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Re: T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz
Hi Rudi
Great.. Well you are on your way. I see there is still a small problem as you have not calibrated so the female female adaptor is subtracted during the Thru calibration. When everything is done right the trace in the Smith chart shall run clockwise along a SW2 circle (the 50ohm changed to 25ohm). You trace is running anticlockwise. In the NanoVNA saver the S21 thru delay is a positive delay. Have you made it negative ?? The calibration shall be so the the two SMA male connector must have same phase reference in S21 and that is done by the subtracting the delay of the female female adaptor. Wheen the T-Adaptor then inserted is adds a s21 delay which causes the trace in the Smith chart to run clockwise Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af reuterr@... Sendt: 9. november 2019 06:01 Til: [email protected] Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz On Sat, Nov 9, 2019 at 12:14 AM, Kurt Poulsen wrote: If you got a SMA male male adaptor try to S11 calibrate at the end ofHello Kurt, Thank you very much for your valuable hints. I made what you reccomendet: 1. Connect the Tee direct to CH0: T-Check_RG316-25cm_CH0-6dB_DSC08176.jpg 2. Add an 6 dB attenuator after the Tee. 3. Shorten the coax cable to RG316 25 cm. 4. Tuned the calibration in NanoVNA-Saver. 5. Adjusted the .S2P file S12 for the 6 dB attenuation. 5. So, up to 450 MHz it is within the 5% Limits. T-Check_Short_CH0-6dB.png Now I know the direction to work on, if neccessary. It is always nice to know your limits :-) 73, Rudi DL5FA |
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NanoVNA-H Big spikes around 300MHz on new unit.
Hello,
A friend of mine has just received a new NanoVNA-H bought from an ebay seller in Essex. It's one of the cased units with black front and all accessories very nicely presented in a box and even a usb-c to usb-c which works with his Android phone app. The problem is that after calibrating it and looking at a VSWR plot of the supplied 50 Ohm load there is a massive spike at around 300MHz. He set the centre frequency to 297MHz with a span of 10MHz and re-calibrated, in order to better see the issue. Scale was set to 0.2/Div. Attached is a screen shot. Has anyone else seen this issue, or know the cause? It can still be returned, but if it is a known issue with a simple fix then that may not be necessary. Thanks, Barry G4MKT |
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VNA fixture for SMA and BNC
#test-jig
Hello,
I recently assembled by SMA and BNC fixture board. You can find the gerbers and Kicad files at The PCB is designed to work with the SMA or BNC versions of my VNA, but is likely going to be useful for NanoVNA too. It has the following features: Built in female calibration standards for open, short, load, and thru. A ZIF socket for easy testing of parts with leads where open, short, load, and thru calibrations may be applied. A flat part of the board for testing SMA parts. The parts can be held down to the board with a toggle clamp or there are holes through the PCB to apply a vacuum to suck the part down to the board. Four inputs for other types of test loads as needed. If you want SMA and BNC boards, you should make separate boards for these, or otherwise the board is going to be too cramped. Dan |
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Re: T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz
On Sat, Nov 9, 2019 at 12:14 AM, Kurt Poulsen wrote:
If you got a SMA male male adaptor try to S11 calibrate at the end of the maleHello Kurt, Thank you very much for your valuable hints. I made what you reccomendet: 1. Connect the Tee direct to CH0: T-Check_RG316-25cm_CH0-6dB_DSC08176.jpg 2. Add an 6 dB attenuator after the Tee. 3. Shorten the coax cable to RG316 25 cm. 4. Tuned the calibration in NanoVNA-Saver. 5. Adjusted the .S2P file S12 for the 6 dB attenuation. 5. So, up to 450 MHz it is within the 5% Limits. T-Check_Short_CH0-6dB.png Now I know the direction to work on, if neccessary. It is always nice to know your limits :-) 73, Rudi DL5FA |
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Re: T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz
Hi Rudy
