diff --git a/config/dev.exs b/config/dev.exs
index b1afcfa7..7d587a49 100644
--- a/config/dev.exs
+++ b/config/dev.exs
@@ -3,6 +3,15 @@ import Config
 # Do not include metadata nor timestamps in development logs
 config :logger, :default_formatter, format: "[$level] $message\n"
 
+# Read-only secondary repo pointing at the local aprs.me dev database.
+# See lib/microwaveprop/aprs_repo.ex — used by APRS calibration tooling
+# only; the main app boots fine without it.
+config :microwaveprop, Microwaveprop.AprsRepo,
+  username: "postgres",
+  hostname: "localhost",
+  database: "aprsme_dev",
+  pool_size: 2
+
 # Configure your database
 config :microwaveprop, Microwaveprop.Repo,
   username: "postgres",
diff --git a/config/runtime.exs b/config/runtime.exs
index c22a1833..5a0a61dd 100644
--- a/config/runtime.exs
+++ b/config/runtime.exs
@@ -1,5 +1,10 @@
 import Config
 
+alias Microwaveprop.Workers.CanadianSoundingFetchWorker
+alias Oban.Plugins.Cron
+
+require Logger
+
 # config/runtime.exs is executed for all environments, including
 # during releases. It is executed after compilation and before the
 # system starts, so it is typically used to load production configuration
@@ -16,9 +21,6 @@ import Config
 #
 # Alternatively, you can use `mix phx.gen.release` to generate a `bin/server`
 # script that automatically sets the env var above.
-alias Microwaveprop.Workers.CanadianSoundingFetchWorker
-alias Oban.Plugins.Cron
-
 if System.get_env("PHX_SERVER") do
   config :microwaveprop, MicrowavepropWeb.Endpoint, server: true
 end
@@ -355,6 +357,24 @@ if config_env() == :prod do
     # pool_count: 4,
     socket_options: maybe_ipv6
 
+  # Optional secondary repo for read-only access to aprs.me's database.
+  # Used by APRS-based 144 MHz calibration tooling. When the env var is
+  # unset we leave the AprsRepo unconfigured; Microwaveprop.Application
+  # logs a warning and skips starting it, and the rest of the app boots
+  # normally.
+  case System.get_env("APRS_DATABASE_URL") do
+    nil ->
+      Logger.warning("APRS_DATABASE_URL not set — Microwaveprop.AprsRepo will not start; APRS calibration disabled.")
+
+      :ok
+
+    aprs_url ->
+      config :microwaveprop, Microwaveprop.AprsRepo,
+        url: aprs_url,
+        pool_size: String.to_integer(System.get_env("APRS_POOL_SIZE") || "2"),
+        socket_options: maybe_ipv6
+  end
+
   config :microwaveprop, MicrowavepropWeb.Endpoint,
     # SSL terminated by Cloudflare tunnel; generated URLs still use https
     url: [host: host, port: 443, scheme: "https"],
diff --git a/config/test.exs b/config/test.exs
index fe101cf5..854b94a4 100644
--- a/config/test.exs
+++ b/config/test.exs
@@ -1,5 +1,6 @@
 import Config
 
+alias Ecto.Adapters.SQL.Sandbox
 alias Microwaveprop.Qrz.Client
 
 # Only in tests, remove the complexity from the password hashing algorithm
@@ -15,6 +16,21 @@ config :microwaveprop, Client,
   plug: {Req.Test, Client},
   retry: false
 
