Hi Christian,
Thanks very much for your explanations.
I'm trying to understand your graph and how you are calculating the error in dB. So I thought I'd try this simple example:
Let's say I have a Load standard whose actual resistance is 53.265 ohms (i.e. Gamma is 0.0316 and Return Loss of 30 dB) and I calibrate my VNA with this standard as its 50 ohm load.
After cal, I measure S11 of this same load. Its Gamma is now 0 (instead of 0.0316) and the corresponding return loss is in the noise of the instrument.
The error in S11 (i.e. Gamma) could be plotted on your graph at the point where DUT Reflection = -30 dB and Load Reflection (Actual) = -30 dB.
But what would be the value of this point? I get a Gamma error of 100% (i.e. 100*(0-0.0316)/0.0316). How are you calculating the dB error of the S11 magnitude?
I'm sure I must be missing something straightforward (maybe it's too early in the morning!)
Again, thanks.
- Jeff, k6jca
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Hi Steve. I think the best answer is you be the judge. Get a hold of a component that you know is your so called golden standard. An R, L or C to start and go measure. Does the value behave as you would expect. Is the error acceptable? If not why not?
After you do a cal, check it and make sure it looks proper. You can have the most expensive cal pieces ever created by mankind and place them on a vna built on a solid gold chassis and get garbage results if the fixtures for the DUT are poor.
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Gentlemen,
I have tried to read this string and accept I have little hope of understanding much of it, albeit I have tagged some of the references in the hope that my understanding might improve with time.
Given that most group members only have a ¡°simple¡± 2 port, one reciever vna (ie nanovna, V2 etc), is it possible to give an understandable resume for us mere mortals who have never been exposed to the use of a professional vna, about the calibration standards for the kit we have got?
Admittedly, all my playing has been just on the vnaV2 devices themselves not connected to a computer, but I am having difficulty seeing much difference between a wide range of standards I have ( smaV2, v2 N, a ¡°cheap¡± N cal set from Isreal, six passable Radiall N 50 ohm standards and some home made sma standards), except for needing to add a slight delay to some. This is up to 3.5ghz on three different V2 devices, one with a 4¡± screen.
Are all my standards good, or am I missing the barn door?
Steve L. G7PSZ
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This is a testmessage only.
Please ignore.
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Re: Newbee with Nano VNA device
On Tue, Oct 6, 2020 at 12:47 PM, Rainer wrote: Hi, Forget everything I said about measuring the antenna with the LNA included. Sorry for not listening to the experts here. This was nonsense what I wrote. I joined the Ham Antenna group in groups.io and got some more info. Rainer
Hi,
I have here to same set ups.
RTL-SDR >> 4.5 meter coax 75 Ohm >> LNA >> Antenna
I disconnected the RTL-SDR from the coax an antenna set up and connected the
Nano VNA to both set ups and yes I can measure SWR, Logmag and get a Smith
circle.
Compared the values of both and they are different which is absolutely clear
for me as Yesterday we optimized one antenna to get a better signal at 174 310
000 and mine was not optimized.
So I guess I spent the bucks for the DC Blocks for nothing but does not
matter. It is leanring material and perhaps one day I can use them somewhere
else :-)
Both set ups are running pointing at the same transmitter 960 km away from
here and later in the afternoon we will compare data of Meteor scatter.
Thanks everybody for the comments which made me analyze everything more.
One interesting thing is that now having measured with the LNA in the line the
good SWR value did move to a higher frequency compared to optimizing without
the LNA.
I am talking about a DIY 4 element YAGI antenna for 174 310 kHz. you can see
my meteor scatter data in the rmob.org under Rainer Ehlert in Mexico San Luis
Potosi. The second set up is still under testing and will be in the same city
on the roof of a friend about 4.5 km away from my site to the Northeast.
Lots of things still to learn. Radio waves are magic :-)
Rainer
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Dave,
I think it is a little worse than you described. With a 30dB return loss standard, a 20dB return loss DUT might indicate a return loss from about 17.6dB to 23.3dB. The error due to the 30dB RL standard, 0.0316, can add (with phase thrown in) to the true reflection, 0.100, to give an apparent reflection magnitude anywhere in that range.
--John Gord
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On Mon, Oct 5, 2020 at 11:19 PM, Dr. David Kirkby, Kirkby Microwave Ltd wrote:
On Mon, 5 Oct 2020 at 22:41, <ray@...> wrote:
Hi, new member here. I'm a reasonably experienced Microwave engineer and
will add a NanoVNA to my bench soon. In the process of reading about this
VNA I've become interested in better understanding the theory behind SOLT
(and TRL) cal standards. I've primarily used commercial SOLT cal kits or
TRL of my own making.
