Re: NanoVNA Under The Covers
On Mon, Aug 5, 2019 at 04:59 PM, tuckvk3cca wrote:
But several people here claim that 70dB is impossible, even with lab
equipment.?Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: hugen@... Date: 05/08/2019
10:52 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users]
NanoVNA Under The Covers Limited by the effective dynamics of SA602 and
AIC3024, external noise cannot be eliminated and NanoVNA can only measure 70dB
return loss.
It is very, very difficult to achieve at 70dB return at 500MHz, and nanoVNA can be measured only in dynamic range, not that the load can be easily implemented, but this is only an ideal situation.
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Re: NanoVNA Under The Covers
But several people here claim that 70dB is impossible, even with lab equipment.?Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: hugen@... Date: 05/08/2019 10:52 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers Limited by the effective dynamics of SA602 and AIC3024, external noise cannot be eliminated and NanoVNA can only measure 70dB return loss.
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Re: NanoVNA Under The Covers
Limited by the effective dynamics of SA602 and AIC3024, external noise cannot be eliminated and NanoVNA can only measure 70dB return loss.
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Re: NanoVNA Under The Covers
If the nano vna assumes these sol are ideal then it should not read 70dB, it should read infinity. If it is not ideal, then why 70dB, why not 40dB or 80dB or 100dB. What exactly are we measuring when it says 70dB?Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: alan victor <avictor73@...> Date: 05/08/2019 02:59 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers This VNA, the nanoVNA, takes the SMA SOL terminations as ideal. The SMA terminations are NOT ideal.If the SMA SOL CAL terminations were? properly described you would find that there is rotation in the open and in the short when these very same terminations are measured AFTER the CAL!!!THAT IS NOT AN ERROR in CAL. IT IS THE VNA MEASUREMENT of the REAL CONNECTOR as described to the VNA. Errors associated with the VNA instrument such as coupler limitations, lack of power flatness, port SWR, etc... are handled by the error correction mathematics built into the VNA firmware.I cannot over emphasize, there is a bit of misconception? about this whole CAL and standard stuff. Hopefully via the forum and with continued use of the instrument some of these "ideas" will jell.Regards,________________________________From: [email protected] < [email protected]> on behalf of Peter Gottlieb <hpnpilot@...>Sent: Monday, August 5, 2019 12:10 AMTo: [email protected] < [email protected]>Subject: Re: [nanovna-users] NanoVNA Under The CoversThat¡¯s right. The VNA cal is defining the load as perfect, so measuring it will, within the repeatability of the VNA and connectors, indeed tell you it is perfect. By measuring a known good load you can then get a better idea of an unknown load.Try calibrating with a 50 ohm load that measures 45 ohms on an ohmmeter. It will show up as a perfect 50 ohm load.Peter> 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.>>
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Re: NanoVNA Under The Covers
Here is the RLB that I have got. I have checked with manual measurements that at the HF end I can get 60dB return loss. I do not expect the nano vna can out perform this unit, but I want to make sense of its 70dB return loss. Is that so difficult for people to understand?Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: Peter Gottlieb <hpnpilot@...> Date: 05/08/2019 03:52 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers How would you measure that kind of return loss accurately?PeterOn 8/4/2019 9:50 PM, Dr. David Kirkby from Kirkby Microwave Ltd wrote:> On Mon, 5 Aug 2019 at 00:32, tuckvk3cca <tuckvk3cca@...> wrote:>>> That 1.005 swr is up at the 5GHz end I presume. At 500MHz you can get>> 70dB.?? I have seen some people complain that some such loads have a bump>> at 1GHz, origin unknown.Sent from my Samsung Galaxy smartphone.>> Why do you assume that you can get 70 dB at 500 MHz? I think you can be> pretty sure if Keysight believed they could get a 70 dB return loss up to> 500 MHz, it would be in the data sheet.>> I very much doubt NPL, NIST, METAS or any other national standards> laboratory could measure 70 dB return loss.>> Dave.>>
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Re: Questions about Firmware
The si5351 manual shows that the internal VCO operates at a maximum of 900MHz and a 4-divide-frequency output with a maximum frequency of 225MHz. In order to output a frequency of 300MHz, the internal VCO needs to be overclocked to 1200MHz. Not every si5351 can be stably overclocked to 1200MHz. As the temperature increases, the internal VCO operating limit frequency of the si5351 will decrease. If you notice a significant spike(>0dB) in your nanoVNA at 300 MHz or 900 MHz, I recommend that you use the 800MHz firmware.
Thank you!
