diff --git a/src/main/java/io/github/dsheirer/module/decode/p25/phase1/P25P1DecoderState.java b/src/main/java/io/github/dsheirer/module/decode/p25/phase1/P25P1DecoderState.java
index 6d584577a..9c9d2d229 100644
--- a/src/main/java/io/github/dsheirer/module/decode/p25/phase1/P25P1DecoderState.java
+++ b/src/main/java/io/github/dsheirer/module/decode/p25/phase1/P25P1DecoderState.java
@@ -671,6 +671,10 @@ private void processAMBTC(P25P1Message message)
                                 urr.getResponse() + " UNIT REGISTRATION");
                     }
                     break;
+                case OSP_IDENTIFIER_UPDATE_TDMA:
+                    //Ignore - in the extended format it is carrying a frequency band for a foreign system and we
+                    //don't allow that to corrupt the real frequency bands for this system.
+                    break;
                 default:
 //                    mLog.debug("Unrecognized AMBTC Opcode: " + ambtc.getHeader().getOpcode().name());
                     break;
diff --git a/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/PDUMessageFactory.java b/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/PDUMessageFactory.java
index 8b8e25090..df994f75e 100644
--- a/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/PDUMessageFactory.java
+++ b/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/PDUMessageFactory.java
@@ -42,6 +42,7 @@
 import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.isp.AMBTCUnitToUnitVoiceServiceRequest;
 import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp.AMBTCAdjacentStatusBroadcast;
 import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp.AMBTCCallAlert;
+import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp.AMBTCFrequencyBandUpdateTDMA;
 import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp.AMBTCGroupAffiliationQuery;
 import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp.AMBTCGroupAffiliationResponse;
 import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp.AMBTCGroupDataChannelGrant;
@@ -245,6 +246,8 @@ public static P25P1Message createAMBTC(PDUSequence pduSequence, int nac, long ti
                 return new AMBTCGroupAffiliationResponse(pduSequence, nac, timestamp);
             case OSP_GROUP_VOICE_CHANNEL_GRANT:
                 return new AMBTCGroupVoiceChannelGrant(pduSequence, nac, timestamp);
+            case OSP_IDENTIFIER_UPDATE_TDMA:
+                return new AMBTCFrequencyBandUpdateTDMA(pduSequence, nac, timestamp);
             case OSP_INDIVIDUAL_DATA_CHANNEL_GRANT:
                 return new AMBTCIndividualDataChannelGrant(pduSequence, nac, timestamp);
             case OSP_MESSAGE_UPDATE:
diff --git a/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/ambtc/osp/AMBTCFrequencyBandUpdateTDMA.java b/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/ambtc/osp/AMBTCFrequencyBandUpdateTDMA.java
new file mode 100644
index 000000000..bd38617eb
--- /dev/null
+++ b/src/main/java/io/github/dsheirer/module/decode/p25/phase1/message/pdu/ambtc/osp/AMBTCFrequencyBandUpdateTDMA.java
@@ -0,0 +1,196 @@
+/*
+ * *****************************************************************************
+ * Copyright (C) 2014-2024 Dennis Sheirer
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>
+ * ****************************************************************************
+ */
+
+package io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.osp;
+
+import io.github.dsheirer.bits.FragmentedIntField;
+import io.github.dsheirer.bits.IntField;
+import io.github.dsheirer.bits.LongField;
+import io.github.dsheirer.identifier.Identifier;
+import io.github.dsheirer.module.decode.p25.identifier.APCO25System;
+import io.github.dsheirer.module.decode.p25.identifier.APCO25Wacn;
+import io.github.dsheirer.module.decode.p25.phase1.message.pdu.PDUSequence;
+import io.github.dsheirer.module.decode.p25.phase1.message.pdu.ambtc.AMBTCMessage;
+import io.github.dsheirer.module.decode.p25.reference.ChannelType;
+import java.util.Collections;
+import java.util.List;
+import org.apache.commons.math3.util.FastMath;
+
+/**
+ * Frequency band update TDMA multi-block format for a foreign system.
+ *
+ * Note: removed the IFrequencyBand interface for this message so that it doesn't get processed as a frequency band for
+ * the current system which would likely collide with the real frequency band for the current system.
