Power at reference mixer
Calculation of the power level at the reference mixer depends on the method used to
obtain the reference signal. Almost all ranges obtain the reference channel signal us-
ing a stationary reference antenna to receive a portion of the radiated transmit signal.
Select one of the two methods below for your configuration.
1. Radiated reference signals
When using a radiated reference, the power at the reference mixer can be deter-
mined from the following equation:
P
RM
= E
RP
– P
D
+ G
REF
– L
1
where P
RM
= Power level at the reference mixer (dBm)
E
RP
= Effective radiated power (dBm)
P
D
= Free-space loss (power dissipation) (dB)
G
REF
= Gain of the reference antenna (dBi)
L
1
= Cable loss between reference antenna and reference mixer (dB)
Caution: P
RM
must not exceed the maximum power level of the mixer
1
P
RM
– Mixer conversion loss
2
must be less than +5 dBm so as to not exceed the 1 dB
compression level for the LO/IF input for the 85309B.
2. Coupled reference signals
When using a coupled reference, the reference channel power level can be de-
termined by subtracting the cable insertion losses and the coupling factor of the
directional coupler and adding amplifier gain, if any, to the output power of the
transmit source.
Power at the test mixer
The power at the test mixer is equivalent to the power at the output of the AUT (cal-
culated earlier) if the mixer is attached directly to the AUT. The power level at the test
mixer can be determined from the following equation:
P
TM
= E
RP
– P
D
+ G
AUT
– L
2
where P
TM
= Power level at the test mixer (dBm)
E
RP
= Effective radiated power (dBm)
P
D
= Free-space loss (power dissipation) (dB)
G
AUT
= Gain of the test antenna (dBi)
L
2
= Cable loss between AUT and test mixer (dB)
Caution: PTM must not exceed the maximum power level of the mixer
1
PTM – Mixer Conversion Loss
2
must be less than +5 dBm so as to not exceed the 1 dB
compression level for the IF input to the 85309B.
Note: If the calculated power level at the
mixer is insufficient to achieve the desired
accuracy from the reference channel, the
transmit power or the reference antenna
gain must be increased.
1. +26 dBm (85320A/B, 85320A/B-H50), +20
dBm (85320A/B-H20).
2. Refer to Table 10 in the “Antenna measure-
ment components catalog” section on
page 58 for mixer conversion loss.
32 | Keysight | Antenna Test – Selection Guide