Questions about finding dBm values

Mohamed Abdul · Oct 26, 2017

Homework Statement

1. A sinusoidal source with RMS voltage V = 11Volts across a resistor R = 50Ohms, determine the dBm value. Hint: you will first have to determine the power delivered and then check the formula for dBm calculations.

2. A type of coaxial cable has a loss of 12dB/100m at some frequency. Determine the ratio of the input voltage to the output voltage for 100m of this cable.

Homework Equations

dBm = 10logbase10(P/1mW)
dB = 20logbase10(V/Vo)

The Attempt at a Solution

For the first one, I found power to be 2.42. I then put 10logbase10(2.42/1000) into my calculator and got -26.16.

For the second 1 I set 12 = 20logbase(V/Vo), divided both sides by 12, and got .6 = logbase10(V/Vo). I then took 10 to the .6 power and got 3.98.

I'm just wondering if my math is right; getting a negative answer for the first one doesn't seem right to me, and I'm unsure if I did the log properly for the second one.

TSny · Oct 26, 2017

For the first question, you need to check your conversion of mW to W.

Your solution of the second question looks correct to me.

Mohamed Abdul · Oct 26, 2017

TSny said:

For the first question, you need to check your conversion of mW to W.

Your solution of the second question looks correct to me.

Wait do get things into standard units wouldn't I just divide by 1000 since there are 1000 mW in one Watt?

TSny · Oct 26, 2017

Mohamed Abdul said:

Wait do get things into standard units wouldn't I just divide by 1000 since there are 1000 mW in one Watt?

In the formula where you have P/(1 mW), you need to make sure the numerator and denominator are in the same units. So, either you can convert P to mW or you can convert 1 mW to Watts.

If you leave P in Watts, then you need to replace the 1 mW by its equivalence in Watts. 1 mW = ? W.

Mohamed Abdul · Oct 26, 2017

TSny said:

In the formula where you have P/(1 mW), you need to make sure the numerator and denominator are in the same units. So, either you can convert P to mW or you can convert 1 mW to Watts.

If you leave P in Watts, then you need to replace the 1 mW by its equivalence in Watts. 1 mW = ? W.

So I'd be dividing by .001 then, thank you for that.

TSny · Oct 26, 2017

Mohamed Abdul said:

So I'd be dividing by .001 then, thank you for that.

If you mean that you would end up dividing P by .001, yes.

Questions about finding dBm values

Homework Statement

Homework Equations

The Attempt at a Solution

Related to Questions about finding dBm values

1. How do I calculate dBm values?
dBm values can be calculated using the formula dBm = 10log(P/1mW), where P is the power in milliwatts. Alternatively, you can use a power meter to directly measure the power and convert it to dBm using the same formula.

2. What is the significance of dBm values?
dBm values are used to measure power levels in a logarithmic scale, making it easier to compare and analyze signals of varying strengths. It is commonly used in telecommunications and signal processing.

3. Can dBm values be negative?
Yes, dBm values can be negative. This indicates a weaker signal strength compared to 0 dBm, which is equivalent to 1 milliwatt of power.

4. How do I convert dBm values to other units of power?
dBm values can be converted to other units of power, such as watts or milliwatts, using the formula P = 10^(dBm/10). This will give you the power value in the desired unit.

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Questions about finding dBm values

Homework Statement

Homework Equations

The Attempt at a Solution

Related to Questions about finding dBm values

1. How do I calculate dBm values?dBm values can be calculated using the formula dBm = 10log(P/1mW), where P is the power in milliwatts. Alternatively, you can use a power meter to directly measure the power and convert it to dBm using the same formula.

2. What is the significance of dBm values?dBm values are used to measure power levels in a logarithmic scale, making it easier to compare and analyze signals of varying strengths. It is commonly used in telecommunications and signal processing.

3. Can dBm values be negative?Yes, dBm values can be negative. This indicates a weaker signal strength compared to 0 dBm, which is equivalent to 1 milliwatt of power.

4. How do I convert dBm values to other units of power?dBm values can be converted to other units of power, such as watts or milliwatts, using the formula P = 10^(dBm/10). This will give you the power value in the desired unit.

Similar threads

Hot Threads

Recent Insights

1. How do I calculate dBm values?
dBm values can be calculated using the formula dBm = 10log(P/1mW), where P is the power in milliwatts. Alternatively, you can use a power meter to directly measure the power and convert it to dBm using the same formula.

2. What is the significance of dBm values?
dBm values are used to measure power levels in a logarithmic scale, making it easier to compare and analyze signals of varying strengths. It is commonly used in telecommunications and signal processing.

3. Can dBm values be negative?
Yes, dBm values can be negative. This indicates a weaker signal strength compared to 0 dBm, which is equivalent to 1 milliwatt of power.

4. How do I convert dBm values to other units of power?
dBm values can be converted to other units of power, such as watts or milliwatts, using the formula P = 10^(dBm/10). This will give you the power value in the desired unit.