How bad are the cheap Chinese BNC adapters from Ebay? - Page 1
Forum section: electronics / testgear

author: Icchan
author_rank: Regular Contributor
timestamp: May 25, 2016, 12:00:55 am
content: This is really somethign that I haven't seen covered in better detail in anywhere.How bad is the performance if an cheap chinese Ebay bought BNC adapters, or any coaxial adapter for that matter, when it comes to attenuation, bandwidth, mechanical fit etc. really?This is right in the park for Dave or w2aew or any YouTuber with proper equipment to tackle!I don't have necessary equipment to test this myself, so I never use these cheap ones for anything past ~200MHZ, but it would be very interesting to know how they compare to something more up marketIt's just that if nobody really knows, we're pretty much limited not to use them in any measurements and people who have the equipment to test, most probably have the money to buy proper ones anyway.T-adapters, 50-ohm terminators, Female to female adapters etc.Do you guys think this would be interesting to know more about?Examples for what I'm talking about: (PM me if the links break)http://www.ebay.com/itm/BNC-Male-To-Dual-Femal-T-Splitter-Barrel-Plug-Adapter-For-CCTV-Camera-DVR-Lot-/321798318797?var=&hash=item4aecacaacd:m:meniCU8YSVjVvEuq-VUawOwhttp://www.ebay.com/itm/1-5-10x-BNC-Coupler-Female-to-Female-Connector-Adapter-for-CCTV-Camera-HFAU-/390729395462?var=&hash=item5af9496d06:m:mwcfgGbNJi55AbuWeh0xTEAhttp://www.ebay.com/itm/1X-N-Type-Male-Plug-to-N-Plug-male-straight-RF-Adapter-coupler-connector-US9-/162052623011?hash=item25bb16caa3:g:YcIAAOSwGotWjToZ

author: xrunner
author_rank: Super Contributor
timestamp: May 25, 2016, 12:03:39 am
content: I know one thing - many are bad simple because of the mechanical precision. I've thrown many away because the tolerance of the male (inside) or female (outside) barrel prevents them from even going together.

author: jjoonathan
author_rank: Frequent Contributor
timestamp: May 25, 2016, 01:55:50 am
content: I have had many issues with cheap ebay connectors but I keep buying them because the inconvenience of tracking down the issues hasn't driven me crazy yet.1 of 10 5-inch BNC cables was completely open1 of 4 Type-N to BNC adapters had a BNC misshapen so badly it didn't mate1 of 5 BNC Ts was intermittently open depending on connection forceI've had much better luck with SMA connectors. 0 issues. But they are more expensive, so perhaps that is to be expected.

author: bitseeker
author_rank: Super Contributor
timestamp: May 25, 2016, 02:02:50 am
content: So, looks like 10-25% annoyance/failure rate. Not too bad, I suppose. I've had about a 20% no-show rate when buying directly from China. Now, if I could somehow sync the two failure events, that'd be quite a nice filter.

author: xrunner
author_rank: Super Contributor
timestamp: May 25, 2016, 02:12:17 am
content: Quote from: bitseeker on May 25, 2016, 02:02:50 amLOL speaking of which I'm going to order some more dual banana to BNC right now due to the fact I've thrown too many in the trash I'm running low ...

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 25, 2016, 02:34:53 am
content: Quote from: jjoonathan on May 25, 2016, 01:55:50 amsame thing here... apart from the above mentioned, i add:-some connectors can easily slide off into pieces.. (but can be put back together, glue is the best friend if you dont want this to happen again)-having said that, the open connection anomaly can be easily fixed by inspection of the internal parts, pull, extend or solder the internal metal part if necessary.-the insulator (center pin white plastic) has poor heat resistance, if you solder the backside of center pin to the pcb, you have to put the mating female\male on the other connection end, otherwise the insulator will shrink and cannot mate anymore, aka useless..-if you happen to buy the cheap 0, 75 or 50 ohm terminator. the resistor or shorting wire is just slided in like that, its a matter of luck if you get a good 50 ohm connection through residual compression force.but i will buy again from china if i have to anytime, since they are cheap and convinience. buying from legit and quality source is not convinience, so thats the indirect annoyance with quality part from my place here.

