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Our comments - Roy Carmon is a very well respected enthusiast
who has, for many years, been a leading figure in the feedhunter groups.
Here are his notes on how to feedhunt.
How to Feed Hunt.
Chapter Two.. The necessaries.
Feedhunting can be done in many ways. I will go through the methods used, but first a little bit
about the equipment that you will need. The rules that apply here are mainly almost governed by budget levels.
A cautionary word would be appropriate here in all respects. As with newspapers, do not believe
all that you see and read in the glossy magazines. By bitter experience I have discovered that
advertising revenue to a magazine is often more important than the truth. Some articles I have read,
and when I have tested the receiver, or piece of equipment, bare no resemblance to their true state.
Also beware of dealers because many are but box shifters. All they are interested in is getting
the boxes that come through the “Goods In” door, back out through the “Goods Out” door and your hard
earned cash in their till. One particular dealer I know has not got a clue what is in the boxes or how
what is in the boxes works, nor what it supposed to do. However there are just a few decent and honest
dealers out there. Many of the better ones do not advertise in the Glossies at all.
Firstly I will mention the dish also known as the reflector, as this should be your first consideration.
Without a dish you are not going to get anywhere. Basically get the dish end right and all the other bits
and pieces will fall into place.
First the Offset Dish.
There are two types of dish that are commonly available. The most common one used is referred to as an Offset
Dish. This dish is slightly egg shaped. The offset configuration is particular useful in smaller dishes because
the LNB (Low Noise Block) does not cast a shadow upon the dish surface, which can reduce signal gain.
This type of dish appears more upright when set up than the centre focus dish. Because of its odd shape
it is more difficult to make and therefore the reflective surface on some is not as good as it is on others.
You can buy some Offset dishes that have a greater width than height; this is specially designed
to compensate for some of the disadvantages that are endemic of the normal offset design. I don’t
want to delve to deeply into antenna theory and design as that subject can fill volumes.
Secondly the Centre Focus Dish, also known as prime focus.
The centre focus dish is totally round in appearance. It has a better surface accuracy due to simpler
construction techniques. The chief thing against the centre focus dish is that the LNB arrangement
casts a shadow across the dish as I mentioned earlier.
There are other types of dishes available but these are usually more expensive than the two mentioned.
They are Cassegrain, Gregorian, and Toroidal.
The Cassegrain dish is a dual reflection system that uses a convex sub reflector and a parabolic
main reflector. It is worthwhile to point out here that both Offset and Centre Focus dishes
are parabolic. The LNB on a Cassegrain dish is usually set in the main reflector and looks back
at the sub reflector.
The Gregorian dish again is a dual reflector dish, but this time with a concave sub reflector.
Again the LNB looks toward the sub reflector, but is set on the sub reflector support arm much
nearer the actual sub reflector. There was for a while on sale in the UK Fibo Gregorian dishes.
These were excellent dishes as they were very efficient gatherers of signal. They came
in two sizes one a 90centimetre, the other a 1.2metre. If you have a chance to get your hands
on one of these I would suggest you snap it up. This illustrates the need to buy your dish
before your LNB, you will learn why very soon.
The next is Toroidal, sometimes referred to as Multi Focus Antenna. This dish is quite a unique
looking object. The first thing you will notice is the wrap around effect. The dish is designed
to reflect signals from more than one satellite and therefore designed for use without a motorised
element Some Toroidal dishes are designed to take up to 16 LNBs! How you gather all those
LNB feeds into one common feed to enter the receiver again is book of its own.
But before considering buying a dish the following has to be considered.
In the UK you are permitted to erect a single dish no larger than 90centimetres without planning
permission. If you live in a terrace, block of flats, or rented accommodation checks with both council
and landlords where applicable must be made. It would also be very considerate to consult with your
neighbours on the dish position. They can look pretty ugly and also can be pretty noises.
The most important thing to take into consideration is from anywhere on your property can you view
the satellites that you wish to receive. Look slightly to the left of due south and formulate
in your mind the arc you wish to view. If necessary get some string, a compass and some pegs
and mark out the arc on the lawn or the patio etc. The ideal arc is 120 degrees, 60 degrees
either side of centre. Look for trees or houses that could get in the dishes view to the
satellite. Can these obstacles be cleared to provide a clear view by simply by raising the
dish higher up on the house wall? Will your neighbour willingly demolish his newly built
conservatory for you? If in doubt ask a local rigger to make a site survey. A site survey
should cost you nothing if you tell him he will be carrying out the installation!
