Different SWR readouts between NanoVNA-H and NanoVNA Saver
I am having different SWR readings between my NanoVNA-H (Not connected to the computer) and NanoVNA saver versions 3.9 and 3.10, NanoVNA-H version 1.0.45
I have followed directions carefully when setting up and verified calibration when the Nano is not connected to the computer.
I don¡¯t believe there is a way to verify calibration when in Nano saver.
This problem appears regardless whether I am using version 3.9 or 3.10 of saver.
An example would be the following:
When Nano is not connected to the computer the SWR for a given VHF frequency would be 1.5.
When connected to Saver it may be 3.4 in saver version 3.9 doing the measurements correctly.
and 4.2 in version 3.10.
When I am thinking about it this is not possible because the SWR is being read off of the Nano unit to the saver.
I have used the manuals for SWR as well as several You Tube videos to verify that I am the measurements correctly.
Thank You,
Steven/kc3dow
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Re: color of correct load, short, and open caps
Hello Keith,
you can easily measure it with a resistance meter between the pin and the housing.
SHORT you will measure 0 ohm.
LOAD you will measure 50 ohm.
Detlev, vy 73 DL7MDH
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Re: color of correct load, short, and open caps
Easy.. Brass insert is the short... White insert is load. 50 ohms
Dg9bfc sigi
Am 31.07.2023 03:14 schrieb Bob Ecclestone VK2ZRE <becclest@...>:
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Hi Keith,
Use your multimeter to measure them.
Suspect you will find the one with the silver cap is the 50 Ohm load.
HTH...Bob VK2ZRE
On 31/07/2023 9:44 am, Keith, KF0KBC wrote:
I have the Nano VNA-h 3.6_MS.
The open is obviously without the pin but what is the difference between load and short? My remaining two caps are either brass with a brass pin
and brass insert or brass with silver bottom cap and white colored insert.
I believe the white insert is the short cap as it seems to calibrate
properly with my vertical antennas.
Keith
KF0KBC
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Re: Measuring the SRF of a capacitor ?
I have been thinking about a test jig to do exactly this and considered using some perf board to both calibrate with OLS and be able to plug in a filter or transformer etc.
I just need to find the best resistors I can get and need advice on finding them. 50 to 5k for baluns too. Great post!
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Re: color of correct load, short, and open caps
Hi Keith,
Use your multimeter to measure them.
Suspect you will find the one with the silver cap is the 50 Ohm load.
HTH...Bob VK2ZRE
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On 31/07/2023 9:44 am, Keith, KF0KBC wrote: I have the Nano VNA-h 3.6_MS.
The open is obviously without the pin but what is the difference between load and short? My remaining two caps are either brass with a brass pin and brass insert or brass with silver bottom cap and white colored insert. I believe the white insert is the short cap as it seems to calibrate properly with my vertical antennas.
Keith
KF0KBC
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color of correct load, short, and open caps
I have the Nano VNA-h 3.6_MS.
The open is obviously without the pin but what is the difference between load and short? My remaining two caps are either brass with a brass pin and brass insert or brass with silver bottom cap and white colored insert. I believe the white insert is the short cap as it seems to calibrate properly with my vertical antennas.
Keith
KF0KBC
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Re: Measuring the SRF of a capacitor ?
On Sun, Jul 30, 2023 at 04:08 PM, Roger Need wrote:
On Sun, Jul 30, 2023 at 09:52 AM, Jim VE7RF wrote:
Can the nano vna be used to measure the SRF of garden variety doorknob
caps,
like HEC HT-50/58 and HT-57 / 59 types in various cap values ?
If so, what's the suggested nano vna cabling config / test setup.
Here is a simple test jig to get you started. Use a short length (6 to 12 inches) of RG-213 or RG-174 with an SMA connector on one end. Strip the jacket off for about 2 inches or so. Separate the shield and inner conductor and put some ring connectors on the end that have the same eye diameter as the bolts that connect to the capacitors. Then make some cal loads (open, short, load) that have the same length dimension as the capacitors and that you can connect to the ring terminals. You want the spacing to be the same as the capacitor to get a good "reference plane." You can use some plastic rod, cardboard tube, dowel etc to get the spacing correct. The open is easy to do and you just need the correct spacing, the short just needs a good conductor (copper tape or coax shield). The 50 ohm load should be a non inductive resistor with the correct spacing . Two 100 ohm in parallel work well. Once you have calibrated you connect the cap and make your measurement. Roger
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Re: Measuring the SRF of a capacitor ?
On Sun, Jul 30, 2023 at 09:52 AM, Jim VE7RF wrote:
Can the nano vna be used to measure the SRF of garden variety doorknob caps,
like HEC HT-50/58 and HT-57 / 59 types in various cap values ?
If so, what's the suggested nano vna cabling config / test setup.
Jim, There are several ways to do the measurement. You can do the S11 shunt method by just building a suitable test jig, calibrating on the jig and then connecting the component. You need to have short leads to avoid adding inductance and be careful not to introduce stray capacitance. When the reactance is equal to zero you are at the SRF frequency. Attached is a plot (with comments) of a AVX .300 nF ceramic capacitor using NanoVNA Saver. You can also do the S21 series method with a test jig between the two ports. With this method you look for the point on the S21 graph where the loss is at a minimum and this is the SRF. The S11 return loss will also have the biggest peak at this point as well. The quality of your test jig in both cases will determine the accuracy of your measurement. Are you looking for something to just get you in the ballpark or something much better than that? Do you have any idea of what frequency the SRF might be? Roger
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Re: Measuring the SRF of a capacitor ?
