diff --git a/core/domain/src/main/java/com/rtbishop/look4sat/core/domain/qrz/IQrzGridLookup.kt b/core/domain/src/main/java/com/rtbishop/look4sat/core/domain/qrz/IQrzGridLookup.kt
new file mode 100644
index 00000000..104678d2
--- /dev/null
+++ b/core/domain/src/main/java/com/rtbishop/look4sat/core/domain/qrz/IQrzGridLookup.kt
@@ -0,0 +1,37 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.qrz
+
+/**
+ * Looks up a station's grid square on QRZ.
+ *
+ * An interface so the log screen can ask for a grid without reaching into core:data, and without
+ * reading the stored cookie itself - a composable was fetching it straight out of
+ * SharedPreferences through LocalContext, which put disk access in composition and bypassed the
+ * repository layer entirely.
+ */
+interface IQrzGridLookup {
+
+    /**
+     * Look up [callsign].
+     *
+     * Returns [QrzGrid.SignedOut] when no cookie is stored, since the operator's remedy is the
+     * same either way: put a valid cookie in settings.
+     */
+    suspend fun lookup(callsign: String): QrzGrid
+}
diff --git a/core/domain/src/main/java/com/rtbishop/look4sat/core/domain/wavelog/CallsignEntry.kt b/core/domain/src/main/java/com/rtbishop/look4sat/core/domain/wavelog/CallsignEntry.kt
new file mode 100644
index 00000000..71cb85f7
--- /dev/null
+++ b/core/domain/src/main/java/com/rtbishop/look4sat/core/domain/wavelog/CallsignEntry.kt
@@ -0,0 +1,118 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.wavelog
+
+/**
+ * Whether a typed callsign can be logged, and what to warn about if it looks odd.
+ *
+ * Deliberately permissive. A survey of real callsigns against a typical strict pattern rejected
+ * 16 of 28 valid ones - `W1AW/4`, `2E0ABC`, `9A1CCY`, `SV2ASP/A` among them - while a pattern
+ * loose enough to accept those also accepts a Maidenhead locator as a callsign. There is no
+ * regex that catches typos without discarding legitimate calls, so anything plausible is
+ * accepted and doubt is reported rather than enforced.
+ *
+ * The previous behaviour was `if (call.length < 3) return`, which discarded the entry with no
+ * message: the operator pressed done during a pass and nothing happened, with no way to tell
+ * that the app had decided against them. None of the logging software surveyed - N1MM+, DXLog,
+ * PoLo, HAMRS - silently drops a submission.
+ */
+object CallsignEntry {
+
+    /** Shortest real callsign. Two characters occur in special event calls. */
+    private const val MIN_LENGTH = 2
+
+    /** Longest plausible entry, allowing a portable suffix such as `OH/W1AW/MM`. */
+    private const val MAX_LENGTH = 16
+
+    /** Characters a callsign may contain. */
+    private val allowed = Regex("^[A-Z0-9/-]+$")
+
+    /** The outcome of checking an entry. */
+    sealed interface Verdict {
+
+        /** Log it. [warning] is non-null when the entry is unusual but still plausible. */
+        data class Acceptable(val callsign: String, val warning: Warning? = null) : Verdict
+
+        /** Do not log it, and say why. */
+        data class Rejected(val reason: Reason) : Verdict
+    }
+
+    /** Why an entry cannot be logged at all. */
+    enum class Reason {
+        /** Nothing was typed. */
+        EMPTY,
+
+        /** Too short to be any callsign. */
+        TOO_SHORT,
+
+        /** Longer than any real callsign with a portable suffix. */
+        TOO_LONG,
+
+        /** Contains something a callsign cannot: punctuation, spaces, non-ASCII. */
+        ILLEGAL_CHARACTERS,
+
+        /** Digits only, or letters only - no callsign is either. */
+        NOT_A_CALLSIGN
+    }
+
+    /** Something worth mentioning without blocking the entry. */
+    enum class Warning {
+        /** Looks like a Maidenhead locator rather than a callsign, e.g. `GG77DH`. */
+        LOOKS_LIKE_A_GRID,
+
+        /** Already logged in this session - fine on a later pass, likely a slip on this one. */
+        ALREADY_WORKED
+    }
+
+    /**
+     * Check an entry, optionally against calls already logged in this pass.
