MX 4102

Background

When Sputnik was put into orbit in 1957 some scientists at the Johns Hopkins Applied Physics Lab came up with the idea of using the doppler shift measured on the ground to solve for the 3 dimensional position of the receiver.  This required a satellite that transmits it's orbital elements.  There are a number of papers on the JHAPL Legacy of Transit web page.  The Navy Navigation Satellite System, as it was officially known, was designed mainly to allow the inertial navigation system on Polaris nuclear subs to be updated.

The very first Transit receiver took up about a dozen six foot high rack cabinets.  The receiver for the Polaris sub was in two cabinets designed to fit through the hatch as so were narrower than a normal relay rack.  The transistor had just come out and integrated circuits were non existent when the Transit satellite system went into operation.  By the time Magnavox built the MX 4102 integrated circuits were common, hence it's small size and much lower price than the very expensive early Transit receivers.

The MX 4102 was designed by Magnavox, Torrence, CA (now Leica Geosystems Group) for use on pleasure boats and since there can be a number of hours between Transit fixes it includes dead reckoning to keep the position updated.  This requires external compass and speed inputs from any number of the common types of sensors used abroad ships and the appropriate interface options for the MX 4102.

The MX 4102 uses a oven controlled oscillator (OCO) marked:
Electronic Research Company
Model EROS 800-MA-97
Mfg. p/n 626358-1 B
Freq 5.00 MHz
s/n 11703
Date 89-17

This is oscillator has a short term stability of 1E-10, equivalent to rack mounted lab type standard oscillators.  A high stability oscillator is needed to measure the doppler curve and to set the receiver tuning offset to account for the doppler shift of the carrier on the low orbiting Transit satellites.

Manuals

The Navigator's Manual and the Installation and Service Manual are dated June 1989.

Power

The unit operates from 10 to 30 Volt Dc power with positive going through the fuse.  the current is just over 1 amp at a cold start and decreases to about 0.8 amps after the oscillator oven has warmed up.

Operation

By setting the approximate position, date and time by pressing INIT repeatedly the receiver can start searching for signals.  When the signal strength at 400 Mhz gets above some threshold the receiver starts looking for the digital modulation.  Now when there is no active satellite or I don't have a high enough antenna gain the receiver beeps and displays no fix (NFX).  Apparently this receiver does not use the signal at 150 Mhz, only the 400 Mhz signal.  This means that the corrections for ionosphere refraction are either approximated or not used.

The front panel has a Vacuum Fluorescent Display (VFD) with buttons below and to the right so the VFD can act as a menu system.  In addition there are a couple of membrane keyboards, one with specific labels related to functions and the other with digits for numerical input.

Satellites

On 1 Jan. 1997 all the Transit satellites were turned over to the Navy Ionospheric Monitoring System (NIMS) and no longer use the Transit data modulation.  Instead they now use a different modulation that's a classified NIMS format.  These satellites are in a fairly high orbit and will stay there for a very long time, i.e. they will not decay and fall to Earth like a low orbiting satellite.  But they are all now very old and so will cease to operate electrically when failures take them off the air. 
The primary navigation frequencies are 149.985 and 399.970 and telemetry on 136.650 MHz.

MX 4200D Differential GPS Receiver

Links

MX Marine, Leica Geosystems Group - offers GPS, DGPS equipment for ships
Hearsat - an orginazation with a mailing list for those listening to satellite signals, NIMS
Center for Ionospheric Research U of Texas- Transit Satellites -
HAARP - Slant-path Total Electron Content and Scintillation based on Transit Satellites using Northwest Research Associates, ITS10 Transit receivers.
Transit 5B-5 der wahrscheinlich älteste aktive Satellit - BableFish Translation - even without translation you can read the frequencies and see the images.