satellitesuperstore.co.uk

System option - Include a Titanium 0.1dB LNB twin output LNB
instead of the LNB with my system.
Order code OPT05TW
Add only £10.00

Heavy duty wall mounts and ground stands are also available from the
wall / ground stand page.

The differences between prime focus
and offset dishes.



A prime focus dish is shown above.
This type of dish is circular NOT oval. It has 3 feed support arms (some use 4 arms) and the 3 arms
converge in the centre. Each arm is 120 degrees apart. The feedhorn uses concentric scalar rings.
The concentric scalar rings reduce noise and improve signal to noise ratio with prime focus dishes.
An offset dish is oval and is higher than it is wide (some are wider than they are high). They use either
one feed support arm (at the bottom of the dish - see bottom left hand picture) or 3 feed support arms
(again all in the bottom 1/2 of the dish - see bottom right hand picture). They require a feedhorn
that is in the shape of a horn without scalar rings.



Larger, higher quality offset dishes will use three support arms as the extra two side support arms
provide better rigidity when dish sizes exceed 1.0m. The offset dish shown above right is the
excellent high gain Raven 1.8m dish.

As a general rule the two types of dishes are simply two ways of doing the same job, however, an
the offset dish, if well engineered usually has significantly more gain than the prime focus dish.
It is never really that simple. It is true that petalised offset dishes usually have poor gain but
a one piece well engineered prime focus dish can be better than a poorly engineered offset dish.
As usual you get what you pay for. Cheap prime focus petalised dishes are to be
avoided and we don't sell them.

Advice on Diseqc Motors.



This is a development where digital receivers now contain software to control a
Diseqc motor (right hand side in photo) rather
than a hardware positioner board to control a standard 36V motor (left hand side in photo) motor.

The problems with Diseqc motors and why the "V box" (link to V Box below) is so necessary with larger dishes.

Diseqc is a new development where digital receivers now contain software to control a Diseqc motor rather
than a five amp hardware positioner board to control a standard motor. The motor control works digitally
down the coax signal lead and a 4-wire control system is not required. Also the concept has become an
industry standard. Sounds good so far but what are the drawbacks?
1. Diseqc motors have all been lightweight universal fit motors with a
thirdary rotating pole that the dish clamps to. They are not designed for a particular dish and they do
not properly bolt onto the back of a dish. Slippage can occur in high winds at the thirdary rotating fixing.
2. The coaxial cable is designed to carry the signal from the LNB to the
satellite receiver. It is also designed to provide power to the LNB. The satellite receiver provides about
500 to 600 mA (0.6A) to power the LNB. Typically an LNB might draw about 300 mA. This leaves 200 to 300mA
(0.3A) to power up a Diseqc motor. Clearly a proper hardware (4 wire control system) positioner which
can provide up to (typically) 3 to 5 amps is a far better system as it can drive better bigger, stronger,
quicker motors. With 300mA a Diseqc motor must be very small. The only way a very small motor can move
a dish is by putting a large gearbox on the end of the motor to provide "leverage". This means that
a Diseqc motor moves very slowly from one satellite to another due to the large amount of gearing.
Small motors & thirdary thinner rotating poles which the dish can slip on are far from ideal for use
with even larger dishes (e.g. 1.0m+ or 90cm + in exposed locations.). Storm force winds in the UK can
provide serious wind loads on a motorised dish. You really do not want to be worrying about whether the
dish is going to come down every time it is windy.

Our opinion of a recent conversation,

I was talking to another dealer the other day. He said he fits a Diseqc motor to the Channel
Master 1.2m dish face. The Channel Master is a heavy dish and the wind loads on a 1.2 can be massive.
In addition, this Channel Master dish is available with a wonderful heavy duty Channel Master
polar mount and actuator (or the big 15 Kg 1224 Supermount H to H motor. See our motorised dishes page.
link below) and yet this dealer fits a (i.e small - usually 3 Kg) universal fit thirdary rotating
pole Diseqc motor to this excellent 1.2m dish face!!! It is like ordering a 6.5 litre Rolls Royce
from a dealer and saying "will you please fit a 1 litre Scoda engine before supplying it."
Absolutely crazy! Unfortunately 99% of dealers (and the magazines) are prepared to go down
this route. What we need is a bit of common sense. Why is wind load never considered? Every year we see
numerous insurance claims. We have never seen a Diseqc motor yet that we would put on a dish of over 1.0m

Our recommendations.

