[MRCA] The backpack GPS project

[chancewolf at me.com]

One thing I noticed just on a brief glance through that brochure is that
they reference field configurations as needing an antenna and preamp both,
so perhaps it's looking for some specific antenna that's just been replaced
in your setup with a generic L1 passive puck type.  

 

 

From: mrca-bounces at mailman.qth.net <mrca-bounces at mailman.qth.net> On Behalf
Of Ray Fantini via MRCA
Sent: Monday, October 6, 2025 7:15 AM
To: mrca at mailman.qth.net; MMRCG at groups.io
Subject: [MRCA] The backpack GPS project

 

Everyone agrees that it's a fun box to have something that weighs thirty
pounds that's strapped to a allice frame to do what the smallest I phone
will do only better, but if you don't understand the attraction to the use
of obsolete and arcane technology you should not be reading this in the
first place.

So far I have determined that the backpack system is a Magnavox MX 4400 and
may be one of the earliest systems out there. Attached is a copy of the
sales brochure from back in 1987, the backpack can be seen on page 5

Test with the system have provided some information, first when the system
powers up it wants to know what "Plan" you want to run. There is a list of
about twenty different navigation plans for locations throughout the world
along with several cryptic modes that I do not understand. Loading the CONUS
US plan results in just a message that the antenna appears to be obstructed
after a while when it cannot find any satellites. One of the other plans, I
cant remember the name right now has somewhat the same results but did
notice that after ten or fifteen minutes the clock function sets itself
correctly so assume something's getting thru. 

Going to assume that this is not just the old NAVSTAR VHF/UHF system but do
not know if its got the smarts to decode modern L1 band data or not? The
antenna definitely looks like a L1 antenna but not certain about the
software. Unfortunately for some weird reason on this version they
eliminated the SATS and STAT buttons. The buttons are there but not labeled.
Assume this set had a limited version of firmware?  All other buttons and
otherwise its identical to the commercial 4400 or 5400 receivers. Will go
thru when I have time and write down all the different navigation plans that
are offered and see if that has any useful information.

 

Ray F/KA3EKH

 

 

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