What is APRS Caching?

APRS Caching is aiming at giving the well known Geocaching concept an amateur radio touch. The idea behind APRS Caching is to connect the fascination of Geocaching with amateur radio. Thus, APRS Caching gives radio amateurs the opportunity to rediscover their fields of interest. APRS Caching can be regarded as a user-friendly project and is according to the Ham Spirit open to criticism, support and change.

How does APRS Caching work?

Basically the APRS Caching system resembles the main features of Geocaching. There are so called caches, which have to be searched for by the logger. After having found the cache the logger can make an entry in the logbook. The difference between APRS Caching and Geocaching is that the logbook entry is carried out by APRS.

Description of the most important terms:

  • APRS
    is the abbreviation of Automatic Packet Reporting System and is used by radio amateurs to send out position data, weather conditions, telemetry and personal messages via radio in real-time.

    stands for Automatic Packet Reporting System - Internet Service and describes the combination of several servers, that distribute APRS packets and are reachable via internet.

  • Position Beacon
    Transmission of actual geographical position.

  • Cache
    The object to be found.

  • Geocacher, logger
    The person that is searching for the cache.

  • Owner
    The person that hid the cache.

  • Drive-In
    A cache that can be easily reached by car.

  • Stage 1
    The first stage of the cache. In single-stage caches, this is the caches target position. In two-stage caches you will get the coordinates for the second stage.

  • Stage 2 (only with two-stage caches)
    The second stage of the cache and its target position.

This example of a APRS cache illustrates the caching process:

The APRS cache called WeatherStation OE8APR-10 is located at the position JN76GO86OT and transmits its static position to the APRS-IS net in regular intervals. The callsign of this APRS station is OE8APR-13. Logger Johann, OE6POD, has located this APRS cache via APRS Caching website and wants to add it to his list of logged caches. As APRS device Johann uses an iPhone with the app iAPRS. To navigate to the coordinates of the cache he uses the app GPS Tour.

As the APRS weather station OE8APR-13 is located on the roof of Andreas house, OE8APR, it is easy to get close to the coordinates. In Geocaching you would even call this a Drive-In. As soon as the logger Johann is in the immediate vicinity of the cache, he transmits a APRS position beacon with his mobile phone. This position beacon is processed by the APRS Caching System and the cache gets automatically logged. The APRS beacon comment is used also for the logbook entry.

To demonstrate a two-stage cache, lets have a look at the following scenario:

The cache owner Johann, OE6POD, publishes an audio cache at the position JN77EG53LR. This cache is an audio recorder module, that, by pushing a button, provides the stage 2- and thus the target coordinates in form of a PSK31 signal.

Logger Andreas, OE8APR, sets out for Johanns cache equipped with an iPhone 4s, the app PSK31 to decode the PSK31 signal as well as a Kenwood TH-D7E with Bluetooth GPS as APRS equipment. After a short search Andreas finds the audio module in a small box, starts the PSK31 app and pushes the button to play the PSK31 signal.

On the mobile phone the following text can be read:

This is the PSK31 audio cache OE6XDG as a part of the APRS Caching project
Owner of this cache is Johann, OE6POD
Stage 2 coordinates are 47.2625, 14.378819
Happy caching!
73 73 73 de OE6XDG OE6XDG sk sk sk

Now the stage 2- and thus the target coordinates are known to finally log the cache. Logger Andreas takes his GPS device to navigate to the new coordinates. At the target coordinates he sends out a position beacon with his TH-D7E via radio. To make sure the beacon gets through Andreas repeats this process to times. As in the previous example the logbook entry is generated automatically.

What cache types are there?

There are single-stage, two-stage and other caches. Single-stage caches provide the ultimate target coordinates where the cache can be logged. Two-stage caches first provide the stage 1 coordinates where you get the target coordinates in some way or other, depending on the cache type. Currently "Other caches" are the traditional Geocaches.

Single-stage caches

An APRS cache has to be an APRS station that sends its position to the APRS net in regular intervals. APRS stations can be iGate, mobiles, portables, weather stations etc. It doesnt matter whether it is a radio transmission or a feed-in in the APRS-IS. This makes it possible for radio amateurs to make themselves a living cache with the help of their APRS-able radio equipment or their mobile phones and the according APRS app.

SOTA caches are summits of the SOTA project. The summits are imported into the APRS Caching service through the SOTA API. This gives the SOTA activators the possibilty to participate to SOTA and APRS Caching at the same time. It is enough to send out an APRS position beacon at time of the summit activation and the SOTA cache is logged.

