Nano VNA Reads Low SWR - Page 1
Forum section: electronics / rf-microwave

author: edtyler
author_rank: Contributor
timestamp: September 09, 2020, 12:54:07 am
content: Hi,I have readhttps://www.eevblog.com/forum/rf-microwave/difference-in-swr-readings-between-nanovna-and-swr-meter/50/and this question is slightly different than what was described there.My test setup:NanoVNA (black open case, small screen) - purchased in September 2019. Sweeping from 144-148 MHz, calibrated with lab quality standards.Homebrew tape measure Yagi fed with 25 feet of Andrew C400 and assorted adapters terminating in a BNC female.When I measure this antenna using the NanoVNA at 146.565 Mhz, the SWR is reported as 1:1.85This seemed pretty good, so I attached a transmitter and a Bird 43 with a 5W element just to verify transmitter output as I usually do in a new setup. The output was lower than expected and the reverse power was much higher, Now I understand about the 5% full scale accuracy of the Bird, but still the reverse power was 1.3W with a forward power of 3.7W.So, I hooked up a MFJ-259B and it reported SWR of 1:3.5 at 146.565. To verify, I hooked up a HP 8753C, sweeping from 130-150MHz, did a one port calibration and observed a SWR of 1:3.27 at 146.565 MHz. To eliminate the cabling, I replaced the antenna with a 50 ohm terminator at the end of the feed line and the result was an SWR of 1:1.12 on the 8753C. The MFJ also reported a similar SWR. The NanoVNA reported 1:09.I then redid the NanoVNA calibration and got nearly identical results to the first trial using the antenna and the dummy load. I removed the feed line and connected a 150 ohm carbon resistor, which read 1:1.68 on the Nano VNA. The 8753C read 1:3.002. An open on the NanoVNA reads 1:2.52, with a stable Smith Chart. A short reads 1:infinity and a 50 ohm standard reads 1:1.0, both with stable smith charts.It appears the Nano VNA's reverse detector is inaccurate on my unit. My question: Is this a common problem and can it be corrected, or should I throw away this Nano VNA and buy another? I don't recall if I had seen this before and with this type of inexpensive tool, one should expect high precision, so prior, minor variations of +/- 1:1.2 did not worry me. 1:1.18 vs 1:3.27 is not acceptable.Thanks for any help or ideas you might have.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 09, 2020, 01:42:18 am
content: If you forget all that antenna and feed line stuff and start with some basics. Make up say a 25 and 100 ohm load, cal the Nano and measure them. Repeat the measurement with the HP. At 150ish MHz and lower, I would expect very similar results between the two and I would expect the SWR to come out very close.For the resistors, I would just tack down a couple of 0805s or 1206s on the backside of what ever connector type you are using. I wouldn't be concerned with with reference plane.Here you can see me run a similar test on the Nano.https://youtu.be/mKi6s3WvBAM?t=2165

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2020, 02:29:06 am
content: Quote from: edtyler on September 09, 2020, 12:54:07 amAdd ferrite RF-choke on the feeder between NanoVNA/Transmitter and antenna. Without good RF choke you're trying to measure antenna with different counterpoise. It means different antenna, different VSWR. This is why you get different results.Quote from: edtyler on September 09, 2020, 12:54:07 amyes, common mode currents on the feeder is a common problem. Especially when you feeding non-symmetrical antennas.In order to fix, you're needs proper coupling between feeder and antenna and good RF-choke.

author: Bud
author_rank: Super Contributor
timestamp: September 09, 2020, 05:25:03 am
content: Quote from: edtyler on September 09, 2020, 12:54:07 amHere is your problem. Your Open is more like 126 Ohm which is far far far from Open. Open should have Infinite impedance and Infinite SWR (not ideal Infinite but a large number nevertheless)

author: edtyler
author_rank: Contributor
timestamp: September 09, 2020, 06:06:01 am
content: @joeqsmith Thanks for the reply. I tried a 150 ohm carbon resistor as I said in my email. The SWR should have been 1:3 but was 1:1/68.I can try other values, but the result at 150 ohms appears to indicate a problem with the NanoVNA, especially since the 8753 showed SWR of 3.001 on the same resistor.Is this a known problem with the Nano VNAs?

