08 Exactly what equipment do I need?
Description
This article is from the TeleVision Receive Only Satellite-TV FAQ, by TVRO Hobbyists drlev@hotmail.com with numerous contributions by others.
08 Exactly what equipment do I need?
There are six basic components to a big dish system: the satellite
dish, the feed assembly, the low-noise block downconverter (LNB), the
positioner/controller, the cable, and the receiver or IRD. The first
component is the satellite dish. The satellite dish is unquestionably
the most visible component of a home satellite system, and can range
from five feet upwards to twelve feet or larger. The "average" size
for a TVRO satellite dish is ten feet, but can be smaller in stronger
signal areas. Most IRDs have a built in controller for moving the
dish. Some receivers require an separate controller, sometimes called
a dish mover, to control the position.
Satellite dishes are also made of a variety of materials. Aluminum
mesh dishes are the most common type, but solid aluminum and
fiberglass dishes are not unusual. Each type has its advantages and
disadvantages. Mesh dishes are usually less expensive than solid
dishes, and easier to transport from the manufacturer and vendor to
the installation site. Solid aluminum and fiberglass dishes generally
have one primary advantage over mesh dishes. Although usually more
expensive, solid dishes are usually better for overall reception
quality, particularly with Ku-Band signals. Whatever type of satellite
dish, a properly peaked antenna with a dish of the appropriate size
should have no problem receiving both C-Band and Ku-Band signals. For
locations subject to extreme weather, such as hurricane-force winds,
extreme heat, or extremely heavy winter snow, Paraclipse made
specially designed satellite dishes (the Classic series) ranging from
12 to 16 feet; these are quite pricey if you can find one, however,
ranging from around $1000 to a whopping $7000 for the 16-footer!
In terms of size, bigger is usually better for a TVRO system.
Satellite signal strengths are almost always stronger in the center of
the signal footprint, where an eight foot dish should have no problem
receiving both C-Band and Ku-Band signals. The farther from the center
of the footprint, the larger the size of the dish needs to be for
quality C-Band reception. A twelve foot or larger dish may be needed
in fringe areas such as Alaska, Maine, south Florida, Hawaii, and
remote areas in Canada. For Ku-Band, size is much less critical and
for Ku- Band only systems, a dish as small as 30 *inches* may
work. However, it is usually not advantageous to have a Ku-Band only
TVRO setup unless it is a fixed installation for reception of a
specialty satellite, such as one with a large amount of international
programming, for example.
The second component is the feed assembly, which is where the real
antenna is located. The feed assembly is used to "funnel" the
satellite signal from the parabolic dish reflector to the antenna
probe, which relays the signal to the LNB antenna for subsequent
frequency conversion and amplification.
The term feedhorn is often used interchangeably with feed assembly;
this is not entirely accurate, as the feedhorn itself is just part of
the overall feed assembly. The scalar ring is used for precision in
focal point adjustment in conjunction with the dish reflector.
Some feed assemblies are designed to mount two or more LNBs. Such
feeds come in two basic types, those that mount one LNB each for each
band, C and Ku, and those that mount one LNB for each polarity,
vertical and horizontal for most satellites aimed at North America, or
right hand and left hand circular for most of those aimed
elsewhere. Hybrid types provide some combination of dual polarity and
dual band.
Multi LNB feeds usually have a separate antenna probe for each
LNB. For dual band, polarity is controlled in the same manner as done
for a standard single LNB feed, usually with a servo motor to
mechanically move the antenna probe to match the desired
polarity. Dual polarity feeds (orthomode) have no moving parts, and
are used primarily in multi receiver installations to provide all
receivers simultaneous access to channels on both polarities,
something impossible with a servo actuated antenna probe. A
disadvantage to using an orthomode feed is that, without the fine
control of the servo motor, signals that deviate from true horizontal
or vertical polarity cannot be optimally received unless the dish is
fixed upon one satellite, and the feed assembly adjusted accordingly.
Another type of feed, called an LNBF, is similar to that used on the
little DBS dishes. An LNBF integrates feed, antenna, and LNB into a
single electronically controlled unit.
The third component is the low-noise block downconverter, or LNB. The
LNB is the component that amplifies the very weak signal reaching the
antenna from the satellite 22,247 miles above the equator, and
converts the downlink frequencies to a lower block of frequencies more
suitable for transmission through the cable to the receiver. The
standard block of frequencies is 950-1450 MHz. Some early block
downconversion systems used a 900-1400 or lower block of frequencies,
and receivers designed specially for those frequencies.