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Re: How to fool yourself you have a good calibration
Dr. David Kirkby from Kirkby Microwave Ltd
On Mon, 5 Aug 2019 at 04:12, Dr. David Kirkby < drkirkby@...> wrote: Take a look at this video. Please understand that it was the first ever
YouTube video I made, I was suffering from Hayfever, so I keep sniffing. I
think it demonstrates just how bad you can perform a calibration, and get
results that look excellent
It is mentioned once in the video, but to make it clear, to stop myself looking a complete idiot, RF connectors should not be rotated. The nuts on SMA males should be rotated, not the whole connector. I did it that way for the video as I was using a phone, and could not hold the phone and loosen/tighten connectors properly. Although I don¡¯t show the return loss in that video, I think the Smith chart shows that using a very poor calibration load, with a return loss of about 4 dB, can look perfect on the Smith Chart. Had I actually shown the magnitude of S11, you would have seen it a bit clearer. It is VERY easy to fool yourself when making VNA measurements. That¡¯s why all the coaxial calibration kits sold by my company include an attenuator with measured data. The user can compare their measurements of the attenuator to ours, measured with an HP calibration kit. Airlines would be useful to include too, but they are costly to make. Dr. David Kirkby BSc MSc PhD CEng MIET Director Kirkby Microwave Ltd --
Dr. David Kirkby,
-- Dr. David Kirkby,
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How to fool yourself you have a good calibration
Dr. David Kirkby from Kirkby Microwave Ltd
Take a look at this video. Please understand that it was the first ever
YouTube video I made, I was suffering from Hayfever, so I keep sniffing. I
think it demonstrates just how bad you can perform a calibration, and get
results that look excellent
--
Dr. David Kirkby,
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Re: NanoVNA Under The Covers
How would you measure that kind of return loss accurately?
Peter
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On 8/4/2019 9:50 PM, Dr. David Kirkby from Kirkby Microwave Ltd wrote: On Mon, 5 Aug 2019 at 00:32, tuckvk3cca <tuckvk3cca@...> wrote:
That 1.005 swr is up at the 5GHz end I presume. At 500MHz you can get
70dB. I have seen some people complain that some such loads have a bump
at 1GHz, origin unknown.Sent from my Samsung Galaxy smartphone. Why do you assume that you can get 70 dB at 500 MHz? I think you can be
pretty sure if Keysight believed they could get a 70 dB return loss up to
500 MHz, it would be in the data sheet.
I very much doubt NPL, NIST, METAS or any other national standards
laboratory could measure 70 dB return loss.
Dave.
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Re: NanoVNA Under The Covers
Dr. David Kirkby from Kirkby Microwave Ltd
On Mon, 5 Aug 2019 at 00:32, tuckvk3cca <tuckvk3cca@...> wrote: That 1.005 swr is up at the 5GHz end I presume. At 500MHz you can get
70dB. I have seen some people complain that some such loads have a bump
at 1GHz, origin unknown.Sent from my Samsung Galaxy smartphone. Why do you assume that you can get 70 dB at 500 MHz? I think you can be pretty sure if Keysight believed they could get a 70 dB return loss up to 500 MHz, it would be in the data sheet. I very much doubt NPL, NIST, METAS or any other national standards laboratory could measure 70 dB return loss. Dave. -- Dr. David Kirkby,
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Re: NanoVNA Under The Covers
Dr. David Kirkby from Kirkby Microwave Ltd
On Mon, 5 Aug 2019 at 00:10, alan victor <avictor73@...> wrote: As a point of reference I looked at the Keysight 909F APC-7 50 ohm
connector. The product specification is SWR DC-to-5 GHz; 1.005. Hence a
return loss of 52 dB. An outstanding connector.
Regards, Yes, I feel its a shame that smaller, higher frequency versions of APC7 are not available. It¡¯s a really nice connector, with no need to worry about the gender as any two APC7 connectors will mate together. I don¡¯t know what the return loss of the lowband (0-2 GHz) load is in my 85050B calibration kit is, but it mabe even better as performance above 2 GHz is irrelevant, as a sliding load is used between 2 & 18 GHz. The kit also includes a broadband load (DC to 18 GHz) for when one is not looking for the ultimate in performance, so avoids using the sliding load which is a PITA to use. Dave. -- Dr. David Kirkby,
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Re: NanoVNA Under The Covers
This VNA, the nanoVNA, takes the SMA SOL terminations as ideal. The SMA terminations are NOT ideal. If the SMA SOL CAL terminations were properly described you would find that there is rotation in the open and in the short when these very same terminations are measured AFTER the CAL!!! THAT IS NOT AN ERROR in CAL. IT IS THE VNA MEASUREMENT of the REAL CONNECTOR as described to the VNA. Errors associated with the VNA instrument such as coupler limitations, lack of power flatness, port SWR, etc... are handled by the error correction mathematics built into the VNA firmware. I cannot over emphasize, there is a bit of misconception about this whole CAL and standard stuff. Hopefully via the forum and with continued use of the instrument some of these "ideas" will jell. Regards, ________________________________ From: [email protected] < [email protected]> on behalf of Peter Gottlieb <hpnpilot@...> Sent: Monday, August 5, 2019 12:10 AM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] NanoVNA Under The Covers That¡¯s right. The VNA cal is defining the load as perfect, so measuring it will, within the repeatability of the VNA and connectors, indeed tell you it is perfect. By measuring a known good load you can then get a better idea of an unknown load. Try calibrating with a 50 ohm load that measures 45 ohms on an ohmmeter. It will show up as a perfect 50 ohm load. Peter 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.
