Formulas that are common in building
Author: Frederick R. Vobbe, W8HDU
August 10, 2008
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The following are some formulas that are handy for antenna work.

This is a main beam power density estimation program intended for use as part of a routine evaluation of RF safety compliance with FCC regulations. Amateur Radio operators licensed by the Federal Communications Commission of the United States of America are required to do a "routine evaluation" of the strength of the RF fields around their stations, subject to certain exemptions. These rules can be found in the FCC's ET Docket No. 93-62. A calculator can be found on the N5XU web site. Power Density Formula
A typical RF field or power density measurement device is composed of a probe, leads and metering instrumentation. The probe is used to detect the field. It can either be a conventional antenna or another type of sensor. The performance and the application of the measuring instrument as a whole depend to a large extent on the design and characteristics of the probe. See the FCC's paper on Measurements of Environmental Fields at Amateur Radio Stations. (PDF) Mean Quared Electric Field Strength formula

SIMPLE FORMULAS

Abbreviations

  • E =VOLTS or (V = VOLTS)
  • P =WATTS or (W = WATTS)
  • R = OHMS or (R = RESISTANCE)
  • I =AMPERES or (A = AMPERES)
  • HP = HORSEPOWER
  • PF = POWER FACTOR
  • kW = KILOWATTS
  • kWh = KILOWATT HOUR
  • VA = VOLT-AMPERES
  • kVA = KILOVOLT-AMPERES
  • C = CAPACITANCE
  • EFF = EFFICIENCY (expressed as a decimal)

    DIRECT CURRENT

  • AMPERAGE .......... I = P E
  • WATTS ............... P = E x I
  • VOLTS ................ E = P I
  • HORSEPOWER .. (V x A x EFF) 746
  • EFFICIENCY ...... (746 x HP) (V x A)
    AC SINGLE PHASE or 1

  • AMPERAGE ............ I = P (E x PF)
  • WATTS .................... P = E x I x PF
  • VOLTAGE ............... E = P I
  • VOLT-AMPS ........... VA = E x I
  • HORSEPOWER ....... (V x A x EFF x PF) 746
  • POWER FACTOR ... INPUT WATTS (V x A)
  • EFFICIENCY ......... (746 x HP) (V x A x PF)

Resistance in series..... Resistance in Series
Resistances in parallel..... Resistance in Parallel
Capacitance in series..... Capacitance in series
Capacitance in parallel..... Capacitance in parallel
    Sinusoidal Voltages and Currents

  • Effective value or RMS =
    0.707 x peak value
    RMS is Root-Mean Square
  • Half Cycle Average value =
    0.637 x peak value
  • Peak value =
    1.414 x effective value
  • Effective value =
    1.11 x average value
inusoidal Voltages and Currents
Resonant Frequency Formulas

* = Where in the second formula
f is in kHz,
and L and C are in microunits.

Resonant Frequency Formulas

Frederick R. Vobbe, W8HDU


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