Re: NanoVNA Under The Covers
|
Re: NanoVNA Under The Covers
I published my findings on the standards multiple messages in the past. I have the white unit and the black and again as I reported the black kit was supplied with significantly better RTL. If I recall, 44 dB at 900 MHz. The white unit standard 50 ohm was pathetic at 18 dB RTL at 900 MHz. As well, I verified both standards on a hp VNA after performing an independent cal with an independent set of standards. I obtained essentially identical results. Regards, Alan ________________________________ From: [email protected] < [email protected]> on behalf of kh6sky <kh6sky@...> Sent: Tuesday, August 6, 2019 12:01 AM To: [email protected] < [email protected]> Subject: Re: [nanovna-users] NanoVNA Under The Covers It would be interesting for those with accurate meters to measure their loads supplied with their nanoVNAs. I am measuring 51.4 ohms with an AN870 meter. This was a white gecko purchase. Not great.
|
Re: NanoVNA Under The Covers
Then, given Thalus, you are somewhere between London and Berlin...... LOL
OK... got it. Yes I did misunderstand you. I think we would find that as the RL numbers go past -40 dB their accuracy also goes way down. It is harder to accurately measure power at those levels. So I am honestly unable to determine which is more accurate, the nanoVNA or the Rigol/RF bridge. But, once the number goes past -30 dB where the two dead nuts agree, I quickly lose interest because it is of no practical value to me.
Great discussion! Let's do it again!
Warren Allgyer
WA8TOD
|
Re: NanoVNA Under The Covers
No you misunderstood me. I am only saying that if you have s 50dB load the
nano is capable of returning that number consistent with your Spectrum
Analyser RF bridge measurements which is impressive for what it is. But
having said that one of your 50dB loads measured 47dB and when you swap
standards the other measured 63dB. Some screws are still loose somewhere I
would say.
The best RLB I have shows me that I have a bunch of dummies all within
60dB of each other. As to their absolute values we will need to take them
to a Paris metric standards lab I am afraid. BTW I am not Down under, I
can take a train to Paris in 4 hours .
toggle quoted message
Show quoted text
On 6 Aug 2019 01:54, "Warren Allgyer" <allgyer@...> wrote: Not so fast my down under friend! LOL
The highest possible quality in the load will lead to the highest quality
measurements. I do not know the quality of the supplied load but, having
lived and worked in the Chinese electronics industry for many years, it is
suspect to me. Nevertheless, the supplied load will give perfectly adequate
measurements with accuracy sufficient for any normal hobbyist or even
professional.
I do not agree that the supplied load is 38 dB. There is not way to
substantiate that number except with a calibrated, lab grade VNA. It may be
38 dB..... but nothing I am able to do can confirm that. And it is of
little consequence anyway. The accuracy rendered by calibrating with a true
38 dB load versus a true 70 dB load is reflected in decimal points so far
to the right that they are not significant for 99% of applications.
I do not calibrate my volt meter or my ammeter to 6 decimal places. I do
calibrate my frequency standards to GPS which is 10 to the minus 12 I
believe but that is only because it is convenient to do so.
My recommendation is to use the supplied load and enjoy both the learning
experience and the utility of a marvelous, low cost instrument.
Warren Allgyer
WA8TOD
|
Re: NanoVNA Under The Covers
It would be interesting for those with accurate meters to measure their loads supplied with their nanoVNAs. I am measuring 51.4 ohms with an AN870 meter. This was a white gecko purchase. Not great.
|
Re: NanoVNA Under The Covers
Not so fast my down under friend! LOL
The highest possible quality in the load will lead to the highest quality measurements. I do not know the quality of the supplied load but, having lived and worked in the Chinese electronics industry for many years, it is suspect to me. Nevertheless, the supplied load will give perfectly adequate measurements with accuracy sufficient for any normal hobbyist or even professional.
I do not agree that the supplied load is 38 dB. There is not way to substantiate that number except with a calibrated, lab grade VNA. It may be 38 dB..... but nothing I am able to do can confirm that. And it is of little consequence anyway. The accuracy rendered by calibrating with a true 38 dB load versus a true 70 dB load is reflected in decimal points so far to the right that they are not significant for 99% of applications.
I do not calibrate my volt meter or my ammeter to 6 decimal places. I do calibrate my frequency standards to GPS which is 10 to the minus 12 I believe but that is only because it is convenient to do so.
