Signal booster oscillation occurs when the outside and inside antennas are too close, leading to a feedback loop that can disrupt cellular networks and damage the booster system[7]. The FCC requires signal boosters to automatically detect and correct oscillation issues by reducing power or shutting down[7].
Detection Methods
* Lights on the Booster: Red lights on the signal booster often indicate oscillation[5].
* Signal Spectral Analysis: This technique can identify weak oscillation signals by analyzing the noise power spectrum at the power-line input of DC/DC converters[3]. It identifies abnormal signal amplitude at certain frequencies that may be caused by front-end or feedback-loop oscillations of the converter[3].
* Muting Transmission: Oscillation detection can be achieved by temporarily muting the transmission of the output signal from the output antenna and comparing power levels within the signal path during muted and unmuted periods[9]. The difference between the power levels indicates the strength of the leakage signal and thus the oscillation[9].
Mitigation Methods
* Antenna Repositioning: Increasing the separation between the internal and external antennas is crucial[4][7]. Vertical separation is more effective than horizontal[4]. For building booster systems, aim for around 20 feet (6 meters) or more[4].
* Antenna Direction Adjustment: If directional antennas are used, ensure the external antenna points away from the internal antenna to minimize signal feedback[4].
* Increase Antenna Isolation: Add physical barriers or shielding between the antennas using metallic sheets or dense materials to reduce signal overlap[4]. In vehicles, metal roofs can provide isolation[4].
* Gain Reduction: Lowering the boosterâs gain can reduce oscillation[4]. Some boosters allow gain adjustment via knobs, touchscreens, or apps[4]. Reducing gain, however, may decrease the coverage area of the amplified signal[7].
* Automatic Limiting Control: Consumer boosters should have automatic limiting control to protect against excessive input signals that could cause output power and emissions to exceed authorized levels[1].
* Attenuators: Inserting an attenuator between the booster and the outside antenna can solve overload issues[4].
* Anti-Oscillation Mechanisms: Consumer boosters should detect and mitigate oscillations in uplink and downlink bands via automatic gain reduction or shutdown[1][4]. Oscillation detection and mitigation should occur automatically within 0.3 seconds in the uplink band and within 1 second in the downlink band[1]. The booster must continue mitigation for at least one minute before restarting, and after five restarts, it should not resume operation until manually reset[1].
[1] https://www.law.cornell.edu/cfr/text/47/20.21
[2] https://www.nerc.com/comm/RSTC_Reliability_Guidelines/Oscillation_Analysis_for_Monitoring_And_Mitigation_TRD.pdf
[3] https://nepp.nasa.gov/files/17340/08_004_2_GSFC_Wang%20Final%20Rport%20Early%20Oscillation%20Detection%20for%20Hybrid%20DC_DC%20Converters%20final%208_09.pdf
[4] https://powerfulsignal.com/support/knowledgebase/consideration/what-is-cell-signal-booster-oscillation/
[5] https://www.weboost.com/blog/antenna-separation-and-why-its-important
[6] https://toshiba.semicon-storage.com/info/docget.jsp?did=67687
[7] https://www.wilsonpro.com/blog/commercial-cell-phone-signal-booster-oscillation-and-overload
[8] https://www.federalregister.gov/documents/2013/04/11/2013-07396/signal-booster-rules
[9] https://patents.google.com/patent/US7593689B2/en