Re: [time-nuts] HP 5370B low frequency modulation
I was surprised to read that crimping is considered most reliable. I
work in broadcast television, and we have rows and rows of video
patch panels. Decades ago, the coaxs were soldered to the MUSA
connectors on the bay, but in recent years they have been terminated
in BNC plugs crimped onto the cables, and those plugged in the back
of the bay-mounted MUSAs. We are very critical of this system: it
may be easy for the installation people to terminate the cables in
their workshop, then plug them in where required, but after several
years these connections prove very unreliable, and frequently need a
good wiggle. Now of course I don't know if it is the crimping, or
poor connection on the BNC centre-pins, but it is not unheard of to
have a poor connection, go to investigate, and find the BNC comes off
the cable in your hand! Perhaps the relevant part of your phrase was
"adequate" crimping.
Peter (London, England)
...Of course, the best is avoiding gold
contacts for solder joints at all and never use nickel plated surfaces for
solder joints!
The NASA does have similar special procedures as the ESA.
The best is using adequate crimping processes where possible.
regards,
Arnold
Good day,
*********** REPLY SEPARATOR ***********
On 27-Jul-07 at 08:29 Peter Vince wrote:
); SAEximRunCond expanded to false
Errors-To:
time-nuts-bounces+kyrrin=bluefeathertech.com+kyrrin=bluefeathertech.com@febo.com
I was surprised to read that crimping is considered most reliable...
<BigSnip>
There is some truth in your tale about the crimps in the broadcast world, but you are also correct to point out that "adequate" (I like to say "proper") crimping is critical to making the connection reliable.
In the avionics world, it is rare that you will find a soldered connection in the wiring harnesses. 99.9% of everything in there is crimped. The difference is that the various contacts and plugs, both conventional and coaxial, are attached by well-trained folk using the best available tools.
When properly done, with the right cable prep (ideally, thermal strippers) and the right crimping tools (mil-spec hex crimps for the coaxials, mil-spec eight-way indent for the conventionals), a crimp connection has the same strength and gas tightness of a cold weld. I've been fortunate, over the years, to have gotten hold of the right tools and dies for everything I do through Boeing's surplus store. The contents of one of my tool chest drawers would have run into five figures worth of spending had it not been for them.
Keep the peace(es).
-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies -- http://www.bluefeathertech.com
kyrrin (at) bluefeathertech do/t c=o=m
"If Salvador Dali had owned a computer, would it have been equipped with surreal ports?"
Hello all together,
nice to find an expert on wiring procedures, all your comments are fully correct Bruce!
For the Boeing B747/ B727/ B737 etc. we had of course all kind of tools for all the different MIL a
nd aerospace connectors and wire-types available. Unfortunately these are quite expensive and
they have to be requalified from time to time for professional use.
For stripping off the wire insulation we did prefer the mechanical way. For each qualified (MIL/Space/
Aerospace) there are different special cutting blades with different 'holes' in for each gauge.
Thermal stripping was not allowed because outgassing. When working with Teflon, Tefzell etc. (but
as well for others as PVC!) the gases are very toxic and agressive for humans and corrosive, specially on the
contact surfaces to be contacted!
(Kapton was an exception because it is nearly impossible to cut properly without any damage to the wire
surface (mech.), but special precautions (venting and cleaning) must be strictly followed when therm.
stripping!)
Good stripping tools and cutter inserts were manufactured by 'Ideal', some cutting blades we got from
the wire manufacturer eg. from Raychem. Such cutting blades do not touch the wire core surface!
The critical points are cold flow and hardening of copper under high pressure. As result the wires tends
to break, with too low pressure the wire strains do not 'cold weld' (in fact gas tight!) and not provide correct
contacts.
For the SpaceLab D2 mission (Spaceshuttle) and for the later Satellite-projects etc. we made very
frequent pull out tests and from time to time microscopic inspections on the crimped section.
After all, yes the persons working with these procedures were special trained and examined.
