pic: Al Kills Analog

[Al Skierkiewicz]

NTSC analog transmission is still the standard in many other countries so some are being sold to brokers for those markets. Since the FCC had originally proposed that the move to digital was to take place in 1996, many stations had been limping along on their old transmitters waiting for the move so those are being scrapped. Low power UHF channels (local special interest stations) are not required to move/vacate for another four years. Some linear/ultra linear transmitter amplifiers (like ours) are able to transmit digital with relatively few modifications. Some digital stations are returning to their analog frequency now that the move is complete using those transmitters. Current technology allows transmitters to have a low power "exciter" that generates the analog or digital signal which feeds a high powered amplifier. In our analog transmitter, a 10 watt exciter fed into a series of 100 watt intermediate power amps (IPAs) that in turn fed into a series of 2kW amplifier modules. The modules are then summed together into an 18kW output. This transmitter is even capable of summing two amplifiers together for a total of 36 kW. Since digital transmission requires an ultra linear transmitter, automatic distortion/precorrection circuitry takes a sample of the output signal, filters out the distortion and then adds that distortion signal of the opposite phase at the exciter to null out the non linearity. I know, you are saying "It's digital! Why a linear amplifier?". Digital transmission is still an analog signal, modulated and filtered, with an encoded serial digital signal.

[Richard Wallace]

Originally Posted by Al Skierkiewicz

/.... I know, you are saying "It's digital! Why a linear amplifier?". Digital transmission is still an analog signal, modulated and filtered, with an encoded serial digital signal.

Thanks for reminding us of this simple, important fact, Al. Analog has not really been killed or scrapped. The systems we nickname 'digital' only look like streams of ones and zeroes when viewed at signal processing time scales. At smaller time scales, which are always of interest when we consider the economics of distributing those signals, they are really analog.

Of course, when a lossless, zero-delay, zero-cost power switching device is invented, linear (analog) power circuits will be obsolete. We are not there yet.