author: edtyler
author_rank: Contributor
timestamp: September 09, 2020, 06:12:01 am
content: @radiolistener - I did a test with just a 150 ohm carbon resistor as described in my original description. The Nano VNA measured a SWR of 1:1.68, the 8753 measured 1:3.001.The antenna setup, including the feedline and all adapters was exactly the same for the NanoVNA and the 8753. Why should a RF choke be needed with one measurement device and not another? Also recall that I used a MFJ-859B and it agreed within a reasonable tolerance with the 8753, as did the Bird 43, considering its 5% full scale spec.Can you explain further why 3 instruments mostly agree and the NanoVNA should need a choke?Thanks,

author: edtyler
author_rank: Contributor
timestamp: September 09, 2020, 06:15:08 am
content: @Bud - I agree, this appears to indicate a problem with the nanoVNA. Especially considering the 150 ohm resistor test I also described.Is this a common problem and is there a fix or should I recycle the NanoVNA and get another one or something else (NanoVNA2?)

author: DH1AKF_Wolfgang
author_rank: Contributor
timestamp: September 09, 2020, 09:03:10 am
content: Before you give it back, you should recalibrate!I'm a member of the NanoVNA newsgroups e.g.https://groups.io/g/nanovna-users/topicsand there was no error like yours.Most errors grounded in misunderstanding of the manual.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 09, 2020, 12:30:43 pm
content: Quote from: edtyler on September 09, 2020, 06:06:01 amQuoteIn the above statement there was no mention of calibration prior to making the measurement. Not being there to watch what you are doing, every detail would need to be stated.I've made many measurements with the Nano and as long as I stay below 300MHz, for the most part it works really well for the $50. If you were asking how many times it requires a power cycle after it locks up from trying to use the poor UI, I would say a lot.QuoteIt's very possible you had made a mistake, then repeated the same mistake. Again, it's difficult to tell from where I am sitting.I am only suggesting that you gain a basic understanding of how to use the tools prior to attempting to make more complex measurements. You may be juggling more than you know.QuoteI borrowed a couple of sets of some lab grade standards not too long ago. The SMA kit wasn't too bad. Maybe $4000. The N, closer to 10. Not something I would use with the Nano. For 1GHz, I have always used the PCBs I show to perform the calibration. For higher frequencies, I plan to still use home made standards (which was the reason for borrowing the lab grade sets, in order to characterize them).No matter. Cal the Nano with your known lab standards and then attach your 150ohm unknown load and repeat this process with the HP using the same standards. I am not suggesting that what ever your unknown 150 ohm carbon resistor is or how you have it attached to the VNA will behave like a pure 150 ohms but I would expect the same results (within reason) from both VNAs.Once you get results that make sense, then try adding your 25' of coax into the mix.

author: radiolistener
author_rank: Super Contributor
timestamp: September 09, 2020, 09:54:43 pm
content: Quote from: edtyler on September 09, 2020, 06:12:01 amYou said that calibration is done. It means that device shows correct values for Open, Load and Short. Since your device shows incorrect values for known load, this is indication that calibration is wrong. So, you're needs to perform proper calibration before measurement.

