Now that’s pretty cool.  In the backpack GPS units I was only aware of the Rockwell-Collins AN/PSN-8 (which I have an example of) and the Texas Instruments AN/PSN-9 (which I’ve been trying to find for years) – and now there’s your Magnavox unit which likely predates both, though I bet it had a different antenna as a packset initially. 

If you can find a date anywhere on the thing I’d be interested to know where it fits in the development stream, and whether or not it was just submitted as a prototype for a competition but not adopted, or maybe as LRIP for field trials or something.  

All of my old GPS units with the Y2K bug will eventually resolve a position if you leave them powered up long enough.  The worst offender was the handheld Magellan Nav 1000M which I’d written off as incapable of resolving a position – but then left it on for hours and hours and found out that it did get a fix eventually (though as others have stated the date will be wrong.)   By way of comparison,  that AN/PSN-8 resolved a position relatively quickly.  I think the date may have even been correct. 

From: [email protected] <[email protected]> On Behalf Of Ray Fantini via MRCA
Sent: Tuesday, September 30, 2025 7:21 AM
To: [email protected]; [email protected]; [email protected]; [email protected]
Subject: [MRCA] Backpack GPS receiver

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