Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Jim,
It renormalization doesn't change the Q in the measured test circuit, but it can compute what the Q would be at the new impedance.
The S parameters are a complete description of a linear 2-port, allowing (with enough calculation) the prediction of the 2-port behavior in any impedance environment.
--John
toggle quoted message
Show quoted text
On Fri, Feb 14, 2025 at 05:31 PM, Jim Lux wrote:
But renormalization just changes the calculation for the S parameters.
It doesn't fix the change in Q.
-----Original Message-----
From: <[email protected]>
Sent: Feb 14, 2025 4:20 PM
To: <[email protected]>
Subject: Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port
renormalization
Jim,
Of course the change in termination impedance changes the filter response. The
point of the renormalization is that the response can be recalculated to show
what it would be at the different impedance. Doing so requires knowledge of
the transfer function and the impedance of both ports.
Similar case: If you know the open circuit voltage and output impedance of a
source, you can compute its output level into any impedance.
--John
On Fri, Feb 14, 2025 at 09:42 AM, Jim Lux wrote:
Since most filters are a series of resonators of some kind or another,
terminating them in a resistance other than the design resistance will
probably change the filter characteristics. Consider a filter that
effectively
has an input that is a RLC circuit, where the R is the terminating impedance
of the source. If you change R from, say, 300 ohms to 50 ohms, then the Q
will be different. That will certainly change the skirts, and will also
probably change the overall passband (since most filters are stacked up
responses of multiple resonances).
|
Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
But renormalization just changes the calculation for the S parameters.
It doesn't fix the change in Q.
toggle quoted message
Show quoted text
-----Original Message----- From: < [email protected]> Sent: Feb 14, 2025 4:20 PM To: < [email protected]> Subject: Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization Jim, Of course the change in termination impedance changes the filter response. The point of the renormalization is that the response can be recalculated to show what it would be at the different impedance. Doing so requires knowledge of the transfer function and the impedance of both ports. Similar case: If you know the open circuit voltage and output impedance of a source, you can compute its output level into any impedance. --John On Fri, Feb 14, 2025 at 09:42 AM, Jim Lux wrote:
Since most filters are a series of resonators of some kind or another,
terminating them in a resistance other than the design resistance will
probably change the filter characteristics. Consider a filter that effectively
has an input that is a RLC circuit, where the R is the terminating impedance
of the source. If you change R from, say, 300 ohms to 50 ohms, then the Q
will be different. That will certainly change the skirts, and will also
probably change the overall passband (since most filters are stacked up
responses of multiple resonances).
|
Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Nizar,
I put series 390 ohm resistors on both port 0 and port 1, creating a 440 ohm environment for the filter, close to the 430 ohm renormalization I showed before (see message 39460).
I then normalized the S21 measurement by connecting the two resistors end for a thru measurement.
Attached is the filter S21 magnitude in the 440 ohm environment. It matches very well with the Z=430 renormalized measurement I posted before, allowing for the loss in dynamic range due to the resistors.
--John
toggle quoted message
Show quoted text
On Fri, Feb 14, 2025 at 10:28 AM, Team-SIM SIM-Mode wrote:
Hi
it seems to me that for a linear or quasi-linear circuit without active
elements, it should be correctly compensated by single precision floating
point calculation using the Z renormalization option and this with the
simplest possible hardware tricks during the measurements, thus avoiding
hardware imperfections of the ferrite core or resistance transformers and
without any calibration alteration.
May be Jhon can illustrate for us response comparaison between H4+Z
renormalization and oxilloscope classic measurements of the same ceramic
filter. it will be very appreciated.
73's Nizar .
|
Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Jim,
Of course the change in termination impedance changes the filter response. The point of the renormalization is that the response can be recalculated to show what it would be at the different impedance. Doing so requires knowledge of the transfer function and the impedance of both ports.
Similar case: If you know the open circuit voltage and output impedance of a source, you can compute its output level into any impedance.