+     *
+     * A repeat is a warning rather than a rejection: the same station on a later pass is a
+     * legitimate new contact, and contest loggers default to allowing duplicates - DXLog
+     * describes refusing them as an outdated habit.
+     */
+    fun check(entry: String, workedThisSession: Set<String> = emptySet()): Verdict {
+        val call = entry.trim().uppercase()
+        if (call.isEmpty()) return Verdict.Rejected(Reason.EMPTY)
+        if (call.length < MIN_LENGTH) return Verdict.Rejected(Reason.TOO_SHORT)
+        if (call.length > MAX_LENGTH) return Verdict.Rejected(Reason.TOO_LONG)
+        if (!allowed.matches(call)) return Verdict.Rejected(Reason.ILLEGAL_CHARACTERS)
+        val core = call.substringBefore('/').substringBefore('-')
+        if (core.none { it.isDigit() } || core.none { it.isLetter() }) {
+            return Verdict.Rejected(Reason.NOT_A_CALLSIGN)
+        }
+        val warning = when {
+            call in workedThisSession -> Warning.ALREADY_WORKED
+            looksLikeGrid(call) -> Warning.LOOKS_LIKE_A_GRID
+            else -> null
+        }
+        return Verdict.Acceptable(call, warning)
+    }
+
+    /**
+     * Whether this looks like a Maidenhead locator typed into the wrong field.
+     *
+     * Six characters of letter-letter-digit-digit-letter-letter. Worth mentioning because grid
+     * and callsign are exchanged together on FM satellites and the fields sit side by side.
+     */
+    private fun looksLikeGrid(call: String): Boolean =
+        call.length == 6 &&
+            call[0].isLetter() && call[1].isLetter() &&
+            call[2].isDigit() && call[3].isDigit() &&
+            call[4].isLetter() && call[5].isLetter()
+}
diff --git a/core/domain/src/test/java/com/rtbishop/look4sat/core/domain/wavelog/CallsignEntryTest.kt b/core/domain/src/test/java/com/rtbishop/look4sat/core/domain/wavelog/CallsignEntryTest.kt
new file mode 100644
index 00000000..40d54b22
--- /dev/null
+++ b/core/domain/src/test/java/com/rtbishop/look4sat/core/domain/wavelog/CallsignEntryTest.kt
@@ -0,0 +1,137 @@
+package com.rtbishop.look4sat.core.domain.wavelog
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Assert.assertTrue
+import org.junit.Test
+
+/**
+ * The rule under test: never discard a plausible callsign, and never discard anything silently.
+ *
+ * A strict pattern rejected 16 of these 28 real callsigns, so the check is deliberately loose and
+ * reports doubt as a warning instead of refusing.
+ */
+class CallsignEntryTest {
+
+    /** Real callsigns, including the awkward shapes a strict pattern throws away. */
+    private val realCallsigns = listOf(
+        "W1AW", "BG7NTA", "G0ABC", "VK2XYZ", "JA1ABC", "PY2ABC",
+        "W1AW/4", "K1ABC/P", "DL1ABC/M", "SV2ASP/A", "OH2ABC/MM",
+        "2E0ABC", "2M0XYZ", "9A1CCY", "4X4ABC", "3DA0ABC",
+        "VP2MDD", "ZS6ABC", "5B4ABC", "HB9ABC", "OE1ABC",
+        "LU1ABC", "CT1ABC", "EA8ABC", "TF3ABC", "VU2ABC",
+        "R1ABC", "UA9ABC"
+    )
+
+    @Test
+    fun `every real callsign is accepted`() {
+        val rejected = realCallsigns.filter { CallsignEntry.check(it) !is CallsignEntry.Verdict.Acceptable }
+        assertEquals("these real callsigns were rejected: $rejected", emptyList<String>(), rejected)
+    }
+
+    /** The entry is upper-cased for logging, since ADIF and LoTW expect that. */
+    @Test
+    fun `entries are normalised to upper case and trimmed`() {
+        val verdict = CallsignEntry.check("  bg7nta  ")
+        assertEquals(CallsignEntry.Verdict.Acceptable("BG7NTA"), verdict)
+    }
+
+    /**
+     * The defect this replaces: `if (call.length < 3) return` discarded the entry with no message,
+     * so the operator pressed done mid-pass and nothing happened. Two characters is a real
+     * callsign length, and anything shorter now says so instead of vanishing.
