Its a fact, that sometimes parts are used which didnt passed the quality control of the producer. Of course these parts are working, but not really well. And they are normaly for the rubbish. That could be the reason for the price. It happend in the past for example with memory chips which were sold at a low price, too.
I used to have a Pro-Sound repair business and the glut of counterfeit parts from the far east was unbelievable. The reputable and well known parts houses were not immune from buying these, most likely unaware. They always made good when it could be proved they were counterfeit (usually sending back suspect parts so they could do a "biopsy" on the suspect parts. It was very frustrating and immensely time consuming to replace sometimes dozens of parts, some quite expensive, only to find a counterfeit part either failed or failed and caused other parts to be destroyed because of the counterfeit part/s. One assumes that the parts you order from reputable parts suppliers would be good from the get go. There were times that I found myself actually testing each active device, when possible, before installing it but even then, that was not an ironclad guarantee it would work. With the difficulty of finding electronic parts these days due to supply chain issues, I can imagine that this problem has been compounded by magnitudes.
I got burned by Amazon once on a part otder. Never again. I will wait longer to get it but at least it not from China!
With regard to "cheap parts" and the industry practice in general, Prolific Technology Inc. has this warning notice for its customers: Please be warned that counterfeit (fake) PL-2303HX (Chip Rev A) USB to Serial Controller ICs using Prolific's trademark logo, brandname, and device drivers, were being sold in the China market. Counterfeit IC products show exactly the same outside chip markings but are generally of poor quality and causes Windows driver compatibility issues. The point is, your concerns are validated ad nauseam. With regard to your specific project, I think you're on the correct path by further evaluating the timing of the oscillator to produce a clean square-wave; some digital oscillators continue to use a LC circuit. Anyway, you're brilliant and your presentations are always appreciated.
Some items: Minor nit-pick, the spikes he sees with the Adafruit board are not harmonics (at least not of the clock board) they appear to be switching noise - their interval looks to be the same as the switching noise he mentioned earlier. Second, I'd be curious to know what kind of inverter he was referring to? is he using a 12vdc to 115 AC inverter, or a switching power supply for his bench? Finally - I worked for a major aftermarket ignition company, and we had some issue with counterfeit power devices (IGBTs and Darlington transistors) from Chinese manufacturing companies. In both cases, we ended up sending THEM devices we bought domestically, because they claimed that they could get nothing else than what they had already sent. That being said, I have ordered a number of boards (including the cheap clock boards) from Amazon and eBay (and saved some bucks in the process) and so far, no issues. However if I did have problems, I would send them back - Amazon is very good on returns. A person saying that they will never order from a particular vendor again because of one issue remind me of those who drive a particular brand of car, because, "20 years ago I had a (fill-in-the-blank brand that they will never buy again) and it left me stranded 100 miles from home!" (or whatever). People, and systems, make mistakes, you just have to roll with it, I suppose.
I learned my lesson. So I canceled my accounts at Ebay and Amazon for about a decade. And I didnt regret it until today. Safe stationary and online trade with real people for to communicate with is much better. It avoid those ugly surprises.
A decent Si5351 is already too cheap to generate any signal that will be used for sending or receiving in the radio by driving mixers and so. We shouldn't go under a certain level... It has a lot of jitters, etc. However, it works well in the NanoVNA, and it is used even in the K3S's new synth block - although, there is a much better (and more expensive) Si570 to do the real work. I'm surprised that even the latter can provide clean enough signals compared to the K3's great features, knowing how much cleaner TX signals it generates than the rest of ham trcvr's. But that's the engineering, after all... to know where you can use cheaper components for a really good output.
Perhaps the SI5351 is really a MS5351, which is a Chinese knockoff. http://www.qrp-labs.com/synth/ms5351m.html
"The results were favourable and in fact in my opinion, the MS5351M has slightly improved performance compared to Si5351A."
This is old news! However perhaps we need a refresher. About twenty years ago the Automotive and Heavy equipment industry was plagued with counterfeit parts and still is to this day, I recall getting directives from the regulating body of fasteners, "bolts" that were marked as being grade five or grade eight bolts and lo and behold they were just cheese bolts. This was discovered after a series of serious fatal accidents where the insurance provider investigated and found the problem. "counterfeit bolts being used in critical areas like steering and braking components" and of course other areas. The aftermarket parts stores would buy these cheap fasteners and jack up the price and sell them to the unsuspecting clientele. But of course it was hard to tell, the standard grade five bolt with 3 lines on the head 120 degrees apart, hey it looks good!!! The same thing happens in the marine industry where the novice boater purchases thru hull components manufactured in some far east country and proceeds to install such on their boat. They never read the fine print on their boat insurance documents that states the vessel must meet US COAST GUARD or ABYC and NFPA 304 standards. Then its also true a lot of them dont even insure their boats. If you do your homework then you would look for UL or ULC approved on the parts. Then there is the marine chandlery who stocks this "EXPLETIVES DELETED" and sells it to whomever wants to buy it. The same individuals use automotive or house wire for installations on their boat, most of the stuff that comes from the far east contains SOY, that is why the Rats love it! Now we hams are so excited to buy a new cheap handheld radio, that for the most part would never meet NTIA standards but hey "I got a deal". Are we that frugal! As for the responsibility of our Governments or regulating bodies, they don't have the resources as in man power to even remotely police this stuff. The USA made some of the finest steel as do Germany and Sweden to name a few, but oh no I can buy what looks equivalent, for a lot less at my favorite big box store or online. The other gentleman on this thread said it. You get what you pay for in most cases. CAVEAT EMPTOR!
True. Many vendors also list bootleg ICs with questionable specs. Building a PCB with those parts is a real gamble.
