diff --git a/test/microwaveprop/geo_test.exs b/test/microwaveprop/geo_test.exs
new file mode 100644
index 00000000..003d2d58
--- /dev/null
+++ b/test/microwaveprop/geo_test.exs
@@ -0,0 +1,98 @@
+defmodule Microwaveprop.GeoTest do
+  use ExUnit.Case, async: true
+
+  alias Microwaveprop.Geo
+  alias Microwaveprop.Radio.Maidenhead
+
+  describe "haversine_km/4" do
+    test "returns 0.0 for identical points" do
+      assert Geo.haversine_km(32.9, -96.8, 32.9, -96.8) == 0.0
+    end
+
+    test "matches a known long-distance pair (DFW to Newington, CT)" do
+      assert_in_delta Geo.haversine_km(32.9, -96.8, 41.714, -72.727), 2333.3, 1.0
+    end
+
+    test "computes a half-circumference for antipodal equator points" do
+      # Half the Earth's circumference at R = 6371 km is ~20015 km.
+      assert_in_delta Geo.haversine_km(0.0, 0.0, 0.0, 180.0), 20_015.0, 1.0
+    end
+
+    test "is symmetric in its arguments" do
+      forward = Geo.haversine_km(32.9, -96.8, 41.714, -72.727)
+      reverse = Geo.haversine_km(41.714, -72.727, 32.9, -96.8)
+      assert_in_delta forward, reverse, 0.0001
+    end
+
+    test "one degree of latitude is roughly 111 km" do
+      assert_in_delta Geo.haversine_km(32.0, -96.0, 33.0, -96.0), 111.195, 0.1
+    end
+  end
+
+  describe "bearing_deg/4" do
+    test "returns 0.0 for due north" do
+      assert Geo.bearing_deg(32.0, -96.0, 33.0, -96.0) == 0.0
+    end
+
+    test "returns ~90 for due east at the equator" do
+      assert_in_delta Geo.bearing_deg(0.0, 0.0, 0.0, 1.0), 90.0, 0.1
+    end
+
+    test "returns 180.0 for due south" do
+      assert Geo.bearing_deg(32.0, -96.0, 31.0, -96.0) == 180.0
+    end
+
+    test "returns a bearing in the range [0, 360)" do
+      bearing = Geo.bearing_deg(32.0, -96.0, 32.0, -97.0)
+      assert bearing >= 0.0 and bearing < 360.0
+      assert_in_delta bearing, 270.0, 1.0
+    end
+
+    test "rounds to one decimal place" do
+      # DFW to Newington - pick any pair, the result must have at most 1 decimal.
+      bearing = Geo.bearing_deg(32.9, -96.8, 41.714, -72.727)
+      assert Float.round(bearing, 1) == bearing
+    end
+  end
+
+  describe "maidenhead_center/1" do
+    test "returns the center of a 4-character grid" do
+      # EM12 is lat 32-33, lon -98 to -96, center (32.5, -97.0).
