What is the possible smalles resolution (in feet) of impedance mismatch detection that is possible to achieve with this? Is it derived only from the phase resolution?
The resolution of a TDR measurement made with a VNA is function of the bandwidth of the sweep. If the swept measurement is performed between a Start frequency of 10 MHz and a Stop frequency of 18 GHz, then the sweep bandwidth is 17990 MHz. For the Lowpass method, the time resolution (step size) will be 1/(2*17990e6) or 27.8 pS. For the Bandpass method, the resolution is half of that (no 2 in the denominator) or 55.6 pS. ( See coppermountaintech.com/time-domain-processing/ for Lowpass vs Bandpass explanation). The time resolution translates to a distance resolution by multiplying by the Guide Velocity, Vg, which is the speed of the RF signals in the cable. This is the speed of light, c, multiplied by the Velocity Factor, which is about 0.66 for solid PTFE dielectric, 0.91 or so for low-loss foamed PTFE and 1.0 for air-line. For a solid PTFE cable, the distance resolution would be 5.5 mm for 27.8 pS and 11 mm for 55.6 pS. This means that each point on the Time Domain screen represents a distance of 5.5 or 11 mm. The number of points chosen for the VNA sweep does not affect this, it only sets the maximum time or distance. If 1,000 points are set, then the maximum time will be 27.8 nS for Lowpass and 55.6 nS for Bandpass. That’s 5.5 or 11 meters maximum range.
Great video! This video quickly got me up and running with TDR on the S5085.
Excellent! We're glad the video worked for you, Brian is a pro! 😀
What is the possible smalles resolution (in feet) of impedance mismatch detection that is possible to achieve with this? Is it derived only from the phase resolution?
The resolution of a TDR measurement made with a VNA is function of the bandwidth of the sweep. If the swept measurement is performed between a Start frequency of 10 MHz and a Stop frequency of 18 GHz, then the sweep bandwidth is 17990 MHz. For the Lowpass method, the time resolution (step size) will be 1/(2*17990e6) or 27.8 pS. For the Bandpass method, the resolution is half of that (no 2 in the denominator) or 55.6 pS. ( See
coppermountaintech.com/time-domain-processing/
for Lowpass vs Bandpass explanation). The time resolution translates to a distance resolution by multiplying by the Guide Velocity, Vg, which is the speed of the RF signals in the cable. This is the speed of light, c, multiplied by the Velocity Factor, which is about 0.66 for solid PTFE dielectric, 0.91 or so for low-loss foamed PTFE and 1.0 for air-line. For a solid PTFE cable, the distance resolution would be 5.5 mm for 27.8 pS and 11 mm for 55.6 pS. This means that each point on the Time Domain screen represents a distance of 5.5 or 11 mm. The number of points chosen for the VNA sweep does not affect this, it only sets the maximum time or distance. If 1,000 points are set, then the maximum time will be 27.8 nS for Lowpass and 55.6 nS for Bandpass. That’s 5.5 or 11 meters maximum range.