Amplifiers have more Pout with single tone than with multipl

B

billcalley

Guest
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
 
In article <1123001026.804449.224520@g44g2000cwa.googlegroups.com>,
billcalley wrote:
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?
Click to expand...
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 (don@misty.com)
 
"billcalley" <billcalley@yahoo.com> wrote in message
news:1123001026.804449.224520@g44g2000cwa.googlegroups.com...
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
Click to expand...
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
 
Cool stuff Bob -- that explanation really clarified it for me!

Best Regards,

-Bill
 
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