开云体育

Hi all,

why blame someone for complaining controversial RL signs !?

Keep cool, please.

Yes, Return Loss has been an issue and some use it in a wrong way.
This caused Trevor S. Bird, former IEEE chief editor, to write an article concerning that.

Most remarkable, however, is the fact that even Trevor S. Bird in that very article was
trapped himself, when he gave this "Return loss definition":



Why ? What’s wrong with that?

His formula for Gamma is the reciprocal part of what is between the absolute lines:

Gamma = (Z1 – Z2) / (Z1 + Z2) (a)
which here is falsely quoted for power transfer
purposes, not (what would be true) for reflexionless
transfer purposes.

But the formula Bird quotes, unfortunalely is the one for reflexionless purposes.

For power match calculating purposes it should be:

Gamma = (Z1 – Z2*) / (Z1 + Z2) (b) the asterisk meaning conjugate complex.

Otherwise for example a perfect complex match would not yield an SWR = 1.0 !


(a) would yield |Gamma| results > 1 and even negative SWR for a strictly passive network with lumped components for simple complex Z1 and Z2:

Try this:

Inner Generator Impedance Z2 = 100 – j 200 Ohm
Load Impedance Z1 = 200 + j 300 = Ohm.

Result:

(a) ?strangely“ yields |Gamma| = 1.612 and SWR = -4.266 and RL = -4.149 dB

(b) ?correctly” yields |Gamma| = 0.447 and SWR = 2.618 and RL = 6.989 dB

so: Trevor S. Bird’s use of (a) inside his RL definition indeed yields negative RL,
even though he just makes it a point that this cannot be and is wrong !

There are more trapped occasions than just Trevir S. Bird’s paper using an inadequate type of
Gamma for power transfer considerations. Even the most wonderful SimSmith at one point does.

By the way: SimSmith is the absolutely best Smith Chart program I ever have seen.
(It also accepts .s1p sweep files as saved by NanoVNA saver without any problems.)

I HIGHLY RECOMMEND SimSmith to all NanoVNA users and that is why I mention it here:

Just google for ‘AE6TY SimSmith’ to find Ward Harriman’s home page



There scroll down a bit to find in dropbox :


It is very advanced. Look at least the Manual.

And … Enjoy !

73, Hans
DJ7BA







-----Ursprüngliche Nachricht-----
Von: [email protected] <[email protected]> Im Auftrag von Martin via Groups.Io
Gesendet: Freitag, 4. Oktober 2019 14:39
An: [email protected]
Betreff: [nanovna-users] Accuracy of calculated values - Nano VNA and Saver



Hi All,



Owen Duffy has recently posted a note about the Nano VNA on his blog.



<>



He makes a few points about the accuracy of calculated values with both the Nano VNA and Saver in particular.



If we first deal with the issue of Return Loss, which is probably the most problematic par, and has certainly caught me out on several occasions.



Just about every instrument I can remember using, has RL shown as a negative curve, even if the units themselves are positive. This is handy if for example you are tuning a filter, as you can see the insertion gain on the uppermost trace and the RL loss on the lower one without them overlapping. It also matches the convention of SWR plots and when measuring the RL of cables it matches the convention of more attenuation being negative.



However Owen makes the point that negative loss is actually gain (double negative) and vice versa, and the existing conventions do indeed lead to confusion and mistakes being made. Maybe return loss should really be called return gain, and then everyone would be happy (well maybe - but this is not a serious suggestion).



However if we put this to one side, there is still the issue of how the values are being calculated, and if they are in fact correct. If not then I think this should be investigated in more detail and fixed, as there would seem to be an opportunity to do this before it propagates further.



Regards,



Martin - G8JNJ







--
Diese E-Mail wurde von Avast Antivirus-Software auf Viren geprüft.

Probably someone tried to measure amplifier with this nanovna and it's CH1 input is burned out. Another possible root of cause - incorrect channel setting for trace.

In order to check, do the following:

1) Open CAL menu and press RESET
2) Open DISPLAY - TRACE and select blue TRACE1, make sure it is enabled
3) return back to DISPLAY menu and open CHANNEL menu and select CH1 THROUGH
4) return back to DISPLAY menu and open FORMAT menu and select LOGMAG
5) try to connect/disconnect CH0 with CH1 with cable and check if blue trace has significant change

if you performed these steps and blue trace does not respond on cable between CH0 and CH1, then your CH1 input doesn't works.

You need to be connected to the Internet in order to use the Web interface
because you need to access cho45's webpage.

NanoVNA-Web-Client includes some Android app source.
It is being actively developed, with automated build tools and even unit tests:


Has anyone tried that Android app?

Thanks - add it to the console command doc.
...Larry

Dry solder joint maybe? Saw some people had issues with the SMA-connectors
not soldered properly

On Fri, 4 Oct 2019 at 19:32, Bob Albert via Groups.Io <bob91343=
[email protected]> wrote:

Yes it works sometimes. The SWR display is particularly erratic. But
even when it works, it's only temporary until it decides to shut down.
The unit hasn't been abused. I am impressed when it works. But then it
stops.
At one point a screw fell out of the little panel and I discovered they
were all in various stages of looseness so I snugged them all up. I doubt
that affected anything.
I tried the PC program to control it and it's more or less the same.
Bob
On Friday, October 4, 2019, 10:21:31 AM PDT, Ken Bozarth <
kwbozarth@...> wrote:

Yes, calibrated fine. S11 works fine. With a direct cable between the
ports, I get the noise centered around 0dB. Removing the cable, the display
is exactly the same. Inserting an attenuator, there is no change.

