Conversion Loss Using The Frequency Offset Mode; An Example Spectrum Of Rf, Lo, And If Signals Present In A Conversion Loss - Agilent Technologies 8719D User Manual

Conversion Loss Using the Frequency Offset Mode

Conversion loss is the measure of efficiency of a mixer. It is the ratio of side-band IF power
to RF signal power, and is usually expressed in dB. (Expressing ratio values in dB amounts to
a subtraction of the dB power in the denominator from the dB power in the numerator.) The
mixer translates the incoming signal, (RF), to a replica, (IF), displaced in frequency by the
local oscillator, (LQ. Frequency translation is characterized by a loss in signal amplitude and
the generation of additional sidebands. For a given translation, two equal output signals are
expected, a lower sideband and an upper sideband.
An Example Spectrum of RF, LO, and IF Signals Present in a
The analyzer allows you to make a swept RF/IF conversion loss measurement, holding the Lo
frequency llxed. You can make this measurement by using the analyzer's frequency offset
measurement mode. This mode of operation allows you to offset the analyzer's source by a
fixed value, above or below the analyzer's receiver. That is, this allows you to use a device
input frequency range that is different from the receiver input frequency range.
The following procedure describes the swept IF frequency conversion loss measurement of a
broadband component mixer.
1. Set the Lo source to the desired CW frequency and power level.
CW frequency = 1000 MHz
Power = 13 dBm
2. Set the desired source power to the value which will provide -10 dBm or less to the
R-channel input. For the HP 8719D/20D, press:
Since the default source output power of the HP 8722D is below 0 dBm, no
Note
reduction in source output power is required for this procedure.
3. Connect the measurement equipment as shown in Figure 3-5. The low pass filter is
required to limit the range of frequencies passed into the R-channel input port. The filter is
selected to pass the IF frequencies for the measurement but prevent the Lo feedthrough
and unwanted mixer products from confusing the phase lock loop operation. A pad is used
Figure 3-4.
Conversion Loss Measurement
M a k i n g M i x e r M e a s u r e m e n t s ( O p t i o n