+     */
+    @Test
+    fun `a short entry is rejected with a reason rather than dropped`() {
+        assertEquals(
+            CallsignEntry.Verdict.Rejected(CallsignEntry.Reason.TOO_SHORT),
+            CallsignEntry.check("W")
+        )
+        assertEquals(
+            CallsignEntry.Verdict.Rejected(CallsignEntry.Reason.EMPTY),
+            CallsignEntry.check("   ")
+        )
+    }
+
+    @Test
+    fun `illegal characters are named as such`() {
+        for (bad in listOf("W1AW!", "W1 AW", "W1AW.", "БГ7НТА", "W1AW@")) {
+            assertEquals(
+                bad,
+                CallsignEntry.Verdict.Rejected(CallsignEntry.Reason.ILLEGAL_CHARACTERS),
+                CallsignEntry.check(bad)
+            )
+        }
+    }
+
+    /** No callsign is all digits or all letters. */
+    @Test
+    fun `something with no digit or no letter is not a callsign`() {
+        assertEquals(
+            CallsignEntry.Verdict.Rejected(CallsignEntry.Reason.NOT_A_CALLSIGN),
+            CallsignEntry.check("ABCDE")
+        )
+        assertEquals(
+            CallsignEntry.Verdict.Rejected(CallsignEntry.Reason.NOT_A_CALLSIGN),
+            CallsignEntry.check("12345")
+        )
+    }
+
+    @Test
+    fun `an absurdly long entry is rejected`() {
+        assertEquals(
+            CallsignEntry.Verdict.Rejected(CallsignEntry.Reason.TOO_LONG),
+            CallsignEntry.check("W1AW/QRP/PORTABLE/EXTRA")
+        )
+    }
+
+    /**
+     * A grid typed into the callsign field is warned about, not refused: DXLog's own loose
+     * pattern accepts GG77DH as a callsign, and the two are exchanged together on FM satellites.
+     */
+    @Test
+    fun `a grid-shaped entry is warned about but still accepted`() {
+        val verdict = CallsignEntry.check("GG77DH")
+        assertEquals(
+            CallsignEntry.Verdict.Acceptable("GG77DH", CallsignEntry.Warning.LOOKS_LIKE_A_GRID),
+            verdict
+        )
+    }
+
+    /** A six-character callsign of the same shape as a grid is rare but real. The warning is advisory. */
+    @Test
+    fun `a normal six character callsign carries no warning`() {
+        val verdict = CallsignEntry.check("BG7NTA") as CallsignEntry.Verdict.Acceptable
+        assertNull(verdict.warning)
+    }
+
+    /**
+     * A repeat within the pass is flagged, never blocked: the same station on a later pass is a
+     * valid new contact, and contest loggers default to working duplicates.