My recommendation is to use the supplied load and enjoy both the learning experience and the utility of a marvelous, low cost instrument.
Warren Allgyer
WA8TOD
|
Re: NanoVNA Under The Covers
Thanks Warren, I think we are now on the same page. So if I use 50dB quality dummies the nano vna can actually measure better than 38dB which is the supplied load. That is impressive for our money.?Sent from my Samsung Galaxy smartphone.
toggle quoted message
Show quoted text
-------- Original message --------From: Warren Allgyer <allgyer@...> Date: 05/08/2019 21:01 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers TuckI am not sure if you are misunderstanding (I don't think so) or simply miss-stating the concept. A load, any load, does not have an inherent return loss. It only has a return loss as measured relative to a reference. Typically the reference is understood to be 50 ohms. Minute differences in the resistance and reactance of the reference load can lead to huge differences in return loss, especially when you are talking RL on the order of 40 or more dB.The numbers that I have shown are not the result of design or calibration routine errors but, in fact, differences in the characteristics of the loads themselves.As a verification I have re-run the tests I made prior with the nanoVNA on my spectrum analyzer/tracking generator/RF bridge combination. It has an inherent dynamic range of 100 dB at a resolution bandwidth of 1 kHz..... 130 dB if I engage the preamp. I again used each of the three loads as a reference on the bridge with the other two measured for return loss in succession. Here is a comparison table of the nanoVNA as compared to the professional setup.As you can see, the results are remarkably close. Especially at return losses less than 40 dB. I have no concerns whatsoever about relying on the nanoVNA results for hobby and home lab use.Warren AllgyerWA8TOD
|
Re: NanoVNA Under The Covers
Yes of course, but all RLBs will give an absolute value of k plus the actual return loss of the DUT. For 50 ohm source and detectors this constant is theoretically 12.09dB but in reality changes with loads and frequency. Part of the calibration process is to eliminate this constant. In practice it also eats into the dynamic range of the generator and detector. So to measure a max of X dB will require borh generator and detector to have X +12dB, assuming the bridge was calibrated with a load that is better than or equal to XdB max in the first place.Sent from my Samsung Galaxy smartphone.
toggle quoted message
Show quoted text
-------- Original message --------From: "Stuart Landau via Groups.Io" <stuartl73@...> Date: 05/08/2019 23:24 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers An opencircuit on a transmission line has infinite impedance. A short circuit has zeroimpedance. An opencircuit,short circuit, or pure reactance terminating a transmission line are incapableof absorbing power fromaforward, or incident, wave. Thus, all incident current and voltage arereflected back toward the source.When this condition occurs,the return loss is said to be 0 dB.?The source:? ttps://www.scte.org/TechnicalColumns/05-10-01%20return%20loss.pdf?If you are measuring the return loss of a device with some attenuation in the path, such as coaxial cable losses, the return loss will be twice the cable loss because the RF travels twice through the attenuation. The first is the incidence wave, the second the reflected wave. The more attenuation in the path, the better the load looks; but it isn't telling you the truth with regard to the device under test.Stuart K6YAZ?Los Angeles, USA-----Original Message-----From: tuckvk3cca <tuckvk3cca@...>To: nanovna-users < [email protected]>Sent: Mon, Aug 5, 2019 1:29 pmSubject: Re: [nanovna-users] NanoVNA Under The CoversNo the return loss of open and short is theoretically 12dB. The RLB has a voltage factor of 8 and the transmission has a factor of 2 .?Sent from my Samsung Galaxy smartphone.-------- Original message --------From: Jeff Anderson <jca1955@...> Date: 05/08/2019? 21:26? (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, Aug? 5, 2019 at 10:06 AM, tuckvk3cca wrote:>> You measure an open load, you measure a shorted load both of which should give> 12dB return loss>I'm probably missing something here, but shouldn't opens and shorts give 0 dB of return loss, not 12?? After all, their Gamma ought to be equal to 1.- Jeff, k6jca
|
Re: NanoVNA Under The Covers
An opencircuit on a transmission line has infinite impedance. A short circuit has zeroimpedance. An open
circuit,short circuit, or pure reactance terminating a transmission line are incapableof absorbing power from
aforward, or incident, wave. Thus, all incident current and voltage arereflected back toward the source.
