Just a quick post about a bad experience with buying a Vector Network Analyser from AliExpress.
Update 10th July.
Thanks to everyone who has commented. I’ve updated the information in the post and added some more information to the end.
Please see the end of the post for updated information.
Original post starts here…..
The “NanoVNA” VNA arrived this morning, from this vendor on Aliexpress :MAXGEEK Tech Store
But when I opened the package I immediately noticed that the back PCB was scratched, and the screen also had a load of light scratches on it, as if it had been used and then perhaps returned and repaired (I’ve no idea) – See the photos at the bottom of the post.
I immediately raised a dispute with the vendor, and their response, was that the VNA I took the photos of, was not the one that they had sent to me, and I was maliciously claiming to get a refund.
I don’t normally video the opening of these sorts of things, but I guess I should do so in future, but they could of course claim I’ve open the box and resealed it etc
Seeing, the chances of any refund from this supplier look remote, I thought I may as well take the back off the analyser and look inside, I found some other things which could be done better
number of serious problems with this device.
Firstly the shielding is missing from the 3 mixer sections, its obvious from the PCB that there should be shielding.
And I noticed that the are NXP SA602 rather than the SA612, as specified in the original design.
The SA602 is only rated to 45Mhz, so despite the analyser being sold as a 900Mhz device, it would really only function on HF. Even if it was fitted with SA612’s, they are only rated to 500Mhz, which is half the claimed performance of the device
Following comments from lots of knowledgeable readers. I see that I was incorrect in my diagnosis, that the mixer chips would not be usable above 45Mhz.
Both the SA602 and SA612 seem to have similar specifications, but the data sheet for the SA612 introduction specifically mentions 500Mhz, but the SA602 didn’t.
I presume there was a reason that the original design used the SA612 rather than the SA602, but this could purely be something to do with availability.
I used to assume that devices with higher numbers in their model name, have a better specification, but I have since learnt from experience, that this isn’t always the case.
I had initially intended to replace the mixers with the SA612, and I have ordered them, however I may not end up replacing them if the analyzer seems to be function reasonable well using the SA602’s
I’m still going to make some shielding for the mixers, from some thin copper sheet, and tack that in place with a few points of solder
Updates 10th July
Doing some more research, and the original design is on github https://github.com/ttrftech/NanoVNA
With links to the original manufacturer, who unfortunately seems to no longer make them,
I also found this post, by the original designer
Which shows the original design and the need for shielding
It also shows what they consider to be the “Bad clone” – which is the one I have.
I’ve no idea what makes the other clone worse than mine, so it would be interesting to see some photos of the PCB from that type.
Thinking about the problem with the display. My best guess is that they are using recycled / recovered screens, taken from other equipment.
I looked at a few videos on youtube, and I’m not sure if the analyser in this video has a plastic protector on it, https://www.youtube.com/watch?v=fGO74yqDRe4
But it looks like it’s not in good condition.
Mine didn’t come with the plastic peel off, screen protector strip, but even if it did, I’ve had instances where I’ve received other LCD screens (e.g Nokia 5110 screens), which were supposed to be new, but which were obviously used, and had burn in of a logo or the date etc in the center of the screen, and yet still had a screen protector on it.
The recyclers seem to just remove the screens, and stick a new plastic protector on them. They don’t even bother to clean the screen before applying the protector, probably because that costs time and money.
Another minor problem with my device is the push button , jog control seems to be partially defective. This could be because the unit is not new, or it could just be a manufacturing fault, its impossible to tell.
One interesting thing I noticed, is that the PCB seems to have an unpopulated set of PCB pads, which looks like its for a micro SD socket.
The original design, seems to show the SD card as used, so it may not be supported in the firmware.
Anyway. I’ll continue with my investigation into this device