12Figure 6. Over-the-air measurement of a 915 MHz RF signal in an office environment with the fluorescent lighting turned on. Shown are the modulation sidebands of the 43 kHz operating frequency of the electronic lighting ballastSources of Interference (continued)Delta markerInterferenceAnother marker function was used to measure the difference between the peak signal level and the largest interference sideband. The “delta marker” function, also found under the [MARKER] menu, reports a -34.11 dB difference between the peak signal and the largest interference just right of the signal peak. The fre-quency difference is 43 kHz, which is the operating frequency of the fluorescent lighting ballast. The other interference sidebands are the harmonics of this 43 kHz frequency.For many wireless systems, these relatively low levels of interference as com-pared to the signal amplitude would not greatly affect the system performance but to some systems, such as a RFID system using passive UHF RFID tags, this level of interference could have a negative effect on system performance.