When this condition occurs,the return loss is said to be 0 dB.
?
The source:? ttps://www.scte.org/TechnicalColumns/05-10-01%20return%20loss.pdf
?
If you are measuring the return loss of a device with some attenuation in the path, such as coaxial cable losses, the return loss will be twice the cable loss because the RF travels twice through the attenuation. The first is the incidence wave, the second the reflected wave. The more attenuation in the path, the better the load looks; but it isn't telling you the truth with regard to the device under test.
Stuart K6YAZ?
Los Angeles, USA
toggle quoted message
Show quoted text
-----Original Message----- From: tuckvk3cca <tuckvk3cca@...> To: nanovna-users < [email protected]> Sent: Mon, Aug 5, 2019 1:29 pm Subject: Re: [nanovna-users] NanoVNA Under The Covers No the return loss of open and short is theoretically 12dB. The RLB has a voltage factor of 8 and the transmission has a factor of 2 .?Sent from my Samsung Galaxy smartphone. -------- Original message --------From: Jeff Anderson <jca1955@...> Date: 05/08/2019? 21:26? (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, Aug? 5, 2019 at 10:06 AM, tuckvk3cca wrote:>> You measure an open load, you measure a shorted load both of which should give> 12dB return loss>I'm probably missing something here, but shouldn't opens and shorts give 0 dB of return loss, not 12?? After all, their Gamma ought to be equal to 1.- Jeff, k6jca
|
Re: NanoVNA Under The Covers
In a bridge, as used in the NanoVNA there is an internal 50 ohm resistor. You have no control of it and you probably can't actually measure it. The bridge will only be in balance when the external termination equals that of the internal resistor. In my very fancy HP, and Narda return loss bridges, the reference resistors (50 ohm SMA) are mounted on connectors as is the unknown port, so you have some control of the bridge.?
In the NanoVNA even a perfect calibration termination, used as the test unknown, will normally require some internal software compensation after the device has been calibrated. The instrument just wants the bridge to be balanced. The instrument then assumes that any additional termination, that balances the bridge as well as the calibration termination is as good as the calibration termination.?
If the device under test doesn't measure the same impedance as the calibration termination, it will show you what it has measured as return loss or as VSWR.
In the past, I have measured very low VSWR (high return loss) devices using my HP 8566B spectrum analyzer to measure the return loss as show by the bridge. A short or open become the full scale reference. This provides me with nearly 100 dB of verifiable dynamic range.
Stuart K6YAZLos Angeles, USA
toggle quoted message
Show quoted text
-----Original Message----- From: Jeff Anderson <jca1955@...> To: nanovna-users < [email protected]> Sent: Mon, Aug 5, 2019 6:41 am Subject: Re: [nanovna-users] NanoVNA Under The Covers Warren, excellent illustrative post demonstrating that if a VNA measures a load to have a return loss of 70 dB, it isn't necessarily so. Over the years I've purchased a number of 50 ohm loads (generic as well as calibration loads) at swap meets, and upon returning home I'll usually do a quick check of their resistance (at DC) with a 4-wire ohm-meter (e.g. HP 3468A).? The measured resistance can deviate significantly from the ideal of 50 ohms. For a 50 ohm load to have a return loss of greater than 70 dB, assuming it has no reactive component, its resistive component must be less than 50.032 ohms.? Anyone can do a quick check of their own calibration load if they have a 4-wire ohmmeter.? This won't be a guarantee of return loss at high frequencies (where reactance effects become more prevalent), but, if you have a selection of a few loads designed for calibration (i.e. designed to minimize reactive effects), I believe this would allow you to find the one which ought to have the best "actual" return loss. - Jeff, k6jca
|
Re: NanoVNA Under The Covers
No the return loss of open and short is theoretically 12dB. The RLB has a voltage factor of 8 and the transmission has a factor of 2 .?Sent from my Samsung Galaxy smartphone.
toggle quoted message
Show quoted text
-------- Original message --------From: Jeff Anderson <jca1955@...> Date: 05/08/2019 21:26 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, Aug? 5, 2019 at 10:06 AM, tuckvk3cca wrote:>> You measure an open load, you measure a shorted load both of which should give> 12dB return loss>I'm probably missing something here, but shouldn't opens and shorts give 0 dB of return loss, not 12?? After all, their Gamma ought to be equal to 1.- Jeff, k6jca
|
Re: NanoVNA Under The Covers
You are correct. In theory, a 6 dB attenuator will give a 12 dB return loss, which another way to test accuracy of the instrument.
