When the author of NanoVNA saver implemented "offset delay" it was discussed in this group. The consensus was that it should be in accordance with the standard definitions used for calibration kit parameters. If a set of commercial loads is supplied they will provide this data. In fact one of the members of this group generated the parameters for the cal loads shipped with the NanoVNA and published them in this group. A screenshot of the calibration entry screen is below.
If you want to add an extension to a calibrated "reference plane" you can do this in NanoVNA Saver by determining the delay in picoseconds through the extension and entering this as a negative number in the Calibration screen. The negative number is by industry convention when a port extension is connected to a reference plane.
An example of this is attaching a 15.5 cm (6 inch) RG-316 cable to a calibrated VNA port. The velocity factor is about 70% so the "electrical length" of the cable is 22.2 cm. The speed of light is about 3.33 ns per meter so the delay is 3.33 * .222 = .74 ns or 740 picoseconds. Entering -740 in NanoVNA Saver gives the result below.
If we do the port extension on a NanoVNA-H4 we need to be aware that the device does not always conform to industry standards. For example the CH0 and CH1 ports should be designated as Port 1 and Port 2 (they are on later generation products). The firmware has had different developers and they chose to use the term "e-delay" or "electrical delay" and used it differently than "offset delay". The correct input for a port extension requires the "round trip" delay to be entered as a positive number . So in this case +1480 picoseconds is required. A screenshot after this entry is attached.
A nice video on this topic was done by W2AEW >>
Summary: NanoVNA Saver uses the conventional term "offset delay" and implements it correctly. Some NanoVNA firmware uses a different variable e-delay and users need to be aware of how to use it correctly.
Roger
Roger Need
