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# Satellite Communications/Ku band transponder characteristics

Question
Hi Dave,

Can SFD values of a whole transponder be adjusted by satellite operators. And for a multi carrier operation is it possible to weight the carrier EIRP values. For example there are 4 carrier in a transponder of 54dBW. Normally we are dividing the power with 10*log(9/36) = 6dB. And 5 dB OBO. Each carrier will have 43dBW. my question is can we have more than 43dBW for some carriers and less than 43dBW for others. Can we do this adjusting by OFD values of each uplink signal. And for commercial Ku satellites is thee one TWTA for 36MHz transponder or not. Geneally speaking what parameters canwe contona transponder.

kind regards
Salim

Hi Salim,

The SFD (or gain) of a transponder can indeed be adjusted by the satellite operators within a certain extend in order to accommodate different applications. For example if the transponder is used to house the return channels of a VSAT network, the gain will be increased. However if the transponder is used as a big DVB outbound, then the gain is reduced (and compensated with a higher EIRP of the earth station) to reduce the influence of noise. However, the SFD is set for the complete transponder.

As for your second question: yes you can weigh each carrier individually. Specially in your case where you seem to lease the whole transponder. Two conditions exist (as far as I see): 1) the aggregate total used PEB must not be bigger than the sum of the individual carries if they were all operated under equal PEB/BW conditions. 2) As the uplink EIRP of some carries increases, it needs to be checked that there is no violation due to uplink EIRP restrictions (in order to avoid adjacent interference).

Distributing power between the carriers is simply done by adjusting the uplink EIRP for each carrier. The OFD cannot be used for that since it is set for the complete transponder bandwidth.

And indeed, a single 36 MHz transponder will operate with a single TWTA.

So in your case, you could increase the uplink EIRP of one carrier and reduce one (or more) carriers in uplink EIRP in order to maintain the same power consumption on the bird.

Kind regards, Dave
Questioner's Rating
 Rating(1-10) Knowledgeability = 10 Clarity of Response = 10 Politeness = 10 Comment Thank You Dave, we will lease whole transponder in order to operate our UAVs smiltenously over satellite. main requirement is HD video transfer from UAV. Regards

Satellite Communications

Volunteer

#### Dave Suffys

##### Expertise

Questions related to design of satellite communication links.

##### Experience

Satellite communication, link budgets, DVB-S2, ACM

Organizations
Newtec

Education/Credentials
Telecommunications engineer, Sales Support Manager at Newtec