:: Satellite Services
Direct
Broadcast Satellite. (DBS) is broadcast by medium and high powered
satellites operating in the microwave Ku band. These high powered,
high frequency satellites make it possible for the signals to
be picked up on a small dish. Digital compression makes it possible
to have many channels on a single satellite. The DSS and DISH
Network systems both have 18 inch satellite dishes. Primestar
has a 3 foot satellite dish. One of the big advantages of DBS
systems is that the small dish does not have to move.
All current DBS systems in the U.S. have nothing but scrambled channels
and require descrambling with their own special receivers. For example
a DSS system can't pick up Primestar, DISH Network, or TVRO signals.
A Primestar system can't pick up DSS, DISH Network, or TVRO signals.
The consumers can only receive programs for their system.
:: Free To Air FTA stands for
"Free to Air"- meaning that the signal is not encrypted
with conditional access.MPEG-2 is not an encryption method although
encryption can be added.
- Dish Network uses the Nagra system of encryption,
- DirecTV uses a News Data system,
These include Saudi TV, Abu Dhabi, Thai TV,
Kuwait TV, Syria TV, Taiwan, Iran, and as we go to press, Bloomberg
TV all on Telstar 5, Ku, which can be received on a .7 meter dish.
The list changes now and then but these and more can be seen today.
GE-1 is the home of a bouquet of channels from Paxton Communication's
PAX TV. PanAmSat 9 at 58 degrees west is home to the RTP, EWTN,
CCTV China, NHK, Deutche Wella, an Arab bouquet in PAL, and a
channel from Colombia.
:: FREESATCARE SATELLITE SYSTEM
Antenna
The satellite transmitting antennas are highly directional, high-gain,
narrow-beam antennas. The parabolic shape of the antenna collects
the very weak microwave signals transmitted from the satellites
and reflects them toward the central area of the LNBF.
Antenna Performance Measure
The overall performance of an antenna system
is referred to as G/T (merit factor), which measures the gain
over the noise temperature. The gain is expressed in decibels,
and the noise is expressed in degrees Kelvin. The higher the G/T,
the better the antenna performance.
Size of antenna
The general rule is "the bigger, the better",
but there are a number of variables to consider. The homeowner
should find that a three meter antenna will give him perfect picture
quality, provided that his LNB and receiver perform well. Ku Band
antennas are relatively smaller than C bad. There are two size
available; 90 cm and 76 cm.
Here is the recommend EIRP levels and recommended antenna size
for Ku-Band:
|
EIRP levels |
Antenna
Size |
|
> 47 |
76 cm (29.9 in.) |
|
< 47 |
90 cm ( 36 in) |
:: The Importance of surface accuracy
The parabolic reflector has to start with an accurate shape and
this shape must remain dimensionally stable if it is to perform
well. Small changes in the surface or the support structure of
the reflector will cause major changes in the way the microwave
signals are amplified and focused at the LNBF. A dimensionally
inaccurate reflector will change the phasing of the reflected
microwaves and instead of amplifying them, it will diminish their
strength. When the reflected signals reconvene at the focal point,
they must arrive in phase or they begin to cancel each other out.
:: Low Noise Block Filter (LNBF)
The LNB is probably the single most important part of the
reception system with regard to picture quality. Some LNBs are
rated by gain, but most are rated by noise temperature, expressed
in K degree. A highly effective LNB for use with a home earth
station might have a rating of 25 K degree, provided there were
no special reception problems to contend with. LNB noise temperature,
antenna elevation and antenna gain (primarily determined by antenna
size) are the main determinants of overall system performance.
This is where the G/T rating comes in. The G/T can be improved
either by increasing the gain of the antenna (making it larger
or by reducing the noise temperature). The LNB also performs the
operation of "downconvert" the 3.7 to 4.2 GHz downlink
frequency to an intermediate frequency, normally 950 to 1450 MHz.
:: Cabling
In TV cabling, the common 20-gauge RG-59 coaxial cable (composed
of two conductors and several layers of insulation) served the
industry when there were only Channels 2 though 13 in the TV spectrum.
