Biswajit.HD
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The obvious statement is that the bigger the dish the more signal it can gather and the weaker satellite signals it can pull in. So your first consideration in choosing a dish is to make a list of satellites you are interested in receiving and look at their footprints then calculate, using a link budget program, the size dish required to receive them. If you are interested in a DBS (direct broadcast system) satellite and only have interest in receiving the programming from that satellite only then purchase and install the recommended system from your local satellite store. If you have interest in receiving multiple satellites then be sure to get a C and Ku-band compatible dish. If you are buying a used mesh satellite dish, be sure it has the smaller diameter perforations or a significant portion of Ku signals will pass through the dish. Do not waste your time buying a fiberglass dish as that is early technology and will be guaranted to have C-band only mesh embedded within. If you have consideration to purchase a solid metal dish, or one piece mesh dish, stand aside from it and sight across it to be sure it is not warped - if so, do not purchase it regardless of the price. In buying a new dish, a solid dish will not necessarily have a greater efficiency rating than a mesh dish; look at the dish specs and see its efficiency rating which is the percent of signal that hits the dish is actually reflected into the feed - the greater the efficiency rating, the more gain the dish will have. In considering a buttonhook feed support or leg feed support dish, today's feeds and LNBs are so compact and lightweight (as compared to the equipment from the early days of the industry) that a buttonhook will provide sufficient support. On the other hand, a feed supported by legs will always be more stable in winds. In another consideration of mesh vs.solid dish, at wind velocity of about 50mph the two offer the same resistance to wind forces; a mesh dish is easier for the actuator to 'push' around though on smaller diameter dishes (less than 2.5m) today's actuators handle a solid dish with minimal problems.
The next consideration in dish selection is the F/D ratio of the dish. In general, the less the F/D, the deeper the dish, the lower the gain and the greater the rejection of unwanted signal. Thus the choice of satellite dish can assist in rejecting terrestrial interference in that the deeper the dish the more narrow will be its acceptance of satellite signals and the less chance unwanted signals will enter the feed assembly. A dish is considered deep with F/D ratios of 0.25 to 0.32 and is considered shallow with F/D ratios of 0.33 to 0.45. So choose a high gain, shallow dish if you have no fears of TI entering your system. Remember that the more shallow the dish the closer to the dish the scalars are set on the feed.
One thing to remember, the deeper the dish and the larger the dish, the narrower is the central reception beam pattern (see side lobe discussion page); the implications of this is that the effect on installation is that the narrower a main beam then the more difficult it is to focus on the satellite while tuning a dish. This is not appreciably noticeable under strong footprints or sizes under 3.0m, but is noticable when tracking Ku satellites and when using a larger dish. A larger dish, for instance a 4.0m diameter dish, has a much more narrower main beam pattern than a 3.0m dish and you have to be more 'dead on' the satellite when tracking them so your elevation/declination/north-south adjustments are more critical. If you use a 5.0m dish it is real easy to loose a satellite while making mount adjustments (due to the narrow receive beam pattern) so choose the highest gain, shallowest dish when possible.
The next consideration in dish selection is the F/D ratio of the dish. In general, the less the F/D, the deeper the dish, the lower the gain and the greater the rejection of unwanted signal. Thus the choice of satellite dish can assist in rejecting terrestrial interference in that the deeper the dish the more narrow will be its acceptance of satellite signals and the less chance unwanted signals will enter the feed assembly. A dish is considered deep with F/D ratios of 0.25 to 0.32 and is considered shallow with F/D ratios of 0.33 to 0.45. So choose a high gain, shallow dish if you have no fears of TI entering your system. Remember that the more shallow the dish the closer to the dish the scalars are set on the feed.
One thing to remember, the deeper the dish and the larger the dish, the narrower is the central reception beam pattern (see side lobe discussion page); the implications of this is that the effect on installation is that the narrower a main beam then the more difficult it is to focus on the satellite while tuning a dish. This is not appreciably noticeable under strong footprints or sizes under 3.0m, but is noticable when tracking Ku satellites and when using a larger dish. A larger dish, for instance a 4.0m diameter dish, has a much more narrower main beam pattern than a 3.0m dish and you have to be more 'dead on' the satellite when tracking them so your elevation/declination/north-south adjustments are more critical. If you use a 5.0m dish it is real easy to loose a satellite while making mount adjustments (due to the narrow receive beam pattern) so choose the highest gain, shallowest dish when possible.
