Ya, I know this is not the right place, but coming back here...cuz this forum is very helpful to me...I work on linux platform and working as a assist. network admin,

I'm very much interested in VSAT's working procedures and satellite communication....

I searched on the net..I googled...but upset cuz..some questions puzzled me.

If anyone help me to make me clear about below questions...I WILL BE VERY HELPFUL. (I am posting here...cuz many vsat/radio engineer might be member of LQ-so, plz help me)

Questions:

Some resource saying that signal weaks down travelling through space; and when collected by VSAT; this signal need to be amplified..so Low-Noise Amplifier(LNA) Plays role to amplify the signal. so, why we use Low noise block down-converter(LNB)???

some resource tell that, satellite use high frequency to transmit signal..so LNB use to produce a similar but little version of received frequency, so the satellite modem can work with the analog signal and demodulate it to digital.

** I am not clear...once LNA amplyfing the noise ?? ?? and LNB downconverting it ?? ?? not making sense at all. .

PLz help ..

yeah, its a weak signal, and weaker still if there is moisture in the atmosphere.fade margins are calculated in so the signal is still usable in all but the worst weather(your directv blinks out during heavy thunderstorms,etc.) the sats are 22600 miles (yes miles) up so theres not alot of signal to work with. there is very little difference between lna and lnb other than the lnb handles a block of frequencies and down converts them(lowers their frequencies) from the microwave range to a range that can sent down normal rg-6 coax and be used by normal electronics.

ok, thanks...but what is the "noise" doing here? (well, i am tired of hearing.."noise is something called unwanted signal" - I know it well.)

LNA- low noise amplifier
LNB- low noise BLOCK downconverter

so, once amplyfing...then down converting it ??

not clear yet..

all things make noise. even a rock make noise. its atoms bouncing into one another generate some level of 'noise' . transistors make a lot of noise, the 'low noise' part is just a label mostly, it's understood that it has to be low noise to pick the sat signal from the circuit/transisor/diode noise of the lnb. lnb's are rated by noise temperate, the lower the better.

I would suggest you (sizth_sense) google and find some resources on general radio tranasmission architectures, learn and understand terms such as 'down convert' and how they are used in the context of radio systems. Then you will see that a satellite communication system is just a specific case of a generic radio transmission system.

Amplifiers comes in all shapes and sizes, a 'low-noise' amplifier is designed to add as little noise to the signal as possible (compared to other amplfier types). All amplfiers add noise, an LNA is designed to add less noise, but at the cost of other performance parameters (e.g. maximum output power).

Thanks all,

I got some idea..after searching google with appropriate terms....now i understand..

LNA- amplifying the signal with as low noise as possible. While;
LNB- also amplifying the signal with low noise and down convert the monster frequency to similar little version to cope working with sat modem.

I must say, again LQ helped me