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On Aug 4, 2019, at 7:22 PM, tuckvk3cca <tuckvk3cca@...> wrote:

The supplied dummy load does give a reproducible 70dB return loss. It is a problem that unless this can be verified independently it is a software problem with the 3 point calibration procedure. I do not know enough about the nano vna architecture to confirm if it has this dynamic range. I do know that I have a return loss bridge and a power meter that can read 70dB. I just need to find some quality dummy loads to confirm firstly that the supplied dummy does have such a low return loss. If it does not then it's obviously the nano vna calibration procedure or hardware that is giving this over optimistic value. If it does the the nano vna is good.Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: alan victor <avictor73@...> Date: 04/08/2019 22:52 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers I suspected that is what you did and sorry there is a problem with that measurement method.There is measurement validation and there is measurement verification.I believe you did a verification which after correction would show an excellent return loss to the extent that removal and re insertion of the 50 ohm load is identical and no errors were made during the cal process.Validation will require an independent set of cal standards. I think you hit upon this in your reply. Not sure. In any case, those standards should be well defined and not necessarily assumed to be ideal. They should be as precise as possible, for example, built with a model definition that is defined and is then used by the VNA for correction of its own inherent errors. There is a degree of uncertainty in this so called correction. Nothing is perfectly corrected. With that said, then an independent measurement of the quality of your 50 ohm standards may occur. Again, these standards under test were NOT part of the calibration sequence.If I recall, measurement uncertainty for a typical instrument would result at best in a 50 dB return loss. Don't hold me to this number. I would have to back track through some old notes. However, my point is, you are treading on an absolute measurement that is better than the uncertainty level. That is an issue.Regards, Alan________________________________From: [email protected] <[email protected]> on behalf of tuckvk3cca <tuckvk3cca@...>Sent: Sunday, August 4, 2019 7:00 PMTo: [email protected] <[email protected]>Subject: Re: [nanovna-users] NanoVNA Under The CoversYes I just use the 3 point calibration from the dummies provided. The 50 ohm load did show -70dB. I then use another sma dummy load I had and it show -40 dB or so. I am not saying I believe my results, that is why ai want to buy a few better ones to counter check. I do have a RL bridge that is good to -60dB up to 500 MHz at least. You can measure down to -78dB if you have an AD8307 power meter which I have. That chip can go down to -90dB in principle.Sent from my Samsung Galaxy smartphone.-------- Original message --------From: jimcking@... Date: 04/08/2019 19:16 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers [Edited Message Follows]I read -70 dB also on two different NanoVnas. Ch0 LogMag @ 50 KHz using the 50 Ohm load that came with the NanoVna. This is the same 50 Ohm that was used in the calibration. The calibration procedure assumes the load to be perfect so return loss shows -70 dB. It goes up with Frequency but is always better than -50 dB.Jim K.

I see lots of people having trouble sourceing what they consider a good
version. I bought his one



I can't really complain

* It came with a battery
* It has 4 traces
* It has screening
* It works to 900 MHz with no need to mess about with the firmware.
* There is no evidence of spurious signals.

Downsides
* The build quality is poor - but that seems to be the case was all of
them. I've yet to see any reports of good build quality.
* No mention of where to get the GPL source code.
* The "open" supplied is worst than just leaving the connector open, as the
added capacitance just makes the "open" less like an ideal open. That is
going to tbe the same for any "open" unless you go to great lengths to stop
it.
* Although the load has an excellent return loss, there is a problem with
it which I overlooked the first time I posted about that.

The first did not work (bad display, which Hugen said is delicate), but
they sent another which is okay. I asked them to send that express mail,
which they did, but it had to be without the battery. So I had to swap that
over. I can't really complain, and its probably a lot safer than buying
from Alibaba, or some obscure Chinese website.

--
Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, CHELMSFORD,
Essex, CM3 6DT, United Kingdom.
Registered in England and Wales as company number 08914892

Tel 01621-680100 / +44 1621-680100

? ?
? ? ? ? - r? ? ? ? {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}I
? ?
? ? -
I suppose we could start a fight over this, but here is what Wikipedia has to say about the sign of return loss. There is no claim made that this is "the last word" on this subject. I learned to use a negative sign a long time ago.

Sign[edit]
Properly, loss quantities, when expressed in decibels, should be positive numbers.[note 1] However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature.[1]The correct definition of return loss is the difference in dB between the incident power sent towards the Device Under Test (DUT) and the power reflected, resulting in a positive sign:
? ? ? ? -? ? R L (? d B? ) = 10? log? 10? ?? ? P? i? ? P? r? ? ? ? {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}}
However taking the ratio of reflected to incident power results in a negative sign for return loss;
? ? ? ? -? ? R? L ′? (? d B? ) = 10? log? 10? ?? ? P? r? ? P? i? ? ? ? {\displaystyle RL'(\mathrm {dB} )=10\log _{10}{P_{\mathrm {r} } \over P_{\mathrm {i} }}}
? ? ? ? - where RL'(dB) is the negative of RL(dB).
Return loss with a positive sign is identical to the magnitude of Γ when expressed in decibels but of opposite sign. That is, return loss with a negative sign is more properly called reflection coefficient.[1] The S-parameter S11 from two-port network theory is frequently also called return loss,[2] but is actually equal to Γ.Caution is required when discussing increasing or decreasing return loss since these terms strictly have the opposite meaning when return loss is defined as a negative quantity.
Stuart Landau K6YAZLos Angeles, USA
-----Original Message-----
From: Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...>
To: nanovna-users <[email protected]>
Sent: Sun, Aug 4, 2019 8:29 am
Subject: Re: [nanovna-users] NanoVNA Under The Covers

