In today's highly developed wireless communications, interference is absolutely unpopular, and it can cause noise, cell phone calls, and communication interference. In a cellular network, interference is actually part of the network. Although more and more networks currently have built-in interference detection, these tools are usually not very effective because they only target several types of signals and may only measure the effects of problems on one channel.
Spectrum analyzers are a tool that engineers rely on to measure and identify sources of interference. There are many different types of spectrum analyzers on the market, but many prefer battery-powered small spectrum analyzers because they need to be able to move freely and correlate data from multiple locations.
Search for interference frequenciesWhen searching for interference, the first challenge is to determine if the interference signal can be measured. In general, the victim receiver is easy to determine, and this is the first place to look. The challenge is that the wireless receiver is capable of detecting very small signals. Therefore, the spectrum analyzer must be set close to the sensitivity of the analog victim receiver in order to "see" what the receiver "sees". For example, the sensitivity of a conventional LTE receiver is approximately -120 dBm. That is, any RF pollution greater than -120dBm on the receiver channel can affect the operation of the receiver.
The spectrum analyzer has two control functions to adjust the sensitivity: reference level (RefLvl) and resolution bandwidth (RBW). The challenge is that when measuring in the air (OTA), the reference level must be kept fairly high (-30dBm) so that the spectrum analyzer is not overloaded when measuring all RF energy.
In most spectrum analyzers, the RBW control function is automatically set based on the user-configured bandwidth. In OTA measurements, the RBW value should be lowered to see small signals that may affect the victim receiver. This combination results in a very low scan rate for most battery powered spectrum analyzers, that is, it is not possible to see small intermittent transients that cause interference.
The real-time spectrum analyzer solves this problem by measuring the spectrum using a narrower filter of RBW faster than the basic swept spectrum analyzer. Figure 1 shows the results of an LTE signal over the air (OTA). In this case, the bandwidth is set to 40 MHz and the default RBW is 300 kHz. Note that it is difficult to determine the radiation at the center of the picture. If there is a narrowband (< 300 kHz) interferer, this setup is almost impossible to see interference.
Figure 1: Example of LTE signal OTA results.
Figure 2 is the same setup using a 1 kHz RBW filter. In this case, it is clear that the LTE channel and effective scan time are only increased to 40 ms. This is one of the primary benefits of using a real-time spectrum analyzer (RTSA) to measure wireless channel interference. These instruments were originally expensive and must be fixed on the desktop, but now there is a battery-powered, USB-based, economical real-time spectrum analyzer on the market that makes RTS a practical choice for search interference.
Figure 2: Real-time spectrum analyzer with 1kHz RBW filter improves the ability to view LTE signals.
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| Laptop Model | Adapter Output |
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| Inspiron Mini 10 10v 1010 1010n 1010v 1011 1011n 1011v | 19v 1.58a, 5517 |
| Inspiron 14V 14VR M4010 N4020 N4030 | 19.5v 4.62a, 7450 |
| Inspiron N4110 N5110 N7110 M5010 | 19.5v 3.34a, 7450 |
| 630M 640M E1405 | 19.5v 4.62a, 7450 |
| Inspiron 15-3521 17-3721 | 19.5v 3.34a, 7450 |
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| Vostro 1710 1710n 1720 1720n | 19.5v 4.62a, 7450 |
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| Latitude D410 | 19.5v 3.34a, 7450 |
| Inspiron 1120, 1121, M101 | 19.5v 3.34a, 7450 |
| Inspiron Mini 1012 1018 | 19v 1.58a, 5517 |
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