In-Band vs. Out-Band Jamming: Understanding the Differences

This page details the difference between in-band jamming and out-band jamming. Jamming signals can originate from both in-band and out-band frequency sources.

In-Band Jamming

With in-band jamming, the jammer’s signal frequency is very close to the RF center frequency of the transmitter being tested. Figure 1 (above) illustrates this concept for a GPS transmitter.

In-band jamming signals are often caused by harmonics, bus systems, and other internal components.

Mitigation Strategies for In-Band Jamming:

To reduce the effects of in-band jamming or to avoid generating these signals, follow these steps:

• Maintain good grounding in the circuit design.
• Shield components as much as possible to avoid unwanted radiation.
• Perform proper layout optimization.
• Use filters (e.g., at the outputs of RF mixers or non-linear components) wherever needed.
• Place the GPS antenna very close to the circuit output port.
• For multimode modems, add band-pass filters (BPFs) before the handset antenna.

Out-Band Jamming

With out-band jamming, the jammer’s signal frequency is different from the RF center frequency of the transmitter under test. Figure 2 (above) depicts out-band jamming affecting a GPS transmitter.

Out-band jamming signals are often caused by nearby wireless transmitters from other systems such as GSM, WCDMA, LTE, WLAN, Bluetooth, etc.

To avoid out-band jamming generation, good grounding rules should be followed in the design. Additionally, filters such as SAW (Surface Acoustic Wave) or band-pass ceramic filters can be used at the antenna input of the GPS receiver.