For motorised use, The Diseqc motor works fine on steel dishes up to 90cm and aluminium dishes up to 1.0m
in "normal" locations. For larger dishes, or exposed locations (e.g. above the gutter on a high pole
or on the west coastline of Scotland or Ireland,) use a V Box and a 36v motor.
The V Box will enable heavy duty (non Diseqc) motors to be used that move the dish quickly and efficiently
without the dangers of breakage or slippage in high winds. (motors that properly bolt onto the back of a dish)

We never make recommendations without explaining the facts and the facts are based on the laws of Physics.
Hopefully you will realise that we are making sense.

THE V BOX PAGE.

Latest Diseqc motor information 17/01/04

We have tested a new "Cryptic" Diseqc motor last weekend.
The reason for testing it was that for the first time a motor became available
that bolted onto the back of a 1.0m aluminum dish. Being a Diseqc motor
it was expected that it would still be slow (and it is) but this looked
very promising as the big problem of “universal fit – fits nothing properly
and slips in the wind had been overcome. We really wanted this solution
to work for us. It was set up with a Digiquest 8000 and using the USALS
facility all satellites were programmed in. Looked great.
However !
Taking hold of the edge of the dish, (at a distance of about 0.5m from the centre
Of rotation) there was play (movement) of about 7 mm. This was found to be in
The actual motor shaft between the rotating output shaft and the motor body
(i.e. in the gearbox) Looking at the shaft the movement was about 0.5 of a degree.
Now - last Saturday there were moderately winds (not gale force) and the dish
Moved on and off the satellite (no signal) every few thirds. Not a “peaky”
Low power satellite! We were on the Hotbird.
We contacted the supplier and were told that there is a certain amount of play
In all Diseqc motors as they use a worm drive to gear them down.
(small low current motor – large gearbox)
The only time you might get play in a 36 volt motor is when it has been used every
day for many years.

A typical e-mail. We get a few of these. (Dated May 03)

Dear David,
Did not believe in UFOs until recently, when looking through my window I saw a UFO descend
vertically and crash. I soon found it was my 1 metre Channel Master dish, still firmly attached to top of
Jaeger mount, having left behind rest of mount, still on top of pole. If you will examine the
top plate of a 128, you will find it is held on by 4 small countersunk screws. In my case,
wind on dish had managed to tear the heads off inadequate sized screws. If you check 128
you will my point, that screws are too small.

Reply,
The 128 is too small a motor for the Channel Master 1.0m as it only weighs 4 KG
The correct motor (2 types) - both weigh 12 KG each
As shown at www.satellitesuperstore.com/dishes-motors2.htm and our motors page
So nothing you say here is a surprise to us as we tell people that every day of the
week and follow other dealers insurance claims round. You should use the Channel
Master polar mount and 12 inch actuator or the 1224 motor with plate.
Dave

Note. The 128 is a 36 volt motor not a Diseqc motor but it was still too small for this dish!

Update Nov 04.

More recently we have had reports of people putting Diseqc motors on 1.2m dishes!
No wonder our insurance premiums are so high these days!

Update 20th July 06
The Technomate TM-2200

We have tested the latest Technomate Diseqc motor and it is better than any previously tested
It works well with 90cm steel or 1.0m aluminium dishes and it does move faster than
other Diseqc motors. There is no noticeable play in the gearing.
We are therefore pleased to include it in our product range. Only dishes
on our site that fall within the size recommendations just noted are
available from us with this motor. For larger dishes or exposed
locations use a 36V motor.