[time-nuts] GPS System Message (was: TV Signals as a frequency reference)

Mark Sims holrum at hotmail.com
Sat Mar 31 14:21:22 EDT 2018


Or on the GPS/GNSS signals...  I was verifying Lady Heather's support for the old SV6/Palisade/Acutime receivers and came across a mention of the "GPS System Message" command.   It is requested by TSIP packet 0x28 and returns packet 0x48.  Newer Trimble receivers (like the Resolution-T don't seem to support the 0x28/0x48 messages. It is only mentioned in the SV6 docs.  The system message is a 22 character ASCII string embedded in the GPS navigation messages.   

If you dig into the GPS ICD docs it says it is used like a "bulletin board" for GPS users and can be a plaintext or encrypted message.  They currently seem to be encrypted...  perhaps a way to distribute P-code keys?

I wonder if any of the newer GNSS sats have some hidden goodies in the signals?

When sent to the SV6, you get a single response.  When sent to a Thunderbolt, you get 31 messages (mostly all the same).   I think the different messages are due to delays in the ground control system updating the satellites or the receiver not tracking particular satellites between updates.

Here a couple of responses from a Thunderbolt:

# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:Z9Mx69BOC1 Lx+:LR3X2 Q
# GPS system message:Z9Mx69BOC1 Lx+:LR3X2 Q
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:Z9Mx69BOC1 Lx+:LR3X2 Q
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V
# GPS system message:X4W-BZXE3/HPU77G49PU1V


# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:5FT16X78CN53GVWVF1/8BW
# GPS system message:5FT16X78CN53GVWVF1/8BW
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:5FT16X78CN53GVWVF1/8BW
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO
# GPS system message:E:S4.A2'3'A65/C5M8 UQO

----------------

> I wonder how many secret services are parasites on the commercial
TV transponders


More information about the time-nuts mailing list