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[TowerTalk] LMR 600 Water-proof Feed Thrus (+ H20 proof'g) DAVIS RF Resp

Subject: [TowerTalk] LMR 600 Water-proof Feed Thrus (+ H20 proof'g) DAVIS RF Response
From: Stephen Davis <>
Date: Sat, 31 Jul 2010 08:42:12 -0400
List-post: <">>
Hi Guys, 

Some observations:
There was a reference to "Silicone Caulk" for sealing the connector threads.  I 
think he meant Silicone grease.  Silicone 
grease is better for a number of reasons, and  although some folks use Silicone 
caulk on the outside of connectors, and to seal wire connections from coax to 
wire antenna feed points, I recommend against it as there can be adverse 
chemical reactions with copper wire and also silicone caulk will seem to adhere 
to PVC and PE (many LMR's) outer jacket but in very short time the seal will 
break down, letting water in.

Jim, K8RI's suggestion for sealing connectors using various waterproof  (edit:  
and definitely UV resistant)  tape, or adhesive lined heat shrink (Jim refers 
to "flooded" heat shrink, which is often the term but most often "adhesive 
lined" is how it is sold)  is an astute observation.   DAVIS RF has AMP mil 
spec cold fusion tape (no heat needed, no mess or stickiness when applying).

  Bottom line:  no matter what connector you use (even N connectors  internally 
sealed w/ rubber seals, which often works well for moisture resistance 
(moisture resistance and WATER resistant are 2 very different aspects),  for 
true water resistance, and avoiding that system failure in the middle of the 
rare DX contact attempt, or contest, or when it is at the top of the tower, 
seal the connectors with waterproof sealing products. 
Another observation:  One contributor questions what feed thrus are available 
for LMR 600 size cable.   LMR 600 can be terminated with UHF, N's or DIN males  
and suitable female/female feedthru "barrel" adaptors , or flange mount females 
can be obtained for each type connector (without checking, the DIN flange 
mounts might be difficult but if out there, I'd supply them).

  Lastly: using adaptors:  female to female barrels, male to female, right 
angles, between series adaptors (such as N's to UHF's), etc  etc:  Don't fear 
the old addage that adaptors increase your cable losses or cause adverse 
impedance bumps.  If good quality, as we sell, the max. insertion loss will be 
only .200 dB AT THE MAX  MUF for the type connector (UHF MUF is 300 MHz and N's 
(most common) are 6 GHz, and the insertion loss to freqcy is linear, so 
particularly at HF, the insertion loss is miniscule.         

Note:  UHF males for LMR-600 are quite expensive.  Better to use N males and an 
adaptor to UHF male.

I hope this is of some help, 
73,   Steve ,  K1PEK, 

DAVIS RF Co.,  Div. of Orion Wire Co., Inc.

Wire, Cable, RF Connectors and wire aerial parts.   LMR, Heliax, Eupen, etc.

Commercial / Military 

 Custom Cable Design

tel:  978-369-1738     Fax:  978-369-3484

On Jul 31, 2010, at 12:01 AM, wrote:

> On 7/30/2010 3:01 PM, jimlux wrote:
>> K0DAN wrote:
>>> I have a variety of cables coming down the tower, including LMR600-U/F, all
>>> of which go into a NEMA box, then surge suppressors, shield grounding, etc.
>>> The box&  cables have been there 10+ years, and as things break or change, I
>>> have found that it's handy to terminate the cables coming off the tower at
>>> ground level, add gender or other adaptors, run short pigtails into the NEMA
>>> box, then continue the runs to other antennas, the shack, etc.
>>> Yes, there is more need to weatherproof the splices, and there are slight
>>> impedance bumps&  losses with the extra splices/connectors, however:
>>> a) you can get anything to fit your feedthrough's into the box
>>> b) If something fails or needs troubleshooting, it's easy to tap into or
>>> swap lines
> You could use 7-16 DIN or N if you want a more weather resistant connector.
> For that matter, maybe you could mount the protective device so the
> threaded part of the connector sticks out through the hole, and use
> silicone caulk to make it rain tight.
>> Or what about SO-239:SO-239 bulkhead feedthroughs?  They're fairly
>> inexpensive, and you can run whatever kind of coax inside the NEMA box
>> that you want to.  Granted, the connectors on the outside won't be
>> weather proof (since PL-259s aren't designed for it)

> Why not?  You can wrap them with  coax seal, tape,  flooded heatshrink, 
> or a combination. If the flooded heat shrink goes up onto the bulkhead 
> connector it will fill the exposed threads with hot glue, thus making it 
> water proof.
> 73
> Roger (K8RI)


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