[time-nuts] HP 5370B low frequency modulation

Chuck Harris cfharris at erols.com
Sun Jul 29 16:18:51 EDT 2007

Hi Didier,

The reason that SMA connectors don't go above 21GHz is there is
a wicked discontinuity in the female connector.  The 141's shield
comes flush with the connector/nut's body, but only the nut's body
touches the shield of the connector.  That leaves a step from the
coax shield to the connector shield... not good!

The APC3.5 solved that problem by making the connector smoothly
transform from the 141's shield to the connector.  To do this, it
has it's own integral center pin, and teflon insulator.  It is really
a better connector... but you have to solder it to the coax.

-Chuck Harris

Didier Juges wrote:
> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+cfharris=erols.com at febo.com RETRY
> Hi Chuck,
> You may be correct, the deformation is not obvious when looking at it with
> the naked eye (never actually measured it, but you prompted my curiosity, so
> now I will have to check :-) That may explain the relative vulnerability of
> these connectors.
> Regardless, the manufacturer of the type of crimp-on SMA connectors we use
> does not recommend their usage above 18 GHz. They do show strange VSWR
> patterns above 18 GHz. I have a particular narrow band product operating
> just above 21 GHz where I was planning to use them (I thought it would be
> close enough), but it did not work well enough. On the other hand, the
> equivalent soldered type is specified up to 26.5 GHz. I know the standard
> SMA spec is only going to 18 GHz but a number of vendors offer 26.5 GHz
> rated SMAs. There may well be 26.5 GHz rated SMA crimp connectors, but not
> from our regular vendor and we do not use them. As a matter of fact, for
> most everything I build that operates above 18 GHz, I prefer buying pre-made
> cable assemblies. Considering the cost of connectors, cables and tooling,
> it's not that much more expensive. For reference, the 21 GHz cables we buy
> are soldered, not crimped, and they work much better than those we made.
> Didier KO4BB

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