Ampliphase

• The system takes a carrier signal 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 lower. A complication is the necessity for a "drive regulator", which implementation is quite simple at 10 kW or lower levels, but is more complicated at higher levels. "Drive regulation" is most effective when the instantaneous power output approaches zero. == Development ==

The Ampliphase system was not developed by RCA, but by McClatchy Broadcasting (a former group owner of AM, FM and TV stations, also a California publisher of newspapers, not to be confused with the present-day McClatchey Broadcasting LLC). The first Ampliphase transmitter was KFBK in Sacramento, CA (50,000 watts full-time). Later known installations were KOH in Reno, NV (5,000 watts days/1,000 watts nights). Other McClatchy AM stations like (KBEE, Modesto, and KMJ, Fresno, both of CA) employed conventional transmitters. Unlike most other commercial designs of AM broadcast transmitters Ampliphase units do not require expensive or large modulation transformers nor modulation reactors, thereby saving on the initial up-front cost. The down-side is the Ampliphase units require more maintenance. The Ampliphase concept trades a lower "Capital" cost for a higher "Expense" cost. Ampliphase achieved a modest improvement in transmitter overall efficiency before other amplification and modulation schemes could replace it. == Obsolescence ==

KFBK in California still maintains an RCA BTA-50H (the "last gasp" of the Ampliphase concept) as an auxiliary transmitter. However, KFBK's main transmitter is a solid-state Harris unit, the prototype for which was later named the DX-50. KOH has long since scrapped its home-built "outphasing" transmitter for conventional units. In the post-WWII era very few transmitters of this type were made, except for special purpose orders that kept the transmitter design nominally commercially viable into the 1970s. With the oil crises of the 1970s and 1980s Pulse Duration and Pulse Step Modulation schemes for AM transmitters took hold at power levels at or beyond 50 kw. Currently, the only manufacturer of AM transmitters that uses phase modulation to achieve AM is SRK Electronics. However, their design is implemented entirely in the digital domain, so avoiding the maintenance issues of the analogue Ampliphase transmitters. ==References==