Re: Measuring swr on fan dipole or windom antenna
Where does the original poster say anything about the "measure cable:"
function? The NanoVNA has an "SWR" function. I use it quite a bit.
Zack W9SZ
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On Fri, Jun 16, 2023 at 8:40?PM Stan Dye <standye@...> wrote: The "measure cable" function was designed to measure a transmission line
(e.g. length of coax), open at the far end, and give you its characteristic
impedance, loss, and length (length only when you give it the correct
velocity factor for the cable). It does this by finding the 1/4 wave
resonant frequency for the full length of cable, and doing the
calculations, assuming it is a transmission line. If instead you have a
wire antenna at the end, or a multi-wire fan dipole attached at the end,
there may be multiple 1/4 wavelength resonance points - it always chooses
the first, so it will only show you one length. The first one it sees may
be of the length of the coax, or it may be of the coax plus one of your
wires, depending on the design of your system. If you instead use the TDR
function, you may be able to see peaks due to reflections from the
feedpoint and each of the wires, but maybe not: if the antenna is closely
matched in impedance, it won't give much of a reflection to see. I've
never tried that - it may be interesting to see what happens.
On Fri, Jun 16, 2023 at 5:53?PM Gary W9TD <w9td@...> wrote:
Steve,
The nano is measuring only the cable length, not the antenna plus cable.
Gary
W9TD
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Re: Measuring swr on fan dipole or windom antenna
On 6/17/23 5:31 AM, DougVL wrote: On Fri, Jun 16, 2023 at 08:48 PM, Steve Johnson wrote:
I would expect it to show the length of the wire segment being used (i.e.
lowest SWR) at a given frequency
BUT with the 'measure cable' function, you cannot specify a frequency, and the function is not intended or designed to measure frequency (it sends a pulse, not a sweep) or measure SWR. it does not send a pulse - what it does is sweep a range of frequencies, and then mathematically transforms the measurement to what it would have been if it were a pulse (or step). MEASURE CABLE measures cable length, impedance and loss.
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Re: Measuring swr on fan dipole or windom antenna
On Fri, Jun 16, 2023 at 08:48 PM, Steve Johnson wrote:
I would expect it to show the length of the wire segment being used (i.e.
lowest SWR) at a given frequency
BUT with the 'measure cable' function, you cannot specify a frequency, and the function is not intended or designed to measure frequency (it sends a pulse, not a sweep) or measure SWR. MEASURE CABLE measures cable length, impedance and loss. -- Doug, K8RFT
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Re: Measuring switch isolation Re: [nanovna-users] Connect VNA thru tuner to antenna
On Fri, Jun 16, 2023 at 07:51 AM, Jim Lux wrote:
typically quite frequency dependent for switches
This is true of most switch topologies. Another frequency-dependent characteristic of mechanical switches which can crop up during testing, especially in the microwave region, is resonances from unterminated switch ports. Always terminate all unconnected ports when trying to measure switches. 73, Don N2VGU.
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Re: Measuring swr on fan dipole or windom antenna
Otherwise the cable
measurement function makes no sense. ** Yes, it is used to measure the length of a real cable :). In your case, you are not measuring a cable but an antenna connected to the end of a cable. When only one port is used, the nanoVNA only knows how to measure impedance versus frequency. Then, it is through calculations, that we make an interpretation. 73 -- F1AMM Fran?ois De la part de Steve Johnson Envoy¨¦ : samedi 17 juin 2023 02:49
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Re: Measuring swr on fan dipole or windom antenna
The "measure cable" function was designed to measure a transmission line
(e.g. length of coax), open at the far end, and give you its characteristic
impedance, loss, and length (length only when you give it the correct
velocity factor for the cable). It does this by finding the 1/4 wave
resonant frequency for the full length of cable, and doing the
calculations, assuming it is a transmission line. If instead you have a
wire antenna at the end, or a multi-wire fan dipole attached at the end,
there may be multiple 1/4 wavelength resonance points - it always chooses
the first, so it will only show you one length. The first one it sees may
be of the length of the coax, or it may be of the coax plus one of your
wires, depending on the design of your system. If you instead use the TDR
function, you may be able to see peaks due to reflections from the
feedpoint and each of the wires, but maybe not: if the antenna is closely
matched in impedance, it won't give much of a reflection to see. I've
never tried that - it may be interesting to see what happens.
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On Fri, Jun 16, 2023 at 5:53?PM Gary W9TD <w9td@...> wrote: Steve,
The nano is measuring only the cable length, not the antenna plus cable.
Gary
W9TD
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Re: Measuring swr on fan dipole or windom antenna
Steve,
The nano is measuring only the cable length, not the antenna plus cable.
Gary
W9TD
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Re: Measuring swr on fan dipole or windom antenna
My NanoVNA shows a single wire length (when measuring cable) for the fan dipole even though there are definitely multiple lengths of wire (all different) in the air. This length stays the same as I roll down the frequency range. I would expect it to show the length of the wire segment being used (i.e. lowest SWR) at a given frequency. Otherwise the cable measurement function makes no sense.
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What DFU software are you using? There are four programs for installing
firmware updates that I know about.
The original one from ST, Dfuse Demo, works well on older computers but
refuses to connect on many newer ones. The symptom is that it never sees
your device. (It's likely some sort of timing issue that makes it
incompatible with some USB controllers.) Sometimes it can be made to work
by switching to another USB port (try a USB 2.0 port if your system has
one), or by inserting a USB hub between the computer and your nanoVNA. ST
no longer supports that software so it won't get fixed.
