Re: QCX mini: RF output BNC or SMA #poll-notice
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SMA connectors have a limited life span measured in only 100's of mating cycles. Check the data sheets for Ampehnol, Pasternack, (etc) parts. The inexpensive SMA's from Asia quite likely are even less robust. I have seen some pretty poorly made SMA connectors which instead of fighting with just end up in the trash.
Also, to be used properly and to spec, SMA connectors need to be installed to a specified torque setting ( see the data sheets ). For general use this is not likely much of an issue until the connectors start to wear but on test and GHZ equipment it can be an issue.
SMA's being tiny are also subject to large forces when longish cables are attached ( think of Archimedes ) and moved around. Cheap SMA's and those not well secured are all the more likely to suffer in this scenario. Mini and micro size USB connectors also suffer for this same reason.
TNC are an excellent choice but never really became as popular as other types - about BNC size but with the added connection security of being screwed on.
Given the choice of SMA or BNC / TNC or something else on portable equipment, I would choose BNC.
On equipment that has SMA connectors, I often use a SMA to BNC adapter / converter such as this:
I place a washer between the adapter and the equipment that allows the adapter to be screwed down securely without any space between the equipement and the adapter in order to provide security and strain relief ( think of Archimedes again ).
cheers, Graham ve3gtc
The NanoVNA group has been seeing some issues with SMA connectors.