[BC] Big copper theft in IA

[Robert Meuser]

Richard

This has been hashed here before. I do not have the link handy but a 
search of the archives will have it if you are interested. One of the 
major papers regarding an transmission in the 30s contained a formula to 
calculate the necessary depth of a radial before it produces any 
significant losses in the system. I ran those numbers and that depth 
which is proportional to both frequency and ground conductivity is 
between 8 and 15 feet. Interestingly part of the calculation makes depth 
an inverse value compared to ground conductivity. That is what was known 
almost 80 years ago.

  Shallow ground systems are cheaper to install if frequent replacement 
is not taken into account. You need a Cat equipped with a plow shear 
designed for laying under ground cable. An offset is that the copper can 
be bought in 25000 or 50000 foot put ups which is less expensive than 
individual smaller reels and is very difficult to steal due to the 
weight but only a properly equipped Cat can take advantage of it.

My personal unscientific experience shows no losses (based on proofs) 
but along with other approaches to array design it helps to produce 
incredibly stable directional arrays. In one project we actually had to 
reduce power because the station was producing too much signal. So that 
is both the theory and practice involved.

On 2/10/12 5:00 PM, RichardBJohnson at comcast.net wrote:
> I don't think you should have 3 feet of lossy dielectric in the capacitor formed by the tower and its ground system. The most expensive power, modulated transmitter power, is simply used to heat the earth over the ground system. The "ground system" is not used to connect anything to the earth. It is used as something to feed the antenna radiator against, i.e., a counterpoise. Minimum losses, i.e., no earth covering at all, would maximize the RF field at a distance. A compromise has been used by broadcasters since the art began in which the radials were buried just deep enough to prevent damage and a ground-screen was layed on the top of the ground near the tower.
>