author: edtyler
author_rank: Contributor
timestamp: September 10, 2020, 04:23:45 am
content: @DH1AKF_Wolfgang and joeqsmith"My test setup:NanoVNA (black open case, small screen) - purchased in September 2019. Sweeping from 144-148 MHz, calibrated with lab quality standards."I am sorry that I did not list the step by step sequence, but it seems like when one gets into a problem deeply sometimes the basic assumptions are missed. To be clear,I calibrated before *each* test and also usually power cycled the NanoVNA, even though the calibration should have been good, at least short term. I did the open and 150 ohm tests 3 times each with nearly identical results.The lab standards I have are R&S for SMA and HP for N. They were used, but verified for correct operation on very high end VNAs. New cost on each set was > $10K, but I bought them used. On the Nano VNA, my unit does not provide feedback when going through the open, short, iso, load steps. It just moves on to the next step. However, when it is done and the cal set stored in memory 0, the unit does *not* report infinite or near infinite SWR.I used the same SMA standards for both the NanoVNA and the 8753 (single port cal only). The NanoVNA showed an incorrect SWR (1:1.68) while the 8753 showed 1:3.001, which is fairly close to ideal.It may be true that I am repeating the same error over and over with the NanoVNA, but the techniques are pretty simple and nearly identical between the NanoVNA and the 8753. You enter cal mode, then follow the steps listed on the display. Not very complicated and not likely to be done wrong. That said, I wish I knew what error I could be making. Can either of you confirm your NanoVNAs show near infinite SWR with an open?I have been using higher end VNAs and other RF tools for a few years. The NanoVNA is about 2 years old and when I initally got it I made a series of measurements to determine how precise and useful it was. As you say, below 300MHz, it is not bad. Actually the part used in my unit is spec'd for < 200MHz, so I limited my testing to that range. SWR, and complex impedance was within about 20% of a lab quality VNA up to about 1:4.0. Through measurements suffered greatly from lack of dynamic range, which measured about 45dB at 150MHz, if I recall. This makes it barely useful for filter design and characterization at lower frequencies. But it was $50 and fits in my pocket, so no complaints, until now.It does sound you both are saying that the expectation of near infinite SWR on an open and roughly 1:3.0 on a 150 ohm resistor are reasonable on a NanoVNA. Sadly, my NanoVNA seems to have packed up and died. It is probably not worth trying to fix, but removing the covers and looking for leakage paths and other issues like cold solder joints and flux deposits might be worth trying.I really appreciate the time all of you have taken to respond to my questions.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2020, 11:05:08 am
content: Quote from: edtyler on September 10, 2020, 04:23:45 amIt's possible that the pretty simple techniques are where you are missing some step. For example you never mention resetting the unit prior to the cal. Even the best standards in the world will not overcome a mistake during the calibration. I agree, it is simple from my perspective but again, not being able to see what you are doing, hard to say.The question of an infinite SWR is new. I showed that 200ohm resistor, which is a poor mismatch, reading correctly.Again, I would make sure you understand how to use it first. Making up some basic standards and testing them is one way to build confidence in the Nano (or any measurement) and cement how to use it. Of course, there is no substitute for reading."I have been using higher end VNAs and other RF tools for a few years. The NanoVNA is about 2 years old and when I initally got it I made a series of measurements to determine how precise and useful it was. As you say, below 300MHz, it is not bad. " "SWR, and complex impedance was within about 20% of a lab quality VNA up to about 1:4.0."If the above statements are true, I am surprised there would be any question. You know the Nano is working. You know how to properly calibrate it. You have the equipment and expertise to verify your results. I'm missing something.It is very possible that once you have a known working setup that you may have problems with your feedline. I have a section of coax that is loaded up with ferrite along with several clip on parts.I was playing around trying to make a crystal filter with some canned software package. These have all been <20MHz.https://www.eevblog.com/forum/rf-microwave/fun-with-crystal-filters/msg3058240/#msg3058240A few of us were playing with some home made attenuators. Here you can see a 50dB unit swept to 1.5GHz with the Nano. Next post I show the same part running on my old HP.https://www.eevblog.com/forum/projects/20db-rf-attenuator-seeking-feedback-to-improve/msg2904926/#msg2904926

