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On Mon, 9 Dec 2019 at 07:56, <erik@...> wrote:

Kurt,

It appears (in my limited understanding) the poor matching to Z0 of CH1
(port 2) is the biggest reason why the T-check is not performing well on
the nanoVNA.

I would not say the matching is poor on port 2. I measured it using my HP
VNA. At least on the NanoVNA sample I have, the return loss on port 2 is
better than the specification on my HP 8720D VNA. I did post some data on
the NanoVNA Facebook group.

I was unable to measure the source match at port 1 well due to the power
coming out of port 1. I had set my HP VNA source power to -20 dBm in an
effort to not cause any non-linearities. Testing at +10 dBm might have been
possible, but I don't know if the results could be trusted. Certainly
switching the NanoVNA off showed excellent match on port 1, and on port 2
is was quite reasonable, and largely independent of whether the unit was
powered on or not.

Erik, PD0EK

Dave

Why not just calibrate for the frequencies you care about and save as your
default?
It doesn't seem like a custom firmware is needed to only see a segment you
want. Since it is less than 300mhz, you would not be using harmonics,
anyway.

Just my opinion.

Marco

Hi Erik
Fantastic ... I did not know you was maintaining TAPR VNA (or I had forgotten it)
Looking forward to follow your project.

My transfer switch is also Sivers Lab but only PM7551 ? with a small control PCB with 5V to 28DC converter.
It went bust recently so now supplied by good old fashion AC/DC converter.
I did measure some WiFi channel filter with the VNWA successfully using a filter for the entire WiFi band to clean up the TX signal. That worked great. One og these days I will try it with the NanoVNA

Kind regards

Kurt







-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af erik@...
Sendt: 9. december 2019 14:30
Til: [email protected]
Emne: Re: [nanovna-users] The T-Check confusion



Hi Kurt.



Thanks. This is the switch I bought: SIVERS LAB PHILIPS COAXIAL SWITCH 28V DC-18Ghz PM7553 Isolation below 1GHz is better than 80dB so I guess below 300MHz good enough.

As I am currently the maintainer for the TAPR-VNA software so I can add whatever I want :-) Using the scikit-rf implementation as example I should be able to add (limited) 10/12 term calibration functionally to the TAPR-VNA SW, including controlling the transfer relay.



Lately I have been trying to optimize and tune various filters such as a 2GHz cavity filter and as I have to tune 5 resonators it would be nice if I did not need to reverse the DUT all the time as for best tuning you need to see S11,S21,S22 and S12 together. So it is more a matter of being kind to SMA cables and connectors and making tuning faster and easier.



For my home build VNA's I can also buy/build a second bridge, add a 4th receiver and put the transfer switch between the LO and the bridges. This will give me a fairly symmetrical setup allowing measurement of the errors in the bridge impedance. Disadvantage is the transfer switch is locked inside one VNA So many options to choose from, sounds like a hobby



--

NanoVNA Wiki: </g/nanovna-users/wiki/home> /g/nanovna-users/wiki/home

NanoVNA Files: </g/nanovna-users/files> /g/nanovna-users/files

Erik, PD0EK

Two questions to answer:

1: Is there anything you can improve for HF by removing/adding it from the current firmware of the nanoVNA?
The only thing I can think of is to force the SI5351 to always use an even number in the final divider and thus reduce the spurs. As a consequence that scanning speed will be somewhat reduced. However these spurs have an neglectable impact so why bother?

2: Who will implement this?
That will depend on the first answer I guess

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

GIN&PEZ;

You are in excellent company. The Romans thought they could avert the zero issue altogether by not using it at all. They must have realized that the number 1 was going to be a problem when they ran out of fingers too. :-)

Is the number 2 the only numerical character used in your proof? I think I can differentiate the zero’s without ambiguity; I’m only uncertain of the ones and lower case L’s. Can I assume all are lower case L’s, and all as being measured Load values?

--
73

Gary, N3GO

The NanoVNA, and most VNA's in general, use the fact they know their transmitted excitation frequency and its harmonics to pick out the desired receive signal to simplify the circuitry.

