power dividers from ali express are a steaming pile - Page 1
Forum section: electronics / testgear

author: graybeard
author_rank: Frequent Contributor
timestamp: July 19, 2019, 06:33:11 am
content: I have an test to do where I need to use some restive power dividers to split and combine signals, so two weeks ago I ordered somepower dividers from Ali Express. They looked like they would be fine for my needs up to a few hundred Megahertz.Here are the power divideres pictured in the ad.You can see they are the classic delta delta design which ideally would use 50 Ohm resistors, but the 51 Ohm resistor shown should work fine.Here are the pictures of the one(s) I received.They are in the Y configuration, not the delta. If they worked, that would be fine. However they are built using 51 Ohms resistors, and that is a big problem. For a Y configuration power divider to work properly the resistors should ideally be 16.7 Ohms. If they used 16 or 18 Ohm resistors they would probably be fine, but they are useless with the 51 Ohm resistors.Tomorrow morning I will call my credit card company and dispute the charge. In my past experience dealing with Ali Express the customer service is designed not to resolve anything and only drags out. Reversing the charges with my credit card company has been the only effective method of solving disputes with ali express vendors.

author: Larry80
author_rank: Contributor
timestamp: July 19, 2019, 06:47:59 am
content: The advertisement has 51 ohm resistors..Chinaman see, chinaman do.

author: Mr. Scram
author_rank: Super Contributor
timestamp: July 19, 2019, 06:51:53 am
content: It looks like a copy made by someone unaware of the actual requirements.

author: Chriss
author_rank: Frequent Contributor
timestamp: July 19, 2019, 07:10:26 am
content: Hi!I'm not an expert for the stuff you working with but inyeresting things.About aliexpress and problem solwing.I use aliexpress very frequently and some time I have problems like you, but I always got solved any sort of problems.My best regards.Sent from my SM-J500F using Tapatalk

author: Fungus
author_rank: Super Contributor
timestamp: July 19, 2019, 07:13:27 am
content: Probably sent the nephew down to the Shehenzen market to grab the first/cheapest thing that looked like what they were supposed to be selling.Still, nothing that can't be fixed by two minutes with a soldering iron.Quote from: graybeard on July 19, 2019, 06:33:11 amNot my experience. Aliexpress has grown precisely because it has a lot of guarantees for buyers.

author: Berni
author_rank: Super Contributor
timestamp: July 19, 2019, 07:36:56 am
content: Still interested in how well does it perform when the correct resistors are inserted.I built my own RF power splitter from soldering SMA connectors together into a triangle shape and then soldering a star configuration of 0402 resistors where the 3 center pins meet together. Then the whole thing was wrapped in adhesive aluminum tape to shield it. It seamed to perform just fine up to the 3GHz that the network analyzer was capable of seeing.

author: nctnico
author_rank: Super Contributor
timestamp: July 19, 2019, 07:48:43 am
content: I'd bin it. The clearance seems to be way too small for the microstrips to work as 50 Ohm traces.

author: radiolistener
author_rank: Super Contributor
timestamp: July 19, 2019, 10:04:57 am
content: Quote from: blueskull on July 19, 2019, 07:43:35 ambut 6 dB power splitter should use 16.7 Ohm resistors, instead of 51 OhmWith 51 Ohm resistors this circuit is "properly designed" power splitter for input/output impedance = 153 OhmI'm surprised how silly mistakes you can find on these products. I also have the same experience, I catch incorrect PCB layout which requires to install jumper and other mistakes.For example, here is very popular SWR bridge on aliexpress:https://www.aliexpress.com/item/32912442432.htmlBut it doesn't works, because it has incorrect PCB layout:It can be fixed by installing jumpers, after that it works:But not so good to declare 3000 MHzActually it is usable up to 500 MHz or may be up to 1 GHz but not more.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 19, 2019, 01:00:09 pm
content: This was the vendors response:Dear friendIt is 50ohmsYou can see our selling pageMaybe you understand wrongWe refund $1 by paypal, ok?Hope you can understandPlease don't open disputeI opened a dispute with Ali Express and I am stopping payment with my credit card.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 19, 2019, 01:19:11 pm
content: Quote from: nctnico on July 19, 2019, 07:48:43 amIn looking at it you are correct. I had not noticed the trace clearance. The resistors being 3 times to large is what jumped out at me.

