Ampliphase

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Ampliphase is the brand name of an amplitude modulation system achieved by summing phase modulated carriers. It was originally marketed by RCA for AM broadcast transmitters.

[edit] How it works

The system takes a carrier frequency and splits it into two identical signals.
The signals are first phase shifted 135 degrees from each other (to provide a base power output with zero modulation from the transmitter).
Each signal is then phase modulated by the audio signal, one signal is positively phase modulated while the other is negatively phase modulated.
The two signals are then amplified to a desired power.
Finally, the two signals are summed in the final output filter stage of the transmitter.

The result is that when the signals are closer in phase, the output amplitude is larger and when the signals are more out of phase, the output is low.

The Ampliphase system was not developed by RCA, but by McClatchey Broadcasting (a group owner of AM, FM and TV stations, and also a California publisher of newspapers), first at KFBK (AM), Sacramento, CA (50,000 watts), and KOH (AM), Reno, NV (5,000/1,000 watts). Other McClatchey AM stations (KBEE, Modesto, and KMJ, Fresno, both of CA) employed conventional transmitters.

The Ampliphase design, originally proposed H. Chireix in 1935 and termed "outphasing" by him, was later sold by McClatchey to RCA, which turned it into a mass-produced product, first at the 50,000 watt level, and, later, at the 10,000 and 5,000 watt levels.

Ampliphase transmitters are universally reviled by their owners and operators, and are most often called by the derisive term "Amplifuzz".