author: edtyler
author_rank: Contributor
timestamp: September 10, 2020, 04:26:30 pm
content: @joeqsmith"If the above statements are true, I am surprised there would be any question. You know the Nano is working. You know how to properly calibrate it. You have the equipment and expertise to verify your results. I'm missing something"And that's my real question. Either I am doing something stupid or the NanoVNA I have is broken. Your help and continued feedback are appreciated.Here is what I did this morning:1) Make sure NanoVNA battery is fully charged.2) Turn on unit. Range is 144-148MHz as previously set3) Select CAL, then RESET4) Select CALIBRATE, then step through OPEN, SHORT, LOAD, ISOLN (2x 50ohm loads), THRU (using supplied 6" cable), then DONE. I used my R&S SMA lab standards and saved the calibration result in memory zero.5) After Pressing DONE, with nothing attached, the display shows the SWR trace above the first horizontal division and the value for SWR is 1:2..38. The impedance is shown at 118 ohms with 3.02nH. Smith chart is stable.6) reinstalling a 50 ohm standard, gives 49.9 ohms and 15.2 nF and a SWR of 1:1.00 SWR trace is at the bottom of the display. Smith chart is stable.7) reinstalling a short standard gives 944miili Ohms and 4.15 nH and SWR of 1:131 (varies from 128-133) SWR trace is at the top of the display. Smith chart is stable.a 150 ohm, non inductive 5% leaded resistor gives 81.8 ohms 4.98 nH and a SWR of 1:1.64 Smit chart is stable.For reference, I recheched the same resistor on my 8753 and it measured an SWR of 1:3.002.Nothing else was done to the NanoVNA and I listed every action taken, This was done on my bench with an ESD pad. The RF environment is typical, with no high power transmitters operating nearby, as shown by a spectrum analyser with a whip antenna that I left running in peak hold mode spanning 1-3200MHz while these tests were in progress. No signal greater than -60dBm, except in the 2.4GHz and 900MHz bands, which had the usual Wifi, BLE and Celluar traffic.Any ideas?

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2020, 05:50:59 pm
content: Quote from: edtyler on September 10, 2020, 04:23:45 amyes, NanoVNA with proper calibration should show almost infinity VSWR for open input.If your NanoVNA shows low VSWR with open input, this is an indication that your calibration is failed. It may be due to calibration mistake or malfunction of some component.Check that calibration is ok before measurement.You can test calibration it in the following way:1) Connect OPEN and make sure NanoVNA shows infinite VSWR, and Smith Chart dot on the right side of circle2) Connect SHORT and make sure NanoVNA shows inifinte VSWR, and Smith Chart dot on the left side of circle3) Connect LOAD and make sure NanoVNA shows VSWR=1.00, and Smith Chart dot in the center of circlealso you can perform additional test:4) Connect 150 Ohm load and make sure NanoVNA shows VSWR about 3.If calibration test is failed, it means that calibration is wrong and you will get incorrect measurements.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2020, 05:52:39 pm
content: I think that last response pretty much says that your two year old Nano is now dead, unless I am missing some other clue.Personally, I suggest you treat yourself to a new V2 or just buy another V1.If you want to know why it was damaged, hard to say. I'm not there to watch over you. If you are connecting it to an outside antenna and not grounding the system prior to attaching the unit, maybe ESD. Maybe you don't always handle it with a ground strap. Maybe you tried to measure an amplifier with it at one point. I've seen SA's and VNAs that were a mess after being overloaded.Still, no big deal to replace it. There are places now that stock them. $50 is hardly worth the time. Just replace it an move on. Or, use the 8753C.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2020, 06:07:16 pm
content: There is possible bad contact on SMA connectors.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2020, 06:18:48 pm
content: I wouldn't expect it to provide repeatable results. Sounds more like it's leaking.

author: ogden
author_rank: Super Contributor
timestamp: September 10, 2020, 07:32:43 pm
content: Most vulnerable part of NanoVNA - mixers. You may consider following test: reset calibration of your Nano and look at S11 logmag (uncalibrated). Up-to 300MHz it shall indicate around -20dB .. -23dB [or better] for open port. If you see way lower value like -30dB or -40dB at let's say 150MHz - port1 (ch0) mixer is dead. Repair is comparably simple BTW.

