[amsat-bb] requesting help on a RF link solution (imaginary ka-band link!)
samudra.haque at gmail.com
Tue Oct 27 03:03:30 PDT 2009
CQ any satellite link budget expert !
I'm trying to do a calculation on my own based upon published specs
for the NASA MRO Ka-band experiment, but am getting some unexpected
results for a Ka-band simplex link with Temp=3000K (hypothetical),
operating with a Signal to Noise ratio (unitless) figure of 1.171
(representing 4.5 dB eb/no with a data rate of 1 Gbps and a bandwidth
of 2.4x10^9 Hz)
Question : is 1 gbps not 1x10^9 bps ?
Question : if both antennas are 3m parabolic (both are the same type)
with 56.4 dBi boresight gain, what would you think the furthest
distance the link can perform with SNR of 1.171. I have actually used
a padding of 3 dB Eb/No in my link budget, so am not worried about any
further signal loss at first (ok, I should be ..) For the exercise, I
am choosing a 10 Watt estimated output on an arbitrary basis.
P_t = 10W
G_t = 56.4 dBi = G_r , can we assume the same gain for TX and RX on a
parabolic dish ?
T = 3000K at receiver
SNR = 1.171 required
B = 2.4E9 Hz, (bpsk, ldpc code 0.5)
DR = 1E9 bps
So, I am puzzled why this link budget says the range with these
parameters is equal to 4.644 x 10^9 Km -- that seems to be a long
distance ! What am I not able to conceptualize.
BTW, I know if I send this out, the answer will come to me soon
thereafter, but for education, I would like to know where the problem
in my understanding lies !
More information about the AMSAT-BB