Mark Schoonover wrote:
2008/4/28 <[EMAIL PROTECTED]>:
On Mon, Apr 28, 2008 at 11:56:26AM -0700, Ralph Shumaker spake thusly:
> band bouncing off the upper atmosphere? And why would small planes
> interfere? Is it their radio equipment? Or are they just "blocking"
> the signal?
They wouldn't. How close are these planes that you are seeing? If you live
in La Mesa and look outside when you notice interference and happen to see
a plane in the air it is because there are always planes in the air over
La Mesa. Small planes carry VHF radios and each plane spends very little
time transmitting. As a pilot I can't conceive of how they would affect
your TV reception.
--
Tracy Reed http://www.ultraviolet.org
Multipath reflections. Over the air TV signals have a pretty short
wavelength in comparison to a passenger jet, or even a small airplane.
You have this metal clad tube flying through the air, probably at a
low altitude. Most over the air TV broadcasting comes from Mt Soledad,
so what happens is the TV signal goes straight to your outdoor/indoor
TV antenna, and another signal bounces off the aircraft, also arriving
at your antenna. Once that happens, there's enough of a delay in the
signal from the aircraft that it interferes with the signal arriving
directly at your antenna. When this happens, the signals add/subtract
from each other, causing multiple images to appear, or parts of the
signal actually getting canceled out and getting snow for part of the
video.
I was thinking something similar, sort of, but different. An antenna
works similar to a tuning fork. If the right frequency is present, it
will start vibrating at that frequency, and retransmitting that frequency.
I remember listening to one radio station (FM 107.9 - a weak signal from
San Clemente), but every once in a while, it would cut out and go
completely blank (frequently at a stop light). After a while, I noticed
that every time this occurred, someone near me was listening to KSON (FM
97.3). And when they would get about 20 to 30 feet away from me, my
station came back. In fact, one time, there were several red lights in
a row. At one, I stayed put after it turned green. True to form, it
happened again. I raced to the next light. As I passed the car tuned
to KSON, my station cut out. I passed them and it came back. At the
next red, it cut out again when they got within range. No other radio
stations being listened to nearby ever had this effect. Even when I was
listening at home, on the stereo in my house, when a car would roll by,
listening to KSON, my signal would cut out.
But your explanation makes more sense. Especially since I see (usually)
only slight pixelation distortions/drops in my digital picture/sound.
Sometimes, it's significant.
Kinda like the way radio reception sometimes can be affected depending
upon where people are near the stereo.
It's also possible to get very long distance TV stations during this
time of year due to tropospheric ducting. Think of layers of clouds in
the atmosphere, they form a kind of 'electronic tube', that acts like
duct in your home. When it's the correct diameter, it'll pass radio
signals through it for very long distances. Some amateurs park near
the glider port close to UCSD listening for VHF beacons from Hawaii...
My mom told me about one time she was talking on her CB radio with some
guy who turned out to be in Texas. She was in Missouri. His signal was
so strong that it sounded like he was right in front of her. But after
about 2 minutes, he was gone. CB transmissions, normally, are only good
for a few miles.
--
[email protected]
http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
