Trent,
It sounds like you have a good handle on things. Since your primary
concern is from external sources (lightning, noise) I would bond to the
outside of the enclosure, taking advantage of skin effect to keep those
external currents "outside the box."
There is, of course, the need for ventilation to allow heat dissipation,
with the conflicting concern for rain/snow/moisture intrusion. A tricky
design problem. :)
I'm guessing you'll be using solar power. This may seem
counterintuitive, but I would try to put all electronics for that system
inside the box, which shields it from antennas. And all power wiring
outside the box should be twisted pair, to minimize radiation of
switching transients produced by the charge regulator. Try to choose a
low noise charge regulator. Genasun makes a line of MPPT charge
regulators that is very quiet, but, so far, they only make them for
small systems. Their largest one is rated for 8A for batteries up to
48V. I'm using one rated for 10A to a 14V LiFePO4 battery.
73, Jim K9YC
On Sun,8/28/2016 5:33 AM, trentkd5ia@aol.com wrote:
Jim,
Thank you for your comments. The plan is to bond all shields and
bypass all the conductors coming into the enclosure, but should they
be bonded to the outside wall or can they be bonded to the inside
wall? The valve box is made of heavy corrugated steel, and it will be
easier to have the connections inside the enclosure rather than
outside, under the ground. Or will it be sufficient to bond and
bypass the coax and other cables at the tower base, twelve feet from
the enclosure?
I didn't exactly plan to have a Faraday cage--this big valve box just
seemed to be the most convenient and inexpensive way to keep my
equipment safe and secure out on the prairie.
73 de Trent K5XM
-----Original Message-----
From: Jim Brown <jim@audiosystemsgroup.com>
To: towertalk <towertalk@contesting.com>
Sent: Sun, Aug 28, 2016 7:25 am
Subject: Re: [TowerTalk] Station grounding in a steel enclosure?
Trent,
Your first problem is that your box is NOT a shield if cables come
through openings in the box without their shield being bonded to the box
at the point where they enter. You must also bond or bypass (with
feedthrough caps) all other leads coming into the enclosure, like power,
control lines, audio lines, keying lines, etc. Any one of these lines
that does not have its shield bonded to the enclosure or come through
the enclosure via a feedthrough capacitor destroys the shielding.
As to where to put the Polyphasers -- I would use the "feed through"
type and bond them to the enclosure.
The larger question is why you need a Faraday cage in the first place.
Few stations do. What most stations need is proper BONDING, proper
grounding, proper power, and proper interconnections between equipment.
Study http://k9yc.com/GroundingAndAudio.pdf
73, Jim K9YC
For On Sat,8/27/2016 10:28 PM, trentkd5ia--- via TowerTalk wrote:
> My remote station is approaching completion. A 70' tower, wireless
internet, solar power and RemoteRig with a TS480 is all operational.
Still in progress are the antennas to be mounted, and lightning
protection. I have a question about grounding. The electronics are
housed in a valve box--a galvanized steel cylinder 5 feet in diameter
and 4 feet tall, with 3 1/2 feet of that in the ground. A removable
steel lid covers it. All cables are in PVC pipe and enter the housing
under ground level, and the valve box is 12 feet from the base of the
tower.
>
> The grounding system will consist of 9 ground rods, 3 connected to
each leg of the tower and extending out from the tower. The valve box
will also be connected to the grounding system. Polyphasers will
protect against surges.
>
> My question is, can I install the surge protectors inside the steel
housing, or should they be mounted outside the valve box? I'm thinking
that the steel cylinder possibly acts as a Faraday cage, and the
grounding connection and surge protection should be attached on the
outside wall of the housing. Any comments or suggestions, please?
>
> Thanks!
>
> Trent K5XM on the windy and lightning prone West Texas plains
>
> _______________________________________________
>
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