The non-linearity has nothing to do with bandwidth as much as with peak amplitude delivered from the transmitter. The visual analog transmitter can be made to handle the digital modulation so long as amplitude linearity is maintained. The problem cited with Klystron transmitters is that it is designed to reach peak power by a non-linear pulsed technique: this may be done because peak transmitter power of an analog visual transmitter is carrying only the sync pulses: the video content is well below peak power and must remain linear. For digital transmission, the transmitter must remain perfectly linear to the peak power radiated. This is why some older transmitters cannot be converted because of the earlier kludge to obtain peak sync power on analog video transmission. Terry Harvey > > From: "John Shutt" <shuttj@xxxxxxxxx> > Date: 2004/06/28 Mon PM 01:21:58 EDT > To: <opendtv@xxxxxxxxxxxxx> > Subject: [opendtv] Re: News: No Motive for HDTV Rollouts > > > ----- Original Message ----- > From: "John Willkie" <johnwillkie@xxxxxxxxxx> > > > Funny how all those stations had to upgrade their transmitters to deal > with > > non-linearity that didn't much matter with analog, but would have > prevented > > them from transmitting digital, if all that changed was sending digital > bits > > on an analog carrier. Only transmitters that were less than 5-6 years old > > didn't routinely have to be upgraded. > > As John knows, an NTSC transmitter is designed from the ground up to > transmit two narrow carriers, one at the visual and one at the aural > freqencies. Modern IOTs can be retuned for wideband operation, but older > klystron transmitters, especially those with separate visual and aural > tubes, simply cannot transmit across the entire 6Mhz band linerally. Some > of the later MSDC klystrons may be an exception, if the aural cabinet is > removed or converted to a second wideband amplifier. I have my doubts about > an old RCA rig, though. > > Then you have NTSC antennas that were peaked for the lowest SWR at the > visual and aural frequencies, not necessarily for flat response across the > band that have to be replaced as well, even if DTV were to occupy the same > frequency as NTSC. > > > That, however, should not be used as any support for Bert's "full HDTV > > transmitter" which is just as non-sensical as your response. Is there > such > > a thing as a semi-HDTV transmitter? > > Excuse me for speaking on his behalf, but perhaps Bert was referring to full > "POWER" HDTV transmitter. He has been known on occasion, and rightly so, to > cite low power and low height DTV transmission facilities as being a large > part of ATSC reception woes. > > > > ---------------------------------------------------------------------- > You can UNSUBSCRIBE from the OpenDTV list in two ways: > > - Using the UNSUBSCRIBE command in your user configuration settings at > FreeLists.org > > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word > unsubscribe in the subject line. > > ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.