|
Re: Measuring ferrite beads
#test-jig
That VNA stuff appears to be more critical to what I was aware of.The technique of nanoVNA designer edy555 is worth reviewing: "Remove the crystal filter and connect the resistors to get through characteristics. Next, disconnect the resistors and take isolation characteristics, and CAL DONE in that state. In this case, the loss due to resistance and the leakage due to wiring and jigs are cancelled." |
|
Re: Chasing ghosts???
#internals
#calibration
I measured on all VNA's the same calibration kit directly on the connector forIs it practical to capture uncorrected data for OSL and DUTs from each VNA, then perform calibration corrections using some PC software, to better isolate hardware from firmware effects? |
|
Re: Measuring ferrite beads
#test-jig
Hi Ulrich
That is probably easy to explain. When doing the Ch0 S11 measurement I anticipate you are using a female bulkhead/PCB SMA adaptor to which you solder the coil. Then there are two likely errors. First the calibration might be wrong is you calibrate at the end of the test cable using the female female adaptor and the SMA male kit as assumed ideal. If that is the case and removing the female female adaptor for being able to fit the SMA female adaptor with coil your calibration plane is "out in the blue air" as you calibrated at the end of the female female adaptor no longer fitted. If the female adaptor and the SMA female adaptor with the coil has same delay it is just fine but no likely and probably shorter for the coil adaptor so you have a residual capacity shunt to the coil lowering the resonance frequency. If you however used my data for the female calibration kit published when calibration at the end of test cable then the calibration plane would be correct at the SMA male adaptor but now the full capacitance of the coil SMA adaptor will lower the true resonance frequency probably even more. The NanoVNA can pull the calibration plane backward by setting a positive delay and if calibrated with the male cal kti at the end of the female female adaptor and the coil adaptor has a shorter delay than the female female adaptor, then you can tune the delay with the coil adaptor without coil fitted to a phase trace showing 0 degree phase for Ch0. The mount the coil and measure S11 reflection. All in all measuring coil with S11 reflection is very difficult and the only way is to create 3 calibration standards using identical SMA adaptors as the one used for soldering the coil to. These three calibration standard having for the short a 2 mm thick rigid shorting disk, for the open the center conductor grinded down to Teflon surface and the for the load 2x100ohm SMD resistor with the center conductor reduced to 0.mm length. Even then the solder used for the SMD resistor represent a fringe C of some 50 to 100fF incl. the fringe C for the center conductor and the open has a small fringe C of maybe 25-50 fF. It all has effect on the resonance frequency. Well the S21 measurements is far better but the condition for a correct measurement is that the source impedance for Ch0 and the load impedance for Ch1 must be 50 ohm clean, neither the case but still closer to reality. You have still some impact from the two SMA adaptor to which you fit the coil which should be modelled away. A trick is to mount a small 2 way pin socket to the two center conductor of the SMA adaptor and create 3 calibration pin pin adaptor with two 100 ohm SMD resistor for load, for open a pin pin adaptor in open condition and for short a shorted pin pin adaptor. The do a standard Refelction calibration in "S21" serial condition and solder the coil to a fourth pin pin adaptor. The you are done and has compensated all the fringe elements. I am pretty sure the NAnoVNA will work in the special reflection calibration mode I "invented" several years ago. During calibration not calibrate isolation but thru is OK (as far as I remember) I have not tested this with the NanoVNA. Else you can converter the S21 measurement saved as a s1p file to S11 with the formula (3*S21-2)/(S21-2) in a spreadsheet. Remember s1p files are pure txt file and show the S parameter data as real and imag numbers and when the math result is present in the spreadsheet save these two columns as a text file and rename to s1p extension. You must create the header line manually in a text editor That was a long story to a short question ? Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af UlrichKraft Sendt: 3. november 2019 15:15 Til: [email protected] Emne: Re: [nanovna-users] Measuring ferrite beads #test-jig Hello Kurt, and others, I still haven't build a robust fixture, but experimetally taking some measurements on EMC bead, or right now on a wire-wound inductor with a 3mm ferrite core for EMC application. I was assuming that the results of measuring Z (S11 channel 0) will closely match the results on measuring Gain (S21 channel 1). So basically I soldered the coil between two SMA connectors and have the SMA cables connected to Ch0 and Ch1. For some reason the frequencies of max. Impedance S11 Z (Ch0) do not even closely match the frequency of min. S21 Gain (Ch1). Z on Ch0 shows max. Impedance at around 140 MHZ, but min. gain is around 260 MHz..... When connecting Ch0 and Ch1 directly the S21 gain looks pretty good (flat at 0db) What am I doing wrong or let's say, what is my misinterpretation of S11 Z and S21 Gain? Or is something wrong with the VNA ? |
|
Re: Integration of a nanoVNA unit into an antenna system as indicator of resonance frequency
Hi Wolfgang,
the search for freqency with best SWR and printing it on the display or via I2C to an external LCD would be great to have. As I'm not a maker of software for the nanooVNA or the used STM32F072C-MCU I've to wait for someone doing it. best 73s de DK3SS Arno |
|
Re: Integration of a nanoVNA unit into an antenna system as indicator of resonance frequency
Hi Alan,