For example, if my SOLT Load standard is 10dB vs 20dB return loss, what
are the consequences? How do I determine how good is good enough for each
standard?
As a rough guide, you need the load to have a return loss of 10 dB higher
than what you are measuring to get a measurement uncertainty of 1 dB. So a
30 dB return loss load will enable measurement of a DUT with a return loss
of 20 dB.
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On Tuesday, October 6, 2020, 01:38:24 PM PDT, Rainer <rsfoto@...> wrote:
Hi,
As this group discusses the Nano VNA I would like to ask if somebody would recommend me a group for Antenna building.
Thanks Rainer
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Hi,
As this group discusses the Nano VNA I would like to ask if somebody would recommend me a group for Antenna building.
Thanks Rainer
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Diving a bit deeper into what I wrote earlier. You can derive from Doug Rytting's presentation (see above) or from the signal flow graph that the uncorrected reflection ¦£m measured by the VNA for a DUT with an actual reflection coefficient of ¦£ is ¦£m = e00 + (e10e01 * ¦£) / (1 - e11 * ¦£). When the VNA assumes an ideal load during calibration (¦£ = 0), it follows that e00 is determined during directly from the calibration measurement ¦£m of the load. Therefore, the error caused by an non-ideal load is (e10e01 * ¦£) / (1 - e11 * ¦£).
Now, you might rightfully point out that you're not interested in the error in e00 but in the error in the measurement of the ¦£ (=S11) of a DUT. That's unfortunately not so easy to write down because it also depends on the reflection of the DUT itself. As Dave stated above, the non-ideality of the load must be significantly less than the S11 of the DUT you want to measure.
To show this better, I dug out my VNA simulation (MATLAB script) that I wrote a long time ago - hoping that I didn't make any errors back then ;-). Here, I simulate an ideal VNA, i.e., no errors in the VNA itself, since we're only interested in the errors caused by a non-ideal load. Furthermore, I simulate a calibration where the VNA assumes the load to be ideal, while it actually isn't. From the attached plot you can see the error this causes in the S11 (= ¦£) measurement of a DUT, depending on the actual S11 of said DUT and the actual reflection of the load.
Some notes:
- I only investigated the error in the magnitude of S11. The phase is of course also affected.
- When measuring for example the return loss of an antenna you might not care whether it's exactly 20 dB. Hence, you might be able to accept a higher error caused by the non-ideal load for low reflection / high return loss.
- As already mentioned, if you know your load standard (i.e., its ¦£) you can correct for it and the measurement error will be much smaller; basically just defined by error/uncertainty in your load standard definition.
Regards
Christian
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About this cloning flap ¡ª note that Willie the Bard Shakespeare was not the first to write up the Hamlet saga, just the best.
;B
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Re: New open source VNA released - excellent performance claimed
On 10/6/20 11:06 AM, Jerry Gaffke via groups.io wrote: If this 6ghz VNA also functions as a spectrum analyzer with tracking generator,
that makes it worth twice as much to me.
Perhaps have a stuffing option to use an external bridge as previously mentioned by Jim Lux.
An external resistive bridge should have a BOM cost dominated by the SMA's.
No need to have the external/internal bridge selection be jumper selected on the main board
if that compromises performance, the external bridge is cheap to build.
Then sell a variety of bridges as accessories.
Perhaps one with an attenuator and booster amp for Jim. well, this is why you'd buy your 8510, and then buy an S-parameter test set to go with it. At some point, though, the optimum development/sales model changes. When the widgets are cheap enough, breaking the function into different boxes isn't necessarily a good idea. I've always thought that a homebuilt e-cal box might be useful. Build it, measure it on a good VNA, then have the parameters stored internally. Relays aren't super expensive, surplus, and if the isolation is good enough, it would work quite well.
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Re: New open source VNA released - excellent performance claimed
If this 6ghz VNA also functions as a spectrum analyzer with tracking generator,
that makes it worth twice as much to me.
Perhaps have a stuffing option to use an external bridge as previously mentioned by Jim Lux.
An external resistive bridge should have a BOM cost dominated by the SMA's.
No need to have the external/internal bridge selection be jumper selected on the main board
if that compromises performance, the external bridge is cheap to build.
Then sell a variety of bridges as accessories.
Perhaps one with an attenuator and booster amp for Jim.
Could there be an external "bridge" with a V/I type sensor, and thus able to measure
a wider range of impedances in the device under test?