Older systems used separate components for signal amplification
(low-noise amplifier, or LNA) and downconversion (block
downconverter). Really old systems didn't downconvert a frequency
block for transmission to the receiver, instead sending in only one
specific frequency requested by the receiver.
C-Band LNBs are rated in degrees Kelvin; Ku-Band LNBs are measured in
decibels (dB) instead of degrees Kelvin. For C-Band LNBs, up to 30
degrees K is usually suggested, but this is simply to maximize picture
quality. For C-band and a large dish reflector, anything up to 100
degrees is adequate for 99% of the video signals out there, and should
give equal or better results to a sub 30 degree LNB on a smaller
dish. Only for very weak signals is a sub 30 degree LNB important on
C-band. For Ku-Band LNBs, a range up to around 1.5 dB should provide
acceptable picture quality.
Note that these numbers only apply to analog-only reception or larger
dish reflectors; for quality digital reception or smaller dish
reflectors, LNBs rated around 20 degrees K or lower for C-Band and 0.7
dB for Ku-Band should be optimal. Make sure that you do some research
before buying LNBs for your system, especially if you desire good
digital reception; LNB noise ratings alone will not tell you if you
have a good LNB or not. For digital reception, just as important or
maybe more so is the frequency stability of the LNB. In general, the
best bet is to try your LNB(s) and see if the picture quality is
acceptable to you.
The LNB has an F-type coaxial cable connection for the signal to
travel, usually from the feed, underground, and then inside the system
owner's home, to the satellite receiver.
The fourth component is the dish positioning assembly. This is the
physical part that precisely positions the dish when commanded to by
the satellite receiver or dish mover. The most common type of
positioning assembly is the linear actuator, which connects near its
middle to the fixed part of the dish mount, and at its end to the
movable portion of the mount or to the reflector. If the satellite
system is located in roughly the eastern part of North America, the
actuator needs to be aligned with the moving end oriented west; if the
satellite system is located in roughly the western part of North
America, the actuator needs to be aligned with the moving end oriented
east. Refer to your actuator's manual for a visual of these positions
or have someone with installation experience help you (not a bad idea,
anyway!). Because of the geometry of the polar dish mount, a linear
actuator cannot physically move the reflector all the way from one
horizon to the other. So, the other type of positioner is known as the
horizon to horizon mount, usually some form or worm and sector gear
arrangement, which as the name indicates, can track the entire arc
between the eastern and western horizons.
The fifth component is the cabling. Most installations use a flat
ribbon cable comprised of separable sections for each of the necessary
functions: 1-two heavy wires for running the actuator motor; 2-two or
three small wires to provide dish position feedback to the receiver;
3-two RG-6 coaxial cables for the LNBs; and 4-three small wires to
control a servo motor. For installations that use more than two LNBs,
a separate RG-6 cable is usually run alongside the ribbon cable for
each additional LNB.
The sixth component is the satellite receiver. The satellite receiver
is arguably the most critical component of any satellite system. The
receiver is used to send a picture and sound to your TV or VCR. Some
receivers do not contain a dish mover, but many receivers are of the
integrated receiver decoder (IRD) variety. Most IRDs contain a built
in dish mover to correctly position the satellite dish for view of the
satellite arc, tune subcarrier audio (more on this later), and other
critical system functions. IRDs are able to not only receive and tune
satellite signals, but also either contain an interface for connecting
an internal decrypting module for decoding encrypted analog
subscription programming, or incorporate a similar apparatus for
decoding encrypted digital subscription programming, or both. Most
modern IRDs also have at least one remote control to facilitate
operation. Many IRD models have a UHF remote and antenna instead of
the "standard" infrared remote which allows the IRD to be controlled
without even being in the same room as the TV. Some remotes are both
infrared and UHF, which allows the UHF portion to be left in another
room after using the infrared portion to program a programmable remote
for use in the main entertainment area. TVRO receivers are renowned
for being quality components for home theater systems. All modern
models have composite (RCA) connections to allow connection to devices
such as audio/video receivers and external monitors. Some also provide
S-VHS connections for convenience with use of other components that
have them, even though the composite video connection is capable of
providing all the analog signal quality that NTSC video is capable of
providing.
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