the effective
noise temperature of the receive antenna. The default temperature is 290
K. All noise figure calculations within a project are computed
relative to the antenna temperature defined in this dialog.The Link Budget report allows you to include antenna parameters and path loss data in the system model. The field strength at the receive antenna can be specified explicitly or derived from transmitter/path loss data you supply. In either case, the Receive Antenna group and Receiver group define all the parameters necessary to model the receive portion of the system.
Receive Antenna
The fields in this group also appear on the antenna tab of the Project Properties dialog box and can be edited there as well.
Ant. Temp (K)
the effective
noise temperature of the receive antenna. The default temperature is 290 K. All noise figure calculations within a project are computed
relative to the antenna temperature defined in this dialog.
Ant. Gain (dBi)
the effective
gain relative to an isotropic antenna (dBi).
Ant. Factor (dB/m)
the antenna
factor (AFE) expressed in dB/meter.
The antenna vendor usually supplies the antenna factor. The receiver input
power at a given frequency is calculated from the field strength present
at the antenna and the antenna factor. The formula relating the parameters
is
Freq (MHz)
the receive frequency
in MHz
Receiver
BER (Req’d)
the bit error
rate performance required to meet receiver sensitivity. This field is
only available for digital demodulation. BER is mathematically related
to Eb/No according to the particular
modulation
scheme chosen for the project. Entering a value in either of these
fields causes the equivalent value to be entered in the related field.
Demodulation Type
displays
the demodulation type selected in the System
Properties dialog box. This information is repeated in this dialog
for convenience.
Sens. Loss (dB)
the loss
in sensitivity (dB) due
to inefficiencies in demodulator implementation.
Eb/No (dB Req’d)
the margin
(dB) above the effective noise floor (MDS)
required to meet receiver sensitivity. For digital demodulation the margin
is in terms of the bit energy to noise density ratio; otherwise, the report
displays S/N (dB, Req’d) next
to the field to allow entry of the required signal-to-noise.
Es/Eb (dB)
the ratio of
the energy per symbol to energy per bit. This parameter is zero for all
modulation schemes except QPSK and
/4 DQPSK in which case
the value is 3.01 dB. The effect of multiple bits per symbol must be included
to relate sensitivity to MDS.
G/T (dB/K)
a figure of merit
used primarily in satellite communications. It is the ratio in dB of the
antenna gain to the sum of the receiver and antenna equivalent noise temperatures,
or
G/T is the same when computed at any reference plane within the system and is proportional to the system’s signal-to-noise ratio, S/N; thus any improvement to G/T constitutes an equivalent improvement to S/N.
Margin (dB)
the margin in
dB beyond that required to meet system sensitivity level (see below),
or Pin - Sensitivity
NF (dB)
the standard noise
figure of the cascaded components.
NF Actual (dB)
the actual
noise figure of the cascaded components. Displayed when the source temperature
is other than 290 K. (See Noise Calculations in
Mathematical
Definitions)
Sensitivity (dBm)
The minimum
system input level necessary to detect the signal.
Sensitivity = S/N (desired margin) + Loss + MDS, or
Sensitivity = Eb/No (desired margin) + Sens. Loss + MDS + Es/Eb (digital)
Sensitivity (dB
V/m)
The minimum system input level (expressed in microvolts/meter)
necessary to detect the signal.
Te (K)
the effective noise
temperature of the cascaded components and pages in degrees Kelvin.
Transmit Model
Checking the Transmit Model box displays the Transmitter group in the dialog. This group has several fields related to transmitter parameters.
Power
the power in dBW (dB
relative to 1 Watt) available at the transmitter output.
Cable Loss
the loss in dB
of the cable linking the transmitter to its antenna.
Ant. Gain
the effective isotropic
gain (dBi) of the transmit antenna.
EIRP
the Effective Isotropic
Radiated Power of the transmitter expressed in dBW.
Range
the line of sight distance
(Km) between transmit and receive antennas.
Path Loss
the path loss (dB)
can be provided by the user or calculated by SysCalc.
User
to enter a loss that
was empirically obtained or calculated by some other program, check the
box labeled Measured Path Loss
and enter the loss in the field.
Calculated
to have SysCalc
calculate the ideal free-space path loss clear the Measured
Path Loss check box. The
path loss will be computed as
Where f is the frequency in MHz and R is the range in meters
IMPORTANT
The value calculated by SysCalc is based on the ideal
loss in free space and does not account for important factors such as
atmospheric or multi-path conditions. Since the calculated value is purely
theoretical it should only be used as a frame of reference for a more
rigorous calculation.
The transmitter power is ultimately converted to a power (dBm) present at the antenna output (receiver input). With path loss computed as above (or provided by the user) the power (dBm) at the antenna output is
where,
PTx is the transmitter power
Cable Loss is the transmitter cable loss
Path Loss is defined as above
GTA is the transmitter antenna gain
GRA is the receiver antenna gain
Receive Model
Clearing the Transmit Model
box displays the Field Strength group in the dialog. This group allows
you to define the field strength present at the receive antenna. The field
strength can be input as
V/m or dBV/m by
checking the appropriate box. The field strength is ultimately converted
to a power (dBm) present at the antenna output (receiver input). With
the antenna factor computed as above the power (dBm) at the antenna output
is
where FS is the field strength (dBuV/m) provided by the user