The RF synthesizer generates two different frequencies separated by a few KHz's. One provides the transmitted test excitation frequency (along with its harmonics) and one provides the local oscillator for its mixer down conversions. The down conversion output is the difference frequency of a few KHz's. As a receiver this mixing will down convert based on difference of the Tx RF excitation and the mixer local oscillator frequency. There is no RF filtering for down conversion image rejection as it does not need it because it knows the expected Rx frequency. This is the first issue for using it as a general receiver.

It can pick out particular harmonics by adjusting the down converter mixer local oscillator frequency slightly relative to the Tx excitation frequency so the difference down conversion frequency is always in the same low (KHz) frequency range. The measurements of relative amplitude and phase are made at the low down converted frequency signal. The narrow bandwidth of the down conversion improves the ability to measurement of the desired signal but limits the use as a general receiver.

Software Defined Radio (SDR) receivers use a direct conversion mixer also known as zero intermediate frequency down conversion. It actually consists of two down conversion mixers that are given local oscillator signals that are exactly 90 degrees out of phase. This produces two outputs that are called 'I' channel ( In phase) and 'Q' channel (quadrature phase) signals that can be mathematically manipulated to recover all types of signal modulation methods. The I and Q channels are also known as baseband signals which are ADC digitized and are low pass filtered to half the desired RF receive bandwidth. The SDR method could be used for VNA measurements but it would be overkill complexity. Modern spectrum analyzers use this method and some also provide VNA capability within the same unit.

If there an improvement in significant performance, yes. However I expect it is a combo of hardware and firmware dedicated to HF that would be required to achieve that goal.

Alan

would it be worthwhile to make a firmware that didn't support harmonics and
limited the VCO to <30MHz

No, negligible firmware is specific to those constraints.

Since I am only interested in RF from 30MHz and below, would it be worthwhile to make a firmware that didn't support harmonics and limited the VCO to <30MHz?

Thanks

RE: "First BNC up to 3ghz is a reliable connector, no different from TNC.
Caveat; use good stuff and make sure you do not interchange
50 ohm BNC with 75 ohm BNC, really they are different!"

Yes they are different, look at the photo at


The 75 ohm BNCs are much more delicate and likely to be damaged because they lack the protection of the 50 ohm BNCs

However, they are physically inter-matable with no damage.
The center pin OD and shield "fongers' ID are identical, so can be inter-mated wtih no damage.
The impedance bump is probably not too bad below 5MHZ because before ATSC, when NTSC was used, virtually every BNC connector installed on 75 ohm coax and used in NTSC video equipment was the 50 ohm variety.
.

Hi Kurt.

Thanks. This is the switch I bought: SIVERS LAB PHILIPS COAXIAL SWITCH 28V DC-18Ghz PM7553
Isolation below 1GHz is better than 80dB so I guess below 300MHz good enough.
As I am currently the maintainer for the TAPR-VNA software so I can add whatever I want :-)
Using the scikit-rf implementation as example I should be able to add (limited) 10/12 term calibration functionally to the TAPR-VNA SW, including controlling the transfer relay.

Lately I have been trying to optimize and tune various filters such as a 2GHz cavity filter and as I have to tune 5 resonators it would be nice if I did not need to reverse the DUT all the time as for best tuning you need to see S11,S21,S22 and S12 together. So it is more a matter of being kind to SMA cables and connectors and making tuning faster and easier.

For my home build VNA's I can also buy/build a second bridge, add a 4th receiver and put the transfer switch between the LO and the bridges. This will give me a fairly symmetrical setup allowing measurement of the errors in the bridge impedance. Disadvantage is the transfer switch is locked inside one VNA
So many options to choose from, sounds like a hobby