+# Read-only secondary repo for aprs.me. Configured here so the app boots
+# under MIX_ENV=test, but uses the SQL.Sandbox in :manual mode so tests
+# that don't touch APRS data don't have to check the DB out. Tests that
+# do query the AprsRepo must call `Ecto.Adapters.SQL.Sandbox.checkout/1`
+# explicitly.
+config :microwaveprop, Microwaveprop.AprsRepo,
+  username: "postgres",
+  password: "postgres",
+  hostname: "localhost",
+  database: "aprsme_test#{System.get_env("MIX_TEST_PARTITION")}",
+  pool: Sandbox,
+  pool_size: 2,
+  ownership_timeout: 60_000,
+  timeout: 60_000
+
 config :microwaveprop, Microwaveprop.Geocoder,
   plug: {Req.Test, Microwaveprop.Geocoder},
   retry: false
@@ -33,7 +49,7 @@ config :microwaveprop, Microwaveprop.Repo,
   password: "postgres",
   hostname: "localhost",
   database: "microwaveprop_test#{System.get_env("MIX_TEST_PARTITION")}",
-  pool: Ecto.Adapters.SQL.Sandbox,
+  pool: Sandbox,
   pool_size: System.schedulers_online() * 2,
   ownership_timeout: 60_000,
   timeout: 60_000
diff --git a/lib/microwaveprop/application.ex b/lib/microwaveprop/application.ex
index 8a7a89ed..7781f48d 100644
--- a/lib/microwaveprop/application.ex
+++ b/lib/microwaveprop/application.ex
@@ -17,6 +17,10 @@ defmodule Microwaveprop.Application do
       MicrowavepropWeb.Telemetry,
       Microwaveprop.PromEx,
       Microwaveprop.Repo,
+      # AprsRepo is optional — only starts when configured with a :url
+      # (dev/test from config blocks, prod from APRS_DATABASE_URL). Missing
+      # config logs a warning and skips startup so the app still boots.
+      aprs_repo_child_spec(),
       {Cluster.Supervisor, [topologies, [name: Microwaveprop.ClusterSupervisor]]},
       {Phoenix.PubSub, name: Microwaveprop.PubSub},
       # Partitioned Task.Supervisor — callers route heavy `async_stream`
@@ -43,7 +47,7 @@ defmodule Microwaveprop.Application do
     # See https://hexdocs.pm/elixir/Supervisor.html
     # for other strategies and supported options
     opts = [strategy: :one_for_one, name: Microwaveprop.Supervisor]
-    result = Supervisor.start_link(children, opts)
+    result = children |> Enum.reject(&is_nil/1) |> Supervisor.start_link(opts)
 
     # Attach the Oban exception telemetry tap so per-worker recovery
     # callbacks and structured logs fire on job failure. Must run after
@@ -92,6 +96,23 @@ defmodule Microwaveprop.Application do
     :ok
   end
 
+  # Returns Microwaveprop.AprsRepo child spec if configured (has a :url
+  # or :database key), otherwise logs a warning and returns nil so the
+  # supervisor children list can filter it out. APRS calibration is an
+  # optional integration with the sister aprs.me database — we never
+  # crash boot when it's unavailable.
+  defp aprs_repo_child_spec do
+    config = Application.get_env(:microwaveprop, Microwaveprop.AprsRepo, [])
+
+    if Keyword.has_key?(config, :url) or Keyword.has_key?(config, :database) do
+      Microwaveprop.AprsRepo
+    else
+      Logger.warning("Microwaveprop.AprsRepo not configured (no :url or :database) — APRS calibration disabled.")
+
+      nil
+    end
+  end
+
   @doc """
   Returns the deployment (image build) timestamp.
 
diff --git a/lib/microwaveprop/aprs_repo.ex b/lib/microwaveprop/aprs_repo.ex
new file mode 100644
index 00000000..14c122a5
--- /dev/null
+++ b/lib/microwaveprop/aprs_repo.ex
@@ -0,0 +1,17 @@
+defmodule Microwaveprop.AprsRepo do
+  @moduledoc """
+  Secondary repo for read-only access to aprs.me's `packets` table.
+
+  Used by `Microwaveprop.Aprs` and the `Mix.Tasks.Calibrate.Aprs144` mix
+  task to pull verified RF hops as ground truth for 144 MHz scoring.
+
+  This repo never owns schema, migrations, or writes — it only ever
+  issues SELECT queries against aprs.me's existing partitioned `packets`
+  table. The connection is configured to fail closed if `APRS_DATABASE_URL`
+  is unset in production.
+  """
+  use Ecto.Repo,
+    otp_app: :microwaveprop,
+    adapter: Ecto.Adapters.Postgres,
+    read_only: true
+end