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Q You mention that the integrated horn LNBs are suitable for dishes
with
a 0.6 F/D.
My dish is a 0.5 F/D. Will it still work OK? |
A The F/D is the ratio of the dish focal length to the dish diameter. The
horn of the LNB is designed to correctly receive signals bouncing off the dish, but not receive noise spilling over from outside the dish. Imagine you are shining
a torch at a dish. If you stand too close to the dish, there will be a circle of light in the centre, but if you stand too far away, you will be illuminating the
dish and the wall behind the dish.
When the LNB is situated at the focal point of the dish, a correct feed horn is designed to only illuminate the dish and no more or less. This angle of
illumination is described by the F/D, and Invacom LNBs with integrated feed horns are designed for dishes with an F/D of 0.55 - 0.65 |
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Q
The signal level meter only gives an indication of the signal level,
not the signal
quality... |
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A The signal level meter only gives an indication of the signal level, not
the signal quality. The important parameter is the C/N or BER, which is not indicated on the level meter. Many cheaper LNBs have a gain which is above the level
specified by Astra. This can cause some receivers to give a poor picture, although they give a high reading on the signal level meter... |
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Q I
am in Cyprus and trying to receive the very weak BBC channels from
Astra 2 at 28.2. However, some of the channels on the same satellite
are very strong.
What LNB do I need? |
A Everyone knows that noise figure is important for an LNB, but in your
instance, the isolation of the LNB will be just as important. This is because the very strong signals on the satellite can interfere with the very weak signals
that you are wanting to see. The strong signals act as noise, so reducing the C/N.
Most people are finding that the Invacom QDF-031, used with a good quality feed horn
matched to the dish, is the best performing combination for these areas, and outperforms other people's LNBs with much larger dishes. |
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Q
On all your 40mm horn products there is a scale on the horn edge from
-30 to +30 what is this for? |
A This scale is for the skew adjustment of the LNB. LNB rotation allows
for the affects of where you are situated on the planet.
Vertical and horizontal signals from, for instance the Astra satellites are nominally in the zero position in say Germany yet in the UK they are offset by 7.5°.
This is called the “skew angle” and it is achieved by rotating the LNB clockwise when looking at the dish. This angle varies with longitude not latitude and you
should be able to obtain the skew settings for your location from the satellite operator or maybe even from their website.
Please note that this skew may well vary from satellite to satellite and if you have a motorised dish it may well have a “motorised skew adjust” as well as a dish
position adjust.
This is the same for all LNBs, and satellite reception generally where you want to line up the LNB with the actual orientation of the vertical and horizontal
polarisation’s coming from the satellite.
If the unit is not in the optimum skew position then performance can be effected, although you may still be able to receive pictures - this will depend on the
signal you are trying to receive (i.e. skew is more important for weaker signals). |
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Q I
notice that the inside diameter of the waveguide on the SNF-031 is
18.5mm.
My feed horn has a diameter of 19.5mm.
Is this 1mm
change important? |
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A Yes it can be. The step will have little affect on the loss, however it
can degrade the cross polar performance of the dish/LNB combination. If you are trying to receive weak signals from a satellite that also has strong signals, the
cross polar isolation is important. |
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Q Can
your LNBs be used to receive weak channels in the USA? |
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A The DSS channels from DirecTV or Dish networks are circular polarised
signals. They cannot be received with our LNBs. However, many Free To Air (FTA) channels are linear polarised, and our LNBs are ideal for these. |
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Q My
VSAT installs are taking a long time to set up.
Is there a quicker
way to set up the levels? |
A A constant output power transmitter will give the
same output power regardless of the input level. This makes installation very quick and easy, with no requirement to adjust the system gain to achieve the correct
output power. However, there are a number of other advantages:
No dependence on cable length
Self stabilising ODU with temperature
No complicated interface with the IDU
Later changes to installation, such as changing cable length, will not affect the EIRP |
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Q Why
does your transmitter mute between bursts? I cannot see the benefit. |
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A The benefit of a muting transmitter
is to the satellite owner, or the person buying the transponder space. Imagine 100,000 transmitters all looking at the same satellite. When they are not
transmitting, they are still producing noise, all going towards the satellite. This limits the maximum number of terminals pointing towards the same satellite.
The Invacom transmitter shuts down between data bursts so preventing any noise being transmitted, allowing more terminals to be pointing towards the same
satellite. This makes the space segment costs cheaper. |
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Q My
satellite provider says that I cannot operate my 2W transmitter at
2W. Can you explain if this is correct? |
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A It all depends on whose transmitter
you have bought. An Invacom 2W transmitter can be operated at 2W without any problems. This is because it will meet all the Eutelsat & Intelsat specifications
when working at its rated power. However, when many manufacturers rate their transmitter at 2W they mean the P1dB ( the output power where the gain has compressed
by 1dB) is 2W. If you were to operate the transmitter at this level, you would splatter unwanted power into adjacent satellite channels. Typically a transmitter
will need to be operated around 1.5dB below it's P1dB power. The typical P1dB for an Invacom 2W transmitter is +35dBm (3W) allowing the unit to meet full
specification at 2W |
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Q I
have a 500 KB/S point to point satellite data link between two sites.
Do I need a DRO or a PLL LNB? |
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A A PLL LNB is much more stable in frequency than a
DRO LNB. For high data rate traffic, a DRO LNB is sufficient. This is because the bandwidth of a high data rate carrier is large, so the frequency tolerance of
the LNB is not so important. However, for a low data rate signal occupying a narrow bandwidth, the stability of the oscillator within the LNB is more important.
For a 500KB/S link, a PLL LNB will be required. |
