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Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after connecting a transmission line into the VNA. You can see some pictures of the result in the attached document after connecting the cable to the VNA in the attached file.
Could someone tell me how to correct the impedance shift introduced by the cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna traces.
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You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith 90 degrees around... A long cable if not calibrated out will show a handfull of circles (as you can see)..
Dg9bfc sigi
Am 15.07.2022 14:20 schrieb dianebonk2@...:
toggle quoted message
Show quoted text
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures of
the result in the attached document after connecting the cable to the VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced by the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a
delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna
traces.
|
What exactly do you want to measure? What is the Device Under test, DUT? Is it the PCB? Is it the cable? Is it the combination of the two? If you just want to measure the PCB you need to do the calibration through the cable.
|
On Fri, Jul 15, 2022 at 05:58 AM, <dianebonk2@...> wrote:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures of the
result in the attached document after connecting the cable to the VNA in the
attached file.
Could someone tell me how to correct the impedance shift introduced by the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a delay
but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna traces.
The most accurate way is to calibrate at the end of the cable using a short, open and a 50 ohm SMD or very small resistor with absolute minimum leads. The other way is to use the electrical delay to compensate for the length of the cable With a 33 cm (12 inch) cable I had to set the edelay to 3.18 ns to get the open at the far right of the smith chart. Try 0.1 nanoseconds (100 picoseconds) for each cm of cable and then keep adjusting until you get close to the far right on the Smith chart. The velocity factor of the cable you use will have an effect so the 100 picoseconds is just an estimate to get you in the ballpark. Roger
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Hello, Thanks for your response I've got -462ps for the delay correction is it good? Best regards. Le ven. 15 juil. 2022 ¨¤ 18:22, Roger Need via groups.io <sailtamarack= [email protected]> a ¨¦crit : On Fri, Jul 15, 2022 at 05:58 AM, <dianebonk2@...> wrote:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures
of the
result in the attached document after connecting the cable to the VNA in the
attached file.
Could someone tell me how to correct the impedance shift introduced by the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a delay
but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna traces.
The most accurate way is to calibrate at the end of the cable using a
short, open and a 50 ohm SMD or very small resistor with absolute minimum
leads.
The other way is to use the electrical delay to compensate for the length
of the cable With a 33 cm (12 inch) cable I had to set the edelay to 3.18
ns to get the open at the far right of the smith chart. Try 0.1
nanoseconds (100 picoseconds) for each cm of cable and then keep adjusting
until you get close to the far right on the Smith chart. The velocity
factor of the cable you use will have an effect so the 100 picoseconds is
just an estimate to get you in the ballpark.
Roger
|
Hello,
Thank you for your answer. My DUT is a PCB trace antenna. Attached is a
picture of the antenna. I need to perform the measurement in the feed line
of the antenna. I am in an internship and the company is designing an
antenna for their Iot device(Bluetooth lower energy communication). They
want the antenna to be as small as possible. I am wondering if the size of
the antenna feed line can skew the antenna measurement.
I succeed to correct the delay I think.
Best regards.
Le ven. 15 juil. 2022 ¨¤ 16:20, Douglas Butler <sherpadoug@...> a
¨¦crit :
toggle quoted message
Show quoted text
What exactly do you want to measure? What is the Device Under test, DUT?
Is it the PCB? Is it the cable? Is it the combination of the two? If you
just want to measure the PCB you need to do the calibration through the
cable.
|
Thanks for your reply. I managed to correct the delay I was asking the same question to my tutor about the size of the cable in relation to the PCB. I am on an internship and I have to design a PCB trace antenna. The company wants the antenna size to be as small as possible to integrate into their IoT device for low-energy Bluetooth communication. I don't think I can get a smaller SMA cable than this for soldering, I will look if you have a proposal, I'm a taker. Attached is the antenna design and the solder image. Best regards Le ven. 15 juil. 2022 ¨¤ 15:35, Siegfried Jackstien < siegfried.jackstien@...> a ¨¦crit : You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be
at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith 90
degrees around... A long cable if not calibrated out will show a handfull
of circles (as you can see)..
Dg9bfc sigi
Am 15.07.2022 14:20 schrieb dianebonk2@...:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures of
the result in the attached document after connecting the cable to the VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced by
the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a
delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna
traces.
|
Hi Dianne,
What model/version of the nanoVNA do you have? many do not cover the 2.4GHz bluetooth frequency band.
What diameter/type of coaxial cable are you currently using? Type RG316 has diameter 2.5mm and RG178 diameter 1.8mm.
My advice is to test your antenna with a length of cable that will be used in the final product with a connector that will be used in that design.
