Advanced AM Power Inputs
Choose a calculation path. Enter carrier power, voltage, modulation depth, and frequency data for a complete AM transmitter estimate.
Formula used
Total AM power: Pt = Pc × (1 + m² / 2)
Total sideband power: Psb = Pc × m² / 2
Each sideband: Pusb = Plsb = Pc × m² / 4
Efficiency: η = Psb / Pt × 100
Carrier from voltage: Pc = Vrms² / R
Modulation from powers: m = √(2 × (Pt / Pc − 1))
How to use this calculator
- Select the calculation mode that matches your known values.
- Enter carrier power, total power, or carrier voltage as required.
- Add the modulation depth as a ratio or percentage.
- Enter load resistance when voltage based power is needed.
- Use carrier and audio frequencies for sideband frequency checks.
- Press calculate and review the result above the form.
- Download the result as CSV or PDF for later records.
Example data table
| Carrier Power | Modulation Index | Total Power | Total Sidebands | Efficiency |
|---|---|---|---|---|
| 100 W | 0.50 | 112.50 W | 12.50 W | 11.11% |
| 100 W | 0.80 | 132.00 W | 32.00 W | 24.24% |
| 100 W | 1.00 | 150.00 W | 50.00 W | 33.33% |
Understanding AM Signal Power
Amplitude modulation carries information by changing carrier amplitude. The carrier frequency stays constant. The audio signal creates two sidebands. One sideband is above the carrier. The other is below it. A normal double sideband full carrier signal uses three power parts. These parts are carrier power, upper sideband power, and lower sideband power.
Carrier power is the largest fixed part. It does not carry the audio message. Sidebands carry information. When modulation depth rises, sideband power rises. Total transmitter output becomes higher. This is why a transmitter can show higher output when audio drive increases.
Why Modulation Index Matters
The modulation index is shown as m. A value of 0 means no modulation. A value of 1 means 100 percent modulation. The envelope reaches its ideal limit. AM theory gives maximum efficiency near 33.33 percent. This happens at m equals 1. The remaining power stays in the carrier.
Values above 1 are risky. The envelope can cross zero. That condition is called overmodulation. It causes distortion. It also spreads energy into unwanted frequencies. For clean operation, the modulation index should usually stay at or below 1. Some systems use processing to control peaks before they reach that point.
Power in the Sidebands
For an AM signal, both sidebands have equal power. Their total power equals carrier power times m squared divided by two. Each sideband receives half of the sideband total. It reports both values. It reports the percentage of total power held by the carrier and by the sidebands.
These values help during bench tests. They also help during homework. If you know total AM power and carrier power, the calculator can estimate modulation depth. If you know carrier voltage and load resistance, it can first find carrier power. Then it completes the full AM power calculation.
Frequency and Bandwidth Checks
AM sideband frequencies depend on the carrier and audio frequency. The upper sideband appears at carrier plus audio frequency. The lower sideband appears at carrier minus audio frequency. For speech or music, many audio frequencies exist at once. The needed bandwidth is normally twice the highest audio frequency.
The bandwidth estimate is simple. It helps compare a signal with channel spacing. It shows why wide audio creates a wide AM signal. Enter the highest audio frequency. Keep the factor at two for double sideband AM. Change it only for teaching examples.
Practical Use Notes
Use RMS voltage when possible. RMS values connect directly with average power in a resistive load. Peak and peak-to-peak options are included for oscilloscope readings. The calculator converts those values to RMS before finding power. Always confirm that the load is mostly resistive. Reactive loads can change real power.
The results are estimates for ideal sinusoidal modulation. Real transmitters include losses, filters, nonlinear stages, and measurement error. Still, the formulas are excellent for learning, planning, and quick checking. Use the warning message to notice excessive modulation. Save the CSV or PDF result when you need a record.
FAQs
What is AM signal power?
AM signal power is the total average power in a modulated carrier. It includes carrier power and both sidebands. The sidebands carry the message information.
What is the main AM power formula?
The standard formula is total power equals carrier power multiplied by one plus m squared over two. It assumes single tone sinusoidal modulation.
What does modulation index mean?
Modulation index shows how strongly the audio changes carrier amplitude. A value of 1 means 100 percent modulation in ideal AM theory.
Why is overmodulation a problem?
Overmodulation happens when m is greater than 1. The envelope can distort, and unwanted frequency components can appear outside the desired channel.
How much power is in each sideband?
Each sideband has carrier power multiplied by m squared over four. Both sidebands are equal for ideal single tone amplitude modulation.
Can I calculate modulation index from total power?
Yes. Use total AM power and carrier power. The calculator rearranges the formula and finds the modulation index from their ratio.
Why does AM efficiency stay limited?
Full carrier AM keeps much power in the carrier. Since the carrier alone carries no message, ideal efficiency reaches only about 33.33 percent at full modulation.
Which voltage should I enter?
Use RMS carrier voltage when available. If your scope shows peak or peak-to-peak voltage, select the matching voltage type before calculating.
What load resistance should I use?
Use the actual resistive load. Radio systems often use 50 ohms. Audio or lab systems may use a different value.
How is AM bandwidth estimated?
Standard AM bandwidth is twice the highest audio frequency. This gives room for both upper and lower sideband frequency ranges.
Are the results exact for real transmitters?
The results are ideal estimates. Real equipment may include losses, harmonic content, meter error, impedance mismatch, and nonlinear amplifier behavior.