author: iMo
author_rank: Super Contributor
timestamp: September 10, 2020, 09:03:49 pm
content: Quote from: edtyler on September 10, 2020, 04:26:30 pmIs that ISOLN cal a correct way how to do it? I do it with ch0 open and ch1 loaded with stock 50ohm (I always use the H4's stock cables attached to the ch0 and ch1 terminals).For the antenna swr measurements I do not do the ISOLN and THRU cal steps, btw.Try to calibrate as radiolistener has written above..

author: ogden
author_rank: Super Contributor
timestamp: September 10, 2020, 09:38:33 pm
content: During ISOLN calibration ch0 must not be reflecting any signal back into VNA, thus shall be loaded using 50Ohms. Ch1 must not act as an antenna, thus it is good idea to "plug" it using 2nd 50Ohm load or short.

author: cdev
author_rank: Super Contributor
timestamp: September 10, 2020, 09:41:32 pm
content: SMA savers or whatever they are called might be a good investment if they dont impact the response. Keep your SMA connectors clean and never rotate them hard if there is resistance, unscrew it and redo it. I also clean mine with IPA.But I agree with the others, the nanovna 2 is so cheap and much better, I would just buy one. Then handle the SMAs with care. I always leave the two fairly decent short cables it came with on, and keep ferrite split beads on those extension cables to decouple them from possible common mode currents.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2020, 10:13:05 pm
content: Quote from: imo on September 10, 2020, 09:03:49 pmQuoteUsing the same parts that you cal with to check the cal is not a real good idea. For example, swap the open and short during the cal, then recheck them and the unit will show what appears to be the correct data. You could swap a 200 ohm for the open and cal to that and it will show it as an open. You could leverage this.QuoteI would run some sort of secondary check like this.****...5) After Pressing DONE, with nothing attached, the display shows the SWR trace above the first horizontal division and the value for SWR is 1:2..38. The impedance is shown at 118 ohms with 3.02nH. Smith chart is stable.6) reinstalling a 50 ohm standard, gives 49.9 ohms and 15.2 nF and a SWR of 1:1.00 SWR trace is at the bottom of the display. Smith chart is stable.7) reinstalling a short standard gives 944miili Ohms and 4.15 nH and SWR of 1:131 (varies from 128-133) SWR trace is at the top of the display. Smith chart is stable.a 150 ohm, non inductive 5% leaded resistor gives 81.8 ohms 4.98 nH and a SWR of 1:1.64 Smit chart is stable.5 is pretty odd though as I would expect the math to show the port as open, even if there were a problem. If say the port had a 1K resistor on it normally, and you went through the cal. Once you open the port, even though it has a 1K, it better read open. That or there is a problem with the math.There was no mention of playing with the firmware prior to the problem and after owning it for two years and getting good results up until now is all really odd.Then again, I am clueless of what a stable Smith chart would be.

author: Bud
author_rank: Super Contributor
timestamp: September 10, 2020, 10:29:40 pm
content: Does this dinky gizmo ( i do not have one ) has settings to specify calibration standards coefficients or electrical delay? Maybe that numbers are incorrectly entered or corrupted which may lead to the problem OP is experiencing.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 10, 2020, 10:44:24 pm
content: Quote from: Bud on September 10, 2020, 10:29:40 pmThere was no way to change he delay or enter coefficients in the older FW. Maybe this has changed. It's been a while since I looked at new firmware.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2020, 11:43:13 pm
content: Quote from: imo on September 10, 2020, 09:03:49 pmYour way is acceptable. Technically both ports should be loaded, but the difference is not significant. So, you can leave CH0 open and load CH1 with stock 50 Ohm.

author: radiolistener
author_rank: Super Contributor
timestamp: September 10, 2020, 11:52:17 pm
content: Quote from: Bud on September 10, 2020, 10:29:40 pmCapacitance is hardcoded to 50 fF. But you can setup delay through menu DISPLAY=> SCALE => ELECTRICAL DELAY.By default delay should be 0 picoseconds

author: joeqsmith
author_rank: Super Contributor
timestamp: September 11, 2020, 01:41:25 am
content: Have you looked into making the settings programmable and using a common format? With the V2, it would seem they must have this by now.

