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Nico,

So you have two issues here...

Th first one is that you will have difficulty knowing what the impedance is near the matching network because your measuring system is affecting the results. That was the point of my previous post.

The second is that even if you knew precisely what impedance you are trying to match inductors and capacitors at 916 MHz. will not have the same values as they do at lower frequencies. An inductor will have series resistance that increases with frequency and parallel capacitance. A capacitor will have lead inductance. So you need to purchase components that have been characterized at 900 MHz.

On Fri, Mar 14, 2025 at 04:00 AM, Nico wrote:

Look at the picture and zoom it (not zoomed it does not show up properly),
you'll see a blurred larger line around the feedline. This is the return path
or, the other half of the transmission line. This is a ground line attached to
the ground plane on layers 2 and 3. I was unsure on how to terminate it close
to the antenna attachment point, so I've just ended it close to it

Nico,

In your case the purchased helical is one half of the antenna. The other half is the "buried" side of the transmission line and the ground plane of your board. When making measurements of the antenna the outer surface of the shield of your connecting RG316 cable is now also part of the antenna. Grab the coax with your hand or attach a wire to the SMA connector nut on the VNA and you will see the SWR change. The situation is similar to what happens on a handheld radio transmitter where the operator is capacitively coupled to the radios antenna system.

You can try reducing the RF current on the coax cable with ferrites but you will not get rid of it entirely. And at this high of a frequency you will still have a considerable length of coax shield radiating until the ferrites.

SUGGESTION: Forget about these "canned" solutions. Download and install
SIMSMITH.



There is also a accompanying tutorial at:



Dave - W?LEV

On Fri, Mar 14, 2025 at 5:51?AM shlomo537678 via groups.io <shlomo537678=
[email protected]> 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!

--

*Dave - W?LEV*


--
Dave - W?LEV

It looks like the cal may not be taking. RESET......COMPLETE
CAL.......STORE in a register. Go back and verify that the OSL displays as
it should. If not, OPEN CASE....INSTALL PROPER LOAD......from the inside
VERIFY WITH DMM that 50-ohms is measured correctly. All this to confirm
the center pin is mating correctly to the connector. Also do same with the
short and DMM.

Dave - W?LEV

On Fri, Mar 14, 2025 at 7:21?PM K3IY via groups.io <oconnorkl=
[email protected]> wrote:

I have been using my nanovna SAA2N for months without issues, and I bought
it from R&L who is an authorized distributer of legitimate Nanovna's. This
morning my issue started after I calibrated the unit. All of my traces
were erratic (see attached picture). Smith chart is a mess of zig zags
instead of arcs. I tried the following and nothing has fixed the issue.
"Reset" and "Reset All" prior to calibration. Tried multiple frequency
ranges and trace points. Tried using both cables. Tested the cables for
shorts/continuity. Tested all three standards (short, open, load) with an
ohm meter, unfortunately I don't have another set to try. Flashed the
firmware. Opened up the case and confirmed good solder joints and
continuity from the N connectors to the board. Wiggled the connections and
nothing changed. Checked again when the battery was fully charged. Also
tried using VNA View and got the same results. The unit was safely stored
in the case between the last time it worked and now. What am I missing?

--

*Dave - W?LEV*


--
Dave - W?LEV

I have been using my nanovna SAA2N for months without issues, and I bought it from R&L who is an authorized distributer of legitimate Nanovna's. This morning my issue started after I calibrated the unit. All of my traces were erratic (see attached picture). Smith chart is a mess of zig zags instead of arcs. I tried the following and nothing has fixed the issue. "Reset" and "Reset All" prior to calibration. Tried multiple frequency ranges and trace points. Tried using both cables. Tested the cables for shorts/continuity. Tested all three standards (short, open, load) with an ohm meter, unfortunately I don't have another set to try. Flashed the firmware. Opened up the case and confirmed good solder joints and continuity from the N connectors to the board. Wiggled the connections and nothing changed. Checked again when the battery was fully charged. Also tried using VNA View and got the same results. The unit was safely stored in the case between the last time it worked and now. What am I missing?

Hello,
In the files section you will find a process to recover from "White Screen Recovery". Follow it PRECISELY STEP by STEP!.
If that does not work you could try, for the lack of a better term, a factory reset.
Push the jog switch down to the left and hold while turning the unit on. Then try the screen recovery.
Clyde KC7BJE

The image that shows a SWR of 2.6 : 1 (the sixth image), all you need to do
is add an inductor in series to cancel the -j 45.6 ohms. At 916 MHz that
would be 7.9 nH.

In reality, 1.86 : 1 is not bad at all. For this sort of application, I'd
declare it complete.

Dave - W ?LEV

On Fri, Mar 14, 2025 at 3:05?AM Nico via groups.io <nicolassimard=
[email protected]> wrote:

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...

--

*Dave - W?LEV*


--
Dave - W?LEV

On Thu, Mar 13, 2025 at 11:20 PM, David McQuate wrote:

Usually a network Q value is first chosen.

You can actually calculate the values of an L-Network's two components without knowing Q. It is sufficient to know just the value of the load impedance and the impedance you want to transform that load to, e.g. 50 ohms.

You can find the equations to calculate the component values for transforming a complex impedance to 50 ohms here:


And this blogpost contains a more general form of the above equations, allowing you to transform a complex impedance to any other complex impedance, not just to 50 ohms:


The equations are complicated, but you can download an EXCEL spreadsheet to calculate them here:


Best,

Jeff, k6jca

Roger,

Thanks for this advice. I'll try it out tonight.

Look at the picture and zoom it (not zoomed it does not show up properly), you'll see a blurred larger line around the feedline. This is the return path or, the other half of the transmission line. This is a ground line attached to the ground plane on layers 2 and 3. I was unsure on how to terminate it close to the antenna attachment point, so I've just ended it close to it.

I'll post results tonight with a few turn of ferrite.

Nic

L-network values with the nano and then with the AT-100M Pro automatic
antenna tuner:

I measured one dipole antenna of mine (antenna fed with 1:1 balun, and
72-ohm Belden 8222 twin lead) with a nanoVNA and asked for a matching
network. It gave me values for C and L.
I then used this antenna tuner:

(AT-100M Pro)
That antenna tuner tells you the values it is using to match the antenna.
The values given by the tuner were approximately the same as what the
nanoVNA told me.
So then i made a simple L-network tuner on a piece of wood. Variable
capacitor (air-spaced blades) and a 4-inch-diameter coil made of 1/4"
copper tubing. I was happy with the result. Am using it on 30 meters at the
moment.

FYI the other Ali Express small tuners that have the word '100' in them,
like ATU-100, have gotten really bad reviews. I have two of these 'AT-100M
Pro' and am happy with them. Good for portable use, rechargeable battery
inside.

WN1Z
Orrin

I'm missing a lot of information to understand (in French) your participation. I remember the last line:

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.

A 3-piece Pi adapter can be upgraded to a 2-piece L adapter.

If impedance matching is the only issue to be addressed, an L adapter will have greater bandwidth than a Pi adapter and lower losses. A Pi adapter artificially increases overvoltages and overcurrents, thus reducing bandwidth.

The measured load impedance is 31.9-58.5j.

OK, but we would need the frequency to show you the possibilities in concrete terms.
--
F1AMM
Fran?ois

-----Message d'origine-----

De la part de shlomo537678
Envoyé : vendredi 14 mars 2025 06:17

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

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!

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.

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...

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