But the important thing is to get something done and working as a VNA
with something like the specs cited. Don't let me slow this down.
Extra features can come with the the next version out,
and then we will all buy yet another VNA.
Jerry, KE7ER
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On Tue, Oct 6, 2020 at 02:13 AM, Hugen wrote: Yes, using binary data transfer, USB-CDC is no problem at all. But this is a
completely restarted project. Jan developed this project completely
independently. We can consider compatibility in the future process, but please
don't put any pressure on Jan now. Although the APP currently provided by Jan
is not perfect, it works very well and already includes simple spectrum
analyzer and signal generator functions. It can also be manually configured
and firmware upgraded, which is a very good innovation and experiment.
On Tue, Sep 29, 2020 at 09:59 AM, Jim Lux wrote:
On 9/29/20 9:27 AM, Jerry Gaffke via groups.io wrote:
I would think attenuators and booster amps may as well be in the external
cables.
Not terribly familiar with all this, perhaps there are special tricks
involved to measure
something like s12 on an amp? Oohh. that's everyone's first guess.. but think about it.. if you want to
measure the S11 of a LNA, you can't put 50dB of attenuation in front of it.
You put 50 dB of attenuation in the stimulus line, then the bridge, then 50dB
of amplifier in the receiver line. Then calibrate as per usual. If your
receiver has good dynamic range, you don't need as much amplifier.
Adding them to a $300 VNA board adds complication and sources of trouble.
Modular is good when it comes to seldom needed features.
True - maybe a different version of the board, that just leaves out the
resistive bridge. And some extra SMA connectors
The ability to use a different bridge would be interesting.
Perhaps lay out the board such that one could insert vertical SMA's
and stir some surface mount parts to accommodate this?
Yet another product variant for Hugen to sell at some time in the future.
But I suspect most nanovna users have never felt the need for an external
bridge.
Requiring an external bridge for all work with the VNA is perhaps a bridge
too far
towards modularity.
Typically, the way it's done is to have two connectors with a removable jumper
between them.
I would venture that for most VNAs that have this, the jumpers have never been
removed except when doing factory cal/re-cal. Or when someone sets the VNA
down on a non-smooth surface and breaks the jumper.
Jerry, KE7ER
On Tue, Sep 29, 2020 at 08:47 AM, Jim Lux wrote:
yes, it's going towards the fieldfox type of capability, not the "bench
VNA" -
The latter would typically bring out the source and receiver inputs with a
loop, so you could use different bridge or insert attenuation to make it
easier to test amplifiers.
This design has a 30dB sep attenuator, but still, if you're testing a LNA
with
a maximum input of -70 dBm (because it's designed to receive signals at
-150
dBm) this probably isn't your box of choice. Assuming he's putting +10
into
the attenuator, the output power will be -20 dBm or around there. That's
enough to saturate a lot of LNAs.
Likewise, if you were testing a 10W PA, you might want a booster amplifier
in
the drive on port 1, and an attenuator in port 2.
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On Mon, Oct 5, 2020 at 10:30 PM, RayC wrote:
Thanks, I got it downloaded and installed. This appears to be for seeing
uncertainty given a specific model VNA and cal kit. It's quite interesting but
if I had my own cal kit, how might I estimate the uncertainties of that?
Suppose I have a load standard that comes out at 52 ohms and some nH of
inductance and I want to set an upper frequency limit. Maybe there are some
rules of thumb. Or maybe I've overlooking a way to use that Keysight
spreadsheet.
Hi Ray, I am surprised the sheet does not allow you to play WHAT IF. I put together a sheet after the old hp seminar and that permitted you to enter coupler errors, cal kit errors, tracking errors and source flatness, coupler directivity, etc... and obtain an error bound for the 4 resulting measured s parameters. I'll see if I can locate the sheet. You might want to look at this note if not already mentioned.
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Re: Newbee with Nano VNA device
Hi,
I have here to same set ups.
RTL-SDR >> 4.5 meter coax 75 Ohm >> LNA >> Antenna
I disconnected the RTL-SDR from the coax an antenna set up and connected the Nano VNA to both set ups and yes I can measure SWR, Logmag and get a Smith circle.
Compared the values of both and they are different which is absolutely clear for me as Yesterday we optimized one antenna to get a better signal at 174 310 000 and mine was not optimized.
So I guess I spent the bucks for the DC Blocks for nothing but does not matter. It is leanring material and perhaps one day I can use them somewhere else :-)
Both set ups are running pointing at the same transmitter 960 km away from here and later in the afternoon we will compare data of Meteor scatter.
