[TowerTalk] Replacing station ground

Wed May 30 15:56:57 EDT 2018

On 5/30/18 12:38 PM, Bob Matthews wrote:
> Hi Bob
> 
> You may want to download the Motorola R56  pdf file online. Also QRZ dot com has a 3 part forum on station grounding hosted by a PE who installs and inspects cell tower sites. Both are a very interesting and informative read.

bear in mind that R56 (and cell towers, and the document from the FAA 
about control tower radio installations) are for commercial 
installations with 24/7 requirements.

They are perfectly happy to overdesign, because failures are expensive. 
Furthermore, for most commercial installations, labor is a bigger cost 
than materials - so whether you buy AWG10, AWG2 or 2/0 copper isn't as 
big a deal.

You may find that it's better to have an inexpensive sacrificial element 
that fails in the event of a big strike, that you can replace at your 
leisure some time after the storm, than to make a bullet proof 
installation suitable for installation at the top of the Empire State 
Building.

> 
> Whenever I pass coax or hardline through box enclosures or panels, I find 1/2” - 1” J-cord connectors work great in keeping out the insects and moisture. Just pick the size that suits your feedline diameter. They are available in standard and Liqui-tite. Home Depot and any electrical supply house usually stock them.
> 
> Usually #4 solid copper wire is adequate for grounding.

In many applications, AWG10 is sufficient.  There are places where 
larger conductors are required by the code, more for mechanical strength.

Do an assessment - is lightning the only hazard, or do you have to worry 
about inadvertent contact with power lines.  In a lot of older suburban 
areas (with overhead utilities) the latter is a significant concern, and 
the kind of overcurrent/duration (potentially for seconds or minutes) 
you get with a distribution line contact is a lot different than the 50 
microsecond, tens of kA you get for lightning.

> 
> Hope this helps you out some.
> 
> Bob Matthews  KT3RR
> Sent from my iPhone
> 
>> On May 30, 2018, at 15:07, Fred Keen via TowerTalk <towertalk at contesting.com> wrote:
>>
>>
>> Hi Bob,
>> I like the MFJ 4603 thru window approach. If your window is not wide or tall enough to get all the connections with it, you might consider making one with plexiglass,
>> see one here: Building the shack - window feed thru panel done!
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>> Building the shack - window feed thru panel done!
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>> Plexiglass window feedthru panel
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>> Be sure to post some pictures of your antenna farm.
>> Fred KC5YN
>>     On Wednesday, May 30, 2018, 1:04:14 PM CDT, Bob Shohet, KQ2M <kq2m at kq2m.com> wrote:
>>
>> I am planning to completely revamp my station placement and station ground and have been thinking about and researching different ways of doing this for several years. I have also studied what was done at many stations at which I have operated, but that only confuses the issue more as each house and terrain is different and every station owner has their own way of doing things.  :-)  I have also spend considerable time reading the Polyphaser material and W8JI and K9YC’s websites.  So I have several questions and would appreciate your help.
>>
>> First, here is what I am planning to do:
>>
>> Install a metal Hoffman box at each tower and then ground the coaxial cables, rotator cables and control cables at the box (the control cables are already grounded to the tower) with a #2 Copper wire grounded connecting to multiple short ground rods (because of the ledge right underneath) and the tower.
>>
>> Then I will run all the cables to a larger metal Hoffman box grounded just outside the shack and a few feet from the utility ground, telco and cable grounds.  Then, in a trench ~ 1’ deep around two sides of the house to form a perimeter ground, I plan to connect a series of 8’ copper clad ground rods culminating with a connection to the Hoffman box outside the shack and to the utility, telco and cable grounds, so that I will have a single-point-ground connected to a perimeter ground in the trench.  I will then fill in the trench when done.
>>
>> Questions:
>>
>> 1) How far away should the trench be from the house foundation?  6”?  A foot?  more?  I know that there should be some separation but do not know how far is best.  I live in Western CT near the NY border where we get a lot of ice and snow and it has gotten down to –20 F; so frost heaves are always an issue.
>>
>> 2) I assume that the best and safest way to connect all the grounds would be to use #2 copper wire running between the Hoffman box and the utility/telco and cable grounds.  Since these ground wires are all connected ABOVE ground, is there any risk to removing the wires and replacing them with a single #2 Copper wire below ground?  If there is risk with removing the utility ground temporarily to do this, then should I simply dig down and then connect #2 copper wire to the same utility ground rod  below ground – thus avoiding the need to remove the utility ground above ground to connect all the grounds?  Is there a problem that could be created by having an oxidized copper clad ground rod of the utility ground with connection above ground and then simply sanding a spot lower on the same rod below ground in the trench and then connecting the Hoffman box to that below ground?
>>
>> 3) I need to get about 6 control cables, 6 rotor cables and 8 coaxial cables into the shack.  How would you suggest that I do so without allowing critters and insects in?
>>
>> I see two potential options:
>>
>> A) There is a small window to the shack about 12” high and 24” wide – if I replaced the window with an aluminum plate (which would be grounded to the single point ground), I will use  standoff coaxial connectors to get the coaxes inside, but I don’t  think that I have enough room to mount everything on the plate, so how do I get the control cables and rotator cables inside without making another hole and allowing the critters in?
>>
>> B) If I don’t replace the window with a panel, then how do I get all the cables inside without allowing critters and insects inside other than making a big hole in the house above the top of foundation and then stuffing it with steel wool and other material?  This would allow cold air and humidity to get into the basement as well and provides a potential way in for all kinds of insects and mice.  Not a desired outcome.
>>
>> 4) Due to the extremely violent wx that I get at my qth I still like the idea of disconnecting everything when not in use.  With this in mind, does it make sense to have another aluminum panel inside the shack mounted on wooden beams near the window (and grounded to the spg with #2 wire) to which I attach all the coaxial, control and rotator cables inside the shack and then simply disconnect them and move them away when not in use?  These outside and inside cables would also be disconnected from all the equipment and outlets and ground inside the shack would be disconnected from the single point ground outside.
>>
>> I would appreciate any thoughts, suggestions or warnings about what I propose.  Thank you for your help!
>>
>> 73
>>
>>
>> Bob KQ2M
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