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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. |
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| 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) |
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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)
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AC SINGLE PHASE or 1ø
- 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)
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Frederick R. Vobbe, W8HDU
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