[mythtv] HDTV Reception (was: DVB Driver for the pcHDTV HD-3000)
Daniel Thor Kristjansson
danielk at mrl.nyu.edu
Wed Feb 2 22:56:00 EST 2005
]This one certainly does well on gain. I honestly haven't a clue what
]impact not having very wide bandwidth has. Are you basically saying
]they aren't very good at omni-directional reception? That's certainly
]true with this one, a few degrees can make a big difference in signal
]quality. Fortunately, everything I care about is within 304 to 307
]degrees from me.
You probably have a log periodic and not a yagi antenna. The log
periodic is an antenna with a bunch of rods fanning out in a horizontal
or vertical plane each rod shorter than the one before it and each set
of rods spaced closer together, coming to a point in the front of the
antenna. This is a broadband antenna (i.e. many channels).
A yagi is the same thing except the rods are evenly spaced and each is
as long as the other. This is a high gain, narrow band antenna. The more
segments (rods) a yagi has the more directional and higher gain it is.
Both types of antenna's usually have a reflector at the back, which is
another rod at an irregular spacing to the others.
For HDTV you usually want a UHF Log Periodic. These are much smaller
than the traditional VHF antennas, i.e. shorter rods, closer spacing.
If just one channel is in a particular direction you may want a Yagi
tuned to that particular station. But be careful, all conducting objects
are antennas and all antennas interact with each other forming one universal
antenna. In practice this means antennas that are tuned to similar
frequencies and have the same polarity (all TV antennas have the
same polarity) they should not go on the same mast, but should be a
spaced a few wavelengths away from each other.
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