[Milsurplus] Backpack GPS receiver

[Mike Feher]

Besides all the PLGRs, I also have an old DAGR here. 73 – Mike 

 

Mike B. Feher, N4FS

89 Arnold Blvd.

Howell NJ 07731

908-902-3831

 

From: milsurplus-bounces at mailman.qth.net <milsurplus-bounces at mailman.qth.net> On Behalf Of Brooke via Milsurplus
Sent: Tuesday, September 30, 2025 5:39 PM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] Backpack GPS receiver

 

Hi Bob:

The new features mostly relate to new frequencies, the clear text L1 signal is still there so very old GPS receivers should still work, they will just have the date wrong.

The problem with the date relates to GPS week rollover.
https://en.wikipedia.org/wiki/GPS_week_number_rollover
The week number goes from 0 to 1,023 then rolls over.
Trimble has a patent on a way to figure out that's happened, but it did not work out.  Some modern GPS receivers allow manually setting the date to get around this.

The SV Messages can be seen with any reasonable GPS receiver, but they are encrypted, see:
https://prc68.com/I/DAGR.shtml#SV_Messages



-- 
Have Fun,
 
Brooke Clarke
https://www.PRC68.com
axioms:
1. The extent to which you can fix or improve something will be limited by how well you understand how it works.
2. Everybody, with no exceptions, holds false beliefs.

-------- Original Message --------

Date: Tue, 30 Sep 2025 13:25:14 -0400
From: Bob  Camp  <mailto:kb8tq at n1k.org> <kb8tq at n1k.org>
To: Ray Fantini  <mailto:RAFANTINI at salisbury.edu> <RAFANTINI at salisbury.edu>
Cc: Milsurplus  <mailto:milsurplus at mailman.qth.net> <milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] Backpack GPS receiver
Message-ID:  <mailto:BAE87226-C15D-4722-BA79-DC4ED2076812 at n1k.org> <BAE87226-C15D-4722-BA79-DC4ED2076812 at n1k.org>
Content-Type: text/plain; charset="utf-8"
 
Hi
 
The basic GPS format has not changed since ?way back?. There have been enhancements. They are supposed to be backwards compatible with older gear. In practice this does indeed seem to be true. There are completely new broadcasts on some bands. The old ones are all still there (at least for now).
 
There are issues with the transition from GPS time to ?real time and date?. On something this old, you just live with it. The date is wrong, but everything else works fine. I have a lot of GPS gear that now works this way.
 
The military folks liked to use the secure GPS broadcasts. That involved having access to the crypto keys for that system. Very few (if any) of us have access to that sort of thing. Various steps might or might not have been taken to disable this functionality (if it was ever present). In some cases those steps also compromise the entire device. Hopefully that?s not the case here.
 
Fun !!!
 
Bob

 



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