评估船用甚高频无线电符合iec接收机标准

technical report U.S. DEPARTMENT OF COMMERCEŽNational Telecommunications and Information Administration Evaluation of Marine VHF Radios:Compliance to IEC Receiver Standards Robert L. SoleBrent Bedford U.S. DEPARTMENT OF COMMERCEWilliam Daley, Secretary Larry Irving, Assistant Secretaryfor Communications and Information October 1999 Executive Summary Themaritimemobilefrequencybandsupportsmaritimecommunicationsworldwide.Appendix18of the ITU Radio Regulations (RR) defines the channels of the maritime mobile service. These channelssupportavarietyofcommunicationfunctionsincluding:publiccorrespondence,intershipandship-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 channelsallocatedto 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 MaritimeDistressandSafetySystem(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 test nine commercial and recreational grade marine VHF radios tothe IEC standard and perform radiated tests in areas where severe cases of interference are occurring.Laboratorytesting of the radios to the IEC standard was performed in Boulder, Colorado. The radiatedtests were performed in Savannah, Georgia on the Savannah River and on the Mississippi River in NewOrleans, Louisiana. Mariners in both locations have been reporting cases of severe interference in themarine 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 laboratory 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 thedesired signal power and then injecting interference into the circuit to reduce the SINAD to 14 dB. Theresulting interference-to-signal ratio (I/S) was then calculated in dB and compared to the minimum IECrequirement. The IEC test procedures were used to measure the receiver sensitivity and to calculate thereceiver co-channelrejectionratio,adjacentchannelselectivity,blocking(saturation)andintermodulationrejection ratio.All of the radios easily exceeded the minimum receiver sensitivity requirement. Four radios failed the co-channel rejection ratio test and only two radios passed the adjacent channel selectivity test. In mostcases the radios which failed were within 3-5 dB of passing the tests. The most important IEC tests, whichare related to the complaints about interference in Savannah and New Orleans, were the intermodulationrejection ratio and blocking tests. Four radios passed the intermodulation test while only one passed theblocking test. Radio L, operating in local mode passed both tests and was the only radio to operatesatisfactorily in New Orleans and Savannah. Radio L had an intermodulation rejection ratio of 81 dB whilethe IEC standard is 68 dB. Therefore, it can be concluded from the results of the IEC tests and radiatedteststhattheIECintermodulationrejectionratioperformancerequirementisnotstringentenoughforradiosoperating in some US ports and waterways. The results of these tests show that the Coast Guard and RTCM should consider the followingitems when developing a marine VHF radio receiver standard based on the IEC standard: the IEC 1097-7test procedures and performance objectives do not adequately take into account the severe intermodulationand blocking interference that is occurring in major US ports and waterways such as Savannah and NewOrleans, the receiver standard should be based on the power levels of the unwanted signals that have beenmeasured in Savannah and New Orleans, and the intermodulation rejection ratio test should be referencedfrom aspecificwantedsignalpowerlevelandaminimumSINAD,ratherthanareceiversmaximumusablesensitivity for a 20 dB SINAD. Table of Contents 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-11.2 Test Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21.3 Test Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-21.4 Test Radios. . . . . . . .