Yes. 73 Peter, DJ7WW -----Original-Nachricht----- Betreff: [nanovna-users] Measuring the SRF of a capacitor ? Datum: 2023-07-30T18:52:46+0200 Von: "Jim VE7RF" <jim.thom@...> An: " [email protected]" < [email protected]> Can the nano vna be used to measure the SRF of garden variety doorknob caps, like HEC HT-50/58 and HT-57 / 59 types in various cap values ? If so, what's the suggested nano vna cabling config / test setup. Jim VE7RF ?
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Re: Measuring the SRF of a capacitor ?
Connect the capacitor to make a reflection measurement. Sweep over a
relatively wide frequency range. As the frequency from above the SRF point
approaches the SRF, the -jX of the capacitor will approach a minimum where
only the R portion of the measurement is evident. Above that frequency
which is the SRF of the capacitor, the curve will exhibit the +jX component
above the SRF - it becomes inductive.
That's all about the definition of resonance: -jX = +jX. Only the
resistive portion remains.
Dave - W?LEV
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On Sun, Jul 30, 2023 at 4:52?PM Jim VE7RF <jim.thom@...> wrote: Can the nano vna be used to measure the SRF of garden variety doorknob
caps, like HEC HT-50/58 and HT-57 / 59 types in various cap values ?
If so, what's the suggested nano vna cabling config / test setup.
Jim VE7RF
-- *Dave - W?LEV*
--
Dave - W?LEV
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Measuring the SRF of a capacitor ?
Can the nano vna be used to measure the SRF of garden variety doorknob caps, like HEC HT-50/58 and HT-57 / 59 types in various cap values ?
If so, what's the suggested nano vna cabling config / test setup.
Jim VE7RF
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Re: Marke moves just by enabling the Smith chart
Thanks for the clarification. In that case I have to apologize to Jim. As you can see, you also misunderstood the meaning of his answer.
@Jim: I'm sorry about that.
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Re: Marke moves just by enabling the Smith chart
I think you misunderstood his comment, it happens across different native languages. I had to read it a second time to realize he was speaking about himself, saying he considers *himself* a "rank amateur", was suggesting he might not have the correct answer, but would try to help you anyway.
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On Sun, Jul 30, 2023 at 04:23 AM, Andrea I2UEA wrote:
On Sat, Jul 29, 2023 at 08:24 PM, Jim Farmer, K4BSE wrote:
Rank amateur with the nanovna with no right to chime in here. But here's a
guess.
@ Jim Farmer: and what gives YOU the right to offend people here?
Congratulations for your ham spirit! In any case I don't think that this group
is only for expert.
However I know how the Smith chart works. Simply, I thought that in this case
the NanoVNA SWR marker behaves in a different way.
Instead, thank you very much to all the other people who kindly explaining
that without any stupid argument.
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Re: Marke moves just by enabling the Smith chart
On Sat, Jul 29, 2023 at 08:24 PM, Jim Farmer, K4BSE wrote:
Rank amateur with the nanovna with no right to chime in here. But here's a
guess.
@ Jim Farmer: and what gives YOU the right to offend people here? Congratulations for your ham spirit! In any case I don't think that this group is only for expert. However I know how the Smith chart works. Simply, I thought that in this case the NanoVNA SWR marker behaves in a different way. Instead, thank you very much to all the other people who kindly explaining that without any stupid argument.
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Re: Marke moves just by enabling the Smith chart
Mmarker tracking on NanoVNA implemented by search min/max verticaal (y) value on selected trace
So for polar trace it seatch minimum/maximum imag value
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Re: Marke moves just by enabling the Smith chart
Although I prefer GNU Octave, many computers today include Python along with their OS. So here's some Python code for finding the SWRs, the second example used:
Zo = 50
Zl = 30 + 1j * 40
rho = (Zl - Zo) / (Zl + Zo)
SWR = (1 + abs(rho)) / (1 - abs(rho))
SWR = 3.0
Actually, this code will execute exactly as is under Octave, too, although that isn't the general case. SWRs for the impedances below, in order, are, from Python 3.9.7:
2.0
3.0
2.0
2.0
3.0
2.0
You can do a lot even if you don't have a specialized transmission line utility.
73,
Maynard
W6PAP
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On 7/29/23 14:56, Barry K3EUI wrote: Which has a lower SWR when using a 50 ohm coaxial cable:
25 + j0
30 + j40
40 + j30
40 - j30
30 - j40
100 + j0
de k3eui
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Re: Marke moves just by enabling the Smith chart
HINT: SimSmith could be our friend.........????
Dave - W?LEV
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On Sat, Jul 29, 2023 at 9:57?PM Barry K3EUI <k3euibarry@...> wrote: Which has a lower SWR when using a 50 ohm coaxial cable:
25 + j0
30 + j40
40 + j30
40 - j30
30 - j40
100 + j0
de k3eui
-- *Dave - W?LEV*
--
Dave - W?LEV
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Re: Marke moves just by enabling the Smith chart
Which has a lower SWR when using a 50 ohm coaxial cable:
25 + j0
30 + j40
40 + j30
40 - j30
30 - j40
100 + j0
de k3eui
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Re: Marke moves just by enabling the Smith chart
Rank amateur with the nanovna with no right to chime in here. But here's a guess. SWR is a scaler quantity and is a minimum when the MAGNITUDE of the impedance is closest to 50 ohms. But on the Smith chart, might the algorithm for finding the minimum be to find the point where the plot lies on the real axis AND is closest to 50 ohms? I can see this happen and I have heard of cases where the "closest" point on the Smith chart doesn't correspond to the lowest SWR. Hard to say not knowing the algorithm for finding the "closest" point on the Smith chart.
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Just quickly, here is a screenshot of the results attached.
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Roger Need
Andrea I2UEA
Barry K3EUI