On Fri, Oct 4, 2019 at 1:08 PM <hellhound604@...> wrote:

Have you calibrated it? If you connect a fly-lead between port 0 &1, what
do you measure ? And a 3dB pad?

--

@in3elx

Hi Rob,
the files you are looking for are here:

/g/nanovna-users/files/Firmware/All%20%28known%29%20publicly%20available%20NanoVNA%20DFU%20files%20from%20May%205,%202019%20through%20to%20Sept%2029,%202019/DMR

Have a fun!

N.V.

Yes it works sometimes.? The SWR display is particularly erratic.? But even when it works, it's only temporary until it decides to shut down.
The unit hasn't been abused.? I am impressed when it works.? But then it stops.
At one point a screw fell out of the little panel and I discovered they were all in various stages of looseness so I snugged them all up.? I doubt that affected anything.
I tried the PC program to control it and it's more or less the same.
Bob

See here for a possible solution



On Fri, 4 Oct 2019 at 19:17, amdiog via Groups.Io <amdiog=
[email protected]> wrote:

Hi, windows does not recognize the port, how should I do?





--

Yes, calibrated fine. S11 works fine. With a direct cable between the
ports, I get the noise centered around 0dB. Removing the cable, the display
is exactly the same. Inserting an attenuator, there is no change.

Thanks for the clarification Erik,
With everything Rune has on his plate I'd hate for him to waste his programming efforts on something the firmware does not implement. Usually all save commands come with a reciprocal load command. In this case I guess the firmware developer(s) were being cautious about corrupting the device with erroneous data.

Herb

Hi, windows does not recognize the port, how should I do?

My unit has developed a problem I can't solve.? It is intermittent.? Sometimes it works well but then it gives me a gratuitous reboot or shuts down and then isn't working.? I recalibrate a few times and it seems to recover for a while.
I don't know what to do, other than scrap the unit and get another.? At the price, it's not all that painful.? I haven't tried it today but it's a crap shoot.
Bob

Have you calibrated it? If you connect a fly-lead between port 0 &1, what do you measure ? And a 3dB pad?

I found the progam DfuSe_Demo_V3.0.6_Setup.exe, but it's a demo. Are there any limitations?

Is there a document that explains the update procedure for those who have never done this?

Thanks

Hi all. I am new to this group. I recently bought a nanovna off Ebay. It's a black one, set up for 900MHz and 2 traces. It will not measure S21. All I get is noise at +/-10dB peak levels. S11 works just fine. Should all nanovna units be able to measure S21 regardless of being a "antenna analyzer" or "vector network analyzer". BTW, what is the difference? Of what value is the 4-trace version? I read that in order to flash a 4-trace firmware onto a 2-trace unit, the pgm needs to be unloaded? I tried upgrading the firmware, installing the boot-loader and I found 3 versions of firmware. The boot-loader seems to work fine, sees the device but when I try to load a firmware file, I get a message "not correct format" or something like that. Both softwares used for operating the unit work OK. Should I send this one back and buy a new one or have I not done something I should have? I am not a programmer. I would like to turn the switch on and use it. Thanks.
Ken

I agree, return loss should be a positive number, and I can remember endless debates in our engineering-team about it, but when you tune filters on a Network analyzer, it is nice to have the insertion loss (S12) and return loss (S11) going the other way on a single screen. My memory is not too good after having a brain tumor and a couple of strokes, but I seem to recall the HP network analyzers (HP8712???) also showing S11 as a negative number, whilst S21 as a positive number. My memory is a bit fuzzy, bit I can remember the one graph, S12 going up (less negative), and S11 going more negative on the same screen, making it easy to tune. Whether it was the default mode for the HP8712 or whether it was a custom-mode, I can’t remember.

Hi,
For filters the steepness of the skirts is important apart from the 3dB bandwidth.
-6DB and -80 dB are a real measure for the skirts!
However ,many filters ( or measuring conditions ) are not attaining the -80dB , so -60dB will have to do.
This is OK as long as you realise or/and that this is CLEARLY mentioned/stated.
I have seen many tables with comparisons of filters and their steepness.
Steepness was then 80/3 or 60/3 dB value.
Older engineers told me that this was better than using the ratio of the frequency of the -3 and -60 dB points because the difference between the types of filters( number of poles/crystal,L-C;etc/etc.) could be better evaluated.
I know of discussions because of mixing between -60 and -80 dB values( don't compare two sorts of beasts)

Jan ON4MMW

The current firmware allows dumping the internal calibration table with the data command
data [0-6]
where
0: S11
1: S21
and
2 /* error term directivity */
3 /* error term source match */
4 /* error term refrection tracking */
5 /* error term transmission tracking */
6 /* error term isolation */
but it is currently NOT possible to upload calibration tables into the nanoVNA

a link about measuring filters

In my own experience coming from a R&D environment, we would specify filters with the -3dB and -60dB (theoretical) points, but for production and customer tests, AND specifications, we would only test the -3dB point and the -45 dB points, as those points were achievable by most equipment. The -60dB point was considered to be theoretical as very few customers could measure it.