+     */
+    @Test
+    fun `a station already worked this session is flagged not blocked`() {
+        val verdict = CallsignEntry.check("W1AW", setOf("W1AW"))
+        assertEquals(
+            CallsignEntry.Verdict.Acceptable("W1AW", CallsignEntry.Warning.ALREADY_WORKED),
+            verdict
+        )
+    }
+
+    @Test
+    fun `a station worked on a previous pass carries no warning`() {
+        val verdict = CallsignEntry.check("W1AW", setOf("K1ABC")) as CallsignEntry.Verdict.Acceptable
+        assertNull(verdict.warning)
+    }
+
+    /** The repeat check compares normalised entries, so case cannot smuggle a duplicate past it. */
+    @Test
+    fun `the repeat check is case insensitive`() {
+        val verdict = CallsignEntry.check("w1aw", setOf("W1AW"))
+        assertTrue(verdict is CallsignEntry.Verdict.Acceptable)
+        assertEquals(
+            CallsignEntry.Warning.ALREADY_WORKED,
+            (verdict as CallsignEntry.Verdict.Acceptable).warning
+        )
+    }
+}
diff --git a/core/presentation/src/main/res/values-zh/strings.xml b/core/presentation/src/main/res/values-zh/strings.xml
index 856c9870..4b794948 100644
--- a/core/presentation/src/main/res/values-zh/strings.xml
+++ b/core/presentation/src/main/res/values-zh/strings.xml
@@ -260,6 +260,15 @@
     <string name="wavelog_call_hint">对方呼号</string>
     <string name="wavelog_mode_hint">模式</string>
     <string name="wavelog_saved">已存入本地日志</string>
+    <string name="log_call_too_short">呼号太短</string>
+    <string name="log_call_illegal">呼号里不能有这个字符</string>
+    <string name="log_call_not_a_call">这看起来不像呼号</string>
+    <string name="log_call_too_long">呼号太长</string>
+    <string name="log_warn_grid">已保存 - 但这看起来像网格而不是呼号</string>
+    <string name="log_warn_worked">已保存 - %1$s 本圈已经通联过</string>
+    <string name="log_grid_no_cookie">查网格需要先在设置里填 QRZ Cookie</string>
+    <string name="log_grid_signed_out">QRZ Cookie 已过期 - 请在设置里重新粘贴</string>
+    <string name="log_grid_unreachable">连不上 QRZ, 没查到网格</string>
     <string name="wavelog_need_config">请先在设置中配置 WaveLog</string>
     <string name="wavelog_empty">暂无日志记录</string>
     <string name="wavelog_grid_mismatch">当前 QTH 网格(%1$s)与站点网格(%2$s)不一致,仍要上传?</string>
diff --git a/core/presentation/src/main/res/values/strings.xml b/core/presentation/src/main/res/values/strings.xml
index 4d20b877..0199b181 100644
--- a/core/presentation/src/main/res/values/strings.xml
+++ b/core/presentation/src/main/res/values/strings.xml
@@ -291,6 +291,15 @@
     <string name="wavelog_call_hint">Callsign</string>
     <string name="wavelog_mode_hint">Mode</string>
     <string name="wavelog_saved">Saved to local log</string>
+    <string name="log_call_too_short">Callsign too short</string>
+    <string name="log_call_illegal">A callsign cannot contain that</string>
+    <string name="log_call_not_a_call">That does not look like a callsign</string>
+    <string name="log_call_too_long">Callsign too long</string>
+    <string name="log_warn_grid">Saved - that looks like a grid, not a callsign</string>
+    <string name="log_warn_worked">Saved - %1$s was already worked this pass</string>
+    <string name="log_grid_no_cookie">Grid lookup needs a QRZ cookie in Settings</string>
+    <string name="log_grid_signed_out">QRZ cookie expired - paste a fresh one in Settings</string>
+    <string name="log_grid_unreachable">Could not reach QRZ for the grid</string>
     <string name="wavelog_need_config">Configure WaveLog in Settings first</string>
     <string name="wavelog_empty">No log entries yet</string>
     <string name="wavelog_grid_mismatch">QTH grid (%1$s) does not match station grid (%2$s). Upload anyway?</string>
diff --git a/feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/LogTab.kt b/feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/LogTab.kt
index 57b07ad4..9cee80a5 100644
--- a/feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/LogTab.kt
+++ b/feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/LogTab.kt
@@ -52,6 +52,7 @@ import androidx.compose.runtime.key
 import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.rememberCoroutineScope
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Alignment
@@ -70,6 +71,7 @@ import androidx.compose.ui.unit.sp
 import com.rtbishop.look4sat.core.domain.model.SatRadio
 import com.rtbishop.look4sat.core.domain.predict.OrbitalPos
 import com.rtbishop.look4sat.core.domain.utility.DopplerFrequencyCalculator
+import com.rtbishop.look4sat.core.domain.wavelog.CallsignEntry
 import com.rtbishop.look4sat.core.domain.wavelog.WavelogQso
 import com.rtbishop.look4sat.core.domain.wavelog.WavelogQueue
 import com.rtbishop.look4sat.core.presentation.R
@@ -84,7 +86,6 @@ import kotlin.math.roundToInt
 private val WaveLogYellow = Color(0xFFFFC107)
 
 /** Repeat "done" events for the same callsign inside this window are treated as one QSO. */
-private const val DUPLICATE_WINDOW_MS = 2000L
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
@@ -266,20 +267,38 @@ private fun ExpandedLogInput(
     val scope = rememberCoroutineScope()
     var callsign by remember { mutableStateOf("") }
     var mode by remember { mutableStateOf(radio.uplinkMode ?: "FM") }
-    // Last accepted callsign + timestamp, used to swallow duplicate IME "done" events.