You can pay from £30 to £200 plus, for a 90centimetre dish.
Next to consider is the LNB, low noise block, that little piece of electronics that dangles
out there on a limb looking at the dish. This is sometimes called the LNA, Low noise Amplifier
or LNC, Low Noise Converter.
Now it is time to explain why you need to buy your dish first.
The LNB can be constructed in many ways, but being I am only going to deal with the Universal
LNB that is used for KU band reception I will therefore keep it reasonably simple.
Universal LNBs come in two types of fitting, the most common being the 40mm; this refers to
size of the feedhorn collar that fits into the clamp at the end of the LNB support arm. The 40mm
will be a complete LNB, the electronics with the feedhorn attached permanently. This is
sometimes referred to as an LNBF. Most offset dishes are designed to accept a 40mm LNB on
there LNB support arms, however many of the better dishes come with an adaptor enabling you to
choose which type of LNB fitting you wish to use. The other type of Universal LNB available is the
C120 Flange Type. The C120 flange type LNB does not come with the feedhorn attached and primarily
designed with the Centre Focus type of dish in mind. Therefore you also need to buy a feedhorn.
A cautionary word here, there are two types of feedhorn available, there are feedhorn available for
use with an Offset dish and different ones for Centre Focus dishes, please ensure you buy the
right one for the type of dish you have elected to buy. I think by now you will be seeing as to
why I recommend buying your dish first.
The LNB with Feedhorn attached, usually 40mm, I recommend to only use with up to an 80centimetre
dish. Any dish above an 80centimetre use a C120 fitting with a good feedhorn, you will not regret it.
Again buying an LNB can depend upon the amount of pennies that you have in the piggy bank.
The real thing for consideration here is to look to the future. Ask yourself how many receivers
do you want to run? Are you going to incorporate Sky into you single dish arrangement?
LNBs can be purchased with either a single Intermediate Frequency (IF) access commonly called
the “F” socket, in other words the LNB cable, which are terminated with an “F” plug. Dual
(2 IF inputs) and Quad (4 IF Inputs) versions are also available. Another quick word of caution
is due here. Quad LNBs can come in two types. The first Quad LNB is one that all you need to do
is connect a receiver direct to the LNB via the IF cable. The second type has four “F” socket
outlets and is often referred to as a Quad Four Port. Each outlet carries a separate function.
These separate functions require a combining unit installing between the LNB and the receivers.
The beauty of the second version is that you can buy combiners that allow you to run as many
receivers as you like, very useful when wiring up flats and hotels, this often referred to as
SMATV. Where as with the Quad version you can only run four receivers.
A single LNB carries out the following functions on commands from the receiver. First I must
explain that the KU band operates from 9700Mhz to 12750MHz. The LNB down converts the signal
from the satellite to an intermediate frequency (Note the term, hence IF) to one between
900 and 2000MHz. The chief reason for this is that a signal at 900 –2000MHz is more easily
carried by a coaxial cable without too much signal loss. It is reconverted at the receiver.
So that a good signal can be received throughout the available spectrum, the signal is divided
into a lower and an upper band. Signals are available in both Vertical and Horizontal polarity,
thus making four different signal functions.
These four bands are all available within the standard LNB on command from the receiver, on a
single LNB, dual, and quad LNB via each IF port.
The Quad Four Port however divides the four elements into an individual port. So for arguments
sake, at port 1 – lower band horizontal, port 2 – upper band horizontal, port 3 - lower
band vertical, port 4 - higher band vertical. Most receivers switch from lower band to higher
band around 11690MHz. The previous statement must not be confused with the
LOF (Local Operating Frequency) of an LNB.
Don’t just go for a single and hope for the best, as your interest in this fascinating hobby
grows you will soon be wishing that you had gone for a Quad LNB. If you are going to
incorporate SKY into your system, you will need to provide a single clean LNB feed to
the Sky Digibox because they do not like distribution units or running off the IF outputs
of some other digital receivers. So you will need at least a dual LNB. Personally I would
recommend that you install a quad right at the outset of your setting up. You will
see why as I progress.
LNBs can be purchased from as little as £15 to well over £200.
The best type LNB to buy is referred to as the Universal LNB sometimes called an LNBF because of its shape.
Most other types of LNB are single output/input and are more specialised and require the receiver
to be fitted with specialist controls within their menus, or the use of auxiliary control units.
I have seen many people who have moved through the analogue stage of satellite reception, up
to digital and maintain their old LNB control systems. Most of them have suffered problems until
they eventually settle for a more simplified Universal LNB system.
