title: LLRP Impinj can't see Antenna Port when tag seen
body: <p>I am currently connecting to an Impinj Speedway reader 220 and I have 2 antennas connected to it.</p>
  
  <p>When I load the Impinj MultiReader application and switch on Display Antenna Port, it gets which antenna the RFID tag was read on back to the application.</p>
  
  <p>I am currently using C# to connect to the reader (though I believe the SDK is similar for all languages). Below is the sample code I am using, however I don't know which configuration option turns on the ability to read the antenna port.</p>
  
  <p>Could someone please let me know which configuration option turns on the option so the AntennaID is returned with the tag?</p>
  
  <pre><code>        MSG_ERROR_MESSAGE msg_err;
          MSG_ADD_ROSPEC msg = new MSG_ADD_ROSPEC();
  
          // Reader Operation Spec (ROSpec)
          msg.ROSpec = new PARAM_ROSpec();
          // ROSpec must be disabled by default
          msg.ROSpec.CurrentState = ENUM_ROSpecState.Disabled;
          // The ROSpec ID can be set to any number
          // You must use the same ID when enabling this ROSpec
          msg.ROSpec.ROSpecID = 123;
  
          // ROBoundarySpec
          // Specifies the start and stop triggers for the ROSpec
          msg.ROSpec.ROBoundarySpec = new PARAM_ROBoundarySpec();
          // Immediate start trigger
          // The reader will start reading tags as soon as the ROSpec is enabled
          msg.ROSpec.ROBoundarySpec.ROSpecStartTrigger =
          new PARAM_ROSpecStartTrigger();
          msg.ROSpec.ROBoundarySpec.ROSpecStartTrigger.ROSpecStartTriggerType =
          ENUM_ROSpecStartTriggerType.Immediate;
          // No stop trigger. Keep reading tags until the ROSpec is disabled.
          msg.ROSpec.ROBoundarySpec.ROSpecStopTrigger = new PARAM_ROSpecStopTrigger();
          msg.ROSpec.ROBoundarySpec.ROSpecStopTrigger.ROSpecStopTriggerType =
          ENUM_ROSpecStopTriggerType.Null;
  
          // Antenna Inventory Spec (AISpec)
          // Specifies which antennas and protocol to use
          msg.ROSpec.SpecParameter = new UNION_SpecParameter();
  
          PARAM_AISpec aiSpec = new PARAM_AISpec();
          aiSpec.AntennaIDs = new UInt16Array();
  
          // Enable all antennas
          aiSpec.AntennaIDs.Add(0);
          // No AISpec stop trigger. It stops when the ROSpec stops.
          aiSpec.AISpecStopTrigger = new PARAM_AISpecStopTrigger();
          aiSpec.AISpecStopTrigger.AISpecStopTriggerType = ENUM_AISpecStopTriggerType.Null;
          aiSpec.InventoryParameterSpec = new PARAM_InventoryParameterSpec[1];
          aiSpec.InventoryParameterSpec[0] = new PARAM_InventoryParameterSpec();
  
          aiSpec.InventoryParameterSpec[0].InventoryParameterSpecID = 1234;
          aiSpec.InventoryParameterSpec[0].ProtocolID = ENUM_AirProtocols.EPCGlobalClass1Gen2;
  
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration = new PARAM_AntennaConfiguration[1];
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0] = new PARAM_AntennaConfiguration();
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0].RFTransmitter = new PARAM_RFTransmitter();
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0].RFTransmitter.HopTableID = 1;
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0].RFTransmitter.ChannelIndex = 1;
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0].RFTransmitter.TransmitPower = 91; // Max power of 32.5 dbm
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0].RFReceiver = new PARAM_RFReceiver();
          aiSpec.InventoryParameterSpec[0].AntennaConfiguration[0].RFReceiver.ReceiverSensitivity = 1; // 1= -80 (the max), 2 = -70, etc.
  
          msg.ROSpec.SpecParameter.Add(aiSpec);
  
          // Report Spec
          msg.ROSpec.ROReportSpec = new PARAM_ROReportSpec();
          // Send a report for every tag read
          msg.ROSpec.ROReportSpec.ROReportTrigger =
          ENUM_ROReportTriggerType.Upon_N_Tags_Or_End_Of_ROSpec;
          msg.ROSpec.ROReportSpec.N = 1;
          msg.ROSpec.ROReportSpec.TagReportContentSelector =  new PARAM_TagReportContentSelector();
  
          MSG_ADD_ROSPEC_RESPONSE rsp = reader.ADD_ROSPEC(msg, out msg_err, 2000);
  </code></pre>