Stuart K6YAZ
toggle quoted message
Show quoted text
-----Original Message----- From: Jeff Anderson <jca1955@...> To: nanovna-users < [email protected]> Sent: Mon, Aug 5, 2019 12:26 pm Subject: Re: [nanovna-users] NanoVNA Under The Covers On Mon, Aug? 5, 2019 at 10:06 AM, tuckvk3cca wrote:
You measure an open load, you measure a shorted load both of which should give
12dB return loss
I'm probably missing something here, but shouldn't opens and shorts give 0 dB of return loss, not 12?? After all, their Gamma ought to be equal to 1. - Jeff, k6jca
|
Re: NanoVNA Under The Covers
On Mon, Aug 5, 2019 at 10:06 AM, tuckvk3cca wrote:
You measure an open load, you measure a shorted load both of which should give
12dB return loss
I'm probably missing something here, but shouldn't opens and shorts give 0 dB of return loss, not 12? After all, their Gamma ought to be equal to 1. - Jeff, k6jca
|
Re: NanoVNA Under The Covers
As has been stated before, the importance of SWR or return loss for most practical users is not how little power is reflected (within reason) but at what frequency is the antenna actually resonant. Once you have been involved in this for a while, you realize how the the antenna environment influences the resonant frequency and SWR.
Stuart K6YAZLos Angeles, USA
toggle quoted message
Show quoted text
-----Original Message----- From: Warren Allgyer <allgyer@...> To: nanovna-users < [email protected]> Sent: Mon, Aug 5, 2019 8:32 am Subject: Re: [nanovna-users] NanoVNA Under The Covers And, just to ground this discussion a bit, for practical purposes in the professional RF and video worlds any return loss in excess of 30 dB is considered excellent. A return loss of 30 dB for example translates to a VSWR of 1.07:1. On Aug 5, 2019, at 11:17 AM, Warren Allgyer via Groups.Io <allgyer@...> wrote:
Hi Tuck(?)
Whether a load shows a return loss of 50 dB, 30 dB or 70 dB depends upon what load was used to calibrate the VNA. As you can see from the chart, all three loads exhibited better than 70 dB when they were used as the calibration source. On the other hand, these very same loads all exhibited in the 30's when checked after calibration with the other load.
The nanoVNA divides the displayed frequency range into 101 "bins". The normal return loss for an open, short, and a nominal load are all known factors. So when you tell the VNA you are using a short it checks each of the 101 bins and determines what correction factor is needed to make that value 'normal". This is done three times, once each for open, short, and nominal load. Then those bin by bin correction factors are applied to any measurement you make on the theory that the calibration procedure has "nulled' out any inaccuracies.
So there is no defined return loss inherent to a particular load. There is only loss as measured against a calibration standard. Anything can be a calibration 'standard'.... but if you use one that is reactive or of a non-standard resistance, the VNA assumes it is correct and reports all subsequent measurements against that standard.
This principle, by the way, can be used to your advantage. Say you have devices to be measured at the far end of a piece of coax. If you apply the calibration standards at the far end of the coax instead of at the instrument you will effectively "null out" the coax and the values reported will be as if the far end device was connected directly to the VNA. It is a very useful technique.
This VNA is an incredible value. I am thrilled with mine!
Warren Allgyer
WA8TOD
PS: "Pete" thinks he is still the lap dog he was as a 10 pound puppy. At 105 lbs he is a lap full!
|
Re: NanoVNA Under The Covers
Tuck
I am not sure if you are misunderstanding (I don't think so) or simply miss-stating the concept. A load, any load, does not have an inherent return loss. It only has a return loss as measured relative to a reference. Typically the reference is understood to be 50 ohms. Minute differences in the resistance and reactance of the reference load can lead to huge differences in return loss, especially when you are talking RL on the order of 40 or more dB.
The numbers that I have shown are not the result of design or calibration routine errors but, in fact, differences in the characteristics of the loads themselves.
As a verification I have re-run the tests I made prior with the nanoVNA on my spectrum analyzer/tracking generator/RF bridge combination. It has an inherent dynamic range of 100 dB at a resolution bandwidth of 1 kHz..... 130 dB if I engage the preamp. I again used each of the three loads as a reference on the bridge with the other two measured for return loss in succession. Here is a comparison table of the nanoVNA as compared to the professional setup.
