# Satellite Communications/Boltzmann constant

Question
Dear Sir,
looking at a very basic link budget in the C/N equation:
C/Nup= EIRPup - FSA - Latm - Lpoint - K - Nbw + G/T and given an average 207 dB loss for the FSA if the Boltzmann constant would not add as a consequence of its negative value then any satellite link would be impractible. My question is what really is this magic number K, I mean it seems to relate to noise, then in theory it should deteriorate the satellite link but in fact it helps the link by compensating the big FSA.
Could you please explain this mistery, that is what the Boltzmann constant physically means.
Regards
Mauro

Hi Mr Mauro,
In Science and Technology, not just in Satellite Link Budgets, one phenomena called NOISE is a must consideration. There are certain parameters which are not well justified either mathematically or scientifically and are called EMPIRICAL. However they are useful for practical implementations. Boltzmann Constant is one such parameter and is purely empirical. The figure going into high -29 level is not verified through any means. And it is considered as A CONSTANT which gives us better guidance for arriving at a practical solution. Why it is attributed to Noise is because characterisation of Noise is also empirically done and only modelling (approximations only) is done to achieve optimised result. The constant helps us in many fields of communications and statistically it has been useful in all applications so far as Noise modelling is considered. Your guess of "it should deteriorate" is NOT valid because IT HAS TO BE THERE for Link budgeting. No Mathematics or Science, as on now, can give any explanation But Boltzmann proposed to include this Constant in all calculations(for Noise Temperature, kT) and proved that it gives good results in Link Calculations. If some one can take interest and do some research on the accuracy of this constant it will improve our performance design results.
Cheers/GTRao
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Thanks for the explanation. Cheers, Mauro

Satellite Communications

Volunteer

#### TIRUMALA RAO G

##### Expertise

Satellite Communications Applications, Link Calculations, Teleports, Earth Stations,VSAT, Tracking, Mobile Communications, Next Generation Networks.

##### Experience

40 Years. Indian Space Research Organisation, PANAMSAT, Satellite Based VSAT Networks, IP Networks.

Organizations
ISRO, PANAMSAT, Engineering Institution for Higher Education (GVP College of Engineering), Consultancy.

Education/Credentials
Graduate in Electronics and Communication Engineering with Distinction. Guiding scholars for their Doctoral thesis in related areas in Academics.