You find the
( here used ) formulas in THE SATELLITE handbook, ARRL edition (
ISBN 0-87259-658-3 8-12 & 8-13 ). These calculations deliver
First we calculate
the path loss ( dB ).
Path loss is
Note : in this
site you can find a small script ( JAVA ) which calculates this
formula above. To see : click here
is the used ( up or down ) frequency ( MHz ) and rho
is the slant range ( km ).
Second the power
ps ( dBmW ).
Power sum is
: actual transponder power ( dBmW ) plus satellite antenna gain ( dBi ) plus
ground station antenna gain ( dBi ) minus
path loss ( dB ).
Remark : use
dBi if comparing iso, for instance
a 0.5 wave dipole in free space delivers ca 2.15 dBi. An antenna
with a gain of 6 dBd has 8.15 dBi. Iso and the 0.5 wave dipol are
total received noise power,
( dBmW ) and
( at the end ) the Signal Noise Ratio,
dB ), see THE SATELLITE handbook or below.
is : ps minus trnp.
If you want
to analyse the own situation : below you find the required formulas.
total received noise : Ptrn
trnp above ).
k is the Boltzmann
factor 1.3810to(-20) in mW/HzK (K=273+C), Trs is the resulting
system temperature in K, B is the bandwidth
in Hz. Remark : 10logk delivers a -198.6 value.
resulting system temperature : Trs.
noise ( a hardware result ), cosmic noise
( received by the antenna ) and earth radiated noise going into the lobs of the
antenna. ( for instance earth radiated noise at a temperature -5C=268K
). Attention, Trs expressed in temperature, see below.
is the receive system temperature in K, Tsky is the temperature of the sky in
K. Tsky is 'seen' by the antenna.
receive system temperature : Tr.
is the ambient
temperature ( hardware ) in K, Ft is
the system noise figure in dB, concerning
the coax, preamp(s) and input(s) in the circuit. Figure 11.3 ( 11-2
), in the satellite handbook, explains more. Very clear is : every
module must be on the right place !
The part ( in the formula above ) :
10to(Ft/10) is the system
noise factor fT.
Signal Noise Ratio : SNR.
is the received signal power,
the power sum,
ps ( see
You find some
calculations ( examples ) in : the VUSat transponder ( fourth submenu
button ). And a script ( JAVA ) which calculates all the formulas, described.
Also reachable via the fifth submenu button.