General > General Technical Chat
Why do so many people here go nuts over very low quality gear from China?
ogden:
--- Quote from: jadew on December 19, 2019, 04:15:09 pm ---
--- Quote from: ogden on December 19, 2019, 03:52:28 pm ---NanoVNA is not poorly designed.
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Yes it is. The harmonic content makes it unusable for anything more than passive networks, and even there, it will have very poor performance.
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Have you actually tried it to say it have very poor performance? Seems you do not get what I am saying. For given BOM/price it is well built. You can't have VNA with pure sine signal source for 40$. You are getting very good price/performance out of NanoVNA.
--- Quote ---Most people who buy it don't realize just how bad it is.
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Explain how bad it is - in more details.
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--- Quote ---LOL, no. NanoVNA do not even pretend to be caliper. Those who buy 40$ NanoVNA or 7$ LCR meter *never* expect performance of "proper instruments" that cost most likely hundred times more.
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Ok... so why buy it then? I wouldn't buy a caliper that doesn't work.
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Because contrary to what you say it works and is very useful. You just have to know it's limitations. Have you actually tried to say it does not work?
jadew:
--- Quote from: OwO on December 19, 2019, 04:25:10 pm ---Nah. For a hobbyist without lots of money the alternative is NO test equipment.
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That is not true. Someone who's willing to use a VNA that doesn't work, has plenty of better options in the used/broken market.
--- Quote from: OwO on December 19, 2019, 04:25:10 pm ---Original NanoVNA is actually really accurate if you keep it in fundamental mode, and S11 measurements after warmup are almost comparable to the old HP stuff. Have you checked out the performance yourself? Measuring passive components are maybe 90% of what a hobbyist will use it for, and even for active components the square wave isn't necessarily a problem if the power is kept low enough.
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Really? Then I would like to refer you to this: https://www.eevblog.com/forum/rf-microwave/nano-vna/msg2783756/#msg2783756
Where you are quoted saying the following:
--- Quote from: OwO on November 14, 2019, 06:02:50 am ---Take what I say with a grain of salt because I'm on the NanoVNA V2 design team, but the original NanoVNA (everything you can find on ebay/aliexpress right now) has severe accuracy problems above 300MHz: https://groups.io/g/nanovna-users/message/6484
What happens is that in harmonic mode the DUT's response to the fundamental frequency bleeds in, and what you are measuring isn't the impedance at the frequency shown, with S11 errors of 3dB in the above plots. It will show perfect calibration but show you wrong impedances once you measure something other than the cal kit.
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--- Quote from: OwO on December 19, 2019, 04:25:10 pm ---What laws and regulations are you talking about that is preventing you from doing the same thing from your country?
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Warranty law, RoHS law, WEEE law for starters. There's a lot more than this.
--- Quote from: OwO on December 19, 2019, 04:25:10 pm ---Current NanoVNA variants are still a long way from encroaching on the market for real network analyzers, but in the next year (maybe by V3) the plan is to get up to performance comparable to the Copper Mountain VNAs (but at 1/10th the cost). There is nothing shady about what we are doing and I think it's all fair competition. OwOComm additionally has a commitment to open source hardware and will release PCB layout files at every product release.
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Like the other products I was talking about, they encroach on the market by selling a too good to be true product, to a customer who then loses the appetite for that said product, and often not because he got what he wanted. The customer loses, manufacturers who make good products lose, future customers also lose, because they might not get to see a good product on the market anymore. The only winner here is the chinese seller who sold something nobody else would have dared to sell.
PS: @ogden, this reply is for you too. Hope it answers your questions.
ogden:
--- Quote from: jadew on December 19, 2019, 04:50:02 pm ---
--- Quote from: OwO on December 19, 2019, 04:25:10 pm ---Nah. For a hobbyist without lots of money the alternative is NO test equipment.
--- End quote ---
That is not true. Someone who's willing to use a VNA that doesn't work, has plenty of better options in the used/broken market.
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Show where we can buy used 300MHz VNA for 40$. Extraordinary claims require extraordinary evidence.
--- Quote ---PS: @ogden, this reply is for you too. Hope it answers your questions.
--- End quote ---
So it seems like you do not have experience with NanoVNA, yet have strong opinion about how bad it is. Kinda reminds me 60Hz versus 144Hz computer screen refresh debate where strongest opponents who said that 144Hz is just marketing gimmick were those who have no actual experience of comparing two.
Just an example from same thread you were referring to:
OwO:
--- Quote ---Really? Then I would like to refer you to this: https://www.eevblog.com/forum/rf-microwave/nano-vna/msg2783756/#msg2783756
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Yeah, there I said accuracy is bad above 300MHz (harmonics mode). Here I said S11 accuracy is good if you keep it to fundamental mode (below 300MHz). Calibration removes errors except linearity and noise, which are easy to check for: noise is obvious; linearity is most easily checked with a length of low loss coax (making at least one circle around smith chart), or simply calibrating at the end of a long cable and then measuring a short, low loss coax.
Most of these are RoHS compliant. When living in "the west" I've had better luck with aliexpress dispute system than I've had with retailer warranty, but YMMV. I don't think aliexpress sellers can really easily get away with selling junk that doesn't work. If your country regulates local businesses tough but gives imports a free ride, it's up to your country to fix that. China has nothing to do with this and does not meddle in other country's internal affairs.
Bud:
You do not need to own a harmonic based architecture VNA to know its deficiencies. Everything OP said is true.
@OP: Regarding the question in the Subj line, it is a basic phenomenon of human greed, people have to make make efforts to overcome it.
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