[Milsurplus] Backpack GPS receiver

[Bob Camp]

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

> On Sep 30, 2025, at 10:20 AM, Ray Fantini via Milsurplus <milsurplus at mailman.qth.net> wrote:
> 
> Anyone who knows me understands that I don’t only work in obsolete military radios but also dabble in computers and other arcane devices. Picked up a couple things at the Gilbert Red Ball show. One is a ADSID III seismic sensor and that’s an entire story on to itself but also picked up a old backpack portable first generation GPS system. I think this is the military version of the Magnavox MX5400 or maybe a MX6102 but have no real idea beyond that. Unlike the older MX4102 terrestrial Navistar system I suspect this is a GPS system being it has the 1575 MHz patch antenna. Its also powered by a 5590 battery and comes all mounted up to a Allice frame. Anyone have any ideas about this? Suspect that the old GPS systems had some form of issue with date and year display but don’t know if that will keep it from displaying something. 
> Attached are some pictures.
>  
> Ray F/KA3EKH
>  
> <IMG_2574.jpg><IMG_2575.JPG>______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net <http://www.qsl.net/>
> Please help support this email list: http://www.qsl.net/donate.html

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20250930/b9c02244/attachment.html>