As you can see, the results are remarkably close. Especially at return losses less than 40 dB. I have no concerns whatsoever about relying on the nanoVNA results for hobby and home lab use.
Warren Allgyer
WA8TOD
|
An antenna without a counterpoise (ground or ground-plane) is just a piece of wire. If you are testing a "rubber duckie" I would recommend mounting it onto a piece of metal; even a piece of aluminum foil would give a truer reading. A whip antenna mounted on a hand-held radio is a poor compromise, but at least the radio and your hand acts as a sort of ground.When I worked for Kenwood USA and Standard Communications we did some antenna testing of this sort.
Stuart K6YAZLos Angeles, USA
toggle quoted message
Show quoted text
-----Original Message----- From: Frank S <ka2fwc@...> To: nanovna-users < [email protected]> Sent: Mon, Aug 5, 2019 9:33 am Subject: Re: [nanovna-users] "Hand capacitance" You can try a short coax loaded with low freq ferrites that fit tight on the coax. It helps (somewhat). Cal at the end of the coax On 8/5/2019 12:13 PM, Mike Brown wrote: I saw similar effects myself when testing the antenna from a handheld
transceiver. As Peter says it is to be expected as, in its intended use,
the human operator together with the conductive part of the rig form the
ground plane that is required by that type of simple vertical antenna.
No hand effects have been noticeable when I have tested HF, VHF & UHF
verticals (all with adequate radial systems) or with VHF/UHF yagis.
There seems to be no need to do anything with the s21 port but it would
probably be good practice to put a 50ohm load on it.
Regards
On Mon, 5 Aug 2019, 15:15 , <spaceopqa@...> wrote:
Hello Peter,
On the device itself.
So I will elaborate a little more, as I would like to use one nanovna at
the field, as a simple SWR measurement tool, and of course operate it
handheld. Maybe it will not occur in a proper HF antenna?
Would you isolate the S21 port, or simply the "open" calibration tool will
suffice?
|
Re: NanoVNA Under The Covers
Yes Warren, what you say is exactly what is done on any return loss bridge. You measure an open load, you measure a shorted load both of which should give 12dB return loss but in practice they differ because of a small O/S error. Then you measure a matched load. This should be infinity but it is not because of the real world components. If you have a power meter like me that can get down to 70 to 80dB then you can measure 60dB or more. The difference is the directivity and gives effectively the dynamic range for the instrument. Actually there is one other parameter called the isolation which I forgot how it is measured. The fact that we use 3 such calibrating loads is exactly because we want to extract these 3 parameters that characterises the bridge and therefore the rest of the instrument at each frequency. I am not disagreeing that a different load can be used as a standard and you will get different results. However a proper calibration as I have done a dozen times should not and had not given such a vast discrepancy between similar loads from 38dB to 70dB as you have shown. That is the issue. Is this a flaw of the software or the design of the bridge or the calibration routine in the nanovna?Sent from my Samsung Galaxy smartphone.
toggle quoted message
Show quoted text
-------- Original message --------From: Warren Allgyer <allgyer@...> Date: 05/08/2019 17:17 (GMT+01:00) To: [email protected] Subject: Re: [nanovna-users] NanoVNA Under The Covers Hi Tuck(?)Whether a load shows a return loss of 50 dB, 30 dB or 70 dB depends upon what load was used to calibrate the VNA. As you can see from the chart, all three loads exhibited better than 70 dB when they were used as the calibration source. On the other hand, these very same loads all exhibited in the 30's when checked after calibration with the other load.The nanoVNA divides the displayed frequency range into 101 "bins". The normal return loss for an open, short, and a nominal load are all known factors. So when you tell the VNA you are using a short it checks each of the 101 bins and determines what correction factor is needed to make that value 'normal". This is done three times, once each for open, short, and nominal load. Then those bin by bin correction factors are applied to any measurement you make on the theory that the calibration procedure has "nulled' out any inaccuracies.So there is no defined return loss inherent to a particular load. There is only loss as measured against a calibration standard. Anything can be a calibration 'standard'.... but if you use one that is reactive or of a non-standard resistance, the VNA assumes it is correct and reports all subsequent measurements against that standard.This principle, by the way, can be used to your advantage. Say you have devices to be measured at the far end of a piece of coax. If you apply the calibration standards at the far end of the coax instead of at the instrument you will effectively "null out" the coax and the values reported will be as if the far end device was connected directly to the VNA. It is a very useful technique.This VNA is an incredible value. I am thrilled with mine!Warren AllgyerWA8TODPS: "Pete" thinks he is still the lap dog he was as a 10 pound puppy. At 105 lbs he is a lap full!
