Hi Samundra,

don't see which path loss you assumed, but for 1 AU (149 mill km), I calculate 286 dB @32 GHz.

Also 3000K seems much to bad.. assume 300K.

So let's add up for 1 AU:

40 dBm (10W) +2x56.4 dBi -286 = -133.2 dBm at RX input

1 Gbit/s assumes 1 GHz bandwidth. 300K is roughly -174 dBm/Hz. 1 GHz = 60dB worse = -116 dBm.

So you end up with -133.2 - (-116) = -17.4 Eb/No.. not good.

If you add 20dB you end up at 2.6 dB Eb/No. Not brilliant, but close. 20dB means 0.1 AU instead of 1 AU = 14.9 Mill km.

I think your result was 4.6E9 m (!), not km.. which is 4.6 mill km. Should be it, if getting back to your assumed 3000K RX.

73s Achim, DH2VA

Date: Tue, 27 Oct 2009 06:03:30 -0400 From: Samudra Haque samudra.haque@gmail.com Subject: [amsat-bb] requesting help on a RF link solution (imaginary ka-band link!) To: Amsat-bb amsat-bb@amsat.org Message-ID: d8c724880910270303k9a3b9cch123289eebcaebf90@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1

Hi, amsat-bb

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 2.4x109 Hz)

Question : is 1 gbps not 1x109 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.

So:

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

f=32.2 GHz

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 109 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 !

Samudra N3RDX

---