yes I use a SPDT relais to switch either the TX to the loop, or the VNA to the loop an the TX is offline in this case. When the relais gets its 12V DC, this is the source supply for the VNA as well (regulates down to 5V with a 7805 regulator ic. It can be seen in the bloc diagram as well. Typical TX-power ist the full 100W. With some efforts in EMI suppression the unit withstands the fieldstrength, not running wild. I could tune under full power. Have put a lot of effort in reduction of any avoidable losses, thus the high Q ist the benefit. The use of extreme low loss capacitors helps a lot (the 300pF comes from China with outstanding performence) (the 3600pF capacitor is made in Germany with glimmer dielectric). Have testet the loop in several QSOs around Europe as listet in my homepage and found it*s a good working antenna anyway. The theory of calculating effciency gives no more than 1%, but my testing brought up a reasonable performence anyway. Many hams uses dipoles or W3DZZ-antennas with our european narrow spaces and in most cases these wires are hung up much too low, thus loosing a lot of efficieny either. So it makes sense to compare what comes out in reality. With the gamma-match I use, it is no problem to achieve over 30dB return loss. I used some good old test equipment to develop this antenna, a vector voltmeter ZPV from Rohde&Schwarz and as Network Analyzer a hp8713B, the foto with the green CRT ist taken from it.. Some extra features like remote control via WiFi to tune up or down the resonance freuency,or switching on and off the nanoVNA with the antenna relais are implemented right now, some more ideas I still have aren*t yet. A lot of fun for a retired engineer! I relize a lot of reads of my homepage since I posted this topic. May be I have to make an english version of it in near future. best 73s |
|
Re: Chasing ghosts???
#internals
#calibration
Hi Erik
Interesting test indeed. I understand that when you did not see any difference between the 3 VNA's and calibrating directly at the 3 VNA's it meant at a SMA female adaptor using the SMA male kit supplied with the NanoVNA. hat is quite OK and understandable they show same resulting S11 reflection. When you use the 1 m cable and semirigid cable you do not explain if it is a SMA male male cable. If so you probably use a female female adaptor to do the short/open test, and if that is the supplied SMA "barrel" you have a loss to consider, which is "mudding" the test, as its reflection impact is different which cable you use. Anyway you are right the 3 bridges are not compensated by any bridge compensation model, which explains differences It is quite a task to implement the 6/12 terms error model like done for the VNWA (in ted software) and the FA-VA5 (in the hardware and software when suing VNWA software), but maybe Rune will pick it up at some point in time for the NanoVNA-saver ? Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af erik@... Sendt: 3. november 2019 14:34 Til: [email protected] Emne: [nanovna-users] Chasing ghosts??? #internals #calibration In all honesty I was not sure if the approach I was following to determine imperfections in a calibration kit made sense. Various wise people on this group have given me hints which, due to lack of knowledge on my side, I probably failed to understand. So I decided to to some more investigations. I used THREE different VNA's VNA 1: NanoVNA (we all love) VNA 2: Home build nanoVNA equivalent. VNA 3: Home build 3 GHz VNA (uses same type of resistive bridge and measurement principles as nanoVNA but it does not use overtone mode) and ONE calibration kit and ONE set of cables. I measured on all VNA's the same calibration kit directly on the connector for calibration, the same 1 meter RG58 cable with OSL and the same 30cm semi rigid cable with OSL All measurements where done till 900MHz. The calibration kit is assumed to be perfect. No compensation factors where used. Any difference seen between these measurements should come from the difference in VNA's After calibration all three VNA's show for the calibration kit a perfect calibration, no difference is seen. In attached pictures you will see the calibrated plots of the measurements on the three different VNA's of the logmag S11 of the long cable (RG58) and the medium cable (semi rigid) with open and short at the end. The only difference between the three pictures is the VNA. Cables and calibration kit are the same. It is safe to conclude there are substantial differences between the three VNA's First picture: VNA 1 (nanoVNA) seems at low frequencies to have a Z0 that best matches the impedance of the cables but shows a substantial deviation above 600MHz Second picture: VNA 2 (home build VNA) has a bit worse Z0 match and seems to have a S11 open of both cables that goes off track above 800MHz Third picture: VNA 3 (3GHzVNA) becomes very noisy above 550MHz (need to investigate why as this is new) but the oscillations of the logmag S11 show no sign of substantial deviation apart from gradual increase in amplitude and the cable loss in dB stays nicely linear with frequency This comparison underpins my initial assumption that the nanoVNA needs a bridge error model to correct the differences (in particular above 300MHz) and until these threeVNA's (with their individual bridge error models) give the same measurement results I better not try to calculate calibration kit error parameters Feedback is welcome -- Erik, PD0EK |
|
Re: Measuring ferrite beads
#test-jig
Hello Kurt, and others,
I still haven't build a robust fixture, but experimetally taking some measurements on EMC bead, or right now on a wire-wound inductor with a 3mm ferrite core for EMC application. I was assuming that the results of measuring Z (S11 channel 0) will closely match the results on measuring Gain (S21 channel 1). So basically I soldered the coil between two SMA connectors and have the SMA cables connected to Ch0 and Ch1. For some reason the frequencies of max. Impedance S11 Z (Ch0) do not even closely match the frequency of min. S21 Gain (Ch1). Z on Ch0 shows max. Impedance at around 140 MHZ, but min. gain is around 260 MHz..... When connecting Ch0 and Ch1 directly the S21 gain looks pretty good (flat at 0db) What am I doing wrong or let's say, what is my misinterpretation of S11 Z and S21 Gain? Or is something wrong with the VNA ? |
|
Re: Integration of a nanoVNA unit into an antenna system as indicator of resonance frequency
Hi Arno,
a good idea! In My EU1KY analyzer I have implemented a function to automatically search the frequency with the best SWR, or the minimal S11. For the makers of the nanoVNA software this is no problem. A good improvement. Best regards, 73, Wolfgang, DH1AKF |
|
Chasing ghosts???
