萨凡纳-加和新奥尔良-拉港区海上甚高频无线电性能评估

technical report U.S. DEPARTMENT OF COMMERCEŽNational Telecommunications and Information Administration Evaluation of Marine VHF Radios:Performance in the Savannah, Ga.and New Orleans, La. Port Areas Robert L. SoleBrent Bedford Larry Irving, Assistant Secretaryfor Communications and Information March 1999 EXECUTIVE SUMMARY Themaritimemobilefrequencybandsupportsmaritimecommunicationsworldwide.Appendix18of the ITU Radio Regulations (RR) defines the channels of the maritime mobile service. These channelssupport a variety of communication functions including: public correspondence, intership, ship-to-coast,coast-to-ship,portoperations,callingandvarioussafetypurposes.Safetyfunctionsincludedistress,searchandrescue,shipmovement,navigation(bridge-to-bridge)communications,andmaritimesafetyinformationbroadcasts.Mariners in the United States and other countries are experiencing interference on channels allocated to the above functions. The Radio Technical Commission for Maritime Services (RTCM)established Special Committee 117 to investigate the interference and determine if the InternationalElectrotechnical (IEC) standard 1097-7 “Global Maritime Distress and Safety System (GMDSS)-Part7: Shipborne VHF Radiotelephone Transmitter and Receiver-Operational and PerformanceRequirements, Methods of Testing and Required Test Results” would be sufficient to protect marineVHF radios from interference. In support of this effort, NTIA, in coordination with the Coast Guard andRTCM SC-117, undertook a task to perform tests on commercial and recreational grade marine VHFradios to the IEC standard and perform radiated tests in areas where severe cases of interference areoccurring. Laboratory testing of the radios to the IEC standard was performed in Boulder, Colorado. Theradiatedtests were performed in Savannah, Georgia on the Savannah River and on the Mississippi Riverin New Orleans, Louisiana Mariners in both locations have been reporting cases of severe interference inthe marine VHF band on the waterways for quite some time now. Some of the channels experiencing theinterferencearekeychannelsusedforsafetyandbridge-to-bridgecommunications.Theinterferenceisverydisruptive to normal operations on the river and is distracting to the radio operators.The IEC tests and radiated tests were based on receiver SINAD measurements. In the IEC 1097- 7 test procedures, the SINAD of a receiver being tested was set to 20 dB by adjusting the desired signalpower and then injecting interference into the circuit to reduce the SINAD to 14 dB. The resultinginterference-to-signalratio(I/S)wasthencalculatedindBandcomparedtotheminimumIECrequirement.In the IEC tests, the interference was simulated using signal generators. The IEC tests simulated adjacentand co-channel interference, receiver saturation (blocking), and intermodulation interference. The radiatedtests used emitters that were present in the electromagnetic environment of the test area to degrade theSINAD.Theradiatedtestingrevealedthatemittersintheenvironmentwerecausingreceiversaturationandintermodulation/cross modulation interference in the radio receivers.Spectrum recordings were taken during the radiated tests when the SINAD measurements were 14 dB or less. These recordings were used to identify the sources of interference in Savannah and NewOrleans. The recordings seem to indicate that the interference is due to NOAA weather broadcasts andland mobile transmitters (1997 Code of Federal Regulations, Parts 90 and 22 Title 47) operating withinand around the marine VHF band. The antennas of the weather broadcast and land mobile transmittersare located very close to the river’s edge in both locations and transmit at higher power levels than themobile marine VHF radios. Both of these factors contribute to the severity of the interference. However,it should be noted that the land mobile transmitters are operating in compliance with respect to the FCCrules and regulations for output power, frequency tolerance, and spurious emissions. The NOAA VHFweather broadcasts also seem to be operating properly. Because they are operating in compliance with the FCC rules and regulations, it would be difficultto impose any operating restrictions on land mobile systems operators. Therefore practical solutions tosolve this problem would be to continue the development of receiver standards through RTCM SC-117,encourage mariners to use radios that are more resistant to interference, and develop antenna sitingguidelines for future deployment of weather broadcast and land mobile transmitters to reduce interference. TABLE of CONTENTS Section 1. Introduction1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11.2 Test Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21.3 Test Radios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .