Power Attenuator Calculator
The calculator enables you to design your own 50 ohm "power attenuator" built with good available resistors of a modest power. So you don't have to use "unavailable" high power resistors. Just use induction free resistors. Don't use wire wound resistors. The Calculator will calculate the resistors effortlessly and with a very good accuracy.
The calculator computes the number of resistors and the values of the resistors, which are based on the E12-series values. Due to the good availability and your own choice of the maximum power of the resistors (e.g. 1/2 watt), you can get exactly what you want. The use of this unique Power Attenuator Calculator eliminates the need for high power resistors, to build a power attenuator.
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Use of the Calculator
Please familiarize yourself with the calculator and type in the data for a
Power Attenuator of 10 dB for an input power of 1.6 W and resistors of 1/4 W.
Type in: 1,6 and 0,25 for 1/4 watt OR 1.6 and 0.25 for 1/4 watt
Type the data in a white input fields. Give [Enter] or [TAB] to enter the value.
Tip: Use [TAB] to move between the 3 white input fields.
The calculator will calculate the number of resistors and their values.
Since the compound resistor R1 has to dissipate 0.83 W, and each resistor can dissipate 1/4 W, at least 0.83/0.25= 3 resistors in parallel are needed.
The compound resistor R1 is formed by 3 resistors of 330 ohm and one resistor of 820 ohms, all in parallel.
Most of the power is dissipated in the 3 resistors of 330 ohm. The resistor of 820 ohm is added to arrive accurately on the wanted value of 96.25 ohms for R1.The 2 resistor of 150 ohms dissipate most of the power in R2. The resistor of 1500 ohms is added to arrive accurately on the wanted value of 71.15 ohms for R2.
R3 has the same value as R1, but dissipates far less power. R3 is formed by 100 ohms and 2700 ohms in parallel.
For an attenuator of the resistors R1 and R3 both have an ohmic value of 96.25 ohms.
R2 is 71.15 ohms.
R1, R2 and R3 dissipate 52%, 33% and 5% of the input power.
The Calculator has no limitations on the input power nor the maximum power of the resistors.
* The Calculator will even work with an input power of more than 5 watts or with resistors of 0.25W or 0.1W.
Play with the values, see what happens, with each new choice.
Just try for fun: PIN = 100 watts to find out that it takes 103 resistors of 1 watt to make an attenuator of 10 dB for an input power of 100 watts. hi
* Don't care about the number of resistors needed. 5 Resistors of 1/2 W will take about the same space as 3 resistors of 1 W. With three or more resistors in parallel, just twist the leads of the resistors together.
Finally you can get less power then 5 watts from your 5 watts QRP set.
With the Power Attenuator Calculator, you can design an attenuator for any input power.
Or go to my web site: Home - PA1B QRPp page