[time-nuts] time-nuts Digest, Vol 189, Issue 37

[Karen Tadevosyan]

Hi Bob,

Your calculation is close to real with QO-100. 
With ERP = +55 dBm we have about 30 dB S/N on RX side.
If so when we changing the TX LO's PN level from 120 dBc/Hz  to 90 dBc/Hz we
lose only 3 dB in terms of RX S/N? 
Not sure if you can even notice ...

Karen, ra3apw

> 
> Hi
> 
> Assuming you know the power level you will be delivering to the sat and
the
> noise figure of the
> receiver on the sat, the calculation is just as presented earlier. If the
antenna
> on the sat has gain,
> that also gets into this and that.
> 
> Using some made up numbers, since I do not have the real ones for this
> exact system:
> 
> You start out with +50 dbm ERP from your antenna.
> You have a link loss of 190 db.
> The sat antenna has 1 db of gain.
> 
> You are delivering 50 - 190 + 1 = -139 dbm to the sat.
> 
> If the noise figure of the sat reciever is 3 db, then it?s noise floor is
-174 + 3 =
> -171 dbm
> 
> That puts a limit on the uplink signal at 171 - 139 = -32 dbc.
> 
> If the noise on your transmitted signal is 32 db down, you will degrade
the
> SNR at the sat by
> 3 db. ( = they add as power not voltage).
> 
> You will need to do some research with Mr Google to come up with the real
> numbers to plug
> into the calculations. They are different for each system design ( your
> antenna, your erp ?.).
> 
> Bob
>