How to make adjacent channel power (ACP) measurements

Posted By : Lanna Cooper

For all transmitting devices, it’s important to ensure your device is only transmitting in its designated channel and not interfering with devices operating in other channels. Today Keysight will be showing you how you can make Adjacent Channel Power measurements to accurately determine whether your device is transmitting where it should be.

Keysight will be discussing adjacent channel power measurements, commonly known as ACP for short, and why they are important for helping your device avoid interference with other devices.

One key requirement for every transmitting device is that it should only transmit within its assigned channel. This prevents interference with signals in adjacent channels, where your device is not licensed to transmit.

For example, if you were using a microwave you wouldn’t want it to interfere with your phone if you’re connecting to a speaker via Bluetooth.

That would be really annoying. So, to avoid such an incident, you need to know how to make ACP measurements. ACP is a measure of the average power your transmitter generates in channels next to your intended channel. What’s more useful, though, is the adjacent channel power ratio, or ACPR, which is the ratio of the power in your intended channel compared to the power in adjacent channels.

ACP measurements use a reference level of 0.00dBm, and you want to have the ACPR be as low as possible. Poor ACPR is an indication of spectral spreading or switching transients for the Device Under Test (DUT), which is a definite problem.

To find the Adjacent Channel Power Ratio, find the power of your main channel and the power of your adjacent channels. Then find the ratios of the two integrals.

But, finding the ACPR value by hand can take time and can be a hassle. So to avoid tedious calculations, you can use a signal analyser with a built-in ACP measurement app.

With the built-in app, all you have to do is specify the channel frequency, bandwidth, and channel offsets for your signal. The ACP measurement takes care of everything else.

The results of an ACP measurement are displayed as a bar graph or as spectrum data (or even as a combination of the two), with data for each adjacent channel For documentation and analysis, it can also be useful to have a table including the actual power of the adjacent channels and the transmitter channel in dBm, as well as the power relative to the carrier in dBc for both the upper and lower side bands.

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