HFU HF Underground

General Category => General Radio Discussion => Topic started by: Matt_B on August 16, 2021, 1741 UTC

Title: EAM Message?
Post by: Matt_B on August 16, 2021, 1741 UTC

I think I just caught part of one on 4724 khz.  :O

Title: Re: EAM Message?
Post by: Matt_B on August 16, 2021, 1800 UTC

So this one's a mystery.  Here's what I thought I heard. 

"Alaska (string of other words that I couldn't make out) (phrase terminator).  W VIRGINIA (unintelligible) WWWVN665 (three unintelligible letters) 60S LOWRDA2QYFQ5CY.  GEOMETRIC OUT"

Anyone have any idea as to what they could've been saying here? In particular, what's "Geometric" mean? I assume it's a call sign?

Title: Re: EAM Message?
Post by: ~SIGINT~ on August 16, 2021, 2212 UTC

Matt, this frequency is part of the USAF High Frequency Global Communications System (HFGCS) and those message are common. Messages are generally simulcast on 4724, 8992, 11175 and 15016.

Primary HFGCS Frequencies 24 Hours: 8992 and 11175
Back up HFGCS Frequencies Day: 13200, 15016
Back up HFGCS Frequencies Night: 4724, 6739

GEOMETRIC is in fact the call-sign of the station transmitting the message. You can expect that call-sign to change every 24 hours.

Here is an example from the 15th:

21:12Z 15 AUGUST 2021 8992.0 kHz USB  (simulcast)
TO: ALL STATIONS
FM: GOAL POST
BXTALV // YN4YB UGQCM FQXNT RTSF6 NWBO

From my experience, this is the typical format:
BXTALV ( message identifier )
YN4YB UGQCM FQXNT RTSF6 ( message traffic )
NWBO ( authentication / checksum )

Title: Re: EAM Message?
Post by: Matt_B on August 17, 2021, 0027 UTC

Quote from: ~SIGINT~ on August 16, 2021, 2212 UTC

Matt, this frequency is part of the USAF High Frequency Global Communications System (HFGCS) and those message are common. Messages are generally simulcast on 4724, 8992, 11175 and 15016.

Primary HFGCS Frequencies 24 Hours: 8992 and 11175
Back up HFGCS Frequencies Day: 13200, 15016
Back up HFGCS Frequencies Night: 4724, 6739

GEOMETRIC is in fact the call-sign of the station transmitting the message. You can expect that call-sign to change every 24 hours.

Here is an example from the 15th:

21:12Z 15 AUGUST 2021 8992.0 kHz USB  (simulcast)
TO: ALL STATIONS
FM: GOAL POST
BXTALV // YN4YB UGQCM FQXNT RTSF6 NWBO

From my experience, this is the typical format:
BXTALV ( message identifier )
YN4YB UGQCM FQXNT RTSF6 ( message traffic )
NWBO ( authentication / checksum )

So basically, orders to Air Force units in the area.  Cool...thanks.

Title: Re: EAM Message?
Post by: ~SIGINT~ on August 17, 2021, 0044 UTC

These messages have a fixed length of 30 characters. They are most likely a "status message". Occasionally there will be longer messages, 100 plus characters. Those will transmitted in either one-shot or with a THIS IS <call-sign>, STANDBY, MORE TO FOLLOW.