[TowerTalk] Solid 160 radial plates?
patrick_g at windstream.net
Tue Aug 28 13:42:56 EDT 2018
Regarding your recommendation to use MAPP gas. Does the new stuff get
hot enough? I understand there has been a downgrading of heat
production with the "new" MAPP gas.
On 8/28/2018 11:41 AM, Jeff DePolo wrote:
> Regarding using ground bus bars as tie points:
>> You could probably shove a bunch
>> of wires in one hole and crank down on the screw, but I'd feel better
>> with soldering them.
> If you can still find them, copper ground bus bars with screw terminals
> would be ideal as you could then braze the wires to the bar. You could fit
> several small (12 AWG or smaller) wires under one screw, and then braze them
> collectively to the bus bar. Avoid soft solder for anything buried, braze
> it with silfos. And of course, never bury uncoated aluminum..
> In broadcast, we typically start with a copper mesh mat encircling the tower
> foundation. Around the "inside" perimeter is copper strap (typically 3" or
> 4"), and again around the "outside" perimeter. The radials are wrapped
> around, and brazed to, the outside perimeter strap. The mesh we use is a
> grid with around 6" spacing. 15% silfos and a mapp gas torch will get the
> job done with a little patience (and no wind), but OE makes the work go even
> faster. The dimension of the mesh-covered area is selected based on a
> combination of factors including base Z, frequency, and cost, but typically
> is somewhere around 20 to 50 feet on each side if square, or a comparable
> radius if trimmed to have a round or octagon footprint.
> You can find somewhat cheaper copper mesh with larger grid spacing. Copper
> "pool mesh" used for equipotential bonding under/around swimming pools is
> pretty easy to find, Google it. However, the grid spacing is usually around
> a foot. I haven't modeled it to see how much less efficient a 12" grid is
> compared to a 3" grid, but I'm guessing it's not going to be appreciably
> The purpose of the close-in ground screen is not necessarily to improve
> efficiency, but to minimize the effects of changing ground conductivity as a
> function of moisture/weather which, particularly in the case of directional
> arrays, can be problematic. For ham purposes, simply encircling the base of
> the tower with copper strap (folded and brazed at the corners) and attaching
> radials to it would be what I would do. But if you're really gung-ho, mesh
> is what the pros typically use, although I've seen plenty of AM's with only
> copper strap around the tower base with 120 radials attached directly to it.
> Personally, I would avoid any kind of mechanical connection from a radials
> to a "grounding plate". I'd use copper everywhere and braze it. The cost
> of all of that stainless hardware, lugs, etc. would be more expensive than
> simply brazing. It also takes less time to install. And, a properly brazed
> joint will outlive any of us on this list.
> --- Jeff WN3A
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