On Wed, Jan 22, 2025 at 11:41 AM, Team-SIM SIM-Mode wrote:
Hi all
something doesn't seem to be working very well, the most recent firmware
1.2.40 of DiSlord installed on SEESII H4, I really appreciated the
characteristic impedance conversion function for SWR measurements and for the
Smith graph, but the impedance values ??of port2 should not change in fact
they are what they are.
but by measuring the input of port2 with the S11 Smith function it gives 77.7
Ohm as long as the conversion value 50-->77.7 Ohm is configured while it is
supposed to give 50 Ohm, then by putting a 50 Ohm load on S11 Smith it
displays the value 50 Ohm,
So the Port2 impedance seems has really changed impedance when we put 50 Ohm
--> 77.7 Ohm if not how can we explain this displayed value which does not
match our 50 Ohm prediction ?
Nizar,
In my other post I mentioned that the NanoVNA measures the actual impedance and gave several screenshots that were S11 shunt measurements. These were made using only CH0 and a test jig. Ch1 was not used for these tests. I pointed out that even when you change reference impedance the impedance measurement is the same for S11 shunt measurements . What I neglected to do was post what happens when you do measurements of CH1 when you change the reference impedance. This was an error on my part and I apologize to the group if this caused confusion and disagreement.
I made a complete set of measurements using CH0 alone in S11 shunt mode and some S11/S21 measurements. I have put them in a pdf report because this group does not permit inline text and photos. It is attached to this post.
You will note that your measurements were correct but the reason why needs to be explained. When you change the reference impedance from 50 ohms the hardware will still make measurements in the same way but the firmware will adjust all the calculations to be based on the new reference impedance. This includes the measurement of CH1 if you are connected directly to it. So if you selected 75 ohms as the reference impedance the measurement of CH1 will be close to 75 ohms even though it is physically closer to 50 ohms. In the attached report I show an example where I put 200 ohms in series between CH0 and CH0 and the measurement on the Smith Chart is 275 ohms (200+75).
Regards - Roger
Roger Need