Most modern digital satellite receivers are designed for use with a Universal LNB.
Which type and brand do I recommend? Well the best buy is the MTI brand, both for price
and performance. Don’t be taken in by flattering noise figures on more expensive LNBs, they
do perform better but the difference is really minimal. I have tried all three of the low
noise figure LNBs and can honestly say that they only appear to come into there own in
really awful weather.
Thirdly the dish moving device, motor, actuator, call it what you like.
A word of warning to exercise extreme caution must be applied here. When buying the dish
ask for the recommended means of moving the dish. Not all types of motors or polar
mounts fit all dishes. Often you need to purchase extra fitments or manufacture fixtures
to get the dish and motor to mate together.
As with all things satellite there are many ways to move a dish. The first I will mention
is DISEqC. This system first invented by Eutelsat moves the dish via the LNB cable.
DISEqC also allows you to use multiple dishes with their various LNBs, but being we
are talking feedhunting using a motorised system I will not get involved with that here.
The advantage of the DISEqC motor is less cables to install and to worry about, therefore
smaller holes in the wall.
The really big disadvantage is that at the moment it can only power a motor sufficient
to take a 1 meter dish, if you want to drive a larger dish with DISEqC you will need
a DISEqC positioner. This extra box converts DISEqC commands to the standard 36 volt dish
motor drive system. Personally I do not like any of the DISEqC system at all.
The next is the 36 Volt Horizon to Horizon motor (H to H). This either requires the receiver
to have the necessary fittings on the rear of the receiver and obviously menu arrangement
to set the motor up. Also it requires a set of control cables, another thing to go through the wall.
As I said before, DISEqC receiver can be used to drive a standard 36 Volt motor but you will
require a specialist box to convert the DISEqC to the 36 Volt motor drive.
Lastly I will cover what is termed as the Polar Mount set up. This consists of two parts, the
polar mount, and the other part is known as the actuator. It is the actuator that provides
the motive power. Another point for consideration here is how much of the arc do you wish to
cover as some polar mounts can be fairly limiting in there movement and therefore coverage of the arc.
The polar mount basically allows the dish to swivel through the arc at the necessary angles,
and attaches the dish to the pole at the same time. The actuator fits between the mount and the
dish and works a little like a car jack, a centre arm screws in and out electronically that pushes
and pulls the dish.
The real advantage of the polar mount is that it is easy to fit a second actuator to chase those
satellites that are in inclined orbit. This can also be done using specially built H to H motors,
but they are expensive. If you are mechanically minded and have the means to locally manufacture
parts then the world is your oyster so to speak.
Lastly in this opening section I will cover the cables needed.
The IF cables carry a live voltage to and from the receiver and LNB. At this point I will
recommend that you turn your receiver off at the mains before attaching or detaching LNB cables.
Although the voltage and amperage in use are fairly low, if the leads are shorted out whilst
attached to the receiver they will damage it.
There are many grades of IF cable, these vary in price from pence per metre to pounds per metre.
The choice is yours. What you can afford and what do you want to get out of your system.
Motor cables are the next consideration unless you are using DISEqC. DISEqC by the way, uses the
LNB IF cable to pass power to the motor control system. I am assured that this is done without
loss to the received signal.
If you choose to use a Jaegar type motor then I would recommend that thicker and preferably
copper cabling are used between the receiver and the motor than most riggers normally use.
This is essential on the two cables that carry the pulse that starts and stops the motor.
When you are cabling, or your installer is cabling, always ensure that at both ends there is
sufficient cable left for possible future movement of dish set up and location of receivers.
A good installer when in the house will always ensure there is enough cable to move anything
to the farthest point with in the room, neatly.
The moral of the story is to use the best cable available. The joy of cheap low price is soon
forgotten when things begin to go wrong, or equipment does not perform as it should do.
Let us now talk about receivers.
What do you want to do? Do you want entertainment from the system? Do you want to feed hunt?
Do you want to store both feed and entertainment channels. You must sort out in your own
mind that what you wish to do.
So you want to feed hunt. Well to feed hunt for yourself you are going to need a receiver
that will find the symbol rate and the Forward Error Correction of a signal, but first
you have got to find a signal to download.
In Chapter 3 I talk about and compare auto symbol rate detecting receivers.
In Chapter 4 I will talk about feed hunting.
In Chapter 5 I talk about having entertainment channels as well as feeds.
In Chapter 6 I will talk about receivers in general.
Chapter 7. Anything you may want me to cover.
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