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Yes, 3.333... is correct value. Normally I use VNWA port extension
window to compute physical length from time.
SDR-Kit 4-pc cal kit, which uses a F-F adapter with dimensions, length =
32.5mm and includes Amphenol marking. Looks very much like:https://www.amphenolrf.com/downloads/dl/file/id/3542/product/5386/031_219_rfp1_customer_drawing.pdf
Based on SDR-Kit calibration parameters, Short difference between Male
and Female is 77.11pS one way.
Measured external surface to plane = 8.5mm (both ends)
Plane to plane = 32.5 - 8.5 - 8.5 = 15.5mm
15.5 * 3.3333 = 51.66pS
Vf = 51.66 / 77.11 = 0.670
Correction for Short cal device calculated Plane to short condition
using 3.3333ps/mm is 11.4mm
Can't tell where the short condition plane is within the device, but
11.4mm between ref and short seems plausible.
On 5/22/20 5:23 PM, Kurt Poulsen wrote:
Hi John and David
Sorry for interfering I this debate. The calculation of the delay is not correct. You state 3ps/mm it is 1/3 = 3.3333333333ps/mm so better to divide by 3. The velocity factor is indicated to 0.67 and for ptfe (Teflon) is 0.695 (some manufacturer state 0.7
The question not yet responded to asked by Dave is why a negative delay and even twice the delay. It is the convention used by the VNWA and to be understood as the time travel from the calibration plane to the reflection point and back again to the calibration plane. A negative because that is the travel time for moving the reflection point back to the calibration plane. In the VNWA the Extension port delay demonstrate clearly this phenomena as adding a positive one way delay, is like moving the calibration plane forward e.g. to the end of a short where the phase and ImageZ (=0) trace then is straight line (Phase reference 180/-180degree).
This is contradiction to the HP and other manufacturer which uses the term offset delay which for calibration standards are a positive number and is just a term describing the one way travel time form calibration plane to reflection point/plane. The calculation inside the HP VNA used this to calculate the double offset for a reflection, so it is a matter of the formulas used.
Fra: VNWA@groups.io <VNWA@groups.io> På vegne af John KN5L
Sendt: 22. maj 2020 23:01
Emne: Re: [VNWA] Insertion delay needed for BNC-BNC couplers UG491A/U (M-M) and UG914/U (F-F)
On 5/22/20 3:11 PM, David Feldman via groups.io wrote:
trying to understand, so please bear with (and correct) me --- I BNC Male Short:
gather that at ~3 pSec/mm, the physical distance between the BNC short
Male ref plane is outside edge. Using drawing above, full length is 15mm. ref plane is recessed a little and short is also recessed a little from end. Lets call ref plane to short as ~13mm. Velocity factor of 0.67.
13mm * 3p/mm * 1/0.67 * 2 = 116.4ps
Measured value is 113.5ps. Physical length for 113.5ps = 12.7mm