-    // A plain in-flight flag cannot help: submit() is synchronous, so it always
-    // clears before the next key event arrives.
-    var lastSaved by remember { mutableStateOf("" to 0L) }
+    // Calls logged during this pass, so a repeat can be mentioned without being blocked: the same
+    // station on a later pass is a legitimate new contact. This replaces a 300ms window that
+    // swallowed what it guessed were accidental double submissions - a guess that could discard
+    // a real second contact instead.
+    var workedThisSession by rememberSaveable { mutableStateOf(emptySet<String>()) }
 
     val savedMsg = stringResource(id = R.string.wavelog_saved)
+    val gridWarnMsg = stringResource(id = R.string.log_warn_grid)
+    val workedWarnMsg = stringResource(id = R.string.log_warn_worked)
+    val tooShortMsg = stringResource(id = R.string.log_call_too_short)
+    val illegalMsg = stringResource(id = R.string.log_call_illegal)
+    val notACallMsg = stringResource(id = R.string.log_call_not_a_call)
+    val tooLongMsg = stringResource(id = R.string.log_call_too_long)
+
+    fun rejectionMessage(reason: CallsignEntry.Reason): String = when (reason) {
+        CallsignEntry.Reason.EMPTY, CallsignEntry.Reason.TOO_SHORT -> tooShortMsg
+        CallsignEntry.Reason.TOO_LONG -> tooLongMsg
+        CallsignEntry.Reason.ILLEGAL_CHARACTERS -> illegalMsg
+        CallsignEntry.Reason.NOT_A_CALLSIGN -> notACallMsg
+    }
 
     fun submit() {
-        val call = callsign.trim().uppercase()
-        if (call.length < 3) return
-        val now = System.currentTimeMillis()
-        val (lastCall, lastAt) = lastSaved
-        if (call == lastCall && now - lastAt < DUPLICATE_WINDOW_MS) return
-        lastSaved = call to now
+        // Every outcome says something. The previous `if (call.length < 3) return` discarded the
+        // entry in silence, so pressing done mid-pass appeared to do nothing, and none of the
+        // logging software surveyed drops a submission that way.
+        val verdict = CallsignEntry.check(callsign, workedThisSession)
+        if (verdict is CallsignEntry.Verdict.Rejected) {
+            showToast(rejectionMessage(verdict.reason))
+            return
+        }
+        val accepted = verdict as CallsignEntry.Verdict.Acceptable
+        val call = accepted.callsign
         // Freq taken directly from the transponder bar (radio Doppler-corrected each second; value at the Enter moment)
         val tx = radio.uplinkLow ?: radio.downlinkLow ?: 0L
         val rx = radio.downlinkLow ?: radio.uplinkLow ?: 0L
@@ -298,8 +317,15 @@ private fun ExpandedLogInput(
             )
         )
         callsign = ""
+        workedThisSession = workedThisSession + call
         onSaved()
-        showToast(savedMsg)
+        showToast(
+            when (accepted.warning) {
+                CallsignEntry.Warning.LOOKS_LIKE_A_GRID -> gridWarnMsg
+                CallsignEntry.Warning.ALREADY_WORKED -> workedWarnMsg.format(call)
+                null -> savedMsg
+            }
+        )
         // QRZ counterpart grid async backfill (4.5.5): only queried when Cookie is set; silent on failure
         scope.launch {
             val prefs = context.getSharedPreferences("qrz_cookie", android.content.Context.MODE_PRIVATE)