IRLP objects in APRS

The purpose of such objects is to show local radio resources in a way that is readable to mobile operators and as compatible as possible with APRS Frequency Objects practice. The object should help answer simple questions:

• where the resource is located,
• on what frequency it operates,
• what access parameters it requires,
• what its status or short description is.

Objects of this type should have local meaning. They should not be transmitted far beyond the area where the resource is actually useful.

1. When to use such an object

An IRLP object is used to describe a local IRLP node and the frequency on which an operator can use it. For a mobile user, the most important things are:

• the IRLP node number,
• the operating frequency,
• the CTCSS tone, DCS, or other access information,
• the node status,
• the callsign or a short description.

2. Example object frame

Schematic example:

;IRLP-1234*111111z5215.00NI02055.00E0438.700MHz T103 -760 IDLE SR5ABC

The frame consists of several parts:

;IRLP-1234*111111z5215.00NI02055.00E0438.700MHz T103 -760 IDLE SR5ABC
|        | |      |        | |        | |          |    |    |    |
|        | |      |        | |        | |          |    |    |    +-- callsign or description
|        | |      |        | |        | |          |    |    +------- status
|        | |      |        | |        | |          |    +------------ shift
|        | |      |        | |        | |          +----------------- tone / access
|        | |      |        | |        +---------------------------- symbol
|        | |      |        | +------------------------------------- longitude
|        | |      |        +--------------------------------------- IRLP symbol table
|        | |      +------------------------------------------------ latitude
|        | +------------------------------------------------------- timestamp
|        +--------------------------------------------------------- object name
+------------------------------------------------------------------ frame type: object

3. Object name

For IRLP objects, the following names are recommended:

IRLP-1234
IRLP12345

The first form is typical for four-digit node numbers. The second may be used if the number has five digits.

Examples:

IRLP-1234
IRLP-5678
IRLP12345

The node number should be visible in the object name, because a mobile operator needs it to use the link.

4. Alive/dead flag and time

For an active object, use:

*

For a fixed object, the following is often used:

111111z

Example:

;IRLP-1234*111111z

5. Coordinates and symbol

In the IRLP format, the I symbol table and symbol 0 are used:

5215.00NI02055.00E0

Breakdown:

5215.00N   latitude
I          IRLP symbol table
02055.00E  longitude
0          symbol

If the exact location should not be published, an approximate position may be used, as long as it still matches the node’s local service area.

6. Frequency

The frequency is given in the comment:

438.700MHz

Recommended format:

xxx.xxxMHz

7. Tone, DCS, and shift

After the frequency, tone, DCS, and shift may be provided.

Examples:

T103       CTCSS tone 103 Hz
C127       CTCSS 127 Hz, tone access and tone transmit
D023       DCS 023
-760       shift -7.6 MHz
-060       shift -600 kHz
+760       shift +7.6 MHz

8. Node status

The status should be short and readable.

Examples:

IDLE    idle
BUSY    busy
OFF_    unavailable

9. Recommended field order

For readability, it is worth keeping the order:

frequency tone/DCS shift status callsign-or-description

Example:

438.700MHz T103 -760 IDLE SR5ABC

Other examples:

145.575MHz T088 -060 IDLE IRLP
439.000MHz D023 -760 BUSY SR9XYZ
438.700MHz Toff -760 OFF_ Local

10. Good practices

• Put the IRLP node number in the object name.
• In the comment, provide the frequency in xxx.xxxMHz format.
• Add tone, DCS, or shift if needed to use the node.
• The status should be short.
• Do not use a long description. A mobile operator should be able to read the key data without scrolling.
• The object should be transmitted locally, in the area where the node is actually useful.

11. Quick reference

;             start of object
IRLP-1234     object name with IRLP node number
IRLP12345     variant for a five-digit number
*             active object
111111z       fixed timestamp
I             IRLP symbol table
0             IRLP symbol
438.700MHz    frequency
T103          CTCSS tone 103 Hz
D023          DCS 023
-760          shift -7.6 MHz
IDLE          example status
SR5ABC        callsign or short description