It is only going to 490MHz and he might use shorter testcable with better performance. If you got a SMA male male adaptor try to S11 calibrate at the end of the male male adaptor and ether use my female calibration data and remember to subtract the female famale delay when calibration the S21. Alternatively do a S11 calibration using the male calibration data (so to speak ideal) and do not subtract the female female delay but instead enable an electrical delay equal to the female female delay. Then you will se improvement but never the right figure. I have forgotten to mention if you use the supplied female female adaptor it has a high loss and that also provided poorer result than a low loss female female. Besides that if you in the spread sheet subtract 1 from the T-Check then you have the "percentage" result right away as 0.1/div = 10%. A good T-Check is never beyond 5% and for the frequency range up to 500MHz for a VNWA it holds in most cases 1-2%. The T adaptor may also be an element of poorer T-Check, a good quality T-Adaptor is mandatory but not so important as long the 10/12 term error correction is not applied, Sorry to disappoint you. Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af reuterr@... Sendt: 8. november 2019 20:05 Til: [email protected] Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz Hello Kurt, Thank you very much for your enlightening words. I thought it was easier to achieve. What only wonders me, how about the T-Check of Erik, that looks good, how does that come? See T-Check_Erik.png 73, Rudi DL5FA |
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Re: T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz
Hello Kurt,
Thank you very much for your enlightening words. I thought it was easier to achieve. What only wonders me, how about the T-Check of Erik, that looks good, how does that come? See T-Check_Erik.png 73, Rudi DL5FA |
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Re: Short-Open-Load - expected reflected power
I too initially questioned the quality of the RF Bridge, primarily due to the price.A transverters-store clone from eBay seller seller25812 was substantially defective: * one of each 100 Ohm pair was disconnected at the balun end * center conductor of the balun reference coax was shorted to shield at both ends * labels for DUT and REF are reversed, relative to schematic for Ukraine version It works OK after correcting... |
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Re: T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz
Hi Rudy
Your problem is that you are not aware how a T-Check is processed. The oscillations you see is because your S11 calibration is done with the reference impedance 50ohm and when you the insert the T adaptor then you measure 25 ohm thru the test cable connected to Ch0 and that is causing impedance transformation. Besides that the output of the T- Adaptor connected to the Ch1 via the test cable is not 50ohm but the input impedance of Ch1 not 50 ohm and this input impedance is not transferred via the Ch1 test cable directly but also subject to impedance transformation thru the Ch1 test cable. All in all a oscillation based on the sum of all these factors. In a real VNA like the VNWA the T-Check measurement is done for a complete calibration of S11, S21, S12 and S22 via a test set and the build in 12/10 term error correction take place. The VNWA software does the figure out the output impedance og the TX port which can be monitored via a custom trace as SS and the input impedance of the RX Port seen via a custom trace called SL. The condition for a T-Check is simply the imperfections of the TX output and RX input is compensated as the were idealy 50 ohm. There is a trick in the VNWA software the a full 12/10 term error correction can be performed by pressing the F2 key on the keyboard as then the t_Check adaptor is sweep in both forward and reverse direction and thus doing a full 12/10 term error correction. By a normal forward or reverse measurement only 6/5 term error correction applied. THE NanoVNA HAVE NO ERROR CORRECTION so you cannot do a T-Check the correct way Kind regards Kurt -----Oprindelig meddelelse----- Fra: [email protected] <[email protected]> P? vegne af reuterr@... Sendt: 8. november 2019 16:28 Til: [email protected] Emne: Re: [nanovna-users] T-Check for my nanoVNA - Results look excellent below 150 MHz and acceptable up to 300 MHz I need help from an expert. My T-Check setup is now 2 x 50 cm RG402 coax cable and a SMA Tee with a 50 Ohm Load, see picture NanoVNA_T-Check_SMA-Tee_RG402_DSC08175.jpg The result, calculated with the spreadsheet from QRP is shown in NanoVNA_T-CheckR-RG402.png The S21 gain shows a big oscillation, see NanoVNA_T-Check-T_RG402-50cm.png If I remove the CH1 coax cable from the SMA Tee S11 looks like: NanoVNA_50-Ohm-Load_RG402.png So, I think the calibration was OK. The attached file NanoVNA_T-Check-T_RG402.S2P can be imported in VNWA, see VNWA_T-Check-T_RG402.png How does that come? What I am doing wrong? 73, Rudi DL5FA |
Kurt Poulsen
gin&pez@arg
Oristo