author: edtyler
author_rank: Contributor
timestamp: September 11, 2020, 01:59:05 am
content: @joeqsmith and othersThanks for the ideas and input. I have ordered a V2 from the HCXQS group. I'll stockpile the failed V1 for disassembly and recycling of the LCD and various parts. As you say, repair is hardly worth it. I have worked with RF stuff for a few years and it is possible that the device was connected to some bench top setup while a legal limit transmitter was in operation a few meters away. I would hope these devices were not that fragile, but who knows. For $50, it is hard to complain about this item.As you mention, I have not upgraded the firmware after the initial upgrade 2 years ago. In general, I never change the firmware/software on test equipment that is working unless I am experiencing a problem that new software is known to fix and I have a way to go back to the old software if the upgrade causes other problems. In this case, the unit was working properly - open SWR was infinity - and now it is not with no change to the firmware.Again - thanks everybody for your help and ideas. My conclusion is that this NanoVNA has a hardware failure.

author: 0culus
author_rank: Super Contributor
timestamp: September 11, 2020, 03:41:53 am
content: They are not well shielded at all, so damage from a high power transmitter nearby is plausible. They also create wideband splatter for a non-trivial distance when sweeping...best turn it off when you want to work the radio!

author: joeqsmith
author_rank: Super Contributor
timestamp: September 11, 2020, 11:08:17 pm
content: Quote from: edtyler on September 11, 2020, 01:59:05 amIt's a really odd condition as I would expect even if the unit had a a large amount of leakage, it would still show an open. The 100ish ohms makes no sense.This guy demonstrates how the calculations really don't care about the absolute values of the standards. With your unit being repeatable and throwing up good numbers for a short and load, it makes no sense why it would compress towards the open.https://www.youtube.com/channel/UCMznY--PyHE4yLc8jfSxmYQDang, 50% down votes for that demo.I'm interested in knowing what the problem is.

author: edtyler
author_rank: Contributor
timestamp: September 15, 2020, 05:43:30 am
content: @joeqsmithInteresting video. As you say, a VNA's calibration transformation equations do not attempt to rationalize the input characteristics. What this implies is that somehow the NanoVNA 'saw' something different during calibration than when not in calibration. To me, this seems like a very significant problem with the way the VNA firmware manages the display during calibration. As you say an open that is not really infinite impedance should consider that same (non-infinite) impedance as an open. However, there must be some value for open, below which the equations give bad results.You asked about my term 'stable Smith chart'. What I was trying to communicate is that the chart had a non-changing appearance. If there was some jitter in the display, that might indicate a poor connection at the SMA port.

author: edtyler
author_rank: Contributor
timestamp: September 15, 2020, 05:50:51 am
content: @0culus The transmitter is only 1500W maximum and the antenna is not very near the test bench. I get a higher power localized RF field from the cell phone sitting on the bench. I do take care to not have the SDR hooked up to any external antenna when other external antennas are transmitting.The wideband sweep is pretty obvious on SDRs. My 8753 does the same thing to both my Flex 6600 and IC-7300 and other SDRs. First time I saw it, I wondered what is that crazy pattern of noise, then realized it was the VNA.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 15, 2020, 12:15:04 pm
content: Quote from: edtyler on September 15, 2020, 05:43:30 amMaybe it's an ordering problem. Anytime I have used the firmware to cal the Nano, I go in the same order as the menu, top down. Still, I would expect if you had deviated from your 2 year old procedure for the Nano, you would have mentioned it. So, I really wonder what the actual problem is as from the information you have supplied, it makes no sense to me. Then again, not being there.....I was looking at YT the other day and noticed the countless videos on the Nano. I had a few running for background noise and came across this gem:https://youtu.be/F0oMpq_Jz5E?t=794This isn't something I would have ever expected to see and stresses the fact that without seeing every detail of what people are doing, its hard to say. I can imagine this person, "I went through my cal and verified it with the same standards that I have been using. I don't understand why my results don't match up" "Yes, I verified these standards"I did like the double 100 ohm axial parts. Dammit, now I want to test that....