+      assert Geo.maidenhead_center("EM12") == {32.5, -97.0}
+    end
+
+    test "returns the center of a 6-character grid at higher precision" do
+      {lat, lon} = Geo.maidenhead_center("EM12kp")
+      assert_in_delta lat, 32.6458, 0.001
+      assert_in_delta lon, -97.125, 0.001
+    end
+
+    test "accepts lowercase grids" do
+      assert Geo.maidenhead_center("em12") == {32.5, -97.0}
+    end
+
+    test "returns nil for invalid grid characters" do
+      assert Geo.maidenhead_center("ZZZZ") == nil
+    end
+  end
+
+  describe "latlon_to_grid4/2" do
+    test "encodes the DFW area as EM12" do
+      assert Geo.latlon_to_grid4(32.9, -96.8) == "EM12"
+    end
+
+    test "encodes Newington, CT as FN31" do
+      assert Geo.latlon_to_grid4(41.714, -72.727) == "FN31"
+    end
+
+    test "encodes the prime-meridian/equator origin as JJ00" do
+      assert Geo.latlon_to_grid4(0.0, 0.0) == "JJ00"
+    end
+
+    test "agrees with Maidenhead.from_latlon/3 at precision 4 for typical US coords" do
+      for {lat, lon} <- [{32.9, -96.8}, {41.714, -72.727}, {40.0, -105.0}, {47.6, -122.3}] do
+        assert Geo.latlon_to_grid4(lat, lon) == Maidenhead.from_latlon(lat, lon, 4)
+      end
+    end
+  end
+end
diff --git a/test/microwaveprop/qrz/record_test.exs b/test/microwaveprop/qrz/record_test.exs
new file mode 100644
index 00000000..aad8baf9
--- /dev/null
+++ b/test/microwaveprop/qrz/record_test.exs
@@ -0,0 +1,100 @@
+defmodule Microwaveprop.Qrz.RecordTest do
+  use ExUnit.Case, async: true
+
+  alias Microwaveprop.Qrz.Record
+
+  describe "from_map/1" do
+    test "returns a struct with all fields nil for an empty map" do
+      assert %Record{
+               call: nil,
+               fname: nil,
+               name: nil,
+               grid: nil,
+               addr1: nil,
+               addr2: nil,
+               state: nil,
+               zip: nil,
+               country: nil,
+               lat: nil,
+               lon: nil
+             } = Record.from_map(%{})
+    end
+
+    test "parses every known string field" do
+      data = %{
+        "call" => "W1AW",
+        "fname" => "Hiram Percy",
+        "name" => "Maxim",
+        "grid" => "FN31pr",
+        "addr1" => "225 Main St",
+        "addr2" => "Newington",
+        "state" => "CT",
+        "zip" => "06111",
+        "country" => "United States"
+      }
+
+      record = Record.from_map(data)
+
+      assert record.call == "W1AW"
+      assert record.fname == "Hiram Percy"
+      assert record.name == "Maxim"
+      assert record.grid == "FN31pr"
+      assert record.addr1 == "225 Main St"
+      assert record.addr2 == "Newington"
+      assert record.state == "CT"
+      assert record.zip == "06111"
+      assert record.country == "United States"
+    end
+
+    test "parses lat and lon as floats from numeric strings" do
+      record = Record.from_map(%{"lat" => "41.714775", "lon" => "-72.727260"})
+
+      assert record.lat == 41.714775
+      assert record.lon == -72.727260
+    end
+
+    test "parses partial float prefixes via Float.parse/1" do
+      # Float.parse/1 returns {41.714, "abc"} — the parser keeps the float.
+      assert %Record{lat: 41.714} = Record.from_map(%{"lat" => "41.714abc"})
+    end
+
+    test "returns nil for unparseable float strings" do
+      assert %Record{lat: nil} = Record.from_map(%{"lat" => "not-a-number"})
+    end
+
+    test "treats non-binary string values as nil" do
+      assert %Record{call: nil} = Record.from_map(%{"call" => 123})
+    end
+
+    test "treats non-binary lat/lon values as nil" do
+      # The parser only accepts binaries — a raw float is rejected.
+      assert %Record{lat: nil, lon: nil} = Record.from_map(%{"lat" => 41.714, "lon" => -72.727})
+    end
+
+    test "leaves a field as nil when the key is absent" do
+      assert %Record{call: "W1AW", fname: nil} = Record.from_map(%{"call" => "W1AW"})
+    end
+
+    test "treats an explicit nil value the same as a missing key" do
+      assert %Record{call: nil} = Record.from_map(%{"call" => nil})
+    end
+
+    test "ignores unknown XML keys" do
+      record = Record.from_map(%{"call" => "W1AW", "eqsl" => "1", "dxcc" => "291"})
+
+      assert record.call == "W1AW"
+      # No crash, no struct pollution.
