If CW carries no data, how does Morse code work?

Morse code is technically the simplest form of Amplitude Modulation (On-Off Keying). The transmitter generates a pure, continuous wave (CW), but the telegraph operator physically connects and disconnects the antenna using a switch (a telegraph key). By chopping the pure wave into long bursts (dashes) and short bursts (dots), the operator forces the presence or absence of the wave to carry the information. Because it requires almost no bandwidth, CW Morse code can punch through massive atmospheric noise.

Why do we test amplifiers with a CW signal?

Because it represents the absolute worst-case thermal scenario. A complex modulated signal (like an audio wave) has peaks and valleys; during the valleys, the amplifier rests and cools down. A CW signal has no valleys; it is a relentless, 100% duty-cycle sine wave. If an engineer injects a high-power CW signal into an amplifier, the transistor will instantly reach its absolute maximum thermal dissipation. If the amplifier survives a 100 Watt CW test without melting, it is guaranteed to survive a 100 Watt modulated signal.

What is the crest factor of a CW signal?

A pure CW sine wave has a Crest Factor (Peak-to-Average Power Ratio) of exactly 3.01 dB. The mathematical peak voltage of the sine wave is 1.414 times higher than the RMS average voltage. When you square that to find power, the peak power is exactly double the average power (a factor of 2 is 3 dB). It is the lowest possible crest factor for an RF wave, making it the most efficient signal to amplify.

System Design

CW (Continuous Wave)

An RF engineer finishes building a 500-Watt power amplifier for a new radar system. Before they connect the complex, pulsed radar signals, they must characterize the amplifier's raw physical limits. They connect a signal generator and set it to output a pure Continuous Wave (CW) tone. Unlike a real-world signal that fluctuates wildly in power, the CW signal is a flawless, unyielding sine wave. The engineer slowly increases the power of the CW tone. Because the wave never stops or dips, the transistor receives no thermal resting periods. The heat sink rapidly climbs in temperature. By pushing the amplifier until the output power stops rising (the P1dB compression point) using a CW signal, the engineer maps the absolute baseline thermal and electrical limits of the transistor, knowing that any modulated signal will be easier for the transistor to handle than the relentless heat of a pure continuous wave.

Category: System Design

Bandwidth: Zero (Theoretically a single spike on a spectrum analyzer)

Primary Use: Amplifier thermal testing, baseline characterization

Signal Power Comparisons

Signal Type	Peak-to-Average Power Ratio (PAPR)	Duty Cycle	Thermal Load on Amplifier
Pulsed Radar	Very High (Short bursts)	Low (e.g., 5%)	Low (Cooling off 95% of the time)
5G OFDM	High (~10 dB)	100% (Continuous data)	Moderate (Varying amplitudes)
CW (Continuous Wave)	Low (3.01 dB)	100% (Relentless sine wave)	Absolute Maximum (Worst Case)

CW Power Math:
For a pure sine wave, the relationship between peak voltage and RMS voltage is:
V_rms = V_peak / √2
Because power is proportional to voltage squared (P = V² / R):
P_average = P_peak / 2
This means the absolute peak power of a CW wave is exactly twice its average power. A factor of 2 in linear power equates to exactly 3.01 dB. Therefore, the Crest Factor of a perfect CW wave is 3.01 dB.

Bandwidth of CW:
A theoretically perfect sine wave that exists for all time has absolutely zero bandwidth. It appears as a single, infinitely thin vertical line on a spectrum analyzer. The moment you turn the wave on or off (like sending Morse code), you introduce transient frequencies, and the bandwidth mathematically expands.

Common Questions

Frequently Asked Questions

Can two CW signals be used to test an amplifier?

Yes. That is called a 'Two-Tone Test'. An engineer will inject two pure CW signals that are very close in frequency (e.g., 1000 MHz and 1001 MHz) into the amplifier simultaneously. When the two waves mix inside the non-linear amplifier, they create false, ghost signals at 999 MHz and 1002 MHz. Measuring the strength of these ghost signals against the pure CW tones is how engineers calculate the amplifier's Third-Order Intermodulation (IMD3) distortion.

Why do Ham radio operators still use CW?

Because it is the most robust communication method available. A modern voice signal requires about 3,000 Hz of bandwidth. A CW Morse code signal requires less than 100 Hz of bandwidth. Because all the transmitter's power is concentrated into a razor-thin sliver of spectrum rather than spread out, the Signal-to-Noise Ratio (SNR) is massively higher. A 5-Watt CW signal can bounce off the ionosphere and reach across the globe, while a 5-Watt voice signal would drown in atmospheric static.

Is CW the same as a Carrier Wave?

Essentially, yes. A 'carrier' is just a pure CW sine wave generated by a local oscillator. It sits waiting to be modified. When the baseband processor alters the amplitude or phase of that carrier wave to embed data, it is no longer a 'Continuous Wave'; it is now a 'Modulated Carrier.'

Related Terms

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System Design

Amplifier Thermal Load Calculator

Input your amplifier's DC supply voltage, quiescent current, and CW output power. Instantly calculate the massive thermal dissipation (in Watts) the transistor's heat sink must survive during a continuous wave saturation test.

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