pic: Al Kills Analog

[Al Skierkiewicz]

Kelli,
I don't really consider myself lucky but I do feel somewhat privileged. I was there when stations were still broadcasting some of their programming in B/W. I was part of the development of stereo for TV in the US and now I have lived to see analog die and digital start.
John,
I started with a PBS station in Peoria, IL that broadcast for 1.5 hours in the morning (Sesame Street and Electric Company) and then turned back on at 4-10PM. This station was off for at least 6 hours each week night and 7-8 hours on the weekend nights when I started. As cable started being the delivery of choice, broadcasters had to maintain 24 hr ops to keep their channel ID on the cable systems. Otherwise, cable operators would put in other programming (infomercials) when we went off the air or would move us to a different channel than our over the air assignment.

What a lot of people don't realize, is that digital TV is possible/affordable because computer memory is cheap and fast so that MPEG files can be processed and decoded in your receiver.

[ebarker]

Oh I don't know about all that newfangled FET 70's stuff. Next thing you know they are gonna want us to do digital and robots or something........

I like what I grew up with, the RCA BTA-5 series for AM broadcast service.

Here is a variant for maritime service - back in the day when we had to 'peak the grids' and 'dip the plates'

RCA Transmitter

[DonRotolo]

Originally Posted by ebarker

back in the day when we had to 'peak the grids' and 'dip the plates'

Grid? Plates?
Oh, you must mean Hollow State components...

[Raym]

So what is going to hapen to all of the analog transmitters?

[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.