Re: Building Pi Network with VNA given values
All four are all 2 element ell networks. If the values have been
calculated correctly each one would provide the required match. (1) has
low-pass characteristics. (4) is a high-pass network. The other two
probably have less frequency selectivity. A Pi matching network could
also do the job. The typical shunt C, series L, shunt C, is a stronger
low-pass filter, so it will attenuate harmonics better. If an element
in a Pi filter is removed, giving it an ell topology, it will not
provide the same match or filtering characteristic. The values of the
remaining two components would both need to be recalculated. There are
theoretically an infinite number of networks that can provide a given
impedance transformation. They will all have different frequency
responses. Even if you stick with a shunt C, series L, shunt C Pi
network, there are many possible sets of component values that will
provide the same impedance transformation, but with different
(transmission) frequency responses. Usually a network Q value is first
chosen.
Dave
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On 2025-03-13 22:16, shlomo537678 via groups.io wrote: Hi All.
I need to build a Pi Network for my circuit as shown in the fig below.
1741926237187.png
So I have a 'Pi Matching Network' in my circuit. The datasheet asked me to build a Pi Matching Network. ( You know, how there is a series component, a source shunt component and a Load shunt component. )
Anyway, my VNA keeps telling me this: The measured load impedance is 31.9-58.5j.
The VNA is automatically generating these four groups below ( group 1 thru 4 ) of available matching parameters on the screen:
1. 5.24pF capacitor for source shunt and 28.8nH inductor in series.
Does that mean, this group does not need a Load Shunt at all? Does this mean that the proper tuning has been achieved with just a capacitor for source shunt and an inductor in series?
2. 23.1nH inductor for source shunt and 12nH inductor in series.
Does that mean, this group does not need a Load Shunt at all? Does this mean that the proper tuning has been achieved with just a inductor for source shunt and an inductor in series?
3. 97.5nH inductor for load shunt and 23.3nH inductor in series.
Does that mean, this group does not need a Source Shunt at all? Does this mean that the proper tuning has been achieved with just a inductor for load shunt and an inductor in series?
4. 15.3nH inductor for load shunt and 5.21pF capacitor in series.
Does that mean, this group does not need a Source Shunt at all? Does this mean that the proper tuning has been achieved with just a inductor for load shunt and a capacitor in series?
If the answer is yes to all the 4 above questions, then I still cant believe that a 'Pi matching Network' can exist with 1 of the 3 components totally missing.
Ty for your reply!
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Building Pi Network with VNA given values
Hi All.
I need to build a Pi Network for my circuit as shown in the fig below.
1741926237187.png
So I have a 'Pi Matching Network' in my circuit. The datasheet asked me to build a Pi Matching Network. ( You know, how there is a series component, a source shunt component and a Load shunt component. )
Anyway, my VNA keeps telling me this: The measured load impedance is 31.9-58.5j.
The VNA is automatically generating these four groups below ( group 1 thru 4 ) of available matching parameters on the screen:
1. 5.24pF capacitor for source shunt and 28.8nH inductor in series.
Does that mean, this group does not need a Load Shunt at all? Does this mean that the proper tuning has been achieved with just a capacitor for source shunt and an inductor in series?
2. 23.1nH inductor for source shunt and 12nH inductor in series.
Does that mean, this group does not need a Load Shunt at all? Does this mean that the proper tuning has been achieved with just a inductor for source shunt and an inductor in series?
3. 97.5nH inductor for load shunt and 23.3nH inductor in series.
Does that mean, this group does not need a Source Shunt at all? Does this mean that the proper tuning has been achieved with just a inductor for load shunt and an inductor in series?
4. 15.3nH inductor for load shunt and 5.21pF capacitor in series.
Does that mean, this group does not need a Source Shunt at all? Does this mean that the proper tuning has been achieved with just a inductor for load shunt and a capacitor in series?
If the answer is yes to all the 4 above questions, then I still cant believe that a 'Pi matching Network' can exist with 1 of the 3 components totally missing.