author: aheid
author_rank: Regular Contributor
timestamp: July 19, 2019, 03:06:11 pm
content: In my experience it works well if you don't claim goods arrived until you've verified what arrived in the mailbox. I usually message seller with complaints and in the 10% of cases the seller is unresponsive I dispute. In every case I got replacement product or money back. YMMV.

author: edavid
author_rank: Super Contributor
timestamp: July 19, 2019, 03:53:43 pm
content: OP, your link doesn't work. Please tell us the seller so we can avoid them.Also... "Standard Pudenda"!!!?! What was that supposed to be?

author: graybeard
author_rank: Frequent Contributor
timestamp: July 19, 2019, 04:50:51 pm
content: Quote from: edavid on July 19, 2019, 03:53:43 pmIt should work now. The seller moved it.https://www.aliexpress.com/item/33045312200.html

author: TurboTom
author_rank: Super Contributor
timestamp: July 19, 2019, 05:17:53 pm
content: I also recently got myself a power splitter via eBay (#152212497183) directly from our far eastern friends. The service was fast and troublefree, so I cannot complain at all. The splitter is of a different type (cascade three-stage Wilkinson), it's less lossy than a pure resistive configuration but not quite as good as a true inductive one...I think I don't like the gull-wing shaped base too much but if it bothers me I can always utilize a hacksaw.... Otherwise, the build quality is okay considering the price I paid.And now for some measurements:Here I did a test of the coupling characteristics from input to the outputs (Trace A and B) with the corresponding other output terminated. Trace C shows the coupling with the second output terminator removed. I'ld say up to 2GHz the splitter works faily well if properly terminated.Trace D in this screenshot shows the coupling between the two outputs (input terminated); traces A~C copied from the previous screenshot and rescaled.And finally, here's the reflectivity at the input with both outputs terminated. Trace B shows the reflectivity of one of my 50Ohms terminators when connected directly to my RLB (normalized with the "out" port open).So I would say the label specifying a frequency range of 380~2500MHz is a little optimistic, but from 500MHz to 2GHz it sould produce acceptable results. Definitely not test equipment grade but better than an SMA "T" for sure.Cheers,Thomas

author: FuzzyOtter
author_rank: Contributor
timestamp: July 19, 2019, 05:46:57 pm
content: Quote from: TurboTom on July 19, 2019, 05:17:53 pmHow are those two PCB mounting screws at the top not shorting the signal to the chassis? It looks like the heads are just barely sitting on top of the microstrip...

author: TurboTom
author_rank: Super Contributor
timestamp: July 19, 2019, 06:24:08 pm
content: Yes I was also worried about that detail. The screws don't touch the striplines but I'm pretty sure they affect their performance. The placement of the two upper screws is particularly peculiar since less "troublesome" locations would have been possible. Maybe I'll do another test with the screws removed. Maybe I'll do it right now...Edit: Okay, here we are:First, Trace A Splitter in "as provided" configuration, Trace B with the cover removed, Trace C with cover and upper two screws removed, and finally Trace D with all screws removed...surprisingly little difference between the traces and none at all between A~C.Second, a comparison of the splitter (A) with an SMA "T" adapter (B), unused leg terminated.

author: thm_w
author_rank: Super Contributor
timestamp: July 19, 2019, 09:52:43 pm
content: It looks like this seller has the wrong item as well:https://www.aliexpress.com/item/32923739011.htmlSo I'm not sure where they are all getting that same photo from.I would have simply done: dispute, product not as described, show them the photos you've taken, and suspect there would be no issues with getting a refund.

