开云体育

Steve,
The nano is measuring only the cable length, not the antenna plus cable.
Gary
W9TD

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.

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.

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

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.

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

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.

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?

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

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@...>:

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

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

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.

I've done similar with antenna analyzers in the past and currently with a VNA. Switches I've used provided sufficient isolation...so far.

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

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

Well guys n gals I found my issue at last!
The coax i was useing is (ok) if I'm using a tuner but horrible if running straight through. I was getting super high swr.
Today I remembered I had a string of RG8U I bought off a guy put ends on it and a ferrite bead near the antenna and a 6 wind choke back by the nano and BOOM working like a champ!
The reflected was so high I couldn't even get a decent reading! ? so at least I know what I need to do now!
Thanks EVERYONE that gave advice. I had a feeling after enuf trial n error something would give!

On 6/14/23 5:08 PM, Jim Lux wrote:

On 6/14/23 2:17 PM, Jim Lux wrote:

On 6/14/23 12:20 PM, DiSlord wrote:

I hope you disable internal NanoVNA calibration and use only NanoVNA Saver calibration
Linear Interpolation (used in internal calibration if points count or frequency range not equal) can give errors

This is a good point..

In addition, you might use a sim program to simulate an ideal line with a small discontinuity, and see what kind of wiggles you get.

Think of this - you're doing an S21 measurement - a small reflection at either end will constructively or destructively interfere with the main line signal.

On a group delay plot like this, you're looking at fractions of a degree in phase -
A reflection (or spurious signal) that is 90 degrees out of phase, and down 40dB would give you approx atan(.01) = .6 degrees.

just to illustrate how a small error can show up in group delay, I simulated what you'd get with a 2 meter cable, and adding a "triple transit" echo (i.e. a reflection at the Port 2 end, then another reflection at the Port 1 end).? So what winds up inside the Port 2 (Ch1) receiver is the sum of the direct signal and an attenuated delayed signal.
60 dB (essentially a -30dB mismatch at each end) gives you about .03 ns of ripple on 9 ns. 40dB is tenths of a ns, etc.
I ran it for 3 cases, 20dB, 40dB, and 60dB down.

and the source code for the plots:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""

phase effects of small time delay

Created on Wed Jun 14 14:40:45 2023

@author: jimlux
"""


import numpy as np
import matplotlib.pyplot as plt

f = np.linspace(1,701,num=1220)

dbdown = 40
cablelength = 2
d1ns = cablelength * 3 / .66 # 2 meters @ 3ns/meter, 0.66 VF
d2ns = 3*d1ns # triple transit

periods = 1000./f #ns

ph1 = d1ns/periods*2*np.pi #radian

ph2 = d2ns/periods*2*np.pi

""" now convert to I/Q """

sig1 = np.cos(ph1) + 1j* np.sin(ph1)
sig2 = np.cos(ph2)+ 1j * np.sin(ph2)

""" sum them
"direct path" is down by half dbdown
"triple reflection" is down by full dbddown """

output = (1-10**(-dbdown/40)) * sig1 + 10**(-dbdown/20)* sig2 #40dB down
""" amplitude and phase """
outamp = np.abs(output)

outph = np.unwrap(np.angle(output) )
outph = outph * 180/np.pi
""" plot them """

plt.figure()
plt.plot(f,20*np.log10(outamp))
plt.xlabel('MHz')
plt.ylabel('magnitude (dB)')
plt.title(" %5.1f meters, %5.1f dB down "%(cablelength,dbdown))

""" compute group delay & plot """

difph = np.diff(outph)
diffrq = np.diff(f)
gd = difph/(360 * diffrq) *1000. #ns
gd = np.around(gd,decimals=3)
plt.figure()
plt.plot(f[:-1],gd)
plt.ylabel('ns')
plt.xlabel('MHz')
plt.title(" %5.1f meters, %5.1f dB down "%(cablelength,dbdown))

On 6/14/23 2:17 PM, Jim Lux wrote:

On 6/14/23 12:20 PM, DiSlord wrote:

I hope you disable internal NanoVNA calibration and use only NanoVNA Saver calibration
Linear Interpolation (used in internal calibration if points count or frequency range not equal) can give errors

This is a good point..
In addition, you might use a sim program to simulate an ideal line with a small discontinuity, and see what kind of wiggles you get.
Think of this - you're doing an S21 measurement - a small reflection at either end will constructively or destructively interfere with the main line signal.
On a group delay plot like this, you're looking at fractions of a degree in phase -
A reflection (or spurious signal) that is 90 degrees out of phase, and down 40dB would give you approx atan(.01) = .6 degrees.

just to illustrate how a small error can show up in group delay, I simulated what you'd get with a 2 meter cable, and adding a "triple transit" echo (i.e. a reflection at the Port 2 end, then another reflection at the Port 1 end). So what winds up inside the Port 2 (Ch1) receiver is the sum of the direct signal and an attenuated delayed signal.

60 dB (essentially a -30dB mismatch at each end) gives you about .03 ns of ripple on 9 ns. 40dB is tenths of a ns, etc.



I ran it for 3 cases, 20dB, 40dB, and 60dB down.

On 6/14/23 12:20 PM, DiSlord wrote:

I hope you disable internal NanoVNA calibration and use only NanoVNA Saver calibration
Linear Interpolation (used in internal calibration if points count or frequency range not equal) can give errors

This is a good point..

In addition, you might use a sim program to simulate an ideal line with a small discontinuity, and see what kind of wiggles you get.

Think of this - you're doing an S21 measurement - a small reflection at either end will constructively or destructively interfere with the main line signal.

On a group delay plot like this, you're looking at fractions of a degree in phase -
A reflection (or spurious signal) that is 90 degrees out of phase, and down 40dB would give you approx atan(.01) = .6 degrees.