Power Meter Control

Power Meter control is an important function for dealing with cable loss and guaranteeing accuracy of RF signals. Currently, these families of signal sources have the capability to work with a variety of USB power meters for improved accuracy control:

· SSG3000X Series

· SSG5000X Series

· SSG5000A Series

· SSG6000A Series

All models currently support the following models of USB Power Sensor:

The USB power meter connects to the instrument over USB feeding back accurate power reading at the DUT connection point. To achieve this connect the USB cable from the power sensor to the front of the signal generator and connect the RF connection on the power meter to the end of the cable where it will meet the device under test like so:

Once the connections are made, utilize the sensor menu to access the features:

When correctly connected, turn on the Sensor State. The measurement field will now update in real time. You can select the units from:

dBm, dBμV, uV, mV, V, nW, uW, mW, or W

Statistics can also be shown for more complete analysis of the power over time.

Auto Zero performs a zeroing function on the power meter itself. This can improve measurement accuracy in a given test setup, but needs to be performed with the signal power off.

To reduce the impact of noise and zero deviation on the measurement results, it is recommended to zero the power sensor in the following situations:

· Warm-up phase just after connecting to the signal source

· Temperature change exceeds 5 ℃

· Connect the power sensor to the RF output at high temperature

· The power sensor has not been zeroed in the past 24 hours

· Before measuring low-power signals, such as signals with expected measured power more than 10 dB below the lower limit of the measurement range

Level Control is an advanced function that utilizes the power meter in live measurements using an RF splitter. A typical setup might look like this:

In this mode, the power meter continually measures a portion of the signal from the coupler or splitter. The ratio is defined in the level control menu allowing the generator to accurately deliver power to the DUT and the power sensor together.

This feature has an additional use case on the SSG5000A specifically. One of the options on this series is the -LP option that includes a built-in step attenuator for reaching lower power levels. Alternatively, engineers can use the level control function on the standard unit with a USB power sensor and an external attenuator to set lower power levels at the DUT as well.

Using the SSG5083A and an NPR6A power sensor, we used the basic sensor mode to correct for signal loss in our primary test cable. 

Even with a decent quality cable, the power sensor adjustment would be required to meet or exceed the ≤ 0.7 dB level accuracy rating of the generator at the DUT connection point. As one would expect, the cable loss becomes greater as frequency increases making it more important in higher frequency applications.

Power meter control is a great capability for getting the most accuracy out of RF signal generators. This capability is included as a standard (free) feature on Siglent’s line of RF signal sources from 2.1 GHz to 40 GHz.