[Cu-wireless] volunteer needed: research cable construction

Mike Lehman rebelmike at earthlink.net
Thu Aug 8 22:30:54 CDT 2002

_Not_ a ham (until they finally get completely rid of that silly Morse
code stuff) but here's a few answers.

Yes, do get exacting directions on how to apply connectors. At these
high frequencies, this is essential. I have no experience with building
cables and connections at these freqs, so getting someone who knows how
to demonstrate or advise (like the fellow you mentioned from Alliance)
the specific cennections you need is a _very_ good idea.

On the solder/no-solder debate...soldering (properly done) is alway
better than crimp-on. Yes, you can get fairly reliable connections with
crimp-ons these days. But if you never want to worry about the
connector, solder it on properly.

Some crimping is still involved, even if you go the extra mile and
solder where appropriate. This is a matter of:
1) Have the correct connectors and tools (including the right soldering
rig) to do the job. Be sure, because there is lots of stuff that is very
close, but not right.
2) Practice. Be willing to redo a connection if it seems not quite
right. Practice. Repeat as necessary.

Waterproofing? Don't use the various silicon sealers on electrical
connectors. I've had very good luck with the tacky black Coax-Seal stuff
that Radio Shack sells. Starting with properly applied shrink tubing
over the connector, a good wrap of this stuff and setting up the
connection so that water sheds easily (instead of pooling in any
fashion) off the connection is the way to go.

Strain relief is also very important. Mainly so that things aren't
flopping in the wind (tie it all down with cable ties) and so that there
is just enough slack so that what vibrations from the wind you do get
are damped out by having just a little slack to absorb it. You don't
want things flapping around in any case. And think about how water will
drip down over the connector and cable when you tie things off. The drip
loop is a very important part of the outdoor cable run so that whatever
moisture does run down the cable has a place to go other than into a
connector or the building.
Mike Lehman

David Young wrote:
> Today I think Sascha and I *may* have made some mistakes in installing
> an antenna and wireless router at his house which will will cost us for
> replacement of a cable in the future. When RF connectors are $5 a pop, and
> LMR-400 is .30 to .50 a foot, we cannot afford avoidable mistakes.
> Your mission, if you choose to accept it, is to help us take the guesswork
> and sloppiness out of our installs.
> Please, someone research cable-building and prepare to tell us
> authoritatively at our meeting next Thursday how to
> 1 apply a crimp connector to LMR-400 cable: must we solder the
>   center pin? if yes/no, why do people disagree on this point?  how do we
>   produce a good crimp, every time? what are the tolerances for applying
>   a crimp connector? how do we test a crimp connection on the bench?
>   in the field?
> 2 strain-relieve and waterproof a crimp connector
> 3 waterproof an attachment made by two N connectors
> 4 avoid ruined cables and unnecessary RF loss
> If you must go to the manufacturers (for example, RF Industries) to find
> authoritative answers, do.
> Also, please find affordable suppliers for the materials we will need to
> produce robust, waterproof connections out of doors. Do not prematurely
> disqualify local hardware stores and electrical supply places.
> I encourage you to try to invite somebody to give this talk. For
> authoritative answers, you might try Stu at Alliance Communications.
> He was really friendly when I talked to him months ago, and he seems to
> have lots of experience in microwave telecom. Also, local ham operators
> (like Mike Lehman, who lurks on this list) may have answers.

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