Performance of China 50 ohm Coaxial Cable - Page 1
Forum section: electronics / general

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 11, 2018, 05:07:05 pm
content: i havent seen a report on this and i read people advising to avoid this china coax cable, i didnt know the seriousness of the advice until today. having dejavu time with my recently bought ADF4355 SG, i put the blame on the cable (my long time usefull and friendly RG174 diy cable), with my recent possession of a (cheapo) VNA now i'm able to analyze it. i just dont believe it, the cable is only usefull at less than 1GHz, more than that, its not 50 ohm "characterized impedance" anymore as claimed. luckily i also have RG402 semi-rigid cable bought from China too sometime ago to compare with, its not so bad, at least i will not in a hurry to search for Gore cable etc and have to wait another 2 weeks to play around. i got more than i wish for, the VNA that i originally bought just to tune some antenna now has opened another can of worm for me, i've been fine along the RG174 cable now it seems not anymore. the radar (ebay and online shop search) is now directed on some coax cable that possibly cost more than a Ki'm starting to think being a burger seller business will expose me a lot lesser to brain and money damage hazard. attached pictures are the report on Impedance and VWSR of terminated RG174 and RG402 china cable from a hobby grade VNA, FWIW...

author: Bud
author_rank: Super Contributor
timestamp: April 11, 2018, 05:17:38 pm
content: Have you checked if RG174 is rated for 7GHz?

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 11, 2018, 05:26:59 pm
content: as usual, no rating if its from misc hunglow brand china. but i read coax cable with sma connections is good for few GHz the only difference the smaller diameter like RG174 will have greater loss per length. with the plot above, my RG174 is not 50 ohm characterized impedance beyond about 500MHz.

author: gregariz
author_rank: Frequent Contributor
timestamp: April 11, 2018, 05:39:38 pm
content: Quote from: Mechatrommer on April 11, 2018, 05:24:27 pmA good quality SMA will be fine until high Ku band at least.My very first job was fitting SMA's to semi-rigid for this band using a 8757 scalar analyzer and looking for ripple across the band. Any air gaps at all in the transition led to non linearities. I came up with a method of cooling the joint in alcohol while the solder was still molten to suck the teflon (and connector with it) back into the copper shield so to eliminate this discontinuity. I'm sure the practice would have given amp a heart attack but it worked.The problem with a lot of chinese coax makers is simply that they skimp on the shielding % to save a few penny's. I've also ordered double braided RG40x test cables from china only to find out that return losses into ideal loads left me with barely 12dB in return loss - how that is possible I am not quite sure. As a result I will not buy Chinese test cables ever - so I typically pay ~ $200 a cable but at least I sleep easy after my measurements. You get similarly poor results with the type of sma-sma cables being brought in from Jameco - but I have used them in product where the requirements were undemanding - I think that is the trick - just use them where there is some forgiveness in loss and return loss. In that case I don't believe it was the cable but the quality of the workmanship and the connectors themselves. The other issue that is now common is Many/Most chinese vendors have gone metric with their copies of Amphenol connectors etc leading to grind of the threads over time, which is a source of another issue - one of the Japanese test equipment makers had that many complaints about it they ditched them and would only use original Amp connectors. A quick tip is if the connector looks like it is chrome plated its probably a poor consumer type - if it is a duller silver plate its generally of the higher quality type.

author: bd139
author_rank: Super Contributor
timestamp: April 11, 2018, 06:26:09 pm
content: This doesn’t surprise me. Weigh 100m of Wun Hung Lo RG174 and then some decent stuff. There’s something missing from the Chinese crap.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 11, 2018, 06:42:32 pm
content: fwiw, i bought the RG174 50ft at ~$10, thats 20 cents per foot length (seller chinarf in 2011 yes i have the stock record inventory), super cheap compared to Gore. its still usefull below 500MHz imho, but if i want to connect 5.8GHz antenna to it, i must get the length tuned to the frequency. i guess this is the reason why few of my rc transmitter got blown off, too much reflected signal damaging the rf amplifier/tranceiver's output. Gore's cable et al are not indestructable too they have their life limit, after that they go out of spec too. beside their bulky size not suitable for portable item like rc unit, the cost might be damaging on my side, so i will need some compromise on this..

