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Greater range techniques page 1
Tips for getting much more range
out of your video transmitters.
The following range extending diagrams
work well for most transmission devices.
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1 | More range
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2 | Safety
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GREATER RANGE TECHNIQUES 1
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Figure 1.
Exaggerated example of
line-of-sight transmission.
The receiving antenna
can literally see the
transmitting antenna.
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The best reception is obtained when the signal
from the transmitting antenna travels through an
unobstructed line-of-sight path as shown in Fig. 1.
As shown here, the receiving antenna can "see" the
transmitting antenna.
However, even when the receiving antenna
can "see" the transmitting antenna,
perfect reception will not necessarily result.
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Figure 2.
Example of multi path
reception. The TV signal
travels directly from the
transmitting antenna X
to the receiving antenna
Z. It can also travel from
X to the ground at Y from
where it is reflected to Z.
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In Fig. 2. it is shown how the signal may travel
directly from the transmitting antenna to the receiving
antenna and at the same time the signal can travel
to some other surface and then be reflected back
to the receiving antenna. Therefore, when two
signals from the same station are received at the
receiving antenna via two paths of differing lengths,
"ghostly" pictures with multiple images will result.
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Figure 3.
Example of reflected path
reception. Because of the
obstacle in the direct path
between TV station X and
receiving antenna Z, the
signal travels to reflecting
surface Y which reflects
the signal to Z.
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In many cases, particularly in large cities, the receiving
antenna cannot "see" the transmitting antenna.
Reception in such cases is possible via a
reflected path as shown in Figure 3.
Here it is shown that the signal from the television
station, point X, travels toward the receiving antenna
but encounters an obstacle.
The signal from X also travels to another large obstacle
to the side, point Y, from where it is reflected to the
receiving antenna, point Z.
The receiving antenna is pointed at Y so it can
pick up the reflected signal from X.
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Figure 4.
Reception in a valley may
be poor or Impossible,
particularly if the distance
from the transmitter
to the receiver is great.
It Is possible that the
refracted energy from
point W will reach the
receiving antenna at Z.
If another hill beyond Z
exists and is in line-of-sight
of X, the signal might be
reflected from Y to Z.
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When hills intervene between the transmitting antenna
and the receiving antenna, as shown in Fig. 4, it may
not be possible to receive signals from the transmitting
station. On the other hand, if the signal from X strikes
a hill on the other side of the receiving location,
point Y, and reflects a signal back to point Z,
reception will be possible.
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Figure 5.
Trees absorb TV signals.
If the antenna does not
extend above the trees,
significant absorption
losses can result.
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The waves transmitted by a television
antenna are affected by foliage.
If, as shown in Fig. 5, the signals must travel through
trees, the trees will absorb some of the energy
and cause less of it to be received by the
receiving antenna.
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Figure 6.
Reception of TV stations
in different directions
may require the use
of more than one antenna
or a rotator.
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When the stations to be received are in different
directions, as shown in Fig. 6, it may be necessary
to use separate antennas for receiving from
different directions or a single antenna mounted
on a rotator. When switching from station A
to station B for example, the antenna is rotated
so that it will point towards B and so on.
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