Re: NanoVNA Under The Covers
I am not sure if I am adding to or further confusing this discussion which has descended into, in my opinion, an argument over the number of angels on a pin head.
First, when a three point calibration is done on any VNA, the result will be to null the return from the load used in the calibration. When the calibration is finished the display will be showing the noise floor of the instrument, not the return loss from the calibration load. The only inference you can draw about the return loss of the load in this is that it is below the noise floor of the instrument.
As an illustration, I have attached a chart showing the results of three different 3 point calibrations. I used two random "50 ohm" terminations from my junk box and the calibration load supplied with the nanoVNA. After each of the three calibrations I recorded the indicated return loss for all three loads in succession.
As you can see from the chart, the reading for any of the the three loads when used as the calibration load is the noise floor i.e. "<-70 dB". What can also be seen from the chart is the symmetry of the readings with different calibration loads. For example, when I calibrate with Load 1, Load 2 indicates -53.6 dB. When I calibrate with Load 2 then Load 1 indicates a similar -54.3 dB.
The point is that, by definition, it is impossible to get an accurate measurement of the return loss of a calibration load on the instrument that was calibrated by that load. The instrument has been set by the calibration to assume that load is perfect and will return only its noise floor level.
The nanoVNA cannot and should not be expected to match the performance of a $15,000 lab instrument. But it does a remarkable job for its cost. In my "lab" I do not care about the difference in return loss between -40.5 and -41.0 dB. What I care about is at what frequency the return loss is best and, at that frequency, whether or not the load is reactive or not. I also care about having an instrument that can show a filter profile and allow me to optimize it for the performance I want. I care about what the input to my linear amplifier looks like for return loss and impedance. For these things I find the performance of the nanoVNA to be more than adequate and the value to be tremendous!
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Re: NanoVNA Under The Covers
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On 8/5/2019 6:41 AM, tuckvk3cca wrote: You are in cloud cuckoo land to think that I believe I am measuring 70dB. Read my post carefully and tell me what are we all measuring when the instrument says 70dB. And stop pushing your expertise and your products.?Sent from my Samsung Galaxy smartphone.
-------- Original message --------From: "Dr. David Kirkby from Kirkby Microwave Ltd" <drkirkby@...> Date: 05/08/2019 12:39 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, 5 Aug 2019 at 09:56, tuckvk3cca <tuckvk3cca@...> wrote:> But several people here claim that 70dB is impossible, even with lab> equipment. Sent from my Samsung Galaxy smartphone.In order to measure a return loss of X dB? with an uncertainty of 1 dB youneed a load with a return loss of of around X + 10 dB. So to guarantee areturn loss of 70 dB you would need a load with a return loss of around 81dB.You are really living in cloud cuckoo land? if you believe that you canmeasure such a return loss.Do the maths and work out the dimensional tolerance of a connector neededto maintain the impedance to that necessary to have a return loss of 70 dB.Assume that the outer is perfect, but work out what the minimum and maximumdimensions on the inner. Then measure the diameter of the inner conductorsof various SMA plugs and tell us what you find.On precision 3.5 mm and N connectors, the inner conductor doesn¡¯t have 4 or6 slots. There are no slots, but instead thin internal fingers whichreduces the expansion in diameter.? (I would assume that the same is trueof metrology grade smaller connectors.)When the male SMA pin enters the female, the female expands in diameter ina way that you can¡¯t predict. The male pin is not like to be dead centre,which again will change the impedance.There is a scientific paper where the authors try to make correctionsbetween different connectors which will mate1) 3.5 mm and 2.92 mm2) 2.4 mm and 1.85 mm3) SMA and 3.5 mmThey worked out corrections for1) 3.5 mm and 2.92 mm2) 2.4 mm and 1.85 mmbut concluded it was not possible to do this with SMA & 3.5 mm due to thevariability of the semi precision connectors.You are living in cloud cuckoo land if you believe that junk about 70 dBreturn loss.I have observed |S11| < -100 dB when making connections with SMA. I don¡¯tbelieve the return loss is 100 dB or even 50 dB.Dave.> -------- 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.> >> --Dr. David Kirkby,
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Re: Questions about Firmware
Hello,
I thank you Hugen for your reply. Now its clear, and over 800MHz I don't have any interest so I played safe and already flashed the 800MHz version.