A virtual cache only exists in form of a location. It is the owner who decides whether the cache is the answer to a question, an interesting landmark, a riddle or the like. The logger is rewarded with an interesting landmark and the sharing of his experiences. Although there are many beautiful places to visit, this kind of cache should be something special.

Two-stage caches

The idea behind this kind of cache is to hide an audio recorder module, that plays an audio signal by pushing a button or any other kind of activation. The goal is to use a digital mode such as CW, PSK31 etc as audio signal. There are no limits to your imagination. The loggers hearing (with CW), a mobile phone or a homebrew decoder are now used to decode the audio signal. The content of the audio signal has to at least contain the stage 2- or the target coordinates. It is for the cache owner to decide on any additional information. Audio recorder modules are available for about €5, see “ISD1820 Audio Sound Recording Module w/ Microphone / Speaker - Deep Blue“ at DealExteme

Near Field Communication is a technology of the future and for this reason cannot be left out. The idea is to use a NFC tag to to deposit the stage 2- or target coordinates. This makes it possible for the logger to detect this tag using a mobile phone or a homebrew NFC reader and thus to receive the stage 2- or target coordinates.

Other caches

As the name already tells, this is a cache designed after the well-known Geocaches. The goal here is to hide a container with a logbook at a specific location. It is up to the cache owner to decide on the cache type. There are traditional Geocaches, multi caches or mystery caches. Here, the common Geocaching rules are to be applied. Further information at https://www.geocaching.com/guide

How can I join?

In order to be able to join APRS Caching as owner or logger, you first need to register on the APRS Caching platform. Registration on APRS Caching is free, requires a valid ham radio callsign, though. As a logger you can start immediately after registration. If you wish to contribute your own cache, this has to be done using the APRS Caching feature. As a logger you need to be able to send out your current geographical location using APRS. It doesnt matter whether this is done via radio transmission or a feed-in in the APRS-IS. This means you can use your ham radio equipment or a mobile phone with a suitable APRS app for this.

Radio hams become living caches

Everybody who is familiar with Geocaching knows that Geocaches hold a static geographical position. The reason for this is based on several details. On the one hand, Geocaches are meant to show loggers interesting locations and long forgotten places. On the other hand, Geocaches cannot update their location in real-time. This is where APRS Caching comes in and allows on update of the geographical position of an APRS cache thanks to the global APRS network that can be reached via radio from nearly everywhere. This enables radio hams whether portable or mobile to function as living cache.

This is how OE6POD becomes a living cache:

Johann, OE6POD, usually always carries a radio with him that has GPS as well as APRS. In case he doesnt have his radio with him, he uses his iPhone with the app iAPRS. Hence, all requirements for the update of this location are met In order to function as a living cache, Johann creates an APRS Cache on the APRS Caching platform. He goes to https://www.aprscaching.com and navigates to the APRS Caching feature. Immediately he will see the button Add cache and in a next step he will have to fill in the most important information on the cache, see How to contribute an APRS Cache?

After having chosen the APRS cache type, Johann will see a field called APRS callsign (with SSID). He then has to enter his callsign (including SSID) that he uses to send out his location to the APRS network. When creating a the APRS Cache the geographical position doesnt have to be accurate, as the exact position will automatically be updated as soon as the first position beacon is sent out. After the creation of the APRS Cache, the APRS Caching service will react to packages containing the source callsign that were indicated in the creation process. Right after creation of the APRS Cache, Johann sends out a position beacon to ensure the update of the geographical position. The creation process is now completed and Johann can function as a living cache, ready to be found by a logger.

Andreas, OE8APR, has also registered as APRS Cache and is taking a ride in his car. He has set his APRS equipment so as to be alerted as soon as he passes another APRS station. After some time the alarm tells him that OE6POD is in his near vicinity. At 145.500 MHz Andreas calls OE6POD and Johann replies instantly. The short QSO is limited to the question whether or not OE6POD is also registered as APRS Cache and they arrange a close meeting point.

Now both Oms and therefore their APRS Caches are at the same geographical position. Both of them send out their current position beacon to ensure their meeting to be logged (if this hasnt already been done anyways). Theoretically it would suffice for both Oms to pass each other and to simultaneously send out an APRS beacon. However, a meeting means that both Oms can add a further logged cache to their list and it may be nice to make new acquaintances.

How to contribute an APRS Cache?

