Graham Brock, Inc.
Broadcast Technical Consultants
Engineering Formulas
Ohms law
Ohms Law is a mathematical equation that shows the relationship between Voltage,
Current and Resistance in an electrical circuit. It is stated as:
V = I x R
R = V / I
I = V / R
Where:
V = Voltage
I = Current (I stands for INTENSITY)
R = Resistance
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Land Requirements for AM Ground Systems
Use the formula below to determine the approximate amount of land
required for the ground system per standard guyed AM tower. This is for
estimating purposes only and should not be considered "Set in Stone" figures.
The calculation is based on STANDARD installations of up to 3 towers, inline
only with 90° spacing. With multiple tower arrays there are too many
variables involved to be able to use a standard calculation formula.
Please contact our office for more information.
Where:
Frequency (MHz) = Frequency (kHz)/1000
Wavelength = 984/Frequency (MHz)
Acreage = (Wavelength/2)/43560
1 Acre = 43,560 Square Feet
How to install ground Radials around a building
Install a 4" Copper ground strap all the way around the building. Install
8' ground rods at approximately 6' intervals and Silver solder each connection
point. At the point where a ground radial intersects with the 4" strap,
silver solder it at that point and then move to the other side of the building
and silver solder the ground radial to that side of the strap (at a point that
would be straight in line if the building where not there). Continue the
ground radial to the edge of the property or to the calculated end point.
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Land Requirements
Use this formula to determine the approximate amount of land required
for a standard guyed FM tower.
Where:
L = 1.75 (A) + 30 Feet
W = 1.5 (A) + 30 Feet
A = Anchor Distance - The typical anchor distance "A" for a standard guyed tower
is normally assumed at 80% of the tower height.
(Tower height X 0.8 = A)
1 Acre = 43,560 Square Feet
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Ballast Formula
Calculate the amount of ballast needed for a non-penetrating roof mount.
Where:
W = Required ballast per tray (three trays per mount) in pounds
P = Wind load of antenna(s) in pounds
H = Distance from center of antenna to roof surface
W = 0.19 (P) (H) - 135
Total Ballast Needed = W (3)