Where can one find the FW change log? (Maybe I find some reasons to skip upgrade and wait for the next one)
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Re: NanoVNA Under The Covers
You are in cloud cuckoo land to think that I believe I am measuring 70dB. Read my post carefully and tell me what are we all measuring when the instrument says 70dB. And stop pushing your expertise and your products.?Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: "Dr. David Kirkby from Kirkby Microwave Ltd" <drkirkby@...> Date: 05/08/2019 12:39 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, 5 Aug 2019 at 09:56, tuckvk3cca <tuckvk3cca@...> wrote:> But several people here claim that 70dB is impossible, even with lab> equipment. Sent from my Samsung Galaxy smartphone.In order to measure a return loss of X dB? with an uncertainty of 1 dB youneed a load with a return loss of of around X + 10 dB. So to guarantee areturn loss of 70 dB you would need a load with a return loss of around 81dB.You are really living in cloud cuckoo land? if you believe that you canmeasure such a return loss.Do the maths and work out the dimensional tolerance of a connector neededto maintain the impedance to that necessary to have a return loss of 70 dB.Assume that the outer is perfect, but work out what the minimum and maximumdimensions on the inner. Then measure the diameter of the inner conductorsof various SMA plugs and tell us what you find.On precision 3.5 mm and N connectors, the inner conductor doesn¡¯t have 4 or6 slots. There are no slots, but instead thin internal fingers whichreduces the expansion in diameter.? (I would assume that the same is trueof metrology grade smaller connectors.)When the male SMA pin enters the female, the female expands in diameter ina way that you can¡¯t predict. The male pin is not like to be dead centre,which again will change the impedance.There is a scientific paper where the authors try to make correctionsbetween different connectors which will mate1) 3.5 mm and 2.92 mm2) 2.4 mm and 1.85 mm3) SMA and 3.5 mmThey worked out corrections for1) 3.5 mm and 2.92 mm2) 2.4 mm and 1.85 mmbut concluded it was not possible to do this with SMA & 3.5 mm due to thevariability of the semi precision connectors.You are living in cloud cuckoo land if you believe that junk about 70 dBreturn loss.I have observed |S11| < -100 dB when making connections with SMA. I don¡¯tbelieve the return loss is 100 dB or even 50 dB.Dave.> -------- 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.> >> --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 09:56, tuckvk3cca <tuckvk3cca@...> wrote: But several people here claim that 70dB is impossible, even with lab
equipment. Sent from my Samsung Galaxy smartphone. In order to measure a return loss of X dB with an uncertainty of 1 dB you need a load with a return loss of of around X + 10 dB. So to guarantee a return loss of 70 dB you would need a load with a return loss of around 81 dB. You are really living in cloud cuckoo land if you believe that you can measure such a return loss. Do the maths and work out the dimensional tolerance of a connector needed to maintain the impedance to that necessary to have a return loss of 70 dB. Assume that the outer is perfect, but work out what the minimum and maximum dimensions on the inner. Then measure the diameter of the inner conductors of various SMA plugs and tell us what you find. On precision 3.5 mm and N connectors, the inner conductor doesn¡¯t have 4 or 6 slots. There are no slots, but instead thin internal fingers which reduces the expansion in diameter. (I would assume that the same is true of metrology grade smaller connectors.) When the male SMA pin enters the female, the female expands in diameter in a way that you can¡¯t predict. The male pin is not like to be dead centre, which again will change the impedance. There is a scientific paper where the authors try to make corrections between different connectors which will mate 1) 3.5 mm and 2.92 mm 2) 2.4 mm and 1.85 mm 3) SMA and 3.5 mm They worked out corrections for 1) 3.5 mm and 2.92 mm 2) 2.4 mm and 1.85 mm but concluded it was not possible to do this with SMA & 3.5 mm due to the variability of the semi precision connectors. You are living in cloud cuckoo land if you believe that junk about 70 dB return loss. I have observed |S11| < -100 dB when making connections with SMA. I don¡¯t believe the return loss is 100 dB or even 50 dB. Dave. -------- 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.
-- Dr. David Kirkby,
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Re: NanoVNA Under The Covers
I am afraid your statement is contradictory. 70dB is the minimum return loss calculated by this instrument. The noise floor is the minimum amplitude voltage the detectors can measure sure but they are both jobs and the same. The instrument cannot just ignore the dummy load and return 70dB if it is actually a 40dB dummy load, surely. I have another rather good dummy load which actually read 42dB. Are you saying that if I had used this for calibration it will now read 70dB?Sent from my Samsung Galaxy smartphone.
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-------- Original message --------From: alan victor <avictor73@...> Date: 05/08/2019 11:49 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers Good day,I believe what you are saying is the noise floor of the instrument is 70 dB below the 0 dB reference line. The 0 dB reference line would represent 0 dB return loss or complete reflection of the incident voltage; a reflection coefficient of unity. Hence, the noise floor of the instrument would prevail and limit the minute reflected voltage that could be detected if the load were a perfect termination to the instrument. Hence a reflection coefficient of zero. This noise floor is 70 dB below the 0 dB reference line... Sure, I agree.I think if you drop the notion that the noise floor is the return loss value you are measuring will be on the same page.Have a great day,Alan________________________________From: [email protected] < [email protected]> on behalf of tuckvk3cca <tuckvk3cca@...>Sent: Monday, August 5, 2019 8:07 AMTo: [email protected] < [email protected]>Subject: Re: [nanovna-users] NanoVNA Under The CoversHere 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.-------- 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: NanoVNA Under The Covers
Good day, I believe what you are saying is the noise floor of the instrument is 70 dB below the 0 dB reference line. The 0 dB reference line would represent 0 dB return loss or complete reflection of the incident voltage; a reflection coefficient of unity. Hence, the noise floor of the instrument would prevail and limit the minute reflected voltage that could be detected if the load were a perfect termination to the instrument. Hence a reflection coefficient of zero. This noise floor is 70 dB below the 0 dB reference line... Sure, I agree. I think if you drop the notion that the noise floor is the return loss value you are measuring will be on the same page. Have a great day, Alan ________________________________ From: [email protected] < [email protected]> on behalf of tuckvk3cca <tuckvk3cca@...> Sent: Monday, August 5, 2019 8:07 AM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] 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. -------- 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: 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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Warren Allgyer
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