--John
toggle quoted message
Show quoted text
On Fri, Feb 14, 2025 at 09:42 AM, Jim Lux wrote:
Since most filters are a series of resonators of some kind or another,
terminating them in a resistance other than the design resistance will
probably change the filter characteristics. Consider a filter that effectively
has an input that is a RLC circuit, where the R is the terminating impedance
of the source. If you change R from, say, 300 ohms to 50 ohms, then the Q
will be different. That will certainly change the skirts, and will also
probably change the overall passband (since most filters are stacked up
responses of multiple resonances).
|
Re: testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Hi
it seems to me that for a linear or quasi-linear circuit without active elements, it should be correctly compensated by single precision floating point calculation using the Z renormalization option and this with the simplest possible hardware tricks during the measurements, thus avoiding hardware imperfections of the ferrite core or resistance transformers and without any calibration alteration.
May be Jhon can illustrate for us response comparaison between H4+Z renormalization and oxilloscope classic measurements of the same ceramic filter. it will be very appreciated.
73's Nizar .
|
testing non-50 ohm filters was Re: [nanovna-users] NanoVNA port renormalization
Since most filters are a series of resonators of some kind or another, terminating them in a resistance other than the design resistance will probably change the filter characteristics. Consider a filter that effectively has an input that is a RLC circuit, where the R is the terminating impedance of the source. If you change R from, say, 300 ohms to 50 ohms, then the Q will be different. That will certainly change the skirts, and will also probably change the overall passband (since most filters are stacked up responses of multiple resonances).
|
Re: NanoVNA port renormalization
Here is an article on ceramic filters by a popular manufacturer Murata.
Attached is an excerpt showing the importance of having a proper matching load for the device. This is for a 455 kHz. IF part with a recommended 3000 ohm load.
As Donald Kirk found in his last posted using a lower impedance load results in a downward shift of the center frequency. PortZ in the NanoVNA will not correct this. Also note that ripple will be affected.
Bottom line - use a proper test setup if you want accurate results.
Roger
|
Re: NanoVNA port renormalization
Hi John and gang,
I decided to keep things relatively simple and just used my signal generator with matching transformer to feed the ceramic filter and then compared response using either a 56 ohm load or a 330 ohm load with my oscilloscope connected across the load for measurement (see attached test setup picture).
To my amazement there was very little difference in bandwidth regardless of the load (56 ohm or 330 ohm load), and the difference may have just been measurement error, but the frequency where the response was down 3 dB and 20 dB was definitely different between the two loads with the frequencies shifted downward when using the 56 ohm load. Also the peak signal frequency (less call this the resonate frequency) shifted downward when using the 56 ohm load.
3 dB down frequencies: 56 ohm load (10.5478 MHz & 10.8608 MHz) = bandwidth of 313 KHz
3 dB down frequencies: 330 ohm load (10.5815 MHz & 10.8831 MHz) = bandwidth of 302 KHz
Not much difference in bandwidth but note that the 56 ohm load shifted the 3 dB down frequencies downward (lets say 28 Khz downward shift when you take the average.)
20 dB down frequencies: 56 ohm load (10.4438 MHz & 10.9778 MHz) = bandwidth of 534 KHz
20 dB down frequencies: 330 ohm load (10.4668 MHz & 10.9998 MHz) = bandwidth of 533 KHz
Really identical bandwidth between the loads as far as I'm concerned which really surprised me but the 56 ohm load shifted the 20 dB down frequencies downward approximately 23 KHz.
Also note that the frequency of peak signal was as follows (lets call this the resonate frequency for lack of a better term):
56 ohm resistor 10.660 MHz
330 ohm resistor 10.690 MHz
This is a difference of 30 KHz which pretty much falls in line with the downward shift in 3 dB and 20 dB points when using the 56 ohm load as noted above.
While this was a pretty simplistic test I do believe it shows that the frequency response of the filter does get altered by the physical load (mostly a shift in the resonate frequency) but on the other hand it's really not as drastic as I would have thought, nevertheless I don't understand how this can be simulated in software but maybe it's so minor that it's not obvious or even critical in this application.
I think the only way to confirm anything goes back to someone using either L pad matching or transformer matching for comparison with the renormalization routine when measuring the ceramic filter.
Don
|
Re: NanoVNA port renormalization
Hi Mike,
Insertion loss and bandwidth measurements nearly identical between the l pad matching system versus using transformers which thankfully is what should have happened. The transformers which improved my dynamic range by about 27 dB allowed me to see the filter response that¡¯s way down in amplitude (way down in the mud so to speak) as you get away from the main resonate frequency and that¡¯s what I was hoping for.