I hope the above is of some help to you
Kind regards
Ed
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I would solder the coax shield to the area labeled GND in the antenna design, not to the ground plane nearby.
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On Fri, Jul 15, 2022 at 11:44 AM, Diane BONKOUNGOU wrote:
Hello,
Thanks for your response I've got -462ps for the delay correction is it
good?
Best regards.
Your display looks OK but 462 ps would be the value for a very short transmission line - about 4.5 cm long. What is the length of your transmission line and what kind of coax is it? Here is a video you might find interesting. It shows how to measure an antenna located inside a product... Roger
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Hello Roger, I have two coaxial cables that came with the NanoVNA. I cut one of them to make the solder. I use the cable I didn't cut to do the calibration and after connecting the one I cut, I correct the delay. That's why the delay is so low. When I do the calibration directly at the input of the NanoVNA and connect my SMA cable, the delay correction is difficult for me, the phase(pink curve) is triangular like in the attached picture. When I made the calibration at the cable I didn't cut and I connect the cable I have cut the phase is just shifted I don't have triangular thing on the curve. Best regards. Le ven. 15 juil. 2022 ¨¤ 22:54, Roger Need via groups.io <sailtamarack= [email protected]> a ¨¦crit : On Fri, Jul 15, 2022 at 11:44 AM, Diane BONKOUNGOU wrote:
Hello,
Thanks for your response I've got -462ps for the delay correction is it
good?
Best regards.
Your display looks OK but 462 ps would be the value for a very short
transmission line - about 4.5 cm long. What is the length of your
transmission line and what kind of coax is it?
Here is a video you might find interesting. It shows how to measure an
antenna located inside a product...
Roger
|
On Mon, Jul 18, 2022 at 02:06 AM, Diane BONKOUNGOU wrote:
Hello Roger,
I have two coaxial cables that came with the NanoVNA. I cut one of them to
make the solder. I use the cable I didn't cut to do the calibration and
after connecting the one I cut, I correct the delay. That's why the delay
is so low. When I do the calibration directly at the input of the NanoVNA
and connect my SMA cable, the delay correction is difficult for me, the
phase(pink curve) is triangular like in the attached picture. When I made
the calibration at the cable I didn't cut and I connect the cable I have
cut the phase is just shifted I don't have triangular thing on the curve.
Best regards.
Diane, Unfortunately you are not using the edelay correctly. Once you have done your SOL directly at the NanoVNA connector you connect your test cable and do NOT attach the open end to anything. You then add edelay until the trace on the Smith chart rotates back towards the far right side on the horizontal axis of the Smith Chart ( the spot where you had a dot with no cable connected). Then you connect it to your device-under-test (DUT) and make your measurement. I suggest you first try attaching the end to some SMD resistors (50 ohm, 100 ohm and 25 ohm) to make sure you get are getting reasonable SWR, Return Loss and impedance numbers. The impedance numbers may not be what you expect because at the frequencies you are using even a slight extension to the DUT will result in a reflection coefficient phase shift. BTW - I am not a fan of using edelay to move the reference plane to the end of the cable. It works OK at HF frequencies because the cable attenuation is very low and a few cm of cable is only a tiny fraction of a wavelength. But at the frequencies you are using results may not be great. I suggest you do your calibration at the end of your test cable using SMD parts and get a better reference plane. Little pin jacks work well for me (photo attached). My last point is that the antenna you are using is an unbalanced antenna. One side is connected to the ground plane of the PCB board it will be used on. You have to do the tests just as it will be used in the final product. The PCB ground plane layout will have a big effect on the antenna characteristics because it forms part of the antenna. You also have to concerned that you don't affect the antenna when you attach your measurement cable. You need a way to prevent the outer surface of the test cable shield from becoming part of the antenna system. You will know this is happening if results change when you grab the cable with your hand. Roger
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Hello Siegfried, Thanks for your response. So If I cut more of my cable could I reduce the number of circles (the phase shift)?. I struggle to correct the delay with a lot of circles. Best regards. Le ven. 15 juil. 2022 ¨¤ 15:35, Siegfried Jackstien < siegfried.jackstien@...> a ¨¦crit : You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be
at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith 90
degrees around... A long cable if not calibrated out will show a handfull
of circles (as you can see)..
Dg9bfc sigi
Am 15.07.2022 14:20 schrieb dianebonk2@...:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem after
connecting a transmission line into the VNA. You can see some pictures of
the result in the attached document after connecting the cable to the VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced by
the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding a
delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna
traces.
|
Rather than cutting the cable, you should calibrate with the cable attached
to the nanovna, attaching the calibration standards at the other end of the
cable, using connector adapters if necessary. This way ensures that all
aspects of the cable (length, loss, etc.) are compensated for by the
calibration, perfectly removing all those circles from the smith chart.
