Amplifiers have more Pout with single tone than with multiple tones?

Question

Hi All, Will an RF amplifier put out more power with a single tone than with multiple tones? For instance, if a (wideband) amplifier is able to have a Pout of +10dBm with a single CW (or modulated) input signal, will this amplifier's output power go down (per tone) if more tones are placed at its input (assuming all tones have the exact same amplitudes but slightly different frequencies). In other words, will the +10dBm output power of the single tone stay at the same level even if we insert 100 more tones into this amplifier at the same time but at different frequencies?

Thanks!

-Bill

billcalley · Accepted Answer

Cool stuff Bob -- that explanation really clarified it for me!Best Regards,-Bill

billcalley · Answer

Thanks for the info Don!-Bill

Don Klipstein · Answer

If you add sinewaves of different frequencies and worst-case or randomly-varying (and at times worst-case) phase relationship to cause peaks to coincide, then peak voltage = RMS voltage times 1.414 times SQR(number of tones).

Some situations get better. For example, a squarewave where the peak voltage is less than the peak voltage of the fundamental alone.

- Don Klipstein ( snipped-for-privacy@misty.com)

Bob Eldred · Answer

By adding tones, you are spreading the amplifiers bandwidth. Putting the power into a wider bandwidth decreases the power on any one frequency making up the band. So, a single CW frequency will have the greatest power, multiple frequencies will share the power. A CW transmission will have a greater range than a modulated transmission for this reason. The same phenomenom occurs in audio. Which is louder and can be heard farther? Ten watts of wide band music or 10 watts of a 1000hz narrow tone like a siren? In your example above, adding 100 tones would require each tone to be -10dBm to maintain +10dBm total. Or, the amplifier would have to deliver +30 dBm to keep each tone at the same amplitude of +10dBm. Bob

Amplifiers have more Pout with single tone than with multiple tones?

Join the Discussion

Didn't find your answer?