Frequency converters
Figure 38. 85309 LO/IF distribution unit and 85320A/B mixer modules.
The 85309B LO/IF distribution unit and the 85320A/B mixers downconvert a micro-
wave signal to an IF signal that can be measured by the PNA. The distributed frequency
converter uses external mixers for microwave downconversion. These mixers can be
located directly at the antenna under test. The frequency of operation depends upon the
frequency range of the external mixers selected.
Features
– Allows mixers to be located at the antenna under test, minimizing RF cable loss
– Allows fundamental mixing to 18 GHz for best sensitivity
– Provides best rejection of unwanted spurious signals
Description
The 85309B LO/IF distribution unit contains LO signal ampliers, which amplify LO drive
power through RF cables to the mixers. The high output power allows the mixers to be
located more than seven meters from the 85309B. Since the 85309B uses a separate LO
amplier for each channel, channel-to-channel isolation of 100 dB is achieved, minimiz-
ing signal leakage from the reference to the test channel and improving the accuracy of
the measurement. There are also IF ampliers located in the 85309B, which serve as a
preamplier for the receiver, reducing the overall system noise gure signicantly.
A leveling detector in the reference mixer is used to provide the proper LO drive to the
mixers. It is important to use equal length cables to both the reference and test mixers
to ensure the same cable loss, and provide the same LO drive power to both mixers.
An internal lter in the reference IF channel is designed to pass frequencies below 20
MHz. This allows the proper IF signal to be passed for both PNA Option 014 and PNA
Option H11.
54 | Keysight | Antenna Test – Selection Guide
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