author: joeqsmith
author_rank: Super Contributor
timestamp: September 15, 2020, 11:38:59 pm
content: In a somewhat attempt to verify what was shown in the amateur radio video, I used two 100 ohm Metal Film 1/2W 1%, two 100 ohm MF 1/4 1% and one 49.9 ohm MF 1/4 1% axial resistors. I trimmed the leads as short as possible to minimize the lead parasitics.It does appear there are some gains to be had. Maybe hand selecting a couple of 1/4W parts wouldn't be too bad.Now that short

author: edtyler
author_rank: Contributor
timestamp: September 17, 2020, 05:18:42 am
content: @joeqsmithI did go in sequence through each step as I later described, top to bottom, in oder, no skips, including ISO and THROUGH. I always use the same procedure and a similar procedure on the 8753.It is kind of hard to tell from the colors in your graph, but I would expect the HP 85033E cal kit to be very good but it looked like it still was not as flat as I would expect, assuming it is the top graph line. That said, it would also depend on what cal kit was used to calibrate your Nano VNA.I've made a few cal standards using 2pc 0402 100 ohm 0.1% non-inductive resistors, soldered to a AMP SMA Male connector. The short was 2 pieces of wire. In order to keep the reference plane as close to the same as possible for all three standards, I mounted the AMP connectors on my mill, and cut the center connector and outside mounting posts to be 0.020" +/- 0.001"above the plane of the connector shell. These actually are pretty accurate, almost as good as the R&S SMA standards. To be complete, the cal kit should have male and female versions of the SMA connectors, but just male cal standards are probably good enough, especially for the NanoVNA.The V2 should be here tomorrow and I'll post preliminary results on that unit.Thanks again for your ideas. It would be nice to get to the bottom of this mystery, but I think spending a lot of time probing the NanoVNA is not really worth the effort. I won;t scrap it though, in case I have time later. I only have a 1GHz bandwidth scope & probes, but maybe that would be good enough.I liked the YouTube video you linked and they talked about some of the issues and features that make the NanoVNA interesting.. The only thing I did not really agree with was the statement that the unit was usable above 300MHz. Perhaps usable has a different meaning for quick SWR measurements. Their comments about variable quality address widely held concerns about buying anything, expecially test equipment from an unaccountable supplier.

author: joeqsmith
author_rank: Super Contributor
timestamp: September 17, 2020, 01:26:34 pm
content: Quote from: edtyler on September 17, 2020, 05:18:42 amFor the problem you describe, you would only use the SOL. Isolation and thru are not used.Your next comment is a bit concerning. We are looking at S11. If the loads were perfect, nothing would be reflected back. If the loads were a short or open, all of the signal would be reflected and we would read 0dBm.In the attached graph, you can see how the 2X100 ohm MF 1/4W parts compare with the 85033e and the Minicircuits ANNE. The Nano wasn't used to collect this data and we are sweeping to 3GHz. That particular ANNE was one of six that I sorted to find the one with the best performance. Notice how the axial parts behave as we start to go up in frequency.Quote from: edtyler on September 17, 2020, 05:18:42 amI just use the PCB standards I've shown for lower frequencies. They work fine for this. Above a GHz, home made loads were out of the question. The shorts and opens were a challenge for me to make. Wire isn't going to cut it for a short.Quote from: edtyler on September 17, 2020, 05:18:42 amI've shown using my Nano, which is about a year newer than yours, running a few experiments above 1GHz.Maybe someone in this forum, or the Nanovna groups would have a look at it for you. Normally, when I use the Nano I use the calibration that is built into my software rather than using the Nano's. I would guess that the open source software would also have this ability. I wonder if you clear your Nano's cal, then cal it using their software, would it still show the same low numbers.Actually, with it being 2 years old, it would be interesting just to see detailed pictures of it. I wonder if it has changed at all.

