Satellite relay system and transmission losses

[Adir_Sh]

Hello.
Below I have a problem I can't quite understand to the full:

http://www.israup.net/images/027d25c3acde86a09bcb9e1ed869560a.png

http://www.israup.net/images/6757f5c30cbcfe051295b1b1e4614489.png

And that is the suggested solution:

http://www.israup.net/images/955a5be90466defb399d78c7693c8e2f.png

Now my question is about that $g_{amp}$ calculation in the solution provided in the solution manual for the book I'm solving from.
If $P_{in}=35 dBW$ and not 30 dBW as it is in the example, and also uplink frequency value changes from the example provided to the question, then how $g_{amp}=18+144=162 dBW$? Shouldn't it be $g_{amp}=18-103=-85 dBW$? -103dBW should reasonably be substracted (and not like 144 being added) since it stands for transmission loss, isn't it?
But the in Psat (out) it seems like they do compensate for it because they do add 162dB...

I have a strong feeling that I miss something here in the idea behind $g_{amp}$. Could it gain the whole uplink loss in some way? I'm quite curious about that really... :uhh:

Thanks.

 

[lewando]

The big typo in example 3.3-1 is the statement: 35dBW + 55dB - 199.1dB + 20 dB = -144.1dBW.

The result should be -89.1dBW.

The idea behind g_amp is that it is variable (within some practical limits) and is whatever it needs to be to produce 18dBW (input to the downlink transmitter antenna).

 

[Adir_Sh]

Another question, same subject

Well, first of all thanks for your quick response lewando
I have another little question:

I found this solution on Chegg.com:

http://www.israup.net/images/06364d1120e02d09bb453073c3d4fb12.png

Everything is clear to me, apart from that multiplication in 6 when calculating the maximum antenna gain. Why 6?

Do you suggest there's probably a mistake? Or maybe I misinterpret once more? :shy:

Thanks.

 

[lewando]

I don't know where that 6 came from. One possibility is that the chegg equation is for a specific antenna. Your working assumption that A_e (the effective aperature) = area is based on unity efficiency of the "antenna area". Perhaps the chegg antenna had less than unity efficiency.

 

[rezeew]

Hello there,

Thank you for bringing this problem to my attention. From what I can see, the solution manual is incorrect and the calculation for g_{amp} should indeed be g_{amp}=18-103=-85 dBW. As you mentioned, the -103 dBW represents the transmission loss in the uplink frequency, so it should be subtracted from the 18 dBW gain of the amplifier to get the total gain of -85 dBW.

I can see how the solution manual may have caused some confusion, but it is important to remember that transmission losses are typically expressed as negative values, so they should be subtracted instead of added. I would suggest bringing this error to the attention of your instructor or the author of the book to ensure that it is corrected for future editions.

I hope this helps clarify the concept of g_{amp} and the calculation involved. Let me know if you have any further questions. Good luck with your studies!