[time-nuts] HP 5370B low frequency modulation

Chuck Harris cfharris at erols.com
Sat Jul 28 14:09:16 EDT 2007

Hi Didier,

I believe you are mistaken about what holds a crimp SMA connector together.
The crimp force is entirely taken up in trying to constrict the circumference
of the solid copper jacket.  Because a cylinder is one of those perfect
structures discovered by the ancients, this crimping pressure doesn't apply a
significant amount of additional pressure to the center insulator.  I have made
numerous shielded opens for network analyzer use by crimping an SMA connector
nut onto a piece of copper semi-rigid shield tube without using any center
insulator, or center pin.

The screw on BNC's that you can get at Radio Shack hardly qualify as a connector.

-Chuck Harris

Didier Juges wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+cfharris=erols.com+cfharris=erols.com at febo.com
> I was referring to the crimp connectors like the SMAs where the cable is
> press-fit in the connector. These work well at t=0 and in low stress
> equipment, but are not too good in high vibration or thermal cycling
> environments. 
> Also, I believe the deformation of the outer conductor where the 1/4"
> semi-rigid cable is squeezed introduces impedance changes and reflections.
> Since most of these cables have Teflon insulation, cold flow and thermal
> expansion create additional problems. These problems are not eliminated by
> using solder type connectors though, as I have seen a number of soldered
> SMAs with cracked solder joint.
> They are very easy to apply though, considerably easier than the solder
> types, and you are less likely to let a badly crimped connector go through
> inspection than a badly soldered one. Problems tend to be obvious. A cold
> solder joint, or too much heat applied to the cable (melting the insulation)
> while soldering are much harder to spot.
> I have occasionally used crimp BNC connectors and they were as you describe
> for the most part. Other than that, my personal experience is mostly with
> solder-type coax connectors.
> The cheap but not inexpensive screw-on BNC connectors you can find at Radio
> Shack do not have an inner sleeve either, if I recall correctly. Not that I
> would recommend using those for ANYTHING (well, I had to try them, so I
> did....)
> Didier KO4BB

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