RG-59 is being replaced by the better performing 18-gauge RG-6
coaxial cable (at the same price). With today's high-frequency
channels and the growing demand for Digital Satellite Systems
(DSS), High Definition Television (HDTV), and interactive services
such as video-on-demand and WebTV, homes need cable with greater
bandwidth and dependability.
:: The difference between RG-6 and RG-59 Coax Cable
RG-59 is a lower grade of coaxial cable, consisting of a smaller
center conductor, a smaller insulating dielectric, and a single
outer shield. It delivers acceptable performance for CATV. RG-59
has a 22 AWG center conductor.
RG-6, on the other hand, has a larger center conductor (18AWG),
a dual or quad shield (2 braids and 2 foils), and a much larger
insulating dielectric. The benefits of using RG-6 cable include:
more bandwidth, is less susceptible to interference, and lower
attenuation per foot. RG-6 delivers exceptional performance for
CATV, satellite and all other video applications, and is considered
the cable of choice for digital TV.
As cable TV companies add new channels and begin to introduce
two-way communication, the bandwidth limitations of RG-59 will
make it obsolete. RG-6, on the other hand, is rated at up to 1.5
gigahertz (GHz) - about double the rating for RG-59. The superior
protection provided by four separate electronic shields within
the cable also ensures that signals traveling through RG-6 remain
intact.
The EIA/TIA 570-A Residential Telecommunication Cabling Standard
specifies Series 6/ RG-6 coaxial cable.
::Receiver
Programming an Mpeg-2 FTA Receiver
Programming of a MPEG2-FTA receiver can be done
by following the steps;
1. Enter the downlink frequency. For example, at the Lyngsat
chart[4], downlink frequency of the transponder can be seen as
11898 Mhz.
2. Enter the LNB Low freq. This is the local oscillator frequency
of the LNB, which is located out at the antenna, which allows
the received signal to be converted into a usable signal within
the receiver. For example C-Band L.O. frequency is 5150 and Ku
band is 10750.
3. Enter L.O. freq under a satellite setup. The receiver uses
these two frequencies to calculate the L-band frequency that all
receivers use to tune the channel.
4. Entered the Symbol Rate (SR). This is the rate the size of
the digital package transmission. This figure can be anywhere
from less than 5000 to over 40,000. For Telstar5 SR is 20000 (
see the forth column that the chart)
The 3/4 is the FEC and is automatically calculated by most receivers.
The PID rate, package identifier, and the FEC, Forward Error Correction,
which corrects bit errors, are automatically calculated by most
receivers. One should be aware of that, contemporary receivers
can sore up to 200 channels. Most of the latest receivers ( i.e.
Satcurier) have it own frequency scanning built it, therefore
the steps give above need not to be applied for that kind of receiver.
Simply open the receiver an and assign type of LNB and press on
the scan button, it will automatically loads all available FTA
cannels.
As it was mentioned previously, list of the available FTA channels
is subject to change without any notice. There maybe some channel
addition or deletion. Therefore user advice to look at the FTA
channels listed at the Lyngsat chart[4] regularly.
:: Receiver Manufacturers
ADI Mediamate DVS-820 |
An FTA box with 2-30 MS/Second symbol rate range and 90-264
Volts mains inp |
| Panasat IRD520 |
Symbol Rate only 18-28 MS/Second so no use for SCPC |
| Echostar DSB9800 |
Symbol rates covered from 18.5-30MS/sec but not SCPC nor
PowerVu. Works ok in C-Band also |
| Hyundai HSS-100c |
will do SCPC & handles symbol rates down below 4000 |
| Pacsat DSR2000 MediaStar D7 |
A capable receiver covering SCPC/MCPC with its 2-36 MS/Second
symbol rate range |
| Sat Cruiser DSR-101 |
Uses a Hitachi CPU (SH7021). It has 800 channel storage
plus a favourite channels menu and is SCPC/MCPC/PoweVu compatible
|
| Vortec (Samsung)VS-9700 |
Symbol rates are 2-45 MSPS |
| Galaxis Sat 500 |
made by Samsung. Only capable of 15-30MS/sec |
|