But no, it is not that complicated as it appears, and the well crimped contacts are the most reliable
connections, but strain reliefs behind the contacts are essential. I do as well, when possible, apply
my crimping tools.
regards,
Arnold
On Fri, 27 Jul 2007 06:22:05 -0700, Bruce Lane wrote:
Good day,
...
On 27-Jul-07 at 08:29 Peter Vince wrote:
...
I was surprised to read that crimping is considered most reliable...
...
There is some truth in your tale about the crimps in the broadcast world, but you are also correct to point out that "adequate" (I like to say "proper") crimping is critical to making the connection reliable.
In the avionics world, it is rare that you will find a soldered connection in the wiring harnesses. 99.9% of everything in there is crimped. The difference is that the various contacts and plugs, both conventional
and coaxial, are attached by well-trained folk using the best available tools.
When properly done, with the right cable prep (ideally, thermal strippers) and the right crimping tools (mil-spec hex crimps for the coaxials, mil-spec eight-way indent for the conventionals), a crimp connection
has the same strength and gas tightness of a cold weld. I've been fortunate, over the years, to have gotten hold of the right tools and dies for everything I do through Boeing's surplus store. The contents of one of my
tool chest drawers would have run into five figures worth of spending had it not been for them.
Keep the peace(es).
-=-=-=-=-=-=-=-=-=-=-=-
Bruce Lane, Owner & Head Hardware Heavy,
Blue Feather Technologies -- http://www.bluefeathertech.com
kyrrin (at) bluefeathertech do/t c=o=m
"If Salvador Dali had owned a computer, would it have been equipped with surreal ports?"
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. If the plastic softens, or cold flows
(typical with Teflon), the crimping pressure will drop over time and
eventually the connection between the shell and the braid becomes loose. The
better crimped coax connectors have a sleeve that slides under the braid
against which the braid is crimped. These are considerably more reliable.
The crimping on the center conductor is typically more reliable, if done
right.
Didier KO4BB
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Peter Vince
I was surprised to read that crimping is considered most reliable.
...
Peter (London, England)
Didier Juges said the following on 07/28/2007 09:39 AM:
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. If the plastic softens, or cold flows
(typical with Teflon), the crimping pressure will drop over time and
eventually the connection between the shell and the braid becomes loose. The
better crimped coax connectors have a sleeve that slides under the braid
against which the braid is crimped. These are considerably more reliable.
The crimping on the center conductor is typically more reliable, if done
right.
I don't know that I've ever seen any crimp connectors that don't have a
sleeve between the coax and the dielectric. Maybe I've just been living
right...
I can say from my own experience since I bought a set of AMP crimp tools
that my success rate in doing crimp connectors is much higher than it
ever was with the solder and clamp types, and that (particularly with
the addition of a $30 stripping tool), it's much faster as well.
Between my hamshack and my lab, I've probably put on around 100 cable
ends, and I shudder to to think what it would have been like doing all
those the "other" way.
For what it's worth, I mainly use connectors from RF Industries
(http://www.rfindustries.com). They have a very wide range available,
they're reasonably priced, and have they've worked well for me. I
usually buy them through Davis RF (http://www.davisrf.com) because
they're really good about small orders of both coax and connectors, but
I think you can buy direct from RF Industries as well.
John
John Ackermann N8UR said the following on 07/28/2007 09:58 AM:
I don't know that I've ever seen any crimp connectors that don't have a
sleeve between the coax and the dielectric. Maybe I've just been living
right...
Argh! I meant to say, between the shield and the dielectric.
John
Didier Juges wrote:
); SAEximRunCond expanded to false
Errors-To: time-nuts-bounces+cfharris=erols.com+cfharris=erols.com@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
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@febo.com [mailto:time-nuts-bounces@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@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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@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
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.
You can (supposedly) mess up an expensive 3.5mm female connector if you mate
it with a male SMA without a fixed center pin. Never done this myself but
have read about it. I have a bad habit of using the 3.5mm-APC7 adapters
from my cal kit for making general SMA connections to the 85046A test set,
and I always wonder if I'm going to mess them up.
The screw on BNC's that you can get at Radio Shack hardly qualify
as a connector.
Yep. You can think of them as random-impedance loads.
-- john, KE5FX