Its replacement, STM32CubeProgrammer, works well on those newer computers
but is too big to run well on some older ones. An interesting gotcha is
that it requires .BIN files, while Dfuse uses the .DFU file format. Current
nanoVNA firmware can be downloaded in both formats; make sure to get the
one you need. (Older ones were only provided as .DFU files.) There is a
utility provided with Dfuse Demo that will convert between the formats; you
may want to install that even if you use STM32CubeProgrammer.
The final option is open source tools; dfu-tool and dfu-util are out there,
may be included with your Linux distribution if you run that OS, and
versions are also available for Windows and macOS. I have no personal
experience with them.
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On Fri, Jun 16, 2023 at 9:20?AM Muggs KC3UDZ <Muggs828@...> wrote: Hello All,
I cannot for some reason get my H4 into DFU mode on my laptop; I don't
have a problem with my desktop computer (running the same version of
NanoVNA App).
Is there something that I should be looking for to remedy this?
BTW, I know the answer is move it to the desktop for firmware updates, but
I'm curios why it's not being found on my laptop.
TIA,
Muggs
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Hello All,
I cannot for some reason get my H4 into DFU mode on my laptop; I don't have a problem with my desktop computer (running the same version of NanoVNA App).
Is there something that I should be looking for to remedy this?
BTW, I know the answer is move it to the desktop for firmware updates, but I'm curios why it's not being found on my laptop.
TIA,
Muggs
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Re: Measuring switch isolation Re: [nanovna-users] Connect VNA thru tuner to antenna
On 6/16/23 4:33 AM, Bryan Curl wrote: Thanks Jim.
Still learning this neat tool.
So just the phase trace is all thats needed on s21 to measure isolation?
Are results frequency dependent?
Bryan, n0luf
Log mag S21 is what I use, and yes, typically quite frequency dependent for switches based on non-RF relays (i.e. most amateur switch boxes). The leakage is mostly due to parasitic C, so the leakage is bigger (worse) at higher frequencies.
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Re: Measuring switch isolation Re: [nanovna-users] Connect VNA thru tuner to antenna
Thanks Jim.
Still learning this neat tool.
So just the phase trace is all thats needed on s21 to measure isolation?
Are results frequency dependent?
Bryan, n0luf
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Don't do "double calibration", it just forces the device to do
interpolation between points.
The note in documentation remains there for misbehaving devices
that would give out or range values when the device is used in an
uncalibrated state.
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Thanks for all of the help. The plots are very enlightening. it seems like this explains this. In response to the on device calibration, is disabling it simply unchecking the apply button? And also the documentation suggests calibrating the device to full range then calibrating in the NanoVna-Saver software. Which one do you suggest?
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Re: Firmware upgrade for original nanovna
On Thu, Jun 15, 2023 at 04:49 PM, Dragan Milivojevic wrote:
In case you were worried about "bricking" your device, don't be. It is
practically impossible to do.
If you do not have the version 0.8 as *.bin (or *.dfu) file I would propose to save it from device before you flash the new version. Dunno how to do it on windows, on linux I use "dfu-util -d 0483:df11 -a 0 -s 0x08000000 -U old_version.bin" to save (upload) the old version to the PC (128 KByte). The tool dfu-util works also for Windows, it is available e.g. from Erik's website together with the manual
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Saa2n has a custom display pcb... So you must buy a "normal" 4 inch display and desolder the flatband cable (if display screen is broken)... Or you must ask the seller to send you a display (if it is not the screen but the display chip)
...
So if you screen is broken (mechanical) then buy a normal 4 inch screen and solder it to your existing pcb....
Yes its not easy.. But doable
(been there.. Did that)
73 sigi dg9bfc
Am 15.06.2023 15:12 schrieb K8HTB <k8htb@...>:
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I have an SAA 2 4 in nano VNA and I need a new screen any place available
to buy a 4-in screen
De K8HTB Joe
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Re: Firmware upgrade for original nanovna
0.8 is an extremely old version. This should work on your device: In case you were worried about "bricking" your device, don't be. It is practically impossible to do. On Thu, 15 Jun 2023 at 12:04, Don Vosper via groups.io <donald.vosper= [email protected]> wrote: Roger,
Thanks for the link.
It doesn't look like my original Nanovna needs updating.
I assume that the updates for the later versions would not be suitable.
Don m5aky
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I have an SAA 2 4 in nano VNA and I need a new screen any place available to buy a 4-in screen
De K8HTB Joe
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Measuring switch isolation Re: [nanovna-users] Connect VNA thru tuner to antenna
On 6/15/23 4:38 AM, Bryan Curl wrote: Hi Jim,
How do you do that?
[
"But it's good to check (and hey, you could use the NanoVNA to measure it)."
]
Bryan, n0luf
Measuring switch isolation. Let's say your switch has a common, and 4 switched outputs A,B,C,D Hook the VNA up to Ch0 to A and Ch1 to B, put a load on Common, set the switch to A, and measure the S21. Or select neither, or C, and measure S21 (which should be lower) You could also hook the VNA Ch0 to Common, Ch1 to output A, then select A (S21 will be the loss/phase shift through the switch) then select one of the others (S21 is the common to unswitched port leakage). If you want to be complete on this kind of thing (or small leakages perturb the system) then you may want to put termination on unused ports and see if it makes a difference.
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Re: Connect VNA thru tuner to antenna
I've done similar with antenna analyzers in the past and currently with a VNA. Switches I've used provided sufficient isolation...so far.
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Donald S Brant Jr
Gary W9TD
Shirley Dulcey KE1L
Muggs KC3UDZ
Ho-Ro
Lou W7HV