author: tautech
author_rank: Super Contributor
timestamp: July 19, 2019, 10:42:49 pm
content: @ TurboTomI note all your screenshots show UNCAL at the top.FYI (and this may be obvious) this originates from a settings change after Normalization to warn the user that sweep results may be affected by post-Normalize adjustments. This is a recent warning addition in the latest 1.2.9.3a SSA firmware announced here:https://www.eevblog.com/forum/testgear/siglent-ssa3000x-spectrum-analyzers/msg2446653/#msg2446653It would be prudent for the user to mention if an UNCAL measurement was in anyway different to one that was taken directly after Normalize.

author: bson
author_rank: Unknown
timestamp: July 20, 2019, 06:27:53 pm
content: Quote from: TurboTom on July 19, 2019, 05:17:53 pmI wouldn't mind buying a bunch of milled low-leakage enclosures like the above (sans the toy PCB). Maybe it's worthwhile buying ten of these and gutting them? I can see using these for all kinds of test fixture and prototype projects. Any good source of cheap milled, but half decent enclosures?

author: radiolistener
author_rank: Super Contributor
timestamp: July 20, 2019, 06:42:52 pm
content: Quote from: graybeard on July 19, 2019, 01:00:09 pmIn your case, you're definitely get different product than described on product description, so aliexpress probably will return your money.

author: radiolistener
author_rank: Super Contributor
timestamp: July 20, 2019, 07:00:48 pm
content: Quote from: bson on July 20, 2019, 06:27:53 pmThere are a new LNA on aliexpress they come in such shielding. Looks very good. RecentlyI got one with spf5189z, unfortunately spf5189z was died very quickly. Probably they using fake. So I ordered replacement for MMIC (also on aliexpress, not sure if it will works, but at least I will try).These LNA has nice shielding case, which can be used for custom projects. I think it's better to buy biastee version, because it is cheaper than LNA:https://www.aliexpress.com/item/-/1000007158078.html

author: Fungus
author_rank: Super Contributor
timestamp: July 20, 2019, 08:06:48 pm
content: Quote from: bson on July 20, 2019, 06:27:53 pmI can't imagine you'll get them cheaper than those 'filled' ones on Aliexpress. Throw away the PCBs.

author: TurboTom
author_rank: Super Contributor
timestamp: July 20, 2019, 10:06:15 pm
content: Quote from: bson on July 20, 2019, 06:27:53 pmMaybe ask a local metal machining shop (or an employee working there to do it after work) to make a buch of these enclosures. Utilizing a modern CNC mill, the job won't be more than two minutes a piece. So you can have many more enclosures like this, even in a "First world" country with high wages than you will get if you strip down such "ready to use" items.Cheers T.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 22, 2019, 11:53:10 am
content: A few minutes before the dispute clock was about to run out I got this BS reply from the vendor extending the time another 3 days."Dear friend So sad for the problem , The profit is very very low when deducting the shipping fee. How about refunding $5 via PayPal account as a compensation? You don't need to return it because the shipment fee you need to pay is expensive Do you agree? My boss will deduct from my salary if refund Could you please cancel the dispute? Thanks"

author: bd139
author_rank: Super Contributor
timestamp: July 22, 2019, 02:06:15 pm
content: Ahh the old sob story. I just reply "nope - whole refund right now please".This crap isn't unusual for aliexpress RF stuff. Last few things I ordered:1. RF termination resistors. All chipped to bits. One didn't even have a bit of microstrip hanging out of the side2. Bliley OCXO. Arrived basically on the original PCB but someone had band sawed around it. When I desoldered it and it the heater in the oven didn't work and complained the seller said I damaged it desoldering it3. "1GHz coaxial terminator". 43 ohms and on my analyser, SWR was at 2:1 at 30MHz4. Si5351A board. Si5351A soldered on backwards. On complaint I was told I had desoldered it and put it back on wrongAt this point there's so much disappointment it's not worth it.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 22, 2019, 02:17:46 pm
content: This was my reply:Only a full refund is acceptable. I will not pay anything for the useless crap you sent me instead of what you advertised.I have had mixed results with RF items. I bought a wideband RF amplifier that was very nice and met all of it's specifications. I also bought some sma cables that were good.