author: BravoV
author_rank: Super Contributor
timestamp: May 25, 2016, 03:09:19 am
content: Quote from: jjoonathan on May 25, 2016, 01:55:50 amSame here when it comes to SMA, they're much better and consistent than BNC only parts, don't now why.

author: FlyingHacker
author_rank: Frequent Contributor
timestamp: May 25, 2016, 03:46:11 am
content: I have a bunch of eBay junk BNC connectors, cables, alligators, bananas, etc.The regular T BNC connectors (where the middle is male, and the two side are female) I got were almost all (10) intermittent. I got some other T's where one end is male, the opposite end is female, and then a second female comes off the side. These were all great.Cables are varied in quality as well. I had one seller send 75ohm cables instead of 50ohm.Would be interesting to test high bandwidth performance. I have not done much past 400MHz with them.

author: ekyle
author_rank: Contributor
timestamp: May 25, 2016, 04:39:40 am
content: I've had good luck with SMA connectors but the "gold" plating seems to wear off quickly.

author: ebastler
author_rank: Super Contributor
timestamp: May 25, 2016, 05:55:48 am
content: Quote from: bitseeker on May 25, 2016, 02:02:50 amHey, those two failure modes are indeed strongly correlated:Those adapters which don't show up will cause zero functional issues!

author: csmithdoteu
author_rank: Contributor
timestamp: May 25, 2016, 06:01:17 am
content: I bought some BNC connectors from a less than reputable source. Most of them don't even connect to my scope without the lock ring getting snagged. Also bought some RG58 and the outer braid can only be described as "copper fluff". You get what you pay for. Amphenol and Belden next time.SMA connectors aren't very rugged and wear out quickly regardless of the vendor from what little experience I have of the.

author: Howardlong
author_rank: Super Contributor
timestamp: May 25, 2016, 06:04:51 am
content: Regarding the SMA females, of the 20k units I've used in production I get about a 1 in 300 fail rate usually due to shorts or a badly finished, closed receptacle. But as they/re 1/10th the price of Macom or Radiall and the application is only up to 2GHz they're otherwise good enough. I don't have any problems with the finish flaking off.The test regime involves two separate full connector connect/disconnect cycles, enough to identify such faults that are missed during visual inspection.Edit: mechanical failure of the connector due to wear is not a failure mode I've ever encountered.

author: bitseeker
author_rank: Super Contributor
timestamp: May 25, 2016, 06:21:50 am
content: Quote from: ebastler on May 25, 2016, 05:55:48 amAh, yes. Quite true.

author: CJay
author_rank: Super Contributor
timestamp: May 25, 2016, 06:58:15 am
content: I've not had issues with the small number of N-BNC adapters I've bought via eBay, I've also used a *lot* of cheap 75R crimp BNC plugs (I think four to five hundred) for CCTV installs and had maybe three or four plugs that were bad, the other failures can usually be attributed to my fingers and working at height.I've also got a number of cheap RCA/Phono to BNC adapters from eBay which all seem to work well.Was it W2AEW or Mr Carlson who said they weren't too bothered about using 75R and 50R hardware interchangeably as the impedance bump was pretty much insignificant or am I doing both of them a disservice and misattirbuting a comment from someone else?

author: rf-loop
author_rank: Super Contributor
timestamp: May 25, 2016, 07:00:47 am
content: Quote from: Icchan on May 25, 2016, 12:00:55 amI'm quite sure that these particular items (links above) are very low quality.Specially opinion for this N.Do not destroy your perhaps expensive equipment N with these crap junk. Save one euro and loose 100 or moreIn China there can also buy higher quality but, it is not easy over internet exept if buy samples from many places and after then do deep investigation about quality. High quality RF connectors (BNC, N, SMA, SMB etc) made in China is possible but then price is not cheap and you know only after you see it in real world in your hand (and perhaps using some tools for inspect quality)These very poor quality made in China or some other country (we often think it is China where made all poor quality but there is many others and even much more bad. But of course China, including Taiwan province, is big, so we see these more. can also see on some Electronics shops in Finland. Go and look twice before buy.Price is not perhaps most important but after you knock your head to problems in reliable measurements it is frustrating in hobby and if do it in work,it is much much more expensive than best connectors price.Huber-Suhner, Spinner, Amphenol, Lemo, etc (I mean original, not counterfeit)Chinese perhaps better quality (not "State of Art" or "High-End" class) but acceptablehttp://www.hoaninc.com/rf-connectorshttp://www.rfcnn.com/about-us.htmlNot very common in eBay.

