Specifications

29
Calculate required power of LO source
P
s
=cablelength(meters)Xcableloss(dB/meter)+P
in
(85309B)
where P
s
=PoweroutoftheLOsource(dBm)
P
in
= Required power into 85309B (0 to 6 dBm)
Select a source that meets your individual preferences and needs. Higher-output power
sources or an amplifier must be used if P
in
is insufficient.
Reference signal level
The reference mixer provides a phase reference for the measurement and a reference
signal for a ratioed measurement (test/reference), to ratio out any variations in signal
levelsfromthesystem.IfyouselectRFandLOsourcesthataresynthesized,orusethe
internal source of the PNA, then 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 9 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.
Determine Cable Length from 85309B unit to mixers
MixersrequireacertainLOdrivepowerlevel;theoutputpowerofthe85309BLO/IF
distribution unit and the RF loss of the cables will determine the maximum allowable
cable lengths. To assure you have enough power at your mixers, use the following
equation to calculate the maximum cable length allowed for your setup:
Cable length (meters) = (P
out
85309B – P
in
mixer)/(cable loss/meter at frequency)
High quality, low loss, phase stable cables are recommended.
Note
ThesameLOcabletypeandlengthisrequired
for both the reference and test mixer modules.
This is to ensure that the insertion losses
through the reference and test mixer module
LOpathsarethesame.UsingthesameLO
cable type also optimizes cable phase track-
ing versus temperature and therefore, system
phase measurement, stability, and accuracy.
When a rotary joint is used, the equivalent
cable length must be added to the reference
mixerLOcableduetotherotaryjointinser-
tion loss. To determine the equivalent cable
length, first determine the insertion loss from
the input to the output of the rotary joint at
themaximumLOfrequency.Then,usinginser-
tionlosscurvesfortheLOcablesbetweenthe
85309B and the mixer module, calculate the
equivalent length in meters at the maximum
LOfrequency.ThereferenceLOcablelength
must be increased by this amount.