On Sun, 4 Aug 2019 at 08:46, tuckvk3cca <tuckvk3cca@...> wrote:

Thanks Gary. I contacted my supplier, EBay and ask if I could get another
set of cal8bration loads.? No luck. The 50 ohm was of very high quality,
return loss -70dB compared to -40dB from another source I had, up to 1GHz.
Anyone knows where to get such loads? Sent from my Samsung Galaxy
smartphone.

Return loss of loads should not stated as a *positive* number as it’s a
loss. A return loss with a negative number could only be obtained from a
negative resistance, such as a Gunn diode amplifier.

A return loss of 70 dB can only found in fairyland! I measured 44 dB, but
stated that the measurement would be subject to large errors as the return
loss of the loads in my 85052B calibration kit were specified as 48 dB.
Really, 70 dB can only be found in fairyland. Another VNA might indicate 70
dB, but the result is meaningless.

Dave G8WRB

- r {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}I
-
I suppose we could start a fight over this, but here is what Wikipedia has to say about the sign of return loss. There is no claim made that this is "the last word" on this subject. I learned to use a negative sign a long time ago.

Sign[edit]
Properly, loss quantities, when expressed in decibels, should be positive numbers.[note 1] However, return loss has historically been expressed as a negative number, and this convention is still widely found in the literature.[1]The correct definition of return loss is the difference in dB between the incident power sent towards the Device Under Test (DUT) and the power reflected, resulting in a positive sign:
- R L ( d B ) = 10 log 10 ? P i P r {\displaystyle RL(\mathrm {dB} )=10\log _{10}{P_{\mathrm {i} } \over P_{\mathrm {r} }}}
However taking the ratio of reflected to incident power results in a negative sign for return loss;
- R L ′ ( d B ) = 10 log 10 ? P r P i {\displaystyle RL'(\mathrm {dB} )=10\log _{10}{P_{\mathrm {r} } \over P_{\mathrm {i} }}}
- where RL'(dB) is the negative of RL(dB).
Return loss with a positive sign is identical to the magnitude of Γ when expressed in decibels but of opposite sign. That is, return loss with a negative sign is more properly called reflection coefficient.[1] The S-parameter S11 from two-port network theory is frequently also called return loss,[2] but is actually equal to Γ.Caution is required when discussing increasing or decreasing return loss since these terms strictly have the opposite meaning when return loss is defined as a negative quantity.
Stuart Landau K6YAZLos Angeles, USA
-----Original Message-----
From: Dr. David Kirkby from Kirkby Microwave Ltd <drkirkby@...>
To: nanovna-users <[email protected]>
Sent: Sun, Aug 4, 2019 8:29 am
Subject: Re: [nanovna-users] NanoVNA Under The Covers

On Sun, 4 Aug 2019 at 08:46, tuckvk3cca <tuckvk3cca@...> wrote:

Thanks Gary. I contacted my supplier, EBay and ask if I could get another
set of cal8bration loads.? No luck. The 50 ohm was of very high quality,
return loss -70dB compared to -40dB from another source I had, up to 1GHz.
Anyone knows where to get such loads? Sent from my Samsung Galaxy
smartphone.

Return loss of loads should not stated as a *positive* number as it’s a
loss. A return loss with a negative number could only be obtained from a
negative resistance, such as a Gunn diode amplifier.

A return loss of 70 dB can only found in fairyland! I measured 44 dB, but
stated that the measurement would be subject to large errors as the return
loss of the loads in my 85052B calibration kit were specified as 48 dB.
Really, 70 dB can only be found in fairyland. Another VNA might indicate 70
dB, but the result is meaningless.

Dave G8WRB

Thanks Gary. I contacted my supplier, EBay and ask if I could get another
set of cal8bration loads.? No luck. The 50 ohm was of very high quality,
return loss -70dB compared to -40dB from another source I had, up to 1GHz.
Anyone knows where to get such loads? Sent from my Samsung Galaxy
smartphone.

It is repeatable. It always shows 70 dB with that same load.

I read -70 dB also on two different NanoVnas. Ch0 LogMag @ 50 KHz using the 50 Ohm load that came with the NanoVna. This is the same 50 Ohm that was used in the calibration. The calibration procedure assumes the load to be perfect so return loss shows 70 dB. It goes up with Frequency but is always better than -50 dB.

Jim K.