[TowerTalk] coax cables

[Steve Katz]

> Actually, if you tin the coax braid after you strip the outer jacket but
> before you trim it, then use a small copper tubing cutter to cut the
> braid,
> assembly and soldering PL-259's are easy.  Just use a small torch, paint
> stripping heat gun, or a big iron to heat the outer conductor of the
> PL-259
> and feed solder into the holes to complete the connection.  After I remove
> the excess (tinned) braid, I trim the dialectric about 1/8" beyond the end
> of the braid and tin the center conductor also before assembly.
> 
> 
> ::Beware of tinning the braid of coaxial cable.  Although I see many do
> this, and I've seen it recommended countless times by fellow hams, it is
> not a recommended process per the cable or connector manufacturers, at
> all.  Tinning the braid of typical PE dielectric cables overheats the
> dielectric causing distortion and even permanent chemistry changes that
> are not good for the cable.  (Note tinning the braid of PTFE cables is not
> an issue, but is typically a waste of time and solder since most PTFE
> coaxial cables have pre-tinned or silver-plated braid materials to which
> solder flows instantly.)  If you refer to the military work instructions
> for the assembly and installation of type PL-259 on coaxial cable, there
> is no mention of tinning the braid, and they are correct.  Worse still is
> when using cellular PE dielectric cables such as all "foam" products
> (Belden 8214, Times LMR400, etc, etc) -- the braids of those types should
> *never* be tinned, as this simple and quick operation greatly exceeds the
> melting point of the cellular PE and routinely causes permanent damage.
> If the correct solder and methods are used, it's easy to flow solder to
> untinned copper braid through the four solder holes found in the PL-259
> connector body, and doing so does not usually risk reflowing the PE
> because the braid temperature doesn't exceed the melting point of solder.
> When a 700 to 900 degree (F) iron is applied directly to the braid, rather
> than via the connector body, the braid temperature is elevated to the iron
> temperature easily and damage is always risked.
> 
> ::In the industry for mass production of PL-259 cable assemblies, the
> standard tool used is a 900W resistance soldering station with its
> associated probes.  That tool is applied to the screwed-on (mounted)
> connector body and elevates the connector body to soldering temperature in
> less than one second.  Solder is applied to the four holes as the
> connector is rotated, and the current is removed.  The entire operation
> takes about five seconds to complete, so current (and thus heat) is only
> applied for that amount of time, which is insufficient time to distort the
> dielectric material.  Distortion is less likely using this method, anyway,
> since no mechanical pressure is exerted on the cable, which is snugly
> resting inside the connector body.  I've overseen production lines
> building more than 2000 such assemblies in an 8-hour shift, and the
> resulting output are 100% sweep tested from 10 kHz through 500 MHz, then
> hipot tested to 1500Vac, and we get about 99.5% yields.  Using a
> soldering-iron "pre-tin the braid" approach, yields drop to less than 30%
> good on the sweep and hipot test.
> 
> ::I can do the same thing with simple tools at a much slower rate, using a
> single-edged razor blade for all trimming, a 120W 1/2" tip Weller SP-120
> iron and ordinary 60/40 rosin core solder -- but with the same
> satisfactory yield.  Production slows to about one connector per minute
> this way, but isn't bad for a ham station.  Results using a torch, or
> using a soldering "gun" are too variable to predict.
> 
> ::Always solder the braid to the connector body first when assembling
> PL-259s.  Wait for the body to cool down to near ambient before soldering
> the center pin.  
> 
> ::I have never had a PL-259 connector fail in service, in 37 years.  Then,
> I do restrict my output power to about 1500W PEP or so....!  -WB2WIK/6
> 
> 
> This is easier done than said.
> 
> Or, you may consider a crimp tool and crimp connectors.  Sorry, I cannot
> remember where I obtained mine but it cost about $50.  MIL spec crimp
> tools
> are several hundred $$.  The crimp connectors are hard to find but are
> available.
> 
> de Paul, W8AEF
> 
> ----- Original Message -----
> From: "David Robbins K1TTT" <k1ttt at arrl.net>
> 
> > Anyone know a good source for custom made coax cables... I hate
> > soldering pl-259's and expect to need a dozen or more cables made for
> > various upgrades planned for this summer.  I would want a place that
> > would use good rg-213, measure it accurately to my lengths, use
> > silver/Teflon pl-259's and solder them well in all 4 holes.
> >
> 
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