+ */
+public class AMBTCFrequencyBandUpdateTDMA extends AMBTCMessage // implements IFrequencyBand
+{
+    private static final IntField HEADER_IDENTIFIER = IntField.length4(OCTET_3_BIT_24);
+    private static final IntField HEADER_CHANNEL_TYPE = IntField.length4(OCTET_3_BIT_24 + 4);
+    private static final FragmentedIntField HEADER_WACN = FragmentedIntField.of(32, 33, 34, 35, 36, 37, 38, 39,
+            40, 41, 42, 43, 44, 45, 46, 47, 64, 65, 66, 67);
+    private static final IntField HEADER_SYSTEM = IntField.length12(OCTET_8_BIT_64 + 4);
+    private static final LongField BLOCK_0_BASE_FREQUENCY = LongField.length32(OCTET_0_BIT_0);
+    private static final int BLOCK_0_TRANSMIT_OFFSET_SIGN = OCTET_4_BIT_32;
+    private static final IntField BLOCK_0_TRANSMIT_OFFSET = IntField.range(OCTET_4_BIT_32 + 1, OCTET_4_BIT_32 + 13);
+    private static final IntField BLOCK_0_CHANNEL_SPACING = IntField.range(OCTET_5_BIT_40 + 6, OCTET_5_BIT_40 + 15);
+
+    private ChannelType mChannelType;
+    private Identifier mWacn;
+    private Identifier mSystem;
+
+    /**
+     * Constructs an instance
+     * @param PDUSequence containing the header and block 0
+     * @param nac for the system
+     * @param timestamp of the PDU sequence
+     */
+    public AMBTCFrequencyBandUpdateTDMA(PDUSequence PDUSequence, int nac, long timestamp)
+    {
+        super(PDUSequence, nac, timestamp);
+    }
+
+    public String toString()
+    {
+        StringBuilder sb = new StringBuilder();
+        sb.append(getMessageStub());
+        sb.append(" WACN:").append(getWacn());
+        sb.append(" FOREIGN SYSTEM:").append(getSystem());
+        sb.append(" ID:").append(getIdentifier());
+        sb.append(" OFFSET:").append(getTransmitOffset());
+        sb.append(" SPACING:").append(getChannelSpacing());
+        sb.append(" BASE:").append(getBaseFrequency());
+        sb.append(" ").append(getChannelType());
+        return sb.toString();
+    }
+
+    public Identifier getWacn()
+    {
+        if(mWacn == null)
+        {
+            mWacn = APCO25Wacn.create(getHeader().getMessage().getInt(HEADER_WACN));
+        }
+
+        return mWacn;
+    }
+
+    public Identifier getSystem()
+    {
+        if(mSystem == null)
+        {
+            mSystem = APCO25System.create(getHeader().getMessage().getInt(HEADER_SYSTEM));
+        }
+
+        return mSystem;
+    }
+
+    public ChannelType getChannelType()
+    {
+        if(mChannelType == null)
+        {
+            mChannelType = ChannelType.fromValue(getHeader().getMessage().getInt(HEADER_CHANNEL_TYPE));
+        }
+
+        return mChannelType;
+    }
+
+    public int getIdentifier()
+    {
+        return getHeader().getMessage().getInt(HEADER_IDENTIFIER);
+    }
+
+    public long getChannelSpacing()
+    {
+        if(hasDataBlock(0))
+        {
+            return getDataBlock(0).getMessage().getInt(BLOCK_0_CHANNEL_SPACING) * 125L;
+        }
+
+        return 0;
+    }
+
+    public long getBaseFrequency()
+    {
+        if(hasDataBlock(0))
+        {
+            return getDataBlock(0).getMessage().getLong(BLOCK_0_BASE_FREQUENCY) * 5L;
+        }
+
+        return 0L;
+    }
+
+    public int getBandwidth()
+    {
+        return getChannelType().getBandwidth();
+    }
+
+    public long getTransmitOffset()
+    {
+        if(hasDataBlock(0))
+        {
+            long offset = getDataBlock(0).getMessage().getInt(BLOCK_0_TRANSMIT_OFFSET) * getChannelSpacing();
+
+            if(!getDataBlock(0).getMessage().get(BLOCK_0_TRANSMIT_OFFSET_SIGN))
+            {
+                offset *= -1;
+            }
+
+            return offset;
+        }
+
+        return 0L;
+    }
+
+    /**
+     * Indicates if the frequency band has a transmit option for the subscriber unit.
+     */
+    public boolean hasTransmitOffset()
+    {
+        return hasDataBlock(0) && getDataBlock(0).getMessage().getInt(BLOCK_0_TRANSMIT_OFFSET) != 0x80;
+    }
+
+    public long getDownlinkFrequency(int channelNumber)
+    {
+        return getBaseFrequency() + (getChannelSpacing() * (int)(FastMath.floor(channelNumber / getTimeslotCount())));
+    }
+
+    public long getUplinkFrequency(int channelNumber)
+    {
+        if(hasTransmitOffset())
+        {
+            return getDownlinkFrequency(channelNumber) + getTransmitOffset();
+        }
+
+        return 0;
+    }
+
+    public boolean isTDMA()
+    {
+        return getChannelType().isTDMA();
+    }
+
+    public int getTimeslotCount()
+    {
+        return getChannelType().getSlotsPerCarrier();
+    }
+
+    public List<Identifier> getIdentifiers()
+    {
+        return Collections.EMPTY_LIST;
+    }
+}