The creation of an APRS Cache requires a free membership on the APRS Caching platform. The first thing you will have to decide on, is the type of cache you would like to create and its geographical position. You need to keep in mind that some cache types (e. g. audio caches) might need regular maintenance (e. g. changing batteries). It it important to keep ones APRS Cache in an adequate operating state.

For creating an APRS Cache, the following data need to be specified:

  • Cache name (solely up to the cache owner)

  • Description
    Here you can give some information on the cache as well as on the history of the cache location. It is important to indicate the specific characteristics of the cache, e. g. The digital mode used in Audio caches or any user specifications.

  • Hint (optional)
    Any hint that will make it easier for the logger to find the cache.

  • Country
    The country in which the cache is located.

  • Locator, Latitude and Longitude
    In a Single-stage cache the actual geographical position has to be indicated. In a Two-stage cache the Stage 1 position has to be given. Here, a bidirectional automatic calculation between locator and the geographical coordinates is carried out. The geographical position will be indicated in decimal degrees and the locator needs to be 10 digits long.

  • Difficulty
    The level of difficulty for the cache according to the general gradation of Geocaches.

    • Easy
      Openly visible and easy to find or solve in a few minutes.

    • Average
      An average experienced Geocacher will be able to find the cache in less than 30 minutes.

    • Challenging
      An experienced Geocacher will see this cache as a challenge and it could take him/her most of the afternoon to find it.

    • Difficult
      A real challenge for experienced Geocachers. It is possible that special skills or knowledge and/or thorough preparation are required in order to find the cache. Several days or attempts may be necessary to raise the treasure.

    • Extreme
      A really serious challenge for body and/or mind Special knowledge and/or equipment are necessary to raise this cache.

  • Terrain
    The level of difficulty of the terrain according to the general gradation of Geocaches.

    • Handicapped accessible
      There are well-developed paths, the terrain is relatively flat and you have to walk less than 1km.

    • Suitable for small children
      The route generally takes you along marked paths, there are no steep elevations or overgrown areas to negotiate. The total route is not longer than 3km.

    • NOT suitable for small children
      The average fit adult or older children should not experience any difficulties with the terrain which could possibly involve cross-country. Geocaches can be confronted with overgrown areas and stepper elevations and may perhaps have routes in excess of 3km.

    • Experienced outdoor enthusiasts only
      The terrain is most probably cross-country. You will have to negotiate heavy over-grown and/or steep elevations or descents (using hands to assist). The route can exceed 16km. An overnight stay may be necessary.

    • Requires special equipment
      Requires special equipment, skills and experience (boot, four-wheel drive, mountaineering/climbing, diving etc.) an absolute necessity or it is otherwise very dangerous.

  • Tags
    Here you can provide information on the cache using key words. For an APRS Cache of the type APRS station you could use key words like weather station, iGate etc. For an Audio cache you could indicate the respective digital mode.

  • Cache type
    For the different kinds of caches see What cache types are there?

  • APRS callsign (with SSID)
    For an APRS Cache it is crucial to indicate the callsign including SSID as it is used by the APRS station to send your position data to the APRS network. Only then an update of the position data is guaranteed.

  • Target Locator, Target Latitude and Target Longitude
    In a Two-stage cache you have to indicate the geographical position of the Stage 2 here. Again, a bidirectional automatic calculation between locator and the geographical coordinates is carried out. The geographical position will be indicated in decimal degrees and the locator needs to be 10 digits long.

  • Photos, videos, sounds and data files
    Photos, videos, sounds and data files can be attached to your cache via the upload masks. This function can used to refer to hints, technical descriptions or circuit diagrams for homebrew kits concerning the cache.

  • Allow rating
    Here, the cache owner can decide who will be allowed to rate the cache.

The average Geocache experienced radio amateur should not experience any difficulties with the APRS Caching system. Inexperienced radio amateurs will find detailed descriptions and assistance on various Geocaching sites relating to this topic. Once you are familiar with the basic Geocaching concept, the APRS Caching will represent an exciting extension for you. It will certainly bring about unexpected challenges but most of all a lot of fun for radio enthusiasts.

Geocaching of a different kind

  • 01
    SOTA Caches

    Log your SOTA activations on APRS Caching too

  • 02
    APRS Caches

    Weather stations, digipeaters, and iGates - turn your APRS stations into APRS Caches

  • 03
    Living APRS Caches

    Even you are able to turn into a living APRS Cache

  • 04
    Geo Caches

    Log your OpenCaching finds with your APRS enabled device