Stan
toggle quoted message
Show quoted text
On Wed, Jul 20, 2022, 2:18 PM Diane BONKOUNGOU <dianebonk2@...> wrote: Hello Siegfried,
Thanks for your response.
So If I cut more of my cable could I reduce the number of circles (the
phase shift)?. I struggle to correct the delay with a lot of circles.
Best regards.
Le ven. 15 juil. 2022 ¨¤ 15:35, Siegfried Jackstien <
siegfried.jackstien@...> a ¨¦crit :
You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be
at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith 90
degrees around... A long cable if not calibrated out will show a handfull
of circles (as you can see)..
Dg9bfc sigi
Am 15.07.2022 14:20 schrieb dianebonk2@...:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem
after
connecting a transmission line into the VNA. You can see some pictures
of
the result in the attached document after connecting the cable to the
VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced by the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by adding
a
delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have antenna
traces.
|
Hello,
Thanks, everyone for your tips.
Finally, this is what I've done.
Best regards
toggle quoted message
Show quoted text
Le jeu. 21 juil. 2022 ¨¤ 00:44, Stan Dye <standye@...> a ¨¦crit : Rather than cutting the cable, you should calibrate with the cable attached
to the nanovna, attaching the calibration standards at the other end of the
cable, using connector adapters if necessary. This way ensures that all
aspects of the cable (length, loss, etc.) are compensated for by the
calibration, perfectly removing all those circles from the smith chart.
Stan
On Wed, Jul 20, 2022, 2:18 PM Diane BONKOUNGOU <dianebonk2@...>
wrote:
Hello Siegfried,
Thanks for your response.
So If I cut more of my cable could I reduce the number of circles (the
phase shift)?. I struggle to correct the delay with a lot of circles.
Best regards.
Le ven. 15 juil. 2022 ¨¤ 15:35, Siegfried Jackstien <
siegfried.jackstien@...> a ¨¦crit :
You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be
at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith
90
degrees around... A long cable if not calibrated out will show a
handfull
of circles (as you can see)..
Dg9bfc sigi
Am 15.07.2022 14:20 schrieb dianebonk2@...:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem
after
connecting a transmission line into the VNA. You can see some
pictures
of
the result in the attached document after connecting the cable to the
VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced
by
the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by
adding
a
delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have
antenna
traces.
|
why not just calibrate at the cable end??
much easier as messing with the long delay ... not?!?
dg9bfc sigi
ps did you check open and short (with cable!!)?!?!?
Am 01.08.2022 um 14:40 schrieb Diane BONKOUNGOU:
toggle quoted message
Show quoted text
Hello,
Thanks, everyone for your tips.
Finally, this is what I've done.
Best regards
Le jeu. 21 juil. 2022 ¨¤ 00:44, Stan Dye <standye@...> a ¨¦crit :
Rather than cutting the cable, you should calibrate with the cable attached
to the nanovna, attaching the calibration standards at the other end of the
cable, using connector adapters if necessary. This way ensures that all
aspects of the cable (length, loss, etc.) are compensated for by the
calibration, perfectly removing all those circles from the smith chart.
Stan
On Wed, Jul 20, 2022, 2:18 PM Diane BONKOUNGOU <dianebonk2@...>
wrote:
Hello Siegfried,
Thanks for your response.
So If I cut more of my cable could I reduce the number of circles (the
phase shift)?. I struggle to correct the delay with a lot of circles.
Best regards.
Le ven. 15 juil. 2022 ¨¤ 15:35, Siegfried Jackstien <
siegfried.jackstien@...> a ¨¦crit :
You have to calibrate at the cable end with open short load
And with such big cable soldered to such a tiny pcb your results will be
at least questionable...
On so high frequencies even an sma to n adaptor will shift your smith
90
degrees around... A long cable if not calibrated out will show a
handfull
of circles (as you can see)..
Dg9bfc sigi
Am 15.07.2022 14:20 schrieb dianebonk2@...:
Hello everyone,
I am a beginner in using the NanoVNA, I have a calibration problem
after
connecting a transmission line into the VNA. You can see some
pictures
of
the result in the attached document after connecting the cable to the
VNA
in the attached file.
Could someone tell me how to correct the impedance shift introduced
by
the
cable? Thanks
I went to the "electrical delay" menu to correct the problem by
adding
a
delay but it got worse. I don't know what to do.
I want to solder the cable afterwards into a PCB where we have
antenna
traces.
|
Douglas Butler
Roger Need