author: edtyler
author_rank: Contributor
timestamp: September 19, 2020, 04:58:45 am
content: @joeqsmithAlthough I could do a one port calibration on the NanoVNA, doing a "full" 2 port is not much more work. But, as you say, my problem is just with S11.Of course, home made SOL, even made with high quality parts and precise construction are not usable at higher frequencies. However, at frequencies below 500MHz, they work well enough for less critical measurements. For critical measurements, much greater care in calibration is needed and more than just the impedance of each standard is important, as you know.This is why that less expensive tools are good only for less critical activities. Your comparisons of the NanoVNA V2 to a HP 8753E are interesting and illustrate the "good enough" nature of the NanoVNA V2. For measuring the SWR or complex impedance of an antenna up to 450MHz, it is fine and much better than the original NanoVNA. Another problem with Tools like the NanoVNA is the wide variation in quality of items labeled as NanoVNA or NanVNA V2. A friend bought one of the NanoVNAs and it was a very poor example with sloppy parts placement, cold solder joints and questionable components.It would be interesting if someone was local to me in Southern California that would like to look at the apparently defective unit with me. Not really interested in sending it anywhere. If it is disassembled, I'll take some pictures and post them here.I did receive my NanoVNA V2. it does fairly well and does not have the incorrect open impedance measurement issue. However, it measures the 150 ohm leaded resistor as 140 ohms at 146 MHz. Other tooling, including the 8753 measures 150 +/- 1 ohm. Not saying this is an issue, just interesting. My use for the V2 is the same as the V1, casual measurements of antennas and feed lines. Also, measurements of swap meet items like attenuators, coax switches, etc. Portability and ease of use are key for my uses.Need to get a more precise understanding of the NanoVNA V2 limits, but it is good enough for now,

author: joeqsmith
author_rank: Super Contributor
timestamp: September 19, 2020, 04:25:31 pm
content: Quote from: edtyler on September 19, 2020, 04:58:45 amI don't have the two V2 yet. OWO and their team keep improving the performance and I am looking forward to seeing some of these newer versions they have.I have the original NanoVNA that my friend sent me that I used in my reviews. Of course that old 70's HP8754A, the HP3589A and now a PNA.I just put together some software for the old 3589A.https://www.eevblog.com/forum/projects/hp3589a-spectrumnetwork-analyzer/msg3203052/#msg3203052The 8754A with the doubler is good for about 2.7GHz but with my home made standards and what not, about 1.5GHz was it. I had constructed an up/down converter for it to run experiments in the 5-7GHz range. Interesting to play with but the results were sketchy at best.My PNA is far more advanced than my other network analyzers, it's still an antique and comes with it's own problems. The hardware is nice with its four receivers but the software looks like a group of fresh outs wrote it that were managed by a fresh out. Progress in writing my own software to control it has been slow and it still needs some work.When I eventually get one of OWO's new units, I may make some sort of review comparing it against my old VNAs. I am not sure what critical activities would be but I've been impressed with the Nano since getting it. When I made that demo, I had no idea how it was going to turn out. IMO, it's one of the best products I have seen in a long time as it allows pretty much anyone access to the tools needed to learn some of the basics.I no longer have an amateur radio license. The only time I have used a VNA to look at an antenna was when I made a demo with the Nano showing how it could be done. It's certainly possible to use it to make these measurements (and many many others) but judging on the comments I received, its beyond the typical ham. I hope that anyone interested in the subject (not just hams, but the EEs and beginner electronic hobbyists) would use the opportunity to learn more about it.Hopefully someone in your area will step up and give you a hand with your original Nano. Enjoy the new V2.***Rough reading....

author: hector.pascal
author_rank: Contributor
timestamp: November 24, 2020, 08:57:15 am
content: Damage to these VNA's from ESD, or mixer overload from nearby RF fields, usually shows up as a very noisy S21 trace. The "open" sandwich clone versions seem more susceptible to this type of damage than the metal cased ones. ESD protection is not included in any of the designs (as far as I can see). This particular problem sounds like different hardware fault to me. If a firmware reload/update doesn't fix it, sadly it's probably toast