+      assert record |> Map.from_struct() |> Map.keys() |> Enum.sort() ==
+               [:addr1, :addr2, :call, :country, :fname, :grid, :lat, :lon, :name, :state, :zip]
+    end
+
+    test "is JSON-encodable via Jason" do
+      record = Record.from_map(%{"call" => "W1AW", "lat" => "41.714"})
+      json = Jason.encode!(record)
+      decoded = Jason.decode!(json)
+
+      assert decoded["call"] == "W1AW"
+      assert decoded["lat"] == 41.714
+    end
+  end
+end
diff --git a/test/microwaveprop/radio/callsign_client_test.exs b/test/microwaveprop/radio/callsign_client_test.exs
new file mode 100644
index 00000000..cdaf638d
--- /dev/null
+++ b/test/microwaveprop/radio/callsign_client_test.exs
@@ -0,0 +1,108 @@
+defmodule Microwaveprop.Radio.CallsignClientTest do
+  use Microwaveprop.DataCase, async: false
+
+  alias Microwaveprop.CallsignLocation.Location
+  alias Microwaveprop.Qrz.Client
+  alias Microwaveprop.Radio.CallsignClient
+
+  setup do
+    Client.reset_session()
+    :ok
+  end
+
+  describe "locate/1" do
+    test "reshapes a cached CallsignLocation into the public shape" do
+      {:ok, _} =
+        %Location{}
+        |> Location.changeset(%{
+          callsign: "W1AW",
+          latitude: 41.714,
+          longitude: -72.727,
+          gridsquare: "FN31pr58"
+        })
+        |> Repo.insert()
+
+      assert {:ok, result} = CallsignClient.locate("W1AW")
+
+      assert result == %{
+               callsign: "W1AW",
+               gridsquare: "FN31pr58",
+               lat: 41.714,
+               lon: -72.727
+             }
+    end
+
+    test "returns only callsign, gridsquare, lat, lon (drops name and address)" do
+      {:ok, _} =
+        %Location{}
+        |> Location.changeset(%{
+          callsign: "W1AW",
+          latitude: 41.714,
+          longitude: -72.727,
+          gridsquare: "FN31pr58"
+        })
+        |> Repo.insert()
+
+      assert {:ok, result} = CallsignClient.locate("W1AW")
+
+      assert result |> Map.keys() |> Enum.sort() == [:callsign, :gridsquare, :lat, :lon]
+    end
+
+    test "renames latitude/longitude to lat/lon" do
+      {:ok, _} =
+        %Location{}
+        |> Location.changeset(%{
+          callsign: "K5QE",
+          latitude: 30.5,
+          longitude: -94.1,
+          gridsquare: "EM30wn"
+        })
+        |> Repo.insert()
+
+      assert {:ok, %{lat: 30.5, lon: -94.1}} = CallsignClient.locate("K5QE")
+    end
+
+    test "propagates {:error, reason} tuples from the underlying lookup" do
+      Req.Test.expect(Client, 2, fn conn ->
+        params = Plug.Conn.fetch_query_params(conn).query_params
+
+        if Map.has_key?(params, "username") do
+          Plug.Conn.send_resp(conn, 200, """
+          <?xml version="1.0" encoding="utf-8"?>
+          <QRZDatabase version="1.34">
+            <Session><Key>session123</Key></Session>
+          </QRZDatabase>
+          """)
+        else
+          Plug.Conn.send_resp(conn, 200, """
+          <?xml version="1.0" encoding="utf-8"?>
+          <QRZDatabase version="1.34">
+            <Session>
+              <Error>Not found: INVALID</Error>
+              <Key>session123</Key>
+            </Session>
+          </QRZDatabase>
+          """)
+        end
+      end)
+
+      assert {:error, _reason} = CallsignClient.locate("INVALID")
+    end
+
+    test "upcases lookups, matching a cached row inserted in different casing" do
+      # The underlying CallsignLocation.lookup/1 upcases the callsign before
+      # the DB read, so a mixed-case request finds an uppercase cache hit.
+      {:ok, _} =
+        %Location{}
+        |> Location.changeset(%{
+          callsign: "W1AW",
+          latitude: 41.714,
+          longitude: -72.727,
+          gridsquare: "FN31pr58"
+        })
+        |> Repo.insert()
+
+      assert {:ok, %{callsign: "W1AW"}} = CallsignClient.locate("w1aw")
+    end
+  end
+end