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

Hi Erik
Using the transfer switch is just a lazy method to swap the direction of the DUT.
Actually dependent of the transfer switch quality you bought you make get poorer isolation between port 1 and port2. Often the isolation in the region of 60dB for such transfer switches.
Although you have isolation calibration e.g. in forward direction it will not be the same in reverse direction. With the NanoVNA + softwares you cannot do independent calibration in the forward and reverse direction so it is not helping you, on the contrary.
Nothing is better than swapping the DUT direction when measuring forward and reverse. You will have different calibration result via the transfer switch for forward and reverse. I did in the past a test set with 4pc. 18GHz SMA microwave relays and used rigid interconnection cable of same phase length. I had isolation up to 140dB with this setup, which was made for my N2PH VNA going to 60MHz. The N2PK VNA was controlled by the VNWA software, which both has separate calibration in forward and reverse direction and did automatic controlled the test set. This way it work also with a transfer relay which I also have works the same way.
So bottom line.. You may develop an interface for you homemade VNA controlling the transfer relay and implement the needed error correction in software. There are no free lunches in this game.
I have no idea if the TAPR VNA software have such facilities.
To the general question about the hobby level then by adding a 10dB attenuator (included in the calibration) between DUT and RX port linearize the measurements quite a lot, so that would be enough in daily use for the accuracy you are after.
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af erik@...
Sendt: 9. december 2019 12:47
Til: [email protected]
Emne: Re: [nanovna-users] The T-Check confusion

I've found and bought an affordable SMA transfer switch (2x2 switch) on eBay and I was hoping it would allow me to extend nanoVNA or one of my home build VNA's to full two port capability by extending the calibration routines in the TAPR VNA software Do I understand correctly that, as you are not able to measure all errors using a transfer switch connected to port 1 and port 2, you can only do the TwoPortOnePath calibration?
What would be the impact of this in practice????
Given I can measure and ensure both ports are rather close to a real 50 ohm using a second VNA: would the inability to correct some errors have a major impact on practical measurements of filters that are sensitive to port mismatch?
Remember for me this is all hobby use and being able to measure with an error less then some/one dB is great

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

NanoVNA has receiver, but it cannot digitize receiver output with enough bandwidth to listen AM or SSB radio. You can try to connect your PC soundcard to SA602 outputs and use HDSDR to listen radio, but there is no low pass filter, so you will get a lot of images. And such modification will ruin VNA functions.

Hi Erik
Just one more practical comment. Whatever you do the single forward and the single reverse measurement s1p files does not carry any information about the port mismatch to take into account for the T-Check calculation.
And besides that I consider this discussion is only of pure interest how T-Check is done the right way, and my report was only to demonstrate some facts. I do not think 99% of the NanoVNA users are benefitted if such facilities was implemented in future and would not try to motivate such a initiative.
This product is great as is and a calibration is tested quite well investing in a semirigid cable of some 25cm both for frequency range up to 500MHz and 900MHz. To 1500MHz is does not show useable trace along the Smithchart circumference.
Kind regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af erik@...
Sendt: 9. december 2019 08:57
Til: [email protected]
Emne: Re: [nanovna-users] The T-Check confusion

Kurt,

It appears (in my limited understanding) the poor matching to Z0 of CH1 (port 2) is the biggest reason why the T-check is not performing well on the nanoVNA.
Would you agree that using a 10dB attenuator between DUT and CH1 (port 2) would solve most of this?
What would be the impact of the remaining non-compensated delay?
Should we add to the instructions that, for best nanoVNA 2 port DUT measurements one should seriously consider using a 10dB attenuator between DUT and CH1 (port 2) till new HW becomes available that solves the poor matching of CH1 (port2)?

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

Is there a way to use it like a "scanner"?

Yes, CH1 is a receiver that looks for signals at the frequency (or harmonic) of CH0.
Keep in mind that nanoVNA steps, rather than sweeps,
so that if set for a wide span will probably miss a narrow bandwidth signal.