author: hendorog
author_rank: Super Contributor
timestamp: April 11, 2018, 10:24:30 pm
content: I normally use semi rigid RG403 or RG405 stuff for FPV antennas at 5.8GHz. They are super easy to make with that due to there being no insulation over the braid.Otherwise I've used RG316. I got all of those from China, and it seemed to work fine.I have some more decent test gear now, and I have different cables for that. You can get basic Megaphase test cables from eBay pretty cheaply.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 12, 2018, 05:38:00 am
content: is this brand any good for T&M purpose?HUBER SUHNER Minibend L

author: hendorog
author_rank: Super Contributor
timestamp: April 12, 2018, 06:05:39 am
content: Quote from: blueskull on April 12, 2018, 05:41:55 amImportant to note that those particular ones are point to point cables. So presumably not designed for repeated bending and connections as would occur with test cables on a VNA.I'd expect them to degrade with use faster than a proper test cable.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 12, 2018, 06:21:15 am
content: Quote from: hendorog on April 12, 2018, 06:05:39 amyes i read that for connection between rf modules. the connectors seem fragile, maybe if i put more care in handling them or put some sort of diy retainer near the connectors to avoid bending in that area, maybe i can put some life span to it, the price new is 1/10X compared to Gore cable used and 1/30X - 1/100X compared to Gore cable new in ebay. so its expendible cost i may give a try. in case its destructed, i may recover the cable and put my own sma connectors to it, i have some stock bought from china (the same batch as in the semi rigid coax picture in OP. i care most on characteristic impedance of the "cable", the connectors i can diy. the cable is rated 24GHz in ads and flexible (not semi rigid) according to the seller.

author: BravoV
author_rank: Super Contributor
timestamp: April 12, 2018, 12:11:04 pm
content: Not sure about Malaysia, here, there are many of those so called electronics scrappers, and usually they scrapped and salvaged mostly outdated cellular towers throughout the time. Here since the GSM started until the latest LTE stuffs, they harvested tons of RF things.And the best part is, I usually can score really-really good used various high quality RF cables, and sometimes still with the really good connectors attached, as they're used as patch/jumper cables. Brands namely like Huber Suhner, Rosenberger, Adrews and etc. Some of them are even in really pristine NOS stuffs.Sort of like these, just examples what available locally here. Sometimes they even sell them less than $1 per pcs.

author: BravoV
author_rank: Super Contributor
timestamp: April 14, 2018, 09:35:08 am
content: Remembered this again, as I just purchased few of these few hours ago, bout 1 meter each, more than enough for my upcoming diy near field probe, only 2 Ringgit Pak Cik.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 14, 2018, 10:40:10 am
content: congratulation brother

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 14, 2018, 11:34:21 am
content: Quote from: gregariz on April 11, 2018, 05:39:38 pmIt's important to clean them once in a while too, and use a torque wrench.

author: Bud
author_rank: Super Contributor
timestamp: April 14, 2018, 03:18:10 pm
content: Torque wrenches cost a fortune....

author: bd139
author_rank: Super Contributor
timestamp: April 14, 2018, 03:38:05 pm
content: Indeed. I saw some idiot using an HP one as a hammer once.

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 14, 2018, 03:51:47 pm
content: it depends on what are you. if you love americana (Keysight, Fluke etc) then yes you need a fortune, but if you dont hate china too much, then there's alternative...https://www.ebay.com.my/itm/0-5N-m-3N-m-opening-8MM-SMA-torque-wrench-RF-connector-opening-spanner/292516601321?hash=item441b591de9:m:mUI4KC35S8i5GEGn7qQWynAfor now i will use only the hand, one eye closed and tongue at the right angle.

author: technogeeky
author_rank: Frequent Contributor
timestamp: April 15, 2018, 01:36:42 am
content: FYI: I boughtthis"MXITA" torque wrench a year ago.It had the specified torque written ion it when I bought it, and it still has exactly the same torque setting today.I am very happy with it for the price.

author: Wirehead
author_rank: Regular Contributor
timestamp: April 16, 2018, 07:30:35 am
content: Just a question but couldn't deduct it from previous posts - you have calibrated the VNA before taking the measurement, right?

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 16, 2018, 07:57:08 am
content: of course its calibrated with Kirkby Cal Kit... i believe with any even the high end brands, the systematic error in measurement (cabling) will not be entirely eliminated, even more so with this hobby grade VNA. but from the result above, i believe my VNA is acceptable for my hobby purpose. previously my measurements with excessive ripple are due to my ignorance (err edit: not my ignorance actually, i just cant measure it before this time) in the cable quality which introduce greater systematic error. fwiw, attached is my report to Dr Kirkby to amend the conclusion of my previous measurement / verification.