author: OwO
author_rank: Super Contributor
timestamp: July 22, 2019, 02:36:30 pm
content: My experience with aliexpress only extends to 2017 when I moved to China and switched to taobao, but what I learned are:1. For electronics parts or other specialized items never buy from sellers with positive feedback rate less than 98%.2. Always check the negative feedback on an item or seller; positive feedback doesn't mean anything but negative feedback does. For example if you are buying lithium cells look for reviews that mention capacity (and pick a listing with sufficient amount of reviews).3. Price is not correlated with quality.I have ~130 orders on my aliexpress account and have only had to open 3 disputes. 2 are item not received (one of which was the fault of my local post which returned the package without even attempting to deliver it) and only one is item not described. On taobao I have not had a dispute so far. I had one issue with a phone I bought, and the seller repaired it at no cost even though the buyer protection was over a long time ago.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 25, 2019, 03:55:16 pm
content: This response from Ali Express illustrates why I have found it necessary on multiple occasions to stop payment with my credit card. Ali Express does not provide any real customer protection.Chris

author: bd139
author_rank: Super Contributor
timestamp: July 25, 2019, 04:13:10 pm
content: paypal / ebay is a safer option (obviously backed with your credit card as well)

author: graybeard
author_rank: Frequent Contributor
timestamp: July 25, 2019, 05:45:55 pm
content: Comparison of a good one vs the piece of shit from Ali ExpressThe is a comparison of the input impedance made with my Siglent SVA1015X

author: Fungus
author_rank: Super Contributor
timestamp: July 25, 2019, 06:32:16 pm
content: Quote from: graybeard on July 25, 2019, 05:45:55 pmYou mean "expensive one" vs. "cheap one"?(...or is it only good because it's made in the USA?)PS: You can pay $30 for one on Aliexpress if you want.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 25, 2019, 08:38:39 pm
content: Quote from: Fungus on July 25, 2019, 06:32:16 pmIf they had sent me the inexpensive one pictured in their ad instead of the crap they sent me I'm sure it would have been acceptable.I meant good vs. crap

author: janoc
author_rank: Super Contributor
timestamp: July 25, 2019, 08:57:30 pm
content: Quote from: OwO on July 22, 2019, 02:36:30 pmI would also add - check what other items is the seller selling before clicking "Buy"! If the store is selling everything from test equipment through camping gear to fashion accessories, don't expect that they will be willing or able to help you if there is a problem. The seller has most likely no clue what they are actually selling (applies to eBay too - tons of similar cases there as well).E.g. this seller that Graybeard is arguing with is selling also batteries, phones, computer accessories, medikits for camping, cheap calculators ... Entire 37+ pages of random junk. And a 94% rating ...I did have a few disputes on AliExpress but mostly either because the item got lost in the mail or I got sent a wrong item. Always resolved to a mutual satisfaction. However, one does need to be a bit reasonable sometimes instead of making an enormous fuss for a few bucks refund - I did accept a discount on some other item from the store once or twice, or a partial refund for a defective (but fixable) item, for example.If you do a chargeback for a $11 item, the vendor loses not only the $11 but they get hit by a fee from the bank too, often double or triple the value of the item. Sure, not the client's problem but why to screw the guy over 3x if they are willing to fix their mistake. Leave the chargeback as the last option.Open dispute, demand a refund, normally it shouldn't be a problem - document that the item is not as advertised. Show pictures of what is on the website vs what you have got - Ali's staffers can't be expected to have a clue that some resistors have wrong values or understand what is that item supposed to do! But if they see that you have got a green gizmo and the website clearly shows a red one, you will get your money back no problem.Sellers also fear negative feedback like a plague because it means a huge loss of business (nobody buys from someone with a 90% feedback vs. 98%) and they could also get banned from AliExpress if there is too much of it. So you have quite a bit of leverage there even without going nuclear with chargebacks right away over an $11 item.

