Looks like the guesses have stopped, so here is what I know
about the problems.
Frame A/A2 is KOPB NTSC channel 10 with interference. Channel 10
is 192-198 MHz, so the 1st harmonic of 96-99 MHz lands here.
Thus I suspected that the interference was from FM radio.
But! Multiple FM traps, both 95-108 and 88-108 MHz, failed to
remove it. I even put a couple directly at the tuner input with
male-to-male F adapters in case it was leaking through the RG6
quad shield. Still no luck. Could the FM be *that* strong?
Seems unlikely. Could it be a different frequency? 2nd harmonic
of 64-66 Mhz ? 3rd of 48-49.5 MHz ? Something other than
harmonic distortion? It turns out that the fix was adding
ferrite sleeves around the coax just before the tuner input.
Which implies that the problem was getting in via common mode.http://en.wikipedia.org/wiki/Braid-breaker
I don't know how one would detect this problem with ATSC.
The ferrite sleeves cost less than $4 each, might help and
should not hurt anything, so I figure why not just put ferrite
on each tuner as standard procedure?
Frames B, C, and G are from the same recording. KOPB channel 27.
The ATSC/8VSB reception was perfect after FEC. So whatever caused
this was at KOPB, or upstream.
Frames D and F are from KRCW channel 33 with a ATSC/8VSB
reception problem. Signal strength 84% (should be fine)
Signal quality 90% (should be fine). Highly directional
antenna, 700 MHz low pass filter, multiple UVSJ in series
as high pass filter, ferrite. Usually comes in poorly on
two different model tuners. Occasionally comes in perfectly,
which would seem to rule out a problem with multipath.
Frame E is KOIN channel 40. The ATSC/8VSB reception was
perfect after FEC. So whatever caused this was at KOIN,