA.
Note that the VNA has a directional coupler, so you'll get only the
reflection, not the incident *plus* the reflection like a TDR. The
nice thing is that with proper VNA calibration, the reflection will
start exactly at time zero and many setup parasitics are suppressed. >>>>>
I could resolve centimeter-sized discontinuities with ease with S11
data from the HP8753D sweeping up to 6GHz.
Hmm. The people I was watching were not doing anything like the
above. How long does data collection take? TDRs are fast.
Joe
The VNA sweeps the whole range in a second or so. The HP5387D has a
wimpy CPU, so it takes a few seconds to do the transform. I also did
the transform after transferring the data to my PC, which is more
laborious, but the actual transform is then basically instantaneous.
(I did not time it.)
My TDR was a Tektronix 7904, with 7T11 and 7S11 plug-ins driven by a
VME DAC and read out with a VME ADC. That was pretty slow, especially
when I averaged measurements to improve the S/N.
Jeroen Belleman
Interesting. I have the 'C' suffix version of your VNA. Can you tell me
whereabouts the fourier transforms options are to be found buried in
the menu options? I've never come across them. Might not be in exactly
the same place, but shouldn't be too far removed....
It's an option. If you have it, there should be a 'TRANSFORM MENU'
item on the screen after pushing the "SYSTEM' button.
Jeroen Belleman
On Sun, 26 Jul 2026 10:41:38 +0200, Jeroen Belleman wrote:
On 7/26/26 10:04, Cursitor Doom wrote:
On Sat, 25 Jul 2026 00:07:40 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 23:29, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 23:17:16 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 20:56, joegwinn@comcast.net wrote:
On Fri, 24 Jul 2026 19:51:18 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 7/24/26 19:07, Cursitor Doom wrote:
Gentlemen,
Does anyone here have a dedicated TDR? I'd previously assumed >>>>>>>>> they were only good for 'distance to fault' applications, but was >>>>>>>>> disabused of my ignorance during a recent read of Tom Lee's
Planar Microwave Engineering, in which it was stated that they >>>>>>>>> can also be used for identifying the value of caps and inductors >>>>>>>>> by means of the shape of the reflection and doing a bit of
integration to it.
A TDR is one of the vanishingly few items of test gear I do not >>>>>>>>> possess. I have a 50ps pulse generator which can be used with a >>>>>>>>> fast 'scope to achieve a certain amount of functionality, but I >>>>>>>>> was wondering how much more useful and versatile a stand-alone >>>>>>>>> TDR might be.
I use a VNA for determining the value of small caps and coils and >>>>>>>>> find it hard to believe any TDR could give better results than >>>>>>>>> that. However, once again I could be wrong. Info, anyone?
I've done both frequency domain and time domain measurements and >>>>>>>> you can easily use Fourier transforms to get from one to the other >>>>>>>> after the fact. Invariably, I found that HP8753D VNA measurements >>>>>>>> followed by an inverse Fourier transform were superior in terms of >>>>>>>> S/N.
My TDR was a Tektronix S-6 sampler and an S-52 pulser, which have >>>>>>>> a slight edge in terms of bandwidth. If I averaged >10k
measurments, the S/N approached that of the HP8753D, but a lot of >>>>>>>> patience was needed.
In the end, sometimes one is better, sometimes the other.
Jeroen Belleman
To this I would add one comment:
VNAs have fairly narrow Receive and Video Bandwidths, often a few >>>>>>> MHz,
so the smallest discontinuity must be tens of meters long.
By contrast, a TDR has a bandwidth in the GHz, so far shorter
discontinuities may be detected.
Joe
No, no, it doesn't work like that. You use the VNA to acquire the
S11 frequency response over its full bandwidth. You then apply an
inverse Fourier transform to the complex S11 frequency data to
obtain the impulse response. Then you apply a time integration to
finally get the TDR plot with an equivalent bandwidth of the full
sweep of the VNA.
Note that the VNA has a directional coupler, so you'll get only the >>>>>> reflection, not the incident *plus* the reflection like a TDR. The >>>>>> nice thing is that with proper VNA calibration, the reflection will >>>>>> start exactly at time zero and many setup parasitics are suppressed. >>>>>>
I could resolve centimeter-sized discontinuities with ease with S11 >>>>>> data from the HP8753D sweeping up to 6GHz.
Hmm. The people I was watching were not doing anything like the
above. How long does data collection take? TDRs are fast.
Joe
The VNA sweeps the whole range in a second or so. The HP5387D has a
wimpy CPU, so it takes a few seconds to do the transform. I also did
the transform after transferring the data to my PC, which is more
laborious, but the actual transform is then basically instantaneous.
(I did not time it.)
My TDR was a Tektronix 7904, with 7T11 and 7S11 plug-ins driven by a
VME DAC and read out with a VME ADC. That was pretty slow, especially
when I averaged measurements to improve the S/N.
Jeroen Belleman
Interesting. I have the 'C' suffix version of your VNA. Can you tell me
whereabouts the fourier transforms options are to be found buried in
the menu options? I've never come across them. Might not be in exactly
the same place, but shouldn't be too far removed....
It's an option. If you have it, there should be a 'TRANSFORM MENU'
item on the screen after pushing the "SYSTEM' button.
Jeroen Belleman
If you don't have the option installed, it looks like you can install it
for free:
<https://www.kirkbymicrowave.co.uk/Everything-you-wanted-to-know-about- >the-HP-8753-VNA/>
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