KE: issue with installation of K3EXREF interface

[Jim Spears]

While installing the K3EXREF SMA-TMP cable, I ran into an interesting issue
which I do not yet know if it is a problem or just interesting.

 

There is a ferrule or something similar over the cable where it attaches to
the SMA fitting that is installed on the back panel.  while tightening the
hex nut down, I must have torqued something as the ferrule broke into two
pieces and fell off.  I finished off the installation and verified that the
GPSDO does provide a suitable 10 MHz signal into the radio.

 

So the question becomes:  is this interesting or a problem?   I took a close
look and the problem might be improper grounding of the shield to the
chassis at the SMA connector end.  

 

If it is deemed to be a potential problem, I can request a new cable from
support.  It will not take long to replace the cable.

 

Jim/N1NK

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[Mike Cox]

Mine broke off too. It appeared for be a crimped ferrule but it split
and fell off as though it were already fractured. I carefully soldered
the coax braid to the connector to maintain the electrical connection. I
was careful not to overheat and melt the dielectric of the coax which
could have shorted the center conductor to the shell. It's working well!

Mike, AB9V

On 4/2/2016 16:16 PM, Jim Spears wrote:

> While installing the K3EXREF SMA-TMP cable, I ran into an interesting issue
> which I do not yet know if it is a problem or just interesting.
>
>  
>
> There is a ferrule or something similar over the cable where it attaches to
> the SMA fitting that is installed on the back panel.  while tightening the
> hex nut down, I must have torqued something as the ferrule broke into two
> pieces and fell off.  I finished off the installation and verified that the
> GPSDO does provide a suitable 10 MHz signal into the radio.
>
>  
>
> So the question becomes:  is this interesting or a problem?   I took a close
> look and the problem might be improper grounding of the shield to the
> chassis at the SMA connector end.
>
>  
>
> If it is deemed to be a potential problem, I can request a new cable from
> support.  It will not take long to replace the cable.
>
>  
>
> Jim/N1NK
>
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[Don Wilhelm-4]

One "trick" that I have adopted when tightening chassis mount BNC and
SMA female connectors is to put a mating connector on the outside of the
connector.  That mating connector can be held tightly with pliers or a
wrench without damage to the female connector that you are trying to
tighten, and you can secure the nut with a wrench.  The mating connector
may or may not have coax connected to it - that makes no difference.

The other thing that is often shown in manuals which is IMHO incorrect
is that the star washer should go between the grounding lug and the
chassis so the teeth of the star washer bite tightly into the metal of
the chassis as well as into the grounding lug - assuring a good ground path.
Another plus for the latter star washer positioning is that once the
star washer begins to 'bite', the grounding lug is not apt to turn as
you secure the nut.

73,
Don W3FPR

On 4/2/2016 6:52 PM, Ron D'Eau Claire wrote:

> Were you only holding the nut while tightening and the ferrule cracked?
>
> That is the first case I've heard of in the 5 years the K3EXREF option has
> been shipped so it's possible there's an issue with some units, especially
> since there are two cases.
>
> I'm curious because we might need to alter the procedure in the manual a bit
> if it's something happening during installation.
>
> 73, Ron AC7AC
>
> -----Original Message-----
> From: Elecraft [mailto:[hidden email]] On Behalf Of Mike
> Cox
> Sent: Saturday, April 2, 2016 2:59 PM
> To: [hidden email]
> Subject: Re: [Elecraft] KE: issue with installation of K3EXREF interface
>
> Mine broke off too. It appeared for be a crimped ferrule but it split and
> fell off as though it were already fractured. I carefully soldered the coax
> braid to the connector to maintain the electrical connection. I was careful
> not to overheat and melt the dielectric of the coax which could have shorted
> the center conductor to the shell. It's working well!
>
> Mike, AB9V
>
> On 4/2/2016 16:16 PM, Jim Spears wrote:
>> While installing the K3EXREF SMA-TMP cable, I ran into an interesting
>> issue which I do not yet know if it is a problem or just interesting.
>>
>>    
>>
>> There is a ferrule or something similar over the cable where it
>> attaches to the SMA fitting that is installed on the back panel.
>> while tightening the hex nut down, I must have torqued something as
>> the ferrule broke into two pieces and fell off.  I finished off the
>> installation and verified that the GPSDO does provide a suitable 10 MHz
> signal into the radio.
>>    
>>
>> So the question becomes:  is this interesting or a problem?   I took a
> close
>> look and the problem might be improper grounding of the shield to the
>> chassis at the SMA connector end.
>>
>>    
>>
>> If it is deemed to be a potential problem, I can request a new cable
>> from support.  It will not take long to replace the cable.
>>
>>    
>>
>> Jim/N1NK
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net Please help support this email
>> list: http://www.qsl.net/donate.html Message delivered to [hidden email]
> ______________________________________________________________
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[Don Wilhelm-4]

Ron,

OK on the SMA connectors.  I have seen several types.  Some are similar
the the BNC chassis mount while others have a "nut" on the outside that
one can grasp with a wrench (and makes my suggestion of screwing on a
mating connector a moot point).

I do believe my points about using a male connector to provide something
for pliers to grasp as well as the star lockwasher placement are valid
points for the chassis mount BNC as well as for *some* SMA connector
applications.

I did not check the exact SMA connector for the K3/S EXT REF SMA
connector before responding, and it has been a while since I have
installed one.
My comments were general and apply only to those BNC and SMA connectors
that fasten directly to the chassis.

73,
Don W3FPR

On 4/2/2016 7:33 PM, Ron D'Eau Claire wrote:

> Don, in this case the lock washer would jam into the opening for the
> connector. If you look at the setup in the manual you'll see that panel hole
> is oversized and the engineers put an o-ring on the connector that centers
> it in the hole. The inside surface of the panel is masked to provide good
> contact with a large flat washer that goes against the rear panel opening
> and provides a good surface for the nut and lock washer that secures the
> connector to bear against.
>
> The connector has a hex cut on the inside ferrule. Tightening is done with a
> wrench or pliers on the nut outside while holding the hex cut ferrule on the
> inside to keep it from turning.
>
> 73, Ron AC7AC
>
>

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