Re: Insertion delay needed for BNC-BNC couplers UG491A/U (M-M) and UG914/U (F-F)

John KN5L

Hi Kurt,

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:

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.

John KN5L

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.
Kind regards

-----Oprindelig meddelelse-----
Fra: <> 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)

Hi Dave,

On 5/22/20 3:11 PM, David Feldman via wrote:
trying to understand, so please bear with (and correct) me --- I
gather that at ~3 pSec/mm, the physical distance between the BNC short
BNC Male 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

John KN5L

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