Rule of 10’s and 3’s 1 pg. discussion paper
Write a one page paper based on the information and examples given below and other research on the Rule of 10’s and 3’s.
Information:
Rule of 10s and 3s, Example 4
In this example, you have an access point that is providing coverage to a specific area of a warehouse via an external directional antenna. The access point is transmitting at 30 mW. The cable and connector between the access point and the antenna creates –3 dB of signal loss. The antenna provides 20 dBi of signal gain. In this example, you will calculate the IR and EIRP values.
It is not always possible to calculate both sides of the chart by using the rule of 10s and 3s. In some cases, no matter what you do, you cannot calculate the mW value by using 10 or 2. This is one of those cases. You cannot set the mW and dBm values to be equal, but you can still calculate the mW values by using the information provided.
- Instead of creating the template and setting 0 dBm equal to 1 mW, enter the value of the transmitter, in this case 30 mW.
- In the dBm column, just enter unknown.
Even though you will not know the dBm value, you can still perform all of the necessary mathematics.
- The cable and connectors introduce 3 dB of loss, so subtract 3 from the dBm column and divide the mW column by 2. So the output of the IR is 15 mW.
- The 20 dBi gain from the antenna increases the dBm by 20, so add 10 twice to the dBm column, and multiply the mW column by 10 twice. So the output of the EIRP is 1,500 mW. You can see in the graphic that the 20 dB gain by the antenna and the –3 dB of loss from the cable results in a 17 dB gain from the original dBm. Even though you do not know what the original dBm value is, you can see that it is 17 dB greater.
RF Math Summary
Many concepts, formulas, and examples were covered in the RF mathematics section, so we will bring things together and summarize what was covered. It is important to remember that the bottom line is that you are trying to calculate the power at different points in the RF system and the effects caused by gain or loss. If you want to perform the RF math calculations by using the logarithmic formulas, here they are:
If you want to use the rule of 10s and 3s, just remember these four simple tasks and you won’t have a problem:
- 3 dB gain = mW × 2
- 3 dB loss = mW ÷ 2
- 10 dB gain = mW × 10
- 10 dB loss = mW ÷ 10
Table 3.2 provides a quick reference guide comparing the absolute power measurements of milliwatts to the absolute power dBm values.
Table 3.2 dBm and milliwatt conversions
