How to Make Burst Power Measurements

Is your power leaking into other channels?

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Transcript: Measuring power from a device that is transmitting continuously is pretty straightforward, but measuring power from a device that is transmitting in bursts can be much more complicated.

Hi, I’m Ally, and welcome to Keysight’s Rapid Measurement Series. Today we’re going to learn how to measure the average carrier power of signals that transmit in bursts like THIS.

Burst power, or transmit power is used to verify the accuracy of the power from your device. Many signals like Bluetooth, GSM/EDGE and NADC transmit in bursts. But we only care about average power of the burst not the power over time.

Wireless carriers are concerned about whether their mobile stations and base stations are transmitting enough power to maintain acceptable call quality. And have sufficient modulation accuracy too ensure that power is not leaking into frequency channels or timeslots allocated for others.

To do this, they must measure burst power. When measuring burst power you’re determining the average power at or above a specified threshold or during a detected burst width. The threshold value may be absolute, or relative to the peak value of the signal. The average carrier power can be calculated based on the burst width and threshold level.

To test these systems, you need to measure the power only during transmission and you need to measure any variation in power during the burst.

As an example, let’s take a look at this GSM signal with our signal analyzer.

We’ve set the radio standard to GSM, to match the signal’s burst power. This analyzer has presets built in, or you could go in and set it up manually based on the spec. You can also manually select a specified burst width or set a predefined threshold, but we are going to use automatic burst detection to make things easier. On the vertical axis, we have amplitude in dBm as you would expect on a signal analyzer.

But, on the horizontal axis, we have time instead of frequency, with a displayed period slightly larger than the burst beginning at 0 and ending at 640 microseconds.

The signal analyzer burst power measurement allows us to see the shape of the burst, the full width of the burst, the threshold level, currently set to -30 dBm, and the output power during the measured burst, which is -10 dBm.

So now we have measured the GSM si ... https://www.youtube.com/watch?v=HNDW48gce-I