[opendtv] Re: Reception Issues
- From: "John Willkie" <johnwillkie@xxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Wed, 24 Oct 2007 13:41:42 -0700
I have new datapoints on this.
The condition came back today; I haven't been able to acquire a DTV signal
in about 3 hours. In the meantime, I've kept my tuner on.
The problem also affects one analog tv station. That is, KFMB-TV (8). No
other analog signals seem to be affected.
Fortunately, I don't have to open the Broadcasting Yearbook to figure this
one out. KFMB-TV shares channel 8 with a station north of Santa Barbara,
about 180 or so miles distant.
From my viewing location, the transmitter for that channel 8 is almost on
the same azimuth (fewer than 15 degrees) as KFMB-TV.
I can see doubled and wavy sync in the picture from time to time, in both
the horizontal and vertical axes. (Someone else will have to explain what
these conditions mean for Bert.) Other analog stations (local and distant)
come in stronger than normal; this one comes in very badly.
I can at least provisionally conclude that the condition I have described
has nothing to do with modulation or my receiver, but is linked to local
atmospheric conditions and regional ducting.
The condition is temperature-related; I had no trouble until the sun heated
up the troposphere about 10:00 a.m. I think it's safe to assume that the
"cliff-effect" is the cause of the DTV drop outs, as distant NTSC signals
are overpowering the local DTV signals.
There's still the question of channel 55 dtv dropping out, but I've seen the
MediaFlo xmt site on Mount Wilson. Assuming they're on 55 there, this could
account for KFMB-DT dropping out.
It is going to be interesting to see when the condition abates. I'm
guessing it will be about 1.5 hours after sunset, as long as the weather
holds.
If I'm correct, this won't be much of an issue post analog. When I get the
time, I'll try to figure out where the interfering stations can be.
One example: I can tune in LPTV KXLA 44 directly in analog: more than 120
miles away. I can't get reception on channel 18,19 and 40 of DTV stations
about 16 miles away.
So: I think John Shutt hit it on the head.
John Willkie
-----Mensaje original-----
De: John Willkie [mailto:johnwillkie@xxxxxxxxxxxxx]
Enviado el: Wednesday, October 24, 2007 1:03 AM
Para: 'opendtv@xxxxxxxxxxxxx'
Asunto: RE: [opendtv] Re: Reception Issues
John;
That could account for it. However, one of those dtv channels would be an
interesting datapoint, because it is on channel 55.
And, the ducting could be outside the Santa Barbara-to-Ensenada corridor.
My first thought was that it didn't make much sense, but it's entirely
possible for the ducting to have been elsewhere, and have interfered with
all DTV reception here. Or, the predictions could have been wrong.
That could also account for something that I'm still not entirely sure
about, but I think I saw KXLA on Channel 4, which is occupied by KNBC. KXLA
uses some translators to spread out their signal. Perhaps one in the high
desert is on channel 4. Or, maybe some technical glitch put the KXLA signal
(callsign in the upper left of the screen) on the KNBC analog stream.
John
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