Don
|
Re: NanoVNA port renormalization
Hi Don,
Missed it. How to the response curves compare?
Mike N2MS
toggle quoted message
Show quoted text
On 02/14/2025 9:19 AM EST Donald Kirk via groups.io < wd8dsb@...
wrote:
Hi Mike,
Not sure you saw my most recent post as I switched to transforms earlier
today to improve my dynamic range and posted pictures of the results.
Don
|
Re: NanoVNA port renormalization
Hi Mike,
Not sure you saw my most recent post as I switched to transforms earlier today to improve my dynamic range and posted pictures of the results.
Don
|
Re: NanoVNA port renormalization
Don,
I use construct resistive minimum loss attenuators for this application but keep in mind the attenuation decreases the dynamic range of the measurement.
Mike N2MS
toggle quoted message
Show quoted text
OOn02/14/2025 9:03 AM EST Donald Kirk via groups.io < wd8dsb@...
wrote:
Sorry, here are the attachments per my previous post.
Don
|
Re: NanoVNA port renormalization
Sorry, here are the attachments per my previous post.
Don
|
Re: NanoVNA port renormalization
Hi John,
As Nizar mentioned renormalization is not available on my NanoVNA which is the NanoVNA-F. This morning I decided to improve my measurement dynamic range so I replaced my L pad matching networks with binocular core transformers that I wound using 2 turns on the primary and 5 turns on the secondary. This does not yield a perfect transformation for a 50 to 330 ohm impedance system but its close (it provides a 50 ohm to 312.5 ohm transformation). Using the transformer improves the dynamic range a lot because the transformers eliminate the 27.74 dB loss encountered when using the two L matching pads.
I've attached a picture of my new plot using the transformers in place of the L matching pads, and I've also attached the Murata datasheet for my ceramic filter and it looks very similar to my results.
Since I don't have a NanoVNA that has normalization I'm going to go and use LTSpice to simulate what happens to the bandpass characteristics of the ceramic filter when it's not properly terminated into its input and output impedances versus when it's terminated into its input and output impedances so see if that provides some clarity to my thinking, as my original instinct is exactly what Roger previously said which is as follows: "Non linear devices or active circuits will not be tested with the impedance they are designed to operate with and simulation using this method will not yield correct results." I might also use my signal generator and scope to measure the passband characteristics using various loads to see if we are dealing with a linear or non linear response.
Just FYI, and thanks for the discussion.
Don
|
Re: NanoVNA port renormalization
Don,
I didn't do that for this test, but at some point in the past I did all that. I had unknown crystal filters and used the NanoVNA renormalization to find the Z that gave the best looking response, then made matching networks to test and then use them.
How does your filter look if you connect it directly (no matching) and use the renormalization?
--John
toggle quoted message
Show quoted text
On Thu, Feb 13, 2025 at 04:57 PM, Donald Kirk wrote:
Hi John,
I'm a little late to the party but this topic peaked my interest and my
thinking is very much aligned with Rogers. I think the one comparison test
you are missing is what filter response curve you get if you properly
terminate the input and the output of the ceramic filter during measurement on
the NanoVNA using simple resistive L matching pads as follows:
Assuming the input and output impedance of the ceramic filter is 330 ohms.
1) Build resistive L matching pads to match 50 ohms to 330 ohms (this would be
a shunt resistance of 54 ohms and a series resistance of 304 ohms when
rounding off values).
2) Connect the 50 ohm side of one matching pad to Port S11 on the VNA and
connect the 50 ohm side on the other matching pad to Port S21 on the VNA, and
connect the 300 ohm side of each matching pads together (this should be done
with your fixture in place but the Ceramic filter replaced with a wire
connecting the 300 ohm sides of the L matching pads together.
3) Do a through calibration on the VNA (this should zero S21 Logmag and S21
Phase to zero.
4) Replace the above mentioned wire that connected the two matching pads
together with the ceramic filter and observe the S21 Logmag filter response on
the VNA and this should become your baseline frequency response curve to
compare with your other methods.
