Influence of rain, snow and storm
The higher the frequency is, the more impact water on a micro-waves.
A higher frequency means a shorter wave length.
The consequence of a heavy downpour is thus signal loss.
Nevertheless there are many misunderstandings concerning the influence of rain and snow on satellite reception, witness the LNB umbrella that is sold.
Absolute nonsense, because the effect of rain on the satellite signal takes place in the atmosphere, to be exact. in troposphere.
What happens there with the satellite signal in the atmosphere such as rain. The two most important causes of signal loss are;
1. Absorption: a part of electromagnetic energy is absorbed by a rain drop and converted into heat.
2. Reflection: rain drops can ensure that electromagnetic energy is diverted from its original direction.
When the distance between the rain drop (or the size of a rain drop) corresponds to the wave length of the satellite signals, loss of signal can occur.
Signal loss from heavy rain can be minimised by capturing a larger signal.
One of the most important and cheapest manners to do is the satellite Parabolic dish designed for this. A heavy downpour can produce a loss of approximately 5 dB per kilometre. The concern here is the quality, not the signal strength.
A 60 cm satellite dish which has not been set-up optimally cannot compensate during a heavy downpour. With a larger satellite dish, the signal is not so marginal. (but once again a good satellite dish with a size of 60 cm which is optimally tuned is sufficent).
Also LNB with a lower noise figure helps. Using low loss, quad shielded cable, especially for longer runs will help.
The lower the elevation angle, the longer the path through the rain, and the higher the losses. The higher the elevation angle, the shorter the path through the atmosphere for a satellite dish which is right under the equator. The satellite operator can help with also. By building in a fork in the transmitted capacity (EIRP), the satellite has to extra reserves to compensate for rain fall. What perhaps you will not be expect that a downpour can cause more interference than snow.
According to research workers who study the phenomenon, this is probable because a snow flake is about 1/8 parts of density of a water drop.
Snow has water, but less, as a result of which absorption or reflection of micro-waves will be less.
Studies have shown that horizontally polarise satellite signals experience more change with rain than vertical polarised signals.
Rain drops change a dish's form, as a result of which, they absorb horizontally polarised signals rather than reflect during their fall. The impact is minimum, depending on of the size of the rain drop and the frequency, but present.
Storms, particularly lightning, are a discharge of electromagnetic waves.
These disturb the electromagnetic waves received from the satellite dish. A lightning storm leads to irrevocable signal loss, but is very local and of short duration. Ku-band satellite signals (around 30GHz) as used by ASTRA for the broadband interactive services, experience more change still with rain. This can even run upto 50 dB. In Betzdorf, where the ku-band uplink dish stands, they have overcome this at another site where another Ku-band uplink is placed. A downpour is locally and lasts on average a couple minutes. The two ku-bands uplink dishes stand with each other in paralell and take the uplink function of each other should one of the two experience changes due to violent rain fall.
FunFiles Satellite Team