Ty for your reply!
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Re: Am I in the right track ?
Do you have a trace inside the board to be the other half of the transmission line?
One turn through the ferrite is not enough. The impedance goes up approximately as the square of the turns.
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Re: Am I in the right track ?
Hi everyone,
No, I haven't abandoned yet ! I got my revised pcb (attached picture) yesterday
1- Revised ground plane dimensions which I made the same as the test board shown in the antenna datasheet.
2- Controlled impedance PREPREG material for the 4 layer PCB.
3- Revised feedline width for 50ohm target impedance
4- Revised return path width in adjacent layer
5- Fixed a jumper trace mistakenly placed in the feedline path.
I have calibrated O-S-L with a 0.1% 50ohms 0603 chip resistor soldered directly on the end of the cable.
I have replaced my RG174 with a brand new RG316 36" extension from Digi-Key
I added a 6" piece of RG316 opened at one end and SMA connected to the extension at the other.
I calibrated with everything attached to the VNA and finally soldered back the open end right where the source swill be.
I have put 2 Fair-rite 61 ferrites on the cable, one at each ends.
I soldered a 0 ohm resistor to bypass the matching network
Picture 1 : New board front
Picture 2 : New board back
Picture 3 : Test measurement setup
Picture 4 : Antenna pcb feedline and return path
Picture 5 : Measurement with board laid on a wood plank (no matching)
Picture 6 : Measurement with board inside its plastic case (no matching)
Picture 7 : Calculated correction values from Sim Smith (High Pass)
Picture 8 : Installed L and C values (High Pass)
Picture 9 : Measurement with L and C installed
I think I have improved the antenna performance with the new board. Maybe I have a better quality setup also. As you can see, once the board is inside the box, it is not too bad. But unfortunately, I'm the kind of who loves to chase perfection. Using the provided numbers from the nanoVNA, I tried to compute some matching network values to better tune the antenna in Sim Smith. I ordered 0603 inductor and capacitor dewsign kits at DigiKey. Not those cheapy ones from Amazon. I installed L and C into my matching network but as you'll see with the pictures, it did not helped at all.
1- Am I going too far, and should I stay with the values from the initial measurements ?
2- What am I missing here ?
3- What would be your advices if I wanted to improve the response to something close to like 2:1 VSWR ?
4- From here, I am really scratching my head...
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Re: Help with LPF Measurement
Very good Mitch.
Happy to see you suceeded in beating the electrons into submission.
Lesson learned... Neatness counts.
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Re: Help with LPF Measurement
yay indeed.. Pretty cool.
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-----Original Message----- From: < [email protected]> Sent: Mar 13, 2025 11:31 AM To: < [email protected]> Subject: Re: [nanovna-users] Help with LPF Measurement Jim, Dave, et al., Thank you very much for your suggestions. I rebuilt the filter using discarded SMA connectors I found in my junk box along with actual 270 pF caps that I ordered overnight from AMZN. It's all on the same board I've reused several times, so please excuse the abrasions, drill attempts, etc. The results are just as you predicted. Images attached. Again, thank you very much for your help. Yay!! Mitch NK3H
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Re: Help with LPF Measurement
THAT looks much better built .. and shows the predicted results ... GOTCHA :-)
looks neat .. and works like it should
so you see its very often not just the components you use but how you arrange them
and as higher you go in frequency as more you have to take care of such things (no way to build such an ugly manhatten style construction for uhf or shf and show predicted results)
i guess main thing is the connectors .. and solder the caps direct to ground (with short leads)
finetuning could be done with the caps and with the coils (if you can move the windings a? bit on the core)
anyway .. you for sure learned something (and others on the group see what to do and what NOT to do if building a filter) ... or in fact we all learned from it :-)
happy homebrewing ... 73
dg9bfc sigi
Am 13.03.2025 um 19:31 schrieb Mitch NK3H:
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Jim, Dave, et al.,
Thank you very much for your suggestions. I rebuilt the filter using discarded SMA connectors I found in my junk box along with actual 270 pF caps that I ordered overnight from AMZN. It's all on the same board I've reused several times, so please excuse the abrasions, drill attempts, etc. The results are just as you predicted. Images attached. Again, thank you very much for your help. Yay!! Mitch NK3H
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Re: Help with LPF Measurement
Jim, Dave, et al.,
Thank you very much for your suggestions. I rebuilt the filter using discarded SMA connectors I found in my junk box along with actual 270 pF caps that I ordered overnight from AMZN. It's all on the same board I've reused several times, so please excuse the abrasions, drill attempts, etc. The results are just as you predicted. Images attached. Again, thank you very much for your help. Yay!! Mitch NK3H
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Re: Help with LPF Measurement
This - get some 4 leg SMA jacks and solder two of the legs to the copper clad at the edge of the board. Cut the upper two legs off. That will give you a nice transition.