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Re: NanoVNA Under The Covers
No. The specification is DC-5 GHz. You can google this if you desire. Have a great day. Alan ________________________________ From: [email protected] < [email protected]> on behalf of tuckvk3cca <tuckvk3cca@...> Sent: Sunday, August 4, 2019 11:32 PM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] NanoVNA Under The Covers That 1.005 swr is up at the 5GHz end I presume. At 500MHz you can get 70dB. I have seen some people complain that some such loads have a bump at 1GHz, origin unknown.Sent from my Samsung Galaxy smartphone. -------- Original message --------From: alan victor <avictor73@...> Date: 05/08/2019 01:10 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers As a point of reference I looked at the Keysight 909F APC-7 50 ohm connector. The product specification is SWR DC-to-5 GHz; 1.005. Hence a return loss of 52 dB. An outstanding connector.Regards,________________________________From: [email protected] < [email protected]> on behalf of alan victor <avictor73@...>Sent: Sunday, August 4, 2019 8:52 PMTo: [email protected] < [email protected]>Subject: Re: [nanovna-users] NanoVNA Under The CoversI 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.
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Re: NanoVNA Under The Covers
That¡¯s right. The VNA cal is defining the load as perfect, so measuring it will, within the repeatability of the VNA and connectors, indeed tell you it is perfect. By measuring a known good load you can then get a better idea of an unknown load.
Try calibrating with a 50 ohm load that measures 45 ohms on an ohmmeter. It will show up as a perfect 50 ohm load.
Peter
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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.
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Re: NanoVNA Under The Covers
That 1.005 swr is up at the 5GHz end I presume. At 500MHz you can get 70dB.? ?I have seen some people complain that some such loads have a bump at 1GHz, origin unknown.Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: alan victor <avictor73@...> Date: 05/08/2019 01:10 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers As a point of reference I looked at the Keysight 909F APC-7 50 ohm connector. The product specification is SWR DC-to-5 GHz; 1.005. Hence a return loss of 52 dB. An outstanding connector.Regards,________________________________From: [email protected] < [email protected]> on behalf of alan victor <avictor73@...>Sent: Sunday, August 4, 2019 8:52 PMTo: [email protected] < [email protected]>Subject: Re: [nanovna-users] NanoVNA Under The CoversI 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.
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Re: NanoVNA Under The Covers
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.
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-------- 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.
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Re: NanoVNA Under The Covers
As a point of reference I looked at the Keysight 909F APC-7 50 ohm connector. The product specification is SWR DC-to-5 GHz; 1.005. Hence a return loss of 52 dB. An outstanding connector. Regards, ________________________________ From: [email protected] < [email protected]> on behalf of alan victor <avictor73@...> Sent: Sunday, August 4, 2019 8:52 PM To: [email protected] < [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 PM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] NanoVNA Under The Covers Yes 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.
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Re: Source of decent NanoVNAs on eBay
I wonder why they didn't put a kickstand on the back so you could prop it up?
Stuart K6YAZLos Angeles, USA
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-----Original Message----- From: Mike Brown <mbmail@...> To: nanovna-users < [email protected]> Sent: Sat, Aug 3, 2019 9:16 am Subject: Re: [nanovna-users] Source of decent NanoVNAs on eBay Thanks for the info - useful to know. I had to laugh when I read this though: "About Us 1.We are professional factory to make kinds of motorcycle CNC accessory,such as kinds of modified brake clutch levers,rearsets,foot pegs,steering dampers,kickstand sidestand,handlebar clamp,swingarm spool bolts and so on." Predumably it means they must have at least one engineer on the premises, even if the wrong type. The Ebay seller I bought from seems to specialise in mobile (cellular) phone cases. Regards Mike On Sat, 3 Aug 2019, 16:48 Dr. David Kirkby from Kirkby Microwave Ltd, < drkirkby@...> wrote: 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
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Re: NanoVNA Under The Covers
Hi Gary,
If you look at the underside of each cover you will see an area around each of the 4 mounting holes, which has been tinned with solder (looks like a washer, but is actually the lower copper surface of each Cover). Without scraping away some paint on the cover surface I can't tell if the surface is gold flashed or not, however when I look at the inside of each hole the through hole plating appears to have been gold flashed. The tinned "washer" on the underside of each mounting hole is of course in direct contact with the brass stand-offs mounted on the PC card carrying the electronics. The thru-hole plating (as well as the mounting screws) carries the earth potential through to top surface of each cover also.
It would appear that it was the designer's intention to make sure the covers are at earth potential. I think that was also noted in the original design notes of edy555 the Japanese Designer, as he had problems with instability early in the design. The covers cured the problem.
73's Pete ZL2iK
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Re: 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 PM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] NanoVNA Under The Covers Yes 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.
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F4WCV
Peter Mulhare