[NLRS] A few odd cents about ATSC/HDTV

[John Kalenowsky]

One of the 'challenges' I'd heard regarding ATSC modulation format was the
need for the RF amplifiers to be extremely linear; one important factor in
linearity being bandwidth as a percentage of the carrier frequency. 5.5 MHz
on RF Channel 2 being TEN percent, while on the order of 2-3 % at High VHF
and on the order of 1 % at what remains of the UHF Band (470-698 MHz).

Similarly multi-path effects vary across frequency and, as I understand,
there is also a percentage impact there.

This seems to be reflected in the preference for UHF 'real' channels by the
TV broadcasters (even though they continue to 'advertise' their legacy
channel numbers). Even the Hi-VHFchannels (174-216 MHz) seem to be less
desired; Chicago Channel 7 went to 'real' channel 52 in the interim, to go
back to 'real' channel 7 but has since moved to 'real' channel 44. The Low
VHF Channels are seeming to be mostly abandoned by the major digital
broadcasters, though I was disappointed to find that a Low Power Digital TV
station has set up on 'real' channel 4 (66-72 MHz) here around
Chicago...substantially limiting any hope that I might have of monitoring
the 70 MHz band for signals from Europe

I also thought I'd read (but can't find anything now), that a narrow
bandwidth interfering carrier within the spectrum of an ATSC signal could
significantly compromise the ability to decode the signal, without even
having to be well placed in frequency. Maybe Phil can comment on that?

73, JK