Depending on where you are, you can probably get jacks mail order in a day.
10 of them for $8
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-----Original Message----- From: < [email protected]> Sent: Mar 12, 2025 11:54 PM To: < [email protected]> Subject: Re: [nanovna-users] Help with LPF Measurement Mitch, Try making the ground connection to your filter very short, say 5mm or so. Also, try multiple ground wires. The currents to ground from all the capacitors in the filter flow through that ground connection, and if it has much inductance it will have a voltage drop that limits the rejection of the filter. If you have the connectors available, a better connection method is to solder an SMA connector shell directly to your ground plane at the input and another directly to the ground plane at the filter output. Then connect the center pins of the connectors to the input and output and connect your cables. If you just have some SMA pigtails (or can make a couple by cutting an SMA cable in half), you can connect the shield of a pigtail to your ground and the center wire to your input and similarly connect an output pigtail. Then connect those pigtail connectors to the NanoVNA. As others have mentioned, making all the component leads as short as you can will help, but the grounding is probably the bigger factor at this point. --John Gord
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Readings are not correct for NanoVNA F V2.
Does anyone have a web-site or youtube that goes through the set-up on using the F V2 for checking Coax lengths. The new one I have does not show the correct length, example a known 15.24m / 50ft coax comes up over 3 times that. Thinking maybe velocity-factor inputs. No help. The H4 VNA I have is spot on with the numbers. Any help would be grateful. Thanks
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Re: Help with LPF Measurement
How do you know it's filtering the harmonics out? Feeding in a square wave (into a non-resistive load) might not have the harmonic structure you expect.
It's really hard to interpret the wiggles after the transition in any meaningful manner, short of dumping them into some software and running an FFT.
And with a sine excitation, you need to pick a couple frequencies to test at - say 30 and 50 MHz.
I'd believe the VNA.
As an experiment you could download ELSIE and build the circuit with the inductance from the leads and see what it gives you.
If you want something simpler, just use the first pi section - shunt C, series L, shunt C.
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-----Original Message----- From: < [email protected]> Sent: Mar 12, 2025 9:48 PM To: < [email protected]> Subject: Re: [nanovna-users] Help with LPF Measurement Hi Jim, Thank you for your suggestions. I will shorten leads and properly dress the components tomorrow. BTW I had no 270 caps but had 50s and 220s, hence the two caps in parallel. You make a really good point in saying "the filter's not working right...." But what I don't understand is why the results from the sig generator/oscilloscope show the filter is filtering out high frequency harmonics pretty well, but the NanoVNA shows a very weird S21 result. It improved slightly when I added the ground leads between the board and the test rig (my bad for missing that!!), but it's not even close to what it should look like. Onwards....Thanks again. Best, Mitch NK3H
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On Mon, Mar 3, 2025 at 07:44 AM, Larry Macionski wrote:
I have fond memories of your Antenna modeling program - from back in the day..
I would load parameters and let the computer run all night. I didn't have a
co-processor nor could afford the $99 then $69 for one, as time went buy.