author: razberik
author_rank: Frequent Contributor
timestamp: May 25, 2016, 08:55:22 am
content: I buy these things always on flea markets. There are always some seller with boxes full of BNC, SMA, N stuff.Manufacturers like Rosenberger, Suhner, Radiall, Amphenol. These are often some old, but high quality connectors/gender changers. One can be confused by black-ish color, but it is usually only colored-silver. When I view quality of machining using some magnifier I see precisely machined piece of hardware. I sometimes receive N-thing with embedded frequency characteristic in pressed label.Picture below doesnt show exactly connector, however, fleamarkets are perfect source for hi-quality cables too. The background is usually some dismantled telcom like obsolete BTSs.http://ok1quido.rajce.idnes.cz/HOLICE_2014/

author: EVS
author_rank: Contributor
timestamp: May 25, 2016, 10:33:44 am
content: Chinese cheap BNC T-adapter from Ebay (similar from Aliexpress). The center pin is not in contact with the main line at all !!!Waste of money...

author: nctnico
author_rank: Super Contributor
timestamp: May 25, 2016, 10:49:28 am
content: Quote from: Icchan on May 25, 2016, 12:00:55 amI buy these regulary to add more to my stockpile. I just don't buy the extremely cheap ones.

author: D3f1ant
author_rank: Frequent Contributor
timestamp: May 25, 2016, 12:16:15 pm
content: I have given up the bottom of the barrel China stuff. Buy brand name connectors and you won't have to ever buy them again, it's a false economy buying junk over and over...not to mention the frustration when the guts falls out of an adapter right in the middle of a debugging session.

author: Icchan
author_rank: Regular Contributor
timestamp: May 25, 2016, 12:22:23 pm
content: Wow... it seems that most people have problems with intermittent connections and mechanical fit... that's something I really wasn't expecting as much for some reasonI always thought that there would be also a lot of problems with bandwidth etc. But I could have presumed, that mechanical problems are the ones most of us would notice first regardless of our equipment.I would really like to see someone do a slew of tests with this... and maybe list of sellers or sources where you can get reasonable quality RF stuff without breaking your bank?So tell me/us your "reputable source of cheap RF stuff" if you have any, and I'll compile a list of them to the first post (and maybe to our hacker-space wiki / some other source) if possible?

author: nctnico
author_rank: Super Contributor
timestamp: May 25, 2016, 01:56:46 pm
content: I usually buy adapters and BNC cables from this Ebay seller:http://stores.ebay.com/sk2store/

author: Earendil
author_rank: Regular Contributor
timestamp: May 27, 2016, 06:44:57 pm
content: Quote from: Howardlong on May 25, 2016, 06:04:51 amI gauge all of my SMA connectors (measure both pin and dielectric depth) and I found that cheap Chinese cr*p tend to be severely out of tolerance. Even some of the stuff I brought from Farnell are out of tolerance. The pin diameter also tends to be out of tolerance, but that's far more difficult to measure.The problem is that if you connect such a connector to a high-quality one then you could easily destroy it without noticing. You will probably only see the damage at high-frequencies.I would be extremely angry if a $2 connector destroyed my >$1000 worth TDR head for example. Yeah, I know, I should always use connector savers. But for certain measurements you don't want any adapters.I also have bad experience with Chinese BNC adapters. It managed to destroy one of my BNC cables by pushing in the center pin (pin hole diameter was too small on the female BNC).

