View source for EAM/Group 3 Prefix

{{AI Draft|Claude}}
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| style="text-align:center; font-size: 90%;" | ''A chart quantifying EAM traffic over a 7 month period; Group 3 Messages in yellow. (Click to view larger version)''
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'''Group 3 Emergency Action Messages''' ('''Group 3 EAMs''' or '''Group 3 Messages''') occupy a distinct structural category within the EAM taxonomy, characterized by specific length clustering patterns, embedded repeated character sequences, and consistent absence of addressee designations. Group 3 Messages are the least common of the four major EAM groups, constituting approximately 3% of total HFGCS traffic.

Group 3 Messages appear to follow standardized formats with strong preferences for particular character counts, particularly 22, 27, 32, and 37 characters. This concentration at specific lengths distinguishes Group 3 from [[EAM/Group 2 Prefix|Group 2]]'s broader length distribution and [[EAM/Group 1 Prefix|Group 1]]'s rigid 30-character format.

== Defining Characteristics ==

Group 3 Messages are distinguished by several consistent structural features:

'''Length clustering:''' Group 3 Messages show strong concentration at specific character counts rather than broad distribution. The most common lengths are 22, 27, 32, and 37 characters, with these four lengths accounting for approximately 60% of all Group 3 traffic. Additional common lengths include 25, 29, 36, 38, and 40 characters.

'''Embedded repeated sequences:''' Approximately 40% of Group 3 Messages contain repeated character sequences of three or more characters embedded within the message. These repetitions appear integrated throughout the message structure rather than at fixed positions. This prevalence of internal repetition is nearly identical to [[EAM/Group 4 Prefix|Group 4 Messages]] (38%) and significantly higher than [[EAM/Group 2 Prefix|Group 2 Messages]] (11%) or [[EAM/Group 1 Prefix|Group 1 Messages]] (1%).

Examples of Group 3 Messages with repeated sequences include:

`DPZUZGM6IOY2KFCGFRLQPR32RPR32G4K` (32 characters - "32R" repeats)

`72NCECWCDHFIWKPWA65V4WAIHRSS6H33S6H73S6HP3NBHNVQ` (48 characters - "S6H" repeats three times)

`72IA225VMX2YRM2EW43F74PAACOHFRCOHFTCOHLVV4` (42 characters - "COH" repeats three times)

`OA4WGYNMK7EDIRJQ4NB66WG7K43KVI43KVIKFOB6IZ5BYD4KVZVFX` (53 characters - "43KVI" and "4KV" repeat)

`64WDQFM7IUKJQLNFEHNFEEOO3RVVCJUEOOKRGSBBBWZCJUEOO3RNTBBUEOOKRV7CIN4` (67 characters - "JUEOO" repeats three times)

The function of these repeated sequences is unknown but may serve as delimiters, error detection codes, formatting markers, or structural indicators similar to those observed in Group 4 Messages.

'''No addressees:''' Group 3 Messages never include "FOR [CALLSIGN]" specifications. Unlike [[EAM/Group 2 Prefix|Group 2 Messages]], which frequently specify intended recipients, Group 3 Messages are always broadcast without addressee designations.

'''Can be 30 characters:''' While rare, Group 3 Messages can be exactly 30 characters long. Eleven documented instances exist, demonstrating that Group 3 does not avoid the 30-character baseline length that dominates [[EAM/Group 1 Prefix|Group 1]] and is common in [[EAM/Group 2 Prefix|Group 2]]. However, 30-character Group 3 Messages represent less than 4% of Group 3 traffic.

'''Range:''' Documented Group 3 Messages range from 22 to 78 characters, though the vast majority fall between 22 and 48 characters.

== Prevalence ==

Group 3 Messages are rare compared to Groups 1 and 2. Observation of traffic patterns shows sporadic appearance, with Group 3 prefixes often appearing for only a few days before disappearing for extended periods. This pattern contrasts sharply with the consistent daily presence of [[EAM/Group 1 Prefix|Group 1]] and [[EAM/Group 2 Prefix|Group 2]] prefixes.

Group 3 activity shows significant month-to-month variation. During typical periods, Group 3 Messages constitute approximately 3% of traffic. However, October and November 2024 showed unusually elevated Group 3 activity at 10% and 11% respectively, suggesting operational factors can significantly affect Group 3 transmission frequency.

== Length Distribution ==

Group 3 Messages show distinctive length clustering that serves as a key identifier:

'''Most common lengths:'''
* 22 characters: 18% of Group 3 traffic
* 27 characters: 19% of Group 3 traffic
* 32 characters: 10% of Group 3 traffic
* 37 characters: 6% of Group 3 traffic

'''Secondary common lengths:'''
* 25 characters: 7% of Group 3 traffic
* 29 characters: 2% of Group 3 traffic
* 36, 38, 40 characters: Each appearing in 3-4% of Group 3 traffic

The strong concentration at 22 and 27 characters is particularly distinctive. These two lengths together account for over one-third of all Group 3 Messages and are rarely observed in other groups. This clustering pattern suggests Group 3 Messages follow predetermined message templates or formatting structures with specific length requirements.

