Satellite Communications/Satellite communication


QUESTION: While operating in C- Band my transmit frequency is near 6.1 GHz.My downlink is fine.but as I approach towards frequency less than 5.925 GHz I could not get the corresponding downlink at all. But in spectrum I can see some carrier is already there.And the satellite is's clear in the spectrum that I am unable to receive downlink for any frequency near that already present carrier. I would like to ask if there is any arrangement on transponders for carrier filter or some carrier suppressor for certain bandwidth only.
Thanks in advance.

ANSWER: Hi Mr Sumit,
The question is not that clear: however I give my reply as I understand your problem.

C- Band Satellite Communication uplink Band is 5.925 GHz to 6.425 GHz.And there
is yet another band which is extension of this in the range of UL of 6.725 GHz to
7.025 GHz and is used only in Indian Satellite and given the name of Extended
C- Band.

Your trying to tune your downlink corresponding to the lowest of C - Band
frequency spectrum of Satellite Uplink seems to be confusing.
No transponder in any satellite has downlink frequency corresponding to 5.925 GHz
uplink and reasonably you could not get the corresponding downlink. What you may
be seeing in the spectrum should be the single unmodulated carrier that is known
as BEACON. This is must in all satellites for identifying the Satellite Number
and positioning of our receive system in LOS of the correct satellite. Actually
there should be TWO Beacons identified for each satellite for redundancy purpose.
This is not carrier but a single unmodulated BEACON. No information or signal is
allowed on this BEACON.

I am sure that polarisation etc have nothing to do with your observation, crosspol
or not.You need not bother about filters and so on because the transponders
have no down link at those carriers of signal.

---------- FOLLOW-UP ----------

QUESTION: Many Thanks.
According to you given uplink frequency band 5.925 to 6.425 GHz for C-Band the corresponding downlink frequency band is 3.7 GHz to 4.2 GHz.But on lyngsat I can see some carriers having downlink frequency lower than 3.7 GHz. So i would like to know  what should be corresponding uplink frequency for a carrier having downlink frequency og 3.6 GHz.Please explain me (1) How downlink frequency can be less than 3.7 GHz i,e 3.6 GHz ? (2)How to calculate corresponding uplink frequency for such carriers? (3)Is 2.225 GHz the universal Satellite LO frequency for every satellite operating in C-Band?

ANSWER: Hi Mr Sumit,
There are certain standards enunciated by ITU for Satellite Communications and the Spectrum allotments is one such standards. In C- Band, the spectrum allotted for this purpose is the one you mentioned in first line of your question and the corresponding DL frequencies are also differing by 2225 MHz. That is THE RULE. Other than those frequencies all over the Globe no other spectrum is allowed to be used. I also mentioned that special frequencies are allocated to be used only for specific purposes and not for SIGNAL.
There are no calculations for UL and DL as any mathematical solutions, however in C Band 2225 is the difference given by ITU, in other bands no such figure is applied UNIVERSALLY.
You may refer to the spectrum allocations for different applications in science and technology by International consortium for further details.
PS: Lyngsat like satellites are using LOWER EXTENDED c BAND for TV applications. If you have to receive them you need to have proper Front end systems and cannot use normal C Band systems. As I already told you the Bands are extended on special sanction both on Upper side and lower side but they are not standard bands for receiving with normal C Band receive system and do require special Hardware.

---------- FOLLOW-UP ----------

Suppose I need to uplink on lower extended C band for TV applications do I need to have special setup/hardware other than normal for doing the same.Let me tell you upconverter I work on can uplink frequency lower than 5.925 GHz also.Also in my spspectrum analyzer I an able to see that lower extended c band modulated carrier. Which means downlink path is fine. Plz suggest

Hi Mr Sumit,
I am not sure as to how you have some Transmitter for uplinking without the space segment identified to you. You are supposed to procure equipment suiting what satellite you are getting and the transponder you are getting lease on. Anyway, if you have uplink and downlink facility for the frequencies you mention, still you are not allowed to use any space in transponders without the Satellite operator allotting you the specific spectrum with its Bandwidth usage and power usage.
I am getting confused as to whether you are technical or commercial in these questions. If technical: If technical, a user can access Transponders for uplinking ONLY with the Satellite Operators AGREEMENT. For down linking if we know the characteristic parameters any one can receive with needed Hardware and software. IF YOU PLAN TO UPLINK TV, PLEASE CONSULT YOUR SATELLITE OPERATOR HOW TO GET THE SIGNAL, BOTH UL AND DL. OK?
You may cancel the question preceding this question since both are same, otherwise I keep getting reminders from All Experts Group.

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


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

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

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

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