Thanks everybody for the comments which made me analyze everything more.
One interesting thing is that now having measured with the LNA in the line the good SWR value did move to a higher frequency compared to optimizing without the LNA.
I am talking about a DIY 4 element YAGI antenna for 174 310 kHz. you can see my meteor scatter data in the rmob.org under Rainer Ehlert in Mexico San Luis Potosi. The second set up is still under testing and will be in the same city on the roof of a friend about 4.5 km away from my site to the Northeast.
Lots of things still to learn. Radio waves are magic :-)
Rainer
|
Re: Newbee with Nano VNA device
To measure the antenna and feedline 'system', disconnect the antenna
feedline from the receiver and connect the end of the feedline to the VNA.
You can not make a credible measurement of the antenna/feedline 'system'
with the preamplifier connected to the feedline.
Dave - W?LEV
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On Tue, Oct 6, 2020 at 3:11 PM Rainer <rsfoto@...> wrote: Hi,
I was thinking about this DC Blocks.
If I understand correctly those DC Block block the DC current and without
DC current my Low Noise Amplifier does not work, correct ?
So if that is the case, why not just turn Bias Tee OFF and I can measure
through ... right ?
BTW I ordered the pack of two. For what do I need them if above is OK ?
Rainer
--
*Dave - W?LEV*
*Just Let Darwin Work*
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Re: Basic Question About Complex Impedance Numbers
Lower case indicates "milli" or 1E-3. So, your reading of -j667m means
-j667 milliohms or -j0.667 ohms. This is known as scientific notation or,
more specifically, engineering notation, engineering being powers of 10
modulo 3.
Also note that M indicated "mega or 1E+6.
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On Tue, Oct 6, 2020 at 11:28 AM <ed.jackson001@...> wrote: Hello all...
I have a dipole that I ran a sweep on with NanoVNA Saver, and a NanoVNA-H.
When looking at the complex impedance at the closest point to resonance
('0' reactance), I get numbers like
56.3-j697m ohms (no 'ohm' symbol on my laptop).
What does the 'm' mean? I'm assuming that means the reactance part is very
close to '0'. Is that correct, or am I all wrong?
Thank you for your time.
--
*Dave - W?LEV*
*Just Let Darwin Work*
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Re: SWR measurement of CB antenna with PL-259
#newbie
On 10/06/2020 11:06 AM, Roy J. Tellason, Sr. wrote:
Amazon has enough money, they don't need any more.
I got a pair of SO239 and BNC adapters from R&L when I ordered my H4, and figure that should cover my needs nicely. I've seen others post links to these particular parts recently in here. $3.95 each.
Also MPJA.com out of Florida has the adapters. No connection to the company other than being a satisfied customer. Vince. -- K8ZW
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Re: Newbee with Nano VNA device
Rainer,
If you remove power from the bias-tee, the LNA no longer works.
But it almost certainly does not short input to output,
and if it did it would not do so without adding extra loads to ground.
Unless it happens to be extremely fancy and have Jim's relay included in the package.
You need to remove the LNA somehow to measure the antenna with the nanovna.
Jerry, KE7ER
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On Tue, Oct 6, 2020 at 08:23 AM, Jim Lux wrote: On 10/6/20 8:11 AM, Rainer wrote:
Hi,
I was thinking about this DC Blocks.
If I understand correctly those DC Block block the DC current and without
DC current my Low Noise Amplifier does not work, correct ?
So if that is the case, why not just turn Bias Tee OFF and I can measure
through ... right ?
BTW I ordered the pack of two. For what do I need them if above is OK ?
Rainer
if your LNA is one that has a relay to bypass it when it's off, then yes,
turning off the power would be what you need.
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Re: Basic Question About Complex Impedance Numbers
I believe the m stands for milli (1/1000). Mark *From:* Jim Lux ( jimlux@... ) *Sent:* Tuesday, October 6, 2020 9:44 AM *To:* [email protected]*Subject:* Re: [nanovna-users] Basic Question About Complex Impedance Numbers On 10/6/20 4:25 AM, ed.jackson001@... wrote: Hello all... I have a dipole that I ran a sweep on with NanoVNA Saver, and a NanoVNA-H. When looking at the complex impedance at the closest point to resonance ('0' reactance), I get numbers like 56.3-j697m ohms (no 'ohm' symbol on my laptop). What does the 'm' mean? I'm assuming that means the reactance part is very close to '0'. Is that correct, or am I all wrong? milli.? so it's 0.697 ohms.
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Bear Albrecht