开云体育

Very good Mitch.
Happy to see you suceeded in beating the electrons into submission.

Lesson learned... Neatness counts.

yay indeed.. Pretty cool.

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:

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

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

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.

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=
mitchelsayare.com@groups.io> 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

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"

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=
outlook.com@groups.io> 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: nanovna-users@groups.io <nanovna-users@groups.io> on behalf of John
Gord via groups.io <johngord@...>
Sent: Thursday, March 13, 2025 1:54 AM
To: nanovna-users@groups.io <nanovna-users@groups.io>
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

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: nanovna-users@groups.io <nanovna-users@groups.io> on behalf of John Gord via groups.io <johngord@...>
Sent: Thursday, March 13, 2025 1:54 AM
To: nanovna-users@groups.io <nanovna-users@groups.io>
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

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

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

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

Alan, exactly right. I failed to do it. I just posted a pic of the result of adding leads from copper plane to the ground on the test rig. Thank you. 73, Mitch

Correct. I failed to connect the ground plane to the connector grounds. I did just that with hookup wire soldered to the copper and connected to the ground of the test rig. A slight improvement. See pic. Many thanks for your help. 73, Mitch NK3H

Alan,

I agree 100% on neatness, lead length, etc. This was supposed to be just a test project in anticipation of properly building the filter. From your comments and others', it appears I need to use appropriate methods from the very start in order to get results even in the ballpark. Advice appreciated. Thank you.

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

HI Dave,

Yes, it's there. The line goes across the very top of the screen, and the print shows "S21 LOGMAG 10 dB/-0.00 dB" in gray. Thanks for any help. Best, Mitch NK3H

The only measurement noted at the top of the screen was S11. Was S21 also
there? I didn't see it.

Dave

<>
Virus-free.www.avg.com
<>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

On Thu, Mar 13, 2025 at 12:39?AM Mitch NK3H via groups.io <mitch=
mitchelsayare.com@groups.io> wrote:

Hi Dave,

S21 is the gray, I think (the not yellow one -- I'm color blind) print at
the top right of the screen in the last two images I posted. It's line is
flat at 0 dB across the frequency range with the test rig shorted and gives
the unusual curve I showed when the filter is used. Connecting the Ports 0
& 1 of the VNA together (without the test rig) also show 0 dB flat across
the frequency range. Is that what you meant?

Many thanks.

Mitch NK3H

--

*Dave - W?LEV*


--
Dave - W?LEV

Well, there's a long history of dead bug construction, and 3D sculptures. But it's the short leads thing that's biting you here. You can solder the capacitor lead to the copperclad really close and use the capacitor as a sort of standoff sticking up. Then solder the lead to the inductor to the other cap lead really close. Extra length in the inductor isn't so bad. And, be careful about the inductor windings being close to the copper clad - the capacitance from the winding to the copper clad is essentially shunting. (The overall effect would be to lower the cutoff frequency of the filter).

This is actually pretty useful for you - the NanoVNA said "the filter's not working right", and as you change things, you'll see it improve. Which is a whole lot better than a sort of handwavey - lead lengths are important. You have a chance to quantitatively see how long a lead makes a difference.

BTW, people designing and building these filters often take the original design, build it up, find out it doesn't quite work, and then adjust the values of the components until it does. Maybe they change the 270 pF to 330pF (to account for the inductance in the leads). This is a lot of the "art" of building RF circuits with real, non-ideal components.

I think we've all been burned by something like this (resistors that are inductors is a notorious one)