#internals
#calibration
In all honesty I was not sure if the approach I was following to determine imperfections in a calibration kit made sense. Various wise people on this group have given me hints which, due to lack of knowledge on my side, I probably failed to understand.
So I decided to to some more investigations. I used THREE different VNA's VNA 1: NanoVNA (we all love) VNA 2: Home build nanoVNA equivalent. VNA 3: Home build 3 GHz VNA (uses same type of resistive bridge and measurement principles as nanoVNA but it does not use overtone mode) and ONE calibration kit and ONE set of cables. I measured on all VNA's the same calibration kit directly on the connector for calibration, the same 1 meter RG58 cable with OSL and the same 30cm semi rigid cable with OSL All measurements where done till 900MHz. The calibration kit is assumed to be perfect. No compensation factors where used. Any difference seen between these measurements should come from the difference in VNA's After calibration all three VNA's show for the calibration kit a perfect calibration, no difference is seen. In attached pictures you will see the calibrated plots of the measurements on the three different VNA's of the logmag S11 of the long cable (RG58) and the medium cable (semi rigid) with open and short at the end. The only difference between the three pictures is the VNA. Cables and calibration kit are the same. It is safe to conclude there are substantial differences between the three VNA's First picture: VNA 1 (nanoVNA) seems at low frequencies to have a Z0 that best matches the impedance of the cables but shows a substantial deviation above 600MHz Second picture: VNA 2 (home build VNA) has a bit worse Z0 match and seems to have a S11 open of both cables that goes off track above 800MHz Third picture: VNA 3 (3GHzVNA) becomes very noisy above 550MHz (need to investigate why as this is new) but the oscillations of the logmag S11 show no sign of substantial deviation apart from gradual increase in amplitude and the cable loss in dB stays nicely linear with frequency This comparison underpins my initial assumption that the nanoVNA needs a bridge error model to correct the differences (in particular above 300MHz) and until these threeVNA's (with their individual bridge error models) give the same measurement results I better not try to calculate calibration kit error parameters Feedback is welcome -- Erik, PD0EK |
|
Re: Two traces...
Tomorrow I'll get busy with Console CommandsPuTTY works, but if your Ubuntu already has Python, then this script enables interacting directly from bash: .. after edits for your path and serial port. By adding to your ~/bash_profile: ch () { python /path/to/nVcmd.py "$*" } Then you can invoke, e.g.: $ ch help Commands: help exit info threads version reset freq offset time dac saveconfig clearconfig data dump frequencies port stat gain power sample scan scanraw sweep test touchcal touchtest pause resume cal save recall trace marker edelay capture vbat transform threshold color vbat_offset $ ch trace 0 LOGMAG CH0 10.000000000 8.000000000 1 LOGMAG CH1 12.000000000 8.000000000 2 SMITH CH0 1.000000000 0.000000000 $ ch marker 1 50 57000 $ ch frequencies > freq $ ch data 0 | paste freq - > my.s1p |
|
Re: 50ohm cal load failed
Mel,
I used a commercially made HP 50 ohm termination as my standard until David Taylor pointed out that even though it was manufactured by HP its s-parameter specs were lukewarm at best. [] - Herb ======================================= Herb, It wasn't me who commented on your HP termination. Must have been another David! Cheers, David -- SatSignal Software - Quality software for you Web: Email: david-taylor@... Twitter: @gm8arv |
|
Re: #Shielding
#shielding
Bridge is most sensitive and reflected signals are smallest (so noise is a larger portion)just look to see how well behaved the LOGMAG signal is on an open port?on closed (with 50-ohm load) when terminated by 50 Ohm calibration load. |
Oristo
Kurt Poulsen
Arno DK3SS
Wolfgang Kiefer
David J Taylor