== Identification Methodology ==

Group 3 Messages present unique identification challenges due to their rarity and structural overlap with other groups.

'''Length-based identification:''' Messages of exactly 22 or 27 characters with no addressee are highly likely to be Group 3, as these lengths are uncommon in other groups. However, definitive identification still requires observing prefix behavior over time.

'''Repeated sequence detection:''' The presence of embedded repeated character sequences (particularly 3+ character repetitions) in messages without addressees suggests Group 3 or Group 4. The shorter length range (22-78 characters) indicates Group 3 rather than Group 4 (36-292 characters).

'''Prefix consistency:''' A prefix can be identified as Group 3 if it is consistently used for messages clustered at characteristic Group 3 lengths (22, 27, 32, 37 characters) and never appears with addressee specifications.

'''Elimination process:''' If a 30-character message with no addressee uses a prefix that is neither the current [[EAM/Group 1 Prefix|Group 1]] prefix nor the current [[EAM/Group 2 Prefix|Group 2]] prefix, and that prefix is observed with other messages at distinctive Group 3 lengths, it is likely Group 3.

'''Sporadic appearance:''' Group 3 prefixes may appear for only a few days or even a single day before disappearing for extended periods. This ephemeral pattern complicates identification, as multi-day observation may not always be possible.

The rarity of Group 3 Messages means that even experienced monitors may go days or weeks without observing any Group 3 traffic.

== Prefix Patterns ==

Group 3 prefix behavior differs significantly from Groups 1 and 2. Rather than showing regular rotation schedules with prefixes remaining active for weeks or months, Group 3 prefixes appear sporadically and often for very short durations.

Examples of observed Group 3 prefix patterns include:

'''Brief appearances:''' Many Group 3 prefixes appear for only one to four days. For instance, during continuous monitoring from June 2023 through February 2024, prefixes W5, QL, and NR each appeared for a single day, while 64 appeared for four days across August-September 2023.

'''Recent sustained activity:''' The October-November 2024 period showed unusual Group 3 consistency, with the DX prefix remaining active across two months and the FJ prefix showing extended usage in October 2024. This sustained activity contrasts with the typical pattern of brief, scattered appearances and suggests operational factors can affect Group 3 usage patterns.

'''July 2025 example:''' The DP prefix was active throughout July 2025, with brief concurrent appearance of the GV prefix. This demonstrates that Group 3 prefixes can show sustained activity similar to Groups 1 and 2 under certain conditions.

Whether Group 3 operates on a rotation schedule similar to Groups 1 and 2 (but with longer intervals between active periods) or represents a fundamentally different usage pattern remains unclear. The variability in appearance patterns suggests Group 3 usage may be tied to specific operational conditions or requirements.

== Relationship to Other Groups ==

Group 3 exists within a four-group EAM taxonomy and shows particularly strong structural similarities to [[EAM/Group 4 Prefix|Group 4]]:

'''Structural similarity to Group 4:''' Both Group 3 (40%) and Group 4 (38%) show nearly identical rates of embedded repeated character sequences. This shared characteristic suggests both groups may serve related operational purposes or employ similar encoding/formatting schemes. The primary distinction is length—Group 3 Messages cluster at shorter lengths (22-48 characters typical) while Group 4 Messages are consistently longer (36-292 characters).

'''Contrast with Groups 1 and 2:''' [[EAM/Group 1 Prefix|Group 1 Messages]] are always 30 characters, never have addressees, constitute ~66% of traffic, and rarely contain repeated sequences (1%). [[EAM/Group 2 Prefix|Group 2 Messages]] have variable lengths (30-163 characters), frequently include addressees, constitute ~26% of traffic, and show moderate repetition rates (11%).

All four groups operate independently with separate prefix systems. The strong structural similarity between Groups 3 and 4, combined with their comparable rarity (~3% each), suggests these groups may represent specialized communication categories distinct from the baseline Group 1 traffic and directed Group 2 communications.

== Operational Context ==

The distinctive characteristics of Group 3 Messages—specific length clustering, embedded repeated sequences, absence of addressees, and sporadic appearance patterns—suggest this group serves a specialized operational purpose within the HFGCS architecture.

The strong preference for 22 and 27 character messages indicates constrained message formats, possibly corresponding to specific types of commands, status updates, or coordination messages with predetermined structures. The prevalence of repeated character sequences (40% of messages) mirrors [[EAM/Group 4 Prefix|Group 4]]'s pattern and suggests both groups may employ similar formatting or encoding schemes for specific operational purposes.

The sporadic appearance pattern and occasional periods of elevated activity (such as October-November 2024) suggest Group 3 usage is tied to specific operational conditions, exercises, or mission requirements rather than continuous baseline communication needs.

However, without access to message content or operational documentation, the specific purpose of Group 3 Messages remains speculative.

== See Also ==
* [[Emergency Action Message]]s
* [[EAM/Group 1 Prefix]]
* [[EAM/Group 2 Prefix]]
* [[EAM/Group 4 Prefix]]
* [[High Frequency Global Communications System]]