[time-nuts] HP 5370B low frequency modulation

[Didier Juges]

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
 
-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Chuck Harris
Sent: Saturday, July 28, 2007 9:27 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP 5370B low frequency modulation

Didier Juges wrote:
> ); SAEximRunCond expanded to false
> Errors-To:
time-nuts-bounces+cfharris=erols.com+cfharris=erols.com at febo.com
> 
> Of course, any method is only as good as it is implemented. Crimping gets
> rid of a number of chemistry problems, and creates few problems in return.
> 
> One problem with crimping coax cables is that crimping the braid is
usually
> done against the plastic (term used generically) insulation between the
> center conductor and the braid.

Not in my experience!  The coax is stripped in a 1/2,1/4,1/8 pattern like
this:

====
------------
----------------
CCCCCCCCCCCCCCCCCCCC
----------------
------------
====

The center conductor is crimped only to the "CCCC" bare center wire.
There is an inner metal sleeve that slips between the shield and
the center insulation.
There is a metal crimp sleeve that slips over the outer insulation
and the shield braid.

The half of the crimp sleeve that is away from the connector restrains
the outer insulation and acts as a strain relief

The half of the crimp sleeve that is close to the connector crimps the
bare shield against the inner metal sleeve forming the ground connection.

-Chuck

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