Read here:
/g/nanovna-users/topic/34079496#2165

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

I've found and bought an affordable SMA transfer switch (2x2 switch) on eBay and I was hoping it would allow me to extend nanoVNA or one of my home build VNA's to full two port capability by extending the calibration routines in the TAPR VNA software
Do I understand correctly that, as you are not able to measure all errors using a transfer switch connected to port 1 and port 2, you can only do the TwoPortOnePath calibration?
What would be the impact of this in practice????
Given I can measure and ensure both ports are rather close to a real 50 ohm using a second VNA: would the inability to correct some errors have a major impact on practical measurements of filters that are sensitive to port mismatch?
Remember for me this is all hobby use and being able to measure with an error less then some/one dB is great

--
NanoVNA Wiki: /g/nanovna-users/wiki/home
NanoVNA Files: /g/nanovna-users/files
Erik, PD0EK

Hi,

I'm quite new to the topic. I learned a lot about the bad design of commonly available antennas and have modified quite a number since then with the help of the Nano.

From what I understand, a VNA is also a receiver (of its own signals). Is there a way to use it like a "scanner"? I do occasionally have to deal with Chinese HF transmitter setups, that only say "UHF" or "VHF" but do not specify the frequency. Normally I go to the company's testlab and have it checked for me.

Is there any practical way to use the NanonVNA for that purpose?

Thomas

Hi Gabriel
You are right it is a matter og software and for that matter firmware. As the NanoVNA is presently it does not have facilities embedded for neither calibration kit data and full 10/12 term error correction and none of the present software packages I know off has. That counts for NanoVNA-saver, NanoVNAsharp, NanoVNApartner or the TAPR adjusted program.
Thee link you provide is not implemented in the NanoVNA-saver but of course of interest for Rune to consider. You say it is trivial to use in NanoVNA-saver but that requires a "software developer brain" my comment are based on what is on hand for everyone.
The VNWA is actually a full two port devise as when fitted with a testset it swaps the direction so your comment is not entirely correct. It has besides a feature in the software (by pressing the F2 key) to do a full two port measurement, without having a testset attached and that is done by mechanically reverting the DUT between the forward and reverse sweep. So you study of the VNWA manual has not been complete.
Kid regards
Kurt

-----Oprindelig meddelelse-----
Fra: [email protected] <[email protected]> P? vegne af Gabriel Tenma White
Sendt: 9. december 2019 09:06
Til: [email protected]
Emne: Re: [nanovna-users] The T-Check confusion

On Mon, Dec 9, 2019 at 12:54 AM, Kurt Poulsen wrote:

Sorry these kind of measurements is only possible with a VNA having
10/12 term error correction facilities.
NanoVNA is not able to do such measurements.

This is wrong. I double checked the VNWA user guide and it is also a T/R VNA just like the Nano, not a full two port VNA. Therefore any calibration types used on the VNWA also apply to the Nano, it's just a matter of software.

What you are describing is the Two Port One Path calibration, which is nothing new and there is an implementation of it in scikit-rf:

Since scikit-rf is a Python library it is also trivial to use in nanovna-saver.

@ Gary O'Neil, N3GO - 8 December 2019
/g/nanovna-users/message/8024

Dear Gary,

Once again, we thank you for your time.

You are right. Yes, this is indeed an endless, multidisciplinary, research
and one of its objectives is to bridge the gap between the now and the
past. Yes, we tried to see the fundamental ideas of quantities and their
ratio measurements in our sow, particularly in the two-port network case.
Well, this is not at all a simple task as it may sounds, because it has to
do with elementary concepts lying on the historical boundaries between
science and philosophy. Anyway, after many years of returning attempts,
we discovered yesterday that we had to restore the "multiplicative balance"
in the two basic, well-known, linear equations, that is instead e.g. of the
mathematical: b1=S11a1+S12a2, the "physical" one: 1.b1=S11.a1+S12.a2.
That was all.

Finally, yes, we also know that you are also absolutely right at all of the
rest matters you rise, including the badly shaped o, O, 0, 1 and l of MS
Courier New font and especially in this particular size. For that last one,
we will try to re-use the font of our choice: Liberation Mono, in an
appropriate size. of course. As of the above matters, unfortunately enough,
we have to invoke, once again, our permanent excuse : in our sow, this is
a research in progress and thus we have to find time to answer all of them.
We are terribly sorry for the inconvenience caused. Please, accept our apologies.

Best regards,

gin&pez@arg