Joe,
At least on the three NanoVNA-H's and one NanoVNA-H4 I have, the standards do have rotating nuts. There was no easy way provided to prevent the centers from rotating, however. I cut a screwdriver slot in a couple of them to hold them, and carefully drilled and tapped another to attach an extending rod to hold on to. It would be nice if the originals had such holding rods, but I guess that would have increased the brass cost.
--John Gord
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On Sun, Feb 28, 2021 at 02:15 PM, Joe wrote:
On 2/28/2021 1:49 PM, Gyula Molnar wrote:
Because the fixing nut, which should rotate, cannot rotate, but forces the
fixed to remain with the middle mandrel and move with it. The result is that
the center pin will sooner or later not connect with the correct torque
because it is worn out from a lot of rotation.
Hello Gyula and all,
This is true for standard SMA connectors, but the short/open/load tools
supplied with the NanoVNA do not have separate rotating collars on them.
The 3 devices are one solid piece each. The two 6 inch jumpers
supplied with the device do have collars that rotate.
I have used the Anritsu Sitemaster and Cellmaster for many years.
During certification training we were taught not to allow the
short/open/load devices to rotate while putting them on the set set.
The proper procedure is to hold the device so it cannot spin and only
turn the outer collar. The reason for this is, as you said, is to
minimize the wear on the center pin. The center male pin is only plated
and constant spinning of it can wear off the plating, causing a bad
connection. If you really are concerned, the solution might be to get a
couple of SMA Male/Female "connector savers". For the occasional user,
this probably will not be a problem.
I've had some of my calibration tools for over 30 years now and they are
still good because I'm careful to use them properly. BTW, Anritsu used N
connectors on their calibration tools.
Quality SMA connectors are good for around 500 connection cycles. BUT
this is if you install and remove them properly, AND if they are quality
connectors. We really don't know the lineage of the ones supplied with
the NanoVNA. Finger tight, like you stated, is fine. Just because you
can put a wrench on them doesn't mean they have to be white knuckle tight.
73, Joe, K1ike