|
You can try a short coax loaded with low freq ferrites that fit tight on the coax. It helps (somewhat). Cal at the end of the coax
toggle quoted message
Show quoted text
On 8/5/2019 12:13 PM, Mike Brown wrote: I saw similar effects myself when testing the antenna from a handheld
transceiver. As Peter says it is to be expected as, in its intended use,
the human operator together with the conductive part of the rig form the
ground plane that is required by that type of simple vertical antenna.
No hand effects have been noticeable when I have tested HF, VHF & UHF
verticals (all with adequate radial systems) or with VHF/UHF yagis.
There seems to be no need to do anything with the s21 port but it would
probably be good practice to put a 50ohm load on it.
Regards
On Mon, 5 Aug 2019, 15:15 , <spaceopqa@...> wrote:
Hello Peter,
On the device itself.
So I will elaborate a little more, as I would like to use one nanovna at
the field, as a simple SWR measurement tool, and of course operate it
handheld. Maybe it will not occur in a proper HF antenna?
Would you isolate the S21 port, or simply the "open" calibration tool will
suffice?
|
I saw similar effects myself when testing the antenna from a handheld
transceiver. As Peter says it is to be expected as, in its intended use,
the human operator together with the conductive part of the rig form the
ground plane that is required by that type of simple vertical antenna.
No hand effects have been noticeable when I have tested HF, VHF & UHF
verticals (all with adequate radial systems) or with VHF/UHF yagis.
There seems to be no need to do anything with the s21 port but it would
probably be good practice to put a 50ohm load on it.
Regards
toggle quoted message
Show quoted text
On Mon, 5 Aug 2019, 15:15 , <spaceopqa@...> wrote: Hello Peter,
On the device itself.
So I will elaborate a little more, as I would like to use one nanovna at
the field, as a simple SWR measurement tool, and of course operate it
handheld. Maybe it will not occur in a proper HF antenna?
Would you isolate the S21 port, or simply the "open" calibration tool will
suffice?
|
Re: NanoVNA Under The Covers
And, just to ground this discussion a bit, for practical purposes in the professional RF and video worlds any return loss in excess of 30 dB is considered excellent. A return loss of 30 dB for example translates to a VSWR of 1.07:1.
toggle quoted message
Show quoted text
On Aug 5, 2019, at 11:17 AM, Warren Allgyer via Groups.Io <allgyer@...> wrote:
Hi Tuck(?)
Whether a load shows a return loss of 50 dB, 30 dB or 70 dB depends upon what load was used to calibrate the VNA. As you can see from the chart, all three loads exhibited better than 70 dB when they were used as the calibration source. On the other hand, these very same loads all exhibited in the 30's when checked after calibration with the other load.
The nanoVNA divides the displayed frequency range into 101 "bins". The normal return loss for an open, short, and a nominal load are all known factors. So when you tell the VNA you are using a short it checks each of the 101 bins and determines what correction factor is needed to make that value 'normal". This is done three times, once each for open, short, and nominal load. Then those bin by bin correction factors are applied to any measurement you make on the theory that the calibration procedure has "nulled' out any inaccuracies.
So there is no defined return loss inherent to a particular load. There is only loss as measured against a calibration standard. Anything can be a calibration 'standard'.... but if you use one that is reactive or of a non-standard resistance, the VNA assumes it is correct and reports all subsequent measurements against that standard.
This principle, by the way, can be used to your advantage. Say you have devices to be measured at the far end of a piece of coax. If you apply the calibration standards at the far end of the coax instead of at the instrument you will effectively "null out" the coax and the values reported will be as if the far end device was connected directly to the VNA. It is a very useful technique.
This VNA is an incredible value. I am thrilled with mine!
Warren Allgyer
WA8TOD
PS: "Pete" thinks he is still the lap dog he was as a 10 pound puppy. At 105 lbs he is a lap full!
|
Warren Allgyer
F4WCV