author: Howardlong
author_rank: Super Contributor
timestamp: May 27, 2016, 07:54:07 pm
content: Quote from: Earendil on May 27, 2016, 06:44:57 pmTo give you a counter example, I test every device myself, and the MTBF on my testing SMA jacks (I use SMA test savers calibrated in-system on my test fixtures) are around 6,000 on/off cycles using these "crap" SMA recptacles. I also test front end sensitivity and return loss at 35 spot frequencies up to over 2GHz. As I already stated, YMMV beyond this, but this is my real-world experience over many tens of thousands of cycles - I even have the hand cramp and blisters to prove it!I would agree though that one should always take care when cycling connectors on expensive equipment. Receptacles with air dielectric like APC 3.5 are particularly prone to expensive mistakes, and the reason I use savers everywhere. Practically speaking, there are almost no situations where I would gain any benefit from not using a saver.

author: Earendil
author_rank: Regular Contributor
timestamp: May 27, 2016, 08:26:28 pm
content: I don't think you'll be able to see the damage at 2 Ghz.Unfortunately I haven't seen any publications that quantify the effects of the damage so it's difficult to be sure.You can find some information about the topic here:http://whites.sdsmt.edu/classes/ee481/maurysma.pdfThe article's first part describe some of the issues. The second part is about improving the SMA connector and the various discontinuities you can get. You can see from the figures that it's above ~10 Ghz where you can see real differences.So what you say is actually consistent with what I expected.I personally don't want to take any risks. If a connector is out-of-tolerance when I gauge it then I simply throw it out.For me it doesn't worth it to buy cheap Chinese connectors. But yeah, I can accept that for production it matters a lot.

author: Howardlong
author_rank: Super Contributor
timestamp: May 27, 2016, 08:35:15 pm
content: Indeed, that is why I was careful to specify the frequency limit I am interested in!

author: Earendil
author_rank: Regular Contributor
timestamp: May 27, 2016, 09:11:59 pm
content: Oh, btw. I also had a male to male BNC adapter that had a dip in the insertion loss at about 500 Mhz if I remember correctly.It turned out that if I squeeze together the two ends then it works correctly. At all other frequencies it worked okay!Problems like this can cause difficult to track down measurement issues. So that's another reason why I buy quality connectors.

author: saturation
author_rank: Super Contributor
timestamp: May 29, 2016, 04:20:49 pm
content: In general no-names are ok but most sellers don't know its impedance rating, there can be quality control issues from different suppliers but they are so dirt cheap that you buy a few test sets from any supplier, and if found good, buy more. The original design is rated to 2-4GHz [ from reputable producers like Amphenol, Pomona ], and impedance ratings, 50 or 75 ohms, so buy a set of adapters from reputable brands to serve as reference and compare whatever it is you buy.In practice, they are used for under 500MHz so its 4x derated and most any perform well in this range.AmphenolRF BNC commercial grade are often very competitively priced from the right vendors versus no-names.http://www.amphenolrf.com/connectors/bnc.html

author: Bellabella
author_rank: Newbie
timestamp: May 30, 2016, 08:12:29 am
content: I think it all depends on the manufacture you selected as well as the certification the manufacture obtained. As you know, there are more and more manufactures who produced connectors in China, and the competition of this kind items become more and more serious. And many sellers made the cheap price to attract the buyers to buy their connectors. However, what the buyers got was always the bad quality connectors. But if you are looking for the good quality connectors, you may contact with this manufacture:http://www.hoaninc.com/rf-coax-connectors:I bought their BNC connectors, and what can I say they were the good manufacture.

author: Earendil
author_rank: Regular Contributor
timestamp: May 30, 2016, 12:23:42 pm
content: Sure. For production it makes sense to contact them for the price cut especially if you have the proper instruments to measure the connectors yourself. But for buying one or two adapters? Why should I bother when I can buy quality brand ones from my distributor. I know that the tolerance and electrical performance of those will be OK. And Amphenol - as mentioned previously - have pretty decent prices.Also these are not readily available on Ebay or Aliexpress.

author: xrunner
author_rank: Super Contributor
timestamp: June 02, 2016, 10:43:02 pm
content: Received a new batch of 5 BNC to banana adapters, and only one will allow a BNC to be connected to it. The 4 others are flawed in some way that I have yet to figure out. You can see in the pic that the BNC will not go on any farther no matter how hard you push or turn. I'll be damned if I can see the problem inside. It has to be a matter of a inside dia. or something, I can not see any macro defect. This is getting really sucky!