Larry, I still use Brian's excellent antenna simulation programs today. In fact, just about every week. (Different story not for here.) But, I run them on both a very new macOS computer and a Windows 10 computer using this app: It works very well. There's a couple features with YO that I haven't gotten working right because of the various calls into and out of a controlling batch file, but overall it's a great experience, still. The best part is that simulations run very quickly - minutes at most instead of overnight. 73, Clarke K1JX
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.NanoVNA-H v3.5_L: white screen - how do I connect USB to fix?
I couldn't connect to the unit and somehow managed to wipe the processor.
I've tried resetting it to reconnect, but the only response I get is in
STM32Cube Programmer 'UR is set by HWrst' or something similar.
I tried shorting BOOT0 to VDD as noted, screen remains white, no connection.
Any suggestions would be appreciated!
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Re: Help with LPF Measurement
Things are beginning to look a bit more like a LPF with the "ground" connected! Other suggestions have been made which are right on. Keep us posted on your progress. Dave - W?LEV <> Virus-free.www.avg.com <> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> On Thu, Mar 13, 2025 at 4:27?AM Mitch NK3H via groups.io <mitch= [email protected]> wrote: Dave,
Thank you for your reply. Very much appreciated.
In order:
1) Done.
2) Yes, I measured all components with my LCR meter (DE 5000).
3) Correct. 50 ohms confirmed by others for this filter.
4) It's possible that some capacitors aren't right for this frequency
range. I'll look into that.
5) I posted the S21 imaged from the VNA, not the SAVER program. I'll work
on that next.
6) Signal generator does not sweep; that's a good idea and will try to
figure something out.
Thanks for your help. I'll spend most of tomorrow working on this. Best,
Mitch NK3H
-- *Dave - W?LEV* -- Dave - W?LEV
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Re: Help with LPF Measurement
You may be looking for the graphical version of the map, but I threw this into the AI Grok app on my iPhone and it listed them all out.
“ Menu Structure Map for the NanoVNA F V2.”
You may or may not know, but these AI apps are amazing and scary all wrapped together but I don’t use search engines any longer, too much hunting and pecking to find the answer where the AI app responds with all the information already consolidated. If you haven’t, I would recommend at least trying it out ..
Tom
73
"Reality is the moment in which we live,
all else is just a memory...
"Make the MOST of Reality”
? KTCNC ?
???????
"Kick the Dust Up"
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On Mar 13, 2025, at 08:59, CLIFTON HEAD via groups.io <aecret@...> wrote:
?Off subject, does anyone know where to get a Menu Structure Map for the NanoVNA F V2. My new one did not come with one. Thanks
________________________________
From: [email protected] <[email protected]> on behalf of John Gord via groups.io <johngord@...>
Sent: Thursday, March 13, 2025 1:54 AM
To: [email protected] <[email protected]>
Subject: Re: [nanovna-users] Help with LPF Measurement
Mitch,
Try making the ground connection to your filter very short, say 5mm or so. Also, try multiple ground wires. The currents to ground from all the capacitors in the filter flow through that ground connection, and if it has much inductance it will have a voltage drop that limits the rejection of the filter.
If you have the connectors available, a better connection method is to solder an SMA connector shell directly to your ground plane at the input and another directly to the ground plane at the filter output. Then connect the center pins of the connectors to the input and output and connect your cables.
If you just have some SMA pigtails (or can make a couple by cutting an SMA cable in half), you can connect the shield of a pigtail to your ground and the center wire to your input and similarly connect an output pigtail. Then connect those pigtail connectors to the NanoVNA.
As others have mentioned, making all the component leads as short as you can will help, but the grounding is probably the bigger factor at this point.