My fixture was not perfect (yours looks much better) as my components had
reasonably long leads and the one thing I noted is that I needed a very good
ground plane connected to the common on my test fixture. My goal was to
measure insertion loss as well as the 3 dB and 20 dB Bandwidth for comparison
with the stated specs of the 10.7 MHz ceramic filter I was testing (part
number SFE10.7MA5-A which was sold by good old Radio Shack).
Here is what I measured.
Insertion Loss = 3.0 dB (spec 6 dB max).
3dB Bandwidth = 290 KHz (spec 280 +/- 50 KHz)
20dB Bandwidth = 540 KHz (spec 650 KHz max)
I've attached a picture showing my results
Just FYI, and I apologize in advance if you have already done the above test
that I mentioned.
Don
|
Re: NanoVNA port renormalization
Hi Donald
I think what you have done physically with your Deeplec Nano-F is almost what is done by jhon but with H4 and z port renormalisation and physically cute & short connection with optimised calibration terminaisons , jhon can renormalise to any Z value quicly , Nano-F does not have this Z renormalisation option .
73s Nizar
|
Re: NanoVNA port renormalization
Hi John,
I'm a little late to the party but this topic peaked my interest and my thinking is very much aligned with Rogers. I think the one comparison test you are missing is what filter response curve you get if you properly terminate the input and the output of the ceramic filter during measurement on the NanoVNA using simple resistive L matching pads as follows:
Assuming the input and output impedance of the ceramic filter is 330 ohms.
1) Build resistive L matching pads to match 50 ohms to 330 ohms (this would be a shunt resistance of 54 ohms and a series resistance of 304 ohms when rounding off values).
2) Connect the 50 ohm side of one matching pad to Port S11 on the VNA and connect the 50 ohm side on the other matching pad to Port S21 on the VNA, and connect the 300 ohm side of each matching pads together (this should be done with your fixture in place but the Ceramic filter replaced with a wire connecting the 300 ohm sides of the L matching pads together.
3) Do a through calibration on the VNA (this should zero S21 Logmag and S21 Phase to zero.
4) Replace the above mentioned wire that connected the two matching pads together with the ceramic filter and observe the S21 Logmag filter response on the VNA and this should become your baseline frequency response curve to compare with your other methods.
My fixture was not perfect (yours looks much better) as my components had reasonably long leads and the one thing I noted is that I needed a very good ground plane connected to the common on my test fixture. My goal was to measure insertion loss as well as the 3 dB and 20 dB Bandwidth for comparison with the stated specs of the 10.7 MHz ceramic filter I was testing (part number SFE10.7MA5-A which was sold by good old Radio Shack).
Here is what I measured.
Insertion Loss = 3.0 dB (spec 6 dB max).
3dB Bandwidth = 290 KHz (spec 280 +/- 50 KHz)
20dB Bandwidth = 540 KHz (spec 650 KHz max)
I've attached a picture showing my results
Just FYI, and I apologize in advance if you have already done the above test that I mentioned.
Don
|
To measure insertion loss, you connect the channel 1 to the common port of the diplexor and channel 2 to one of the output ports while terminating the unused port with a 50 Ohm load. Move channel 2 to the other output port and terminate the remaining output port with 50 Ohms.
To measure isolation you connect channel 1 to one of the output ports and channel 2 to the other while termination the common port in 50 Ohms. Switch the connections on the output ports to measure the other isolation.
Gary
W9TD
|
Hi Joe
You seems need an S21 Logmag measurement , Knowing that dynamic range of H4 on the UHF are limited to 50db you should not expect more then -45db values for the isolation measurements between the Two bands, obviously you need a 401 sweep points , and many complete 401 point calibrations for each bands (with isolation and Throught) , each calibration should be focused on the desired slice of the band under test, you need to reset the old calibration for each new calibration to be sure to avoid interpolation errors ,
Good Luck.
73's Nizar
|
I have a NanoVNA-H4,
I have no problems checking antenna SWR etc.
But what I want to do now is to check the performance of a "Diplexor"
You know one of these things that splits/combines a 2 meter and 440 antenna into one common output.
You know one of these.
<>
I want to measure the insertion losses for each band.? and then the amount of isolation between the bands.
Can anyone show me a video on how to do this? OR give me a step by step on how to do it?
Joe WB9SBD
|
Roger Need
Gary W9TD