author: Kjelt
author_rank: Super Contributor
timestamp: July 25, 2019, 08:58:37 pm
content: I only had three disputes with ali all pretty expensive ($150, $45 and $65) and all were decided in my favour no problems.State your case short and clear with pictures.In your case you take a screenshot of what you expected , then a picture of what you received, make small calculation that the impedance is different and useless that you want the original, period.Then they probably would decide in your favour simply because you did not receive the promised product.In my case it was fake products that looked identical and luckily the pcb contained the incorrect sticker so i gotmy money back and keep the product.

author: graybeard
author_rank: Frequent Contributor
timestamp: July 25, 2019, 09:51:38 pm
content: Quote from: janoc on July 25, 2019, 08:57:30 pmI gave the vendor a chance to give me a refund and he offered me $1. I hope he does get hit with bank fees for refusing to make this right.

author: chris_leyson
author_rank: Super Contributor
timestamp: July 25, 2019, 10:16:16 pm
content: I would just change the resistors to 16.7 Ohm, 2 x 33 Ohm mounted on top of each other will get you close enough. I would just chalk it up to experience and beware in future. Caveat emptor. If I need a splitter or combiner first choice is MiniCircuits.

author: Berni
author_rank: Super Contributor
timestamp: July 26, 2019, 05:36:03 am
content: Just show a picture side by side of what the listing shows and what you got.The seller has no idea what this even is so don't expect him to understand. Take whatever he gives you in return, let that be a lesson for how to buy this stuff from china and replace the resistors in it to make it work correctly. No need to chew out the seller for it because he didn't do it on purpose.Sometimes even sellers that know what they are doing make a blunder. I just bought a Agilent 3300A DC Load mainframe from ValueTronics on ebay. It was listed as For Parts and the listing said it powers on and shows an error. The price was right and i bought it, but then found out there is absolutely nothing wrong with it apart from a little cosmetic damage here or there. It shows the error if there are no modules installed inside it. This is a big test equipment dealer and they even offer modules for these load mainframes on there website, you would expect them to know what they are doing. Ah well there loss my gain and it did come packaged incredibly well (As you usual get from these dealers)

author: graybeard
author_rank: Frequent Contributor
timestamp: July 26, 2019, 05:39:51 am
content: I did show a side by side pictures. But it seems that is not good enough. AliExpress agrees it is not what I ordered but they will not give me a refund because they say I have not proven it does not work.

author: Berni
author_rank: Super Contributor
timestamp: July 26, 2019, 06:03:12 am
content: Well technically it does work as a power divider, it just has terrible tolerance for input impedance and due to that terrible return loss.The seller has not provided any performance metrics in the listing. So as far as ali-express is concerned the seller did provide you with a working product but you are unsatisfied with its performance.But because nor the seller nor the people at ali-express are not engineers they don't understand just how terrible this level of performance is. Its not worth chewing them out over it, replacing the resistors costs you next to nothing Besides lets face it, even if you got the right value resistors they would only be +/- 5% tolerance ones. The most valuable thing on here are the SMA connectors and those seam fine (Tho id keep them away from any high quality cables due to the infectious RF connector plague)

author: ebclr
author_rank: Super Contributor
timestamp: July 28, 2019, 04:14:02 pm
content: That's is the correct wiring I suppose. Is that correct

author: graybeard
author_rank: Frequent Contributor
timestamp: July 29, 2019, 05:27:30 pm
content: Quote from: ebclr on July 28, 2019, 04:14:02 pmNo, the circuit you are showing is an RF impedance bridge, not a power divider.These are the two standard configurations for 2-way (3-port) 50 Ohm resistive power divider.Chris

author: Sparky49
author_rank: Regular Contributor
timestamp: July 29, 2019, 08:42:13 pm
content: Quote from: OwO on July 22, 2019, 02:36:30 pmI personally have trouble overcoming this point... Need to try harder...