Equipment Setups

There are several equipment setups which are supported by SDR Calibrator, the simplest being a signal generator connected to an SDR (or even just an SDR without a signal generator). Depending on the level of accuracy needed, as well as the type of test or test parameters, additional equipment may be needed. Below is list of the supported equipment setups ([USER_SET] in the parameters indicates a parameter that is required, but you may set to your desired value):

Unconnected SDR

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In this setup, the SDR is simply connected to the controlling PC. If a 50-ohm terminal is connected to the measurement port, this setup is used to measure noise parameters such as displayed average noise level (DANL). In this case, only the SDR module will be loaded, regardless of other equipment parameters added in the profile. Using the following parameters in the Power section of the profile will announce this setup for tests which do not require the use of a stimulus:

power_stimulus = None

Signal generator connected to an SDR

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This is the basic setup for measuring a stimulus with the SDR. In this case, the power set on the signal generator is taken as the "true" power applied to the SDR. In this case, the SDR and Signal Generator modules will be loaded. Using the following parameters in the Power section of the profile will announce this setup for tests which are able to apply a stimulus:

power_stimulus = 'single_cw'
power_level_mode = 'normal'
power_level = [USER_SET]

Signal generator connected to an SDR through a programmable attenuator

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Since signal generators tend to be more accurate with higher power levels, whereas attenuators tend to be far less power level dependent, this is a more accurate way to apply lower power levels to the SDR. In this case, the SDR, Signal Generator, and Programmable Attenuator modules will be loaded. To achieve the power_level requested at the SDR interface, the programmable attenuator will turn on its attenuators to bring the signal generator output level as close to the profile's power_base_power as possible. The signal generator will then be set to the "left-over" power defined by the difference between the power_level and the amount of attenuation the programmable attenuator was able to achieve.

Using the following parameters in the Power section of the profile will announce this setup for tests which are able to apply a stimulus (you must enter a power level of your choosing in dBm):

power_stimulus = 'single_cw'
power_level_mode = 'attenuator'
power_base_power = [USER_SET]
power_level = [USER_SET]

Power verification with a power meter

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Most tests which measure a power level and apply a stimulus can also verify the power level with a power meter. In this case, the RF Switch and Power Meter modules are loaded in addition to the other equipment modules already loaded. During the test, while the stimulus is being setup, the following additional steps are performed:

• The switch is turned from the SDR to the power meter
• The stimulus is turned on
• The power meter reads the power level, which is then used to calculate the "true power" at the SDR input port
• The stimulus is turned off
• The switch is turned from the power meter to the SDR

This setup can be used with the either of the two setups described above for applying the stimulus. If the programmable attentuator is used, the "true power" is calculated to be the power measured by the power meter minus the attenuation applied by the programmable attenuator. If the programmable attenuator is not used, the "true power is calculated to be the power measured by the power meter directly. This "true power" is then scaled according to the RF switch's calibration if one was set in the profile.

_Please note: Most power meters cannot measure below powers of ~-50dBm accurately because of noise and bandwidth constraints. If your test will use powers below this level and an accurate power reading is necessary, you must use the programmable attenuators to control the power level or you must write a power meter driver which uses a signal analyzer (or something similar) to accurately measure the power at lower power levels.

Using the following parameters in the Power section of the profile will announce this setup for tests which are able to measure power levels (typically any test measuring power with the SDR):

power_verification = 'power_meter'