[TowerTalk] NEMA Box for poly phaser and Coax connections

Jim Brown jim at audiosystemsgroup.com
Sun Dec 31 16:59:19 EST 2017

On 12/31/2017 11:40 AM, CEPitts wrote:
> I know bigger is always bigger than smaller due to possibly having to 
> add items *(Box size)* 

KF7P sells a lot of antenna system accessories, including "Hoffman" 
boxes with multiple arrestors inside. Chris sells good stuff -- he 
exhibits at Pacificon and Visalia. Hoffman boxes are hinged 
non-conductive weatherproof enclosures with a weatherproof strip at the 
hinged door.

Taking that idea but implementing it differently, W6GJB and I built an 
entry box with 8 arrestors mounted to the conductive backplate. It's a 
big box, nearly the biggest I could find, roughly 20 x 16 x 8 inches. 
The arrestors are mounted so that connectors are vertical. We cut holes 
directly beneath each arrestor for cables to enter from antennas and 
another for the #4 stranded Cu going to the ground system. There are two 
4-in PVC conduit stubs cut into the backplate that to through the wall 
into the shack. I paid about $220 for the enclosure at a local 
electrical supply. I might have saved $10 buying on line (I had already 
checked), but I prefer to support a local vendor who goes to the trouble 
of stocking stuff like this. Not only did the counterman know exactly 
what I was looking for, he knew exactly where to look and found three 
pieces in stock!

I added conventional compression-type strain reliefs in the holes, 
making the opening large enough to pass a coax connector. To increase 
the o.d. of the cables, I added several layers of heat shrink to the 
coax where it enters the box, so that the strain reliefs nearly close 
the opening when tightened.

I chose the Array Solutions AS-302U arrestors, both because I liked the 
circuit and because the GDT is user replaceable. I'm still using a bunch 
of Polyphasers on a big Cu entry panel cut into the wall for some 
antennas, but I've gotten very tired of having to replace the entire 
arrestor when a lightning hit (or antenna fault) fries the GDT.  Not 
only is it expensive, but it's a 2-man job to replace the arrestor 
because of where it's mounted. Now, as they fry, the antennas will be 
shifted to the new box. All my wire antennas have already been moved to 
the new box. It's been my experience that these are the only ones that 
fry -- my towers are distant from the shack, so most lightning energy 
discharges at the tower.

Note that I am NOT encouraging the use of lightning arrestors at your 
tower -- I'm only talking mechanics here -- and I strongly recommend 
that you look at the 4O3A 8x2 switch. It's RF performance is FAR 
superior, and it's quite well built.

73, Jim K9YC

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