[TowerTalk] LMR-900

[Joe Subich, W4TV]

Jim,

 > Would that make an adequate RF connection? I'd
 > guess that the answer depends on the frequency of interest. Or
 > would only a crimp-type connector be capable of an adequate
 > connection?

In theory it would depend on the thickness of the inner shield
vs. frequency (skin depth) and whether the inner shield was
insulated (aluminum oxide is an insulator) and the electrical
length between the connection point (e.g., clamp?) and the
end of the shield.  If the connection is to the outer shield
and the two shields are insulated the losses can get very
high.

If the connections are to the outer shield and the interface
between the shields is slightly semi-conducting (aluminum
oxide) low-level mixing can occur (IMD/increased noise).

All of these effects are predictably frequency dependent
based on shield thickness vs. skin depth and connection
length to the end of the shield.  As the impedance from
the connection point to the inside of the inner shield
increases, the less the cable behaves like a coax and the
larger the fields between the shields.

73,

    ... Joe, W4TV

On 7/17/2010 12:14 PM, Jim Brown wrote:
> On Sat, 17 Jul 2010 11:45:43 -0400, Joe Subich, W4TV wrote:
>
>> Connector installation techniques should always insure there is
>> an adequate RF connection between the connector body and the
>> INSIDE of the inner shield.
>
> Interesting. Let's say I'm installing an Amphenol PL-259 on
> something like LMR400 or Commscope 3227 (similar shield
> construction). The connector is a tight screw-on fit to the
> jacket, the braid and foil continue all the way to the point where
> they butt into the hole for the center, and I solder all four
> holes carefully, with the foil and braid (hopefully) in contact
> under the solder. Would that make an adequate RF connection? I'd
> guess that the answer depends on the frequency of interest. Or
> would only a crimp-type connector be capable of an adequate
> connection?
>
> 73, Jim K9YC
>
>
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