--John Gord
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Re: Help with LPF Measurement
There are a bunch of them online. Have you tried Googling? Compare the menu that you think is right to your NanoVNA because there are several variations. On Thu, Mar 13, 2025 at 8:59?AM CLIFTON HEAD via groups.io <aecret= [email protected]> wrote: Off subject, does anyone know where to get a Menu Structure Map for the
NanoVNA F V2. My new one did not come with one. Thanks
________________________________
From: [email protected] <[email protected]> on behalf of John
Gord via groups.io <johngord@...>
Sent: Thursday, March 13, 2025 1:54 AM
To: [email protected] <[email protected]>
Subject: Re: [nanovna-users] Help with LPF Measurement
Mitch,
Try making the ground connection to your filter very short, say 5mm or
so. Also, try multiple ground wires. The currents to ground from all the
capacitors in the filter flow through that ground connection, and if it has
much inductance it will have a voltage drop that limits the rejection of
the filter.
If you have the connectors available, a better connection method is to
solder an SMA connector shell directly to your ground plane at the input
and another directly to the ground plane at the filter output. Then
connect the center pins of the connectors to the input and output and
connect your cables.
If you just have some SMA pigtails (or can make a couple by cutting an SMA
cable in half), you can connect the shield of a pigtail to your ground and
the center wire to your input and similarly connect an output pigtail. Then
connect those pigtail connectors to the NanoVNA.
As others have mentioned, making all the component leads as short as you
can will help, but the grounding is probably the bigger factor at this
point.
--John Gord
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Re: Help with LPF Measurement
Off subject, does anyone know where to get a Menu Structure Map for the NanoVNA F V2. My new one did not come with one. Thanks ________________________________ From: [email protected] < [email protected]> on behalf of John Gord via groups.io <johngord@...> Sent: Thursday, March 13, 2025 1:54 AM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] Help with LPF Measurement Mitch, Try making the ground connection to your filter very short, say 5mm or so. Also, try multiple ground wires. The currents to ground from all the capacitors in the filter flow through that ground connection, and if it has much inductance it will have a voltage drop that limits the rejection of the filter. If you have the connectors available, a better connection method is to solder an SMA connector shell directly to your ground plane at the input and another directly to the ground plane at the filter output. Then connect the center pins of the connectors to the input and output and connect your cables. If you just have some SMA pigtails (or can make a couple by cutting an SMA cable in half), you can connect the shield of a pigtail to your ground and the center wire to your input and similarly connect an output pigtail. Then connect those pigtail connectors to the NanoVNA. As others have mentioned, making all the component leads as short as you can will help, but the grounding is probably the bigger factor at this point. --John Gord
|
Re: Help with LPF Measurement
Mitch,
Try making the ground connection to your filter very short, say 5mm or so. Also, try multiple ground wires. The currents to ground from all the capacitors in the filter flow through that ground connection, and if it has much inductance it will have a voltage drop that limits the rejection of the filter.
If you have the connectors available, a better connection method is to solder an SMA connector shell directly to your ground plane at the input and another directly to the ground plane at the filter output. Then connect the center pins of the connectors to the input and output and connect your cables.
If you just have some SMA pigtails (or can make a couple by cutting an SMA cable in half), you can connect the shield of a pigtail to your ground and the center wire to your input and similarly connect an output pigtail. Then connect those pigtail connectors to the NanoVNA.
As others have mentioned, making all the component leads as short as you can will help, but the grounding is probably the bigger factor at this point.
--John Gord
|
Re: Help with LPF Measurement
Hi Jim,
Thank you for your suggestions. I will shorten leads and properly dress the components tomorrow. BTW I had no 270 caps but had 50s and 220s, hence the two caps in parallel.
You make a really good point in saying "the filter's not working right...." But what I don't understand is why the results from the sig generator/oscilloscope show the filter is filtering out high frequency harmonics pretty well, but the NanoVNA shows a very weird S21 result. It improved slightly when I added the ground leads between the board and the test rig (my bad for missing that!!), but it's not even close to what it should look like. Onwards....Thanks again. Best, Mitch NK3H
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Re: Help with LPF Measurement
Hi Jim,
Correct. I failed to connect them. I've repaired it and get a slight improvement. See pic just posted. Many thanks. Best, Mitch NK3H
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Roger Need
Taracait