Reference Signal Level; Calculating Reference Power - Agilent Technologies 85301B Configuration Manual

Select a source that meets your individual prefer-
ences and needs. The higher-output power sources
are useful when the distance between the LO source
and the 85309A LO/IF, distribution unit is longer
than the standard allowable cable lengths shown
in Tables 6 through 11. By using the cable inser-
tion loss curves (Figures 12 and 13) the additional
cable length can be calculated for the higher-output
power sources. The 1 Hz frequency resolution
(Option 008) is recommended for both the RF and
LO sources to provide a system frequency resolu-
tion of 1 Hz instead of 1 kHz.

Reference signal level

The reference mixer provides a phase reference for
the measurement, and a reference signal for a
ratioed measurement (b2/a1) to ratio out any vari-
ations in signal levels from the system. Since both
the RF and LO sources are synthesized, phase
locking the receiver is not required. The only
requirement for the reference channel is that the
signal level be high enough to achieve the desired
accuracy for the measurement. Figure 2 shows the
magnitude and phase errors as a function of signal-
to-noise ratio; this also applies to errors contributed
by the reference channel. For most applications, it
is desirable to maintain a 50 to 60 dB signal-to-
noise ratio. For fundamental mixing (2 to 18 GHz),
the sensitivity is -113 dBm; maintaining a 50 to 70 dB
signal-to-noise ratio would require a reference
channel signal level of -40 to -60 dBm.
13
Record the model number of the selected LO
source in Figure 18.

Calculating reference power

Calculation of the reference channel power level
depends on the method used to obtain the refer-
ence signal. Use the sections below to determine
the reference channel power level for either a radi-
ated reference signal or a coupled reference signal.
Radiated reference signals
When using a radiated reference, the reference
channel power level can be determined from the
following equation:
P (REF) = P + P /P
r t r
where P (REF) = Power level at the output of the reference
r
antenna
P = Transmit power level (dBm)
t
P /P = Transfer function of the range
r t
G (REF) = Gain of the reference antenna
14
Record the reference antenna gain in Figure 18.
Record the calculated reference channel power
15
level Pr (REF) in Figure 18.
If the calculated reference channel power level
is insufficient to achieve the desired accuracy
from the reference channel, the transmit power
or the reference antenna gain must be
increased.
Coupled reference signals
When using a coupled reference, the reference
channel power level can be determined by sub-
tracting the cable insertion losses and the coupling
factor of the directional coupler and adding ampli-
fier gain, if any, to the output power of the transmit
source. Insertion loss curves for 85381 series cables
are shown in Figures 12 and 13.
16 Record the calculated reference channel power
level Pr (REF) in Figure 18.
+ G (REF)
t
13