On 2022-05-31 05:50:-0700, you wrote:
Hi, out of curiosity I've made a measurement of my nanovna H4 stock RG316 cable
I flashed v1.2 last night. Using cal from 2.5-32.5 MHz, 401 p. Changed freq range to 3-5 MHz
I have 3X RG316
3660mm
4580mm
4580mm
One connected M-F, and the other connected M-M, for a total length of
12.820m
Following the user manual...
Mult length X 4 = 51.280
Initial VOP estimate 70% yields frequency
4095164 Hz
So I chose a freq range of 3-5 MHz.
Initial length reported as 13.20m. When I removed a M-M adapter on the end, the length lost 10mm, which is reasonable.
13.2-12.820=0.38 which is significantly off, but VOP is a possible reason.
remove M-M adapter > 13.19m
VOP 70>68 > 12.82m.
So changing the VOP from 0.70 to 0.68 changed the reported length to what I physically measured.
Screen and s1p attached.
The phase might have been more accurate for finding the exact distance, but I just threw this together for example.
Continuing...
I got interrupted for 30 minutes, during which the nVNA was running and charging.
Returning, I reconnected the coax in exactly the same way and at the same location on the bench.
This time reported length is 12.88m, a change of 60mm.
I turned on phase, and moved the marker to the phase change. f = 3.955 MHz, vs my estimated 4.095164. Close enough.
I changed the freq range to 3.8-4.2 MHZ, with the understanding that the new range would use interpolated values.
Orig range 2.5-32.5 MHz = 75 kHz/step.
New range 3.8-4.2 MHz >> 400 kHz, meaning that only 3-4 original cal points are included in the interpolation. At least the target is in the middle of that range.
I recalibrated 3.8-4.2 MHz, 401 p. SOLI.
Length still reported as 12.88m. Phase f = 3.956 MHz.
Screen images and s1p files attached.
Note that changing VOP to 67% >> 12.69m, 69% >> 13.07mm, so this is as close as I can get.
The uncertainties are the changing length reported over time, the actual coax VOP, and the accuracy of the nVNA (see changing length).
I didn't have time to compare with TDR.
~R~
72/73 de Rich NE1EE
The Dusty Key
On the banks of the Piscataqua
Rich NE1EE