Which signal consumes the less bandwidth?

时间：04-08 整理：3721RD 点击：

Hello, I wonder which of the two signals consume the less bandwidth:

1. An unmodulated carrier of low phase noise (eg. 130dBc @ 1KHz)

2. A single sideband suppress carrier signal (eg. USB) modulated by a single 1KHz tone.

I am trying to key a transmitter on CW or CDW using the less possible bandwidth. Should I just switch on/off the carrier at low speeds or should I use a balanced modulator to SSB modulate it with a 1KHz tone?

Unmodulated carrier is best.
The modulated signal can not be better (narrower band) than the carrier itself.

Since most of the signal power is at the carrier I was wondering if also most of the signal bandwidth is at the carrier too.

Is there any technical explanation article for your consideration, I cannot find any?

Bandwidth and power are different things. An unmodulated carrier has zero bandwidth.

In theory an SSB suppressed carrier signal modulated with say 1kHz is identical to a carrier - just shifted by 1kHz. In practice the SSB signal cannot be as pure.

Keith

If you switch it on and off, now the signal is modulated (ASK = amplitude shift keying) and the modulation determines the bandwidth.

Usually, you would consider the amplitude and phase noise a modulation of an ideal carrier.

I understand what you are trying to do, but you can not get rid of the carrier phase noise this way. All the side tones have the same phase noise as the carrier, even if you would be able to build an ideal modulator.