This chapter covers several RF-deck-specific options and related features that can be used in a number of different applications. Several of these options are touched on in other chapters of this guide but this chapter is to serve as a central information point on items directly affecting signal levels into and out of the instrument. The relevant options are
• Option 32: Source 2 re-direct to Port 1 (requires Option 31- dual sources). This is used for signal combining typically and can be particularly useful for IMD measurements.
• Option 51: Access loops to source paths and coupled test and reference paths. Options 51, 61, and 62 are mutually exclusive.
• Option 61/62: Step attenuators added to the source and coupled test paths as well as access loops.
Note
Options 51, 61, and 62 are mutually exclusive.
• Option 53: External ALC access to allow for leveling in different places in the setup (e.g., after a pre-amplifier added into a source loop path).
As one can gather from the above descriptions, the source loops, the source-side attenuators and the amplifier access can all be geared toward increasing or decreasing the drive power of the VNA’s internal source. This may be useful for:
• Inserting a driver amplifier for power amplifier measurements (where the DUT test conditions require a higher drive level than the VNA normal port power specifications would support).
• Increasing power for very high loss measurements (in an antenna setup, for example) where signal-to-noise ratio may be a challenge.
• Decreasing the power below normal ALC range for extremely sensitive devices (e.g., very high gain amplifiers or devices with very low compression points).
The reference and test loops and attenuators (and the amplifier) correspondingly alter the levels going into the instrument’s downconverters. Commonly, the level must be reduced to avoid instrument compression when measuring high power DUTs. The level may also need to be increased in very high loss situations (the antenna example again) which could be done with the amplifier in the loop or by directly injecting the signal into the downconverter (when reflectometry on that port is not needed).