Connector adapter loss/failure - Page 1
Forum section: electronics / general

author: tkamiya
author_rank: Super Contributor
timestamp: August 12, 2018, 07:48:53 pm
content: I just stumbled into something odd/amazing/unexpected.I recently had my spectrum analyzer calibrated. If I feed 30Mhz test signal into input using Andrew Heliax with N on one side and BNC on the other, I see a solid signal. Level is accurate, and I can wiggle all I want and the level is spot on.Then, I took N/BNC adapter and attached it to input side. Then used known-good BNC/BNC cable to connect cal signal to input. I see 10db lower than above. Huh? I wiggle the BNC side by grasping on strain releaf. Level goes up and down between 10db too low to what's expected. I repeat this with 3 different cable of different construction and I see the same result.Just for sanity check, I use Heliax again and it's rock solid.To my surprise, all N/BNC adapter by Amphenol purchased from a reputable and well respected company failed this test. Cheap Chinese kind passed except for one. Right now, I don't know what to make of this. Amphenols were purchased in July 2017. They are basically new with no visible damage.The company that sold me the Amphenols refunded me already. (thanks!) So money isn't an issue. But I commonly use these connectors. 10db is a big difference. Fluctuations are even more troublesome.Before anyone asks, no, I did not torque them down. It's a general purpose kind. But I recently got a hands-on training from a tech at my cal-lab. So I know it's not too lose nor too tight. Besides, the problem seems to be the BNC section.Anyone have anything to say about this?

author: TheSteve
author_rank: Unknown
timestamp: August 12, 2018, 08:01:06 pm
content: You say it is a known good BNC/BNC cable - are you sure the center pin meets spec? Did you check the connection with an ohm meter to see if the center pin is even making contact with the adapters(obviously while removed from the SA).

author: tkamiya
author_rank: Super Contributor
timestamp: August 12, 2018, 08:25:27 pm
content: I tested it with another spectrum analyzer. As to pin meeting specification, I have no means to measure that. I didn't do the ohm meter test because it is not likely to show up at DC. But I can certainly try.

author: mzzj
author_rank: Super Contributor
timestamp: August 12, 2018, 08:37:15 pm
content: 10db loss @ 30Mhz is pretty likely showing up also on DC resistance measurent.

author: ArthurDent
author_rank: Super Contributor
timestamp: August 12, 2018, 11:08:25 pm
content: I'm assuming you've already verified that the BNC connectors are 50 ohm and not 75 ohm connectors. That could cause some problems.https://www.iitk.ac.in/ibc/BNC.pdfhttp://www.cctvinstitute.com.br/bnc-75-or-50-ohms.html

author: tkamiya
author_rank: Super Contributor
timestamp: August 13, 2018, 12:04:35 am
content: Yes, they are 50 ohms. I don't own any 75 ohm kind and I know the difference.Couple of interesting findings since my last update.On another Spec Analyzer, I cannot duplicate the problem.Even though it looks clean, I went ahead and cleaned the connector on the problem analyzer with alcohol pads. No visual change, but significant improvement was seen. Also, if I back off the tightness just a little, I can also see improvement. This is true only on few connectors. Rest of them doesn't seem to mind at all.I am still not sure what's going on.