On 4/1/12 3:01 AM, Dr. David Kirkby wrote:
On 03/31/12 09:38 PM, Jim Lux wrote:
On 3/31/12 1:15 PM, Brooke Clarke wrote:
Hi Achim:
SMA RF connectors have a very limited life (number of matings) until
they are worn out.
I don't think so. Yes, they're only rated for 500 cycles, but there's a
paper by a guy at Maury Microwave that I ran across when trying to get
statistics on the reflection coefficient variation, and he set up a
automated rig to mate/demate SMAs something like 10,000 times.
I suspect that the jig he built does a better job of aligning them than
what humans do. We put them on not quite square, move them around until
the thread mates etc. I wonder if his jig tried to replicate a human or
not?
Nope.. back and forth in a straight line. He was measuring repeatability.
I suspect that there is a WIDE variation among mfrs in terms of life
performance and manufacturing precision.
Yes, I've worked in places where they use the cheapest they can get, and
others where the more expensive, but much better quality Huber and
Shuner connectors are used. I would expect the more expensive ones,
which are machined more accurately, would last for more
There is also a relationship between the torque you tighten them and
their life.
I happen to work somewhere where I can't get my boss to buy a torque
wrench for them, despite we use a lot of SMA connectors. I don't know
how common that practice is. Everywhere else I have worked does use a
torque wrench.
I one tried a quick experiment tightening them up by hand as tight as
possible, then seeing how many extra turns it required to torque them to
whatever the torque wrench was set to (not all SMA torque wrenches are
set to the same figure). As far as I can tell, there is no way of even
roughly estimating how tight they should be by saying "hand tight + x
turns".
Yes.. if you're talking about finger tight, there's a lot of
variability. With an inexpensive open end wrench, though you can get
pretty consistent.. perhaps it's the "Calibrated thumb" on the little
wrench?
Not anywhere as good as the "click" on the real torque wrench.
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