Difference, The difference between the Lodestar 3 and 3D is the frequency coverage. For purposes of clarity, the variant designators of Roman numeral III is used interchangeably with Arabic number 3.
Technology: Solid state.
Variants: Lodestar, Lodestar II,  Lodestar IID, Lodestar III. and Lodestar IIID.
Frequency ranges:

Lodestar 3 - 250 to 550 KHz and 1600 to 2800 KHz, Included are spot frequencies for 500 and 2182 KHz, Bandspread range is 285 to 315 KHz.
Lodestar 3D covers 250 to 550 KHz and a small band of frequencies of  plus 18 KHz and minus 17 KHz centered on 2182 KHz. A spot frequency for 500 KHz is also provided.
Modes: for both variants: A1, A2, A3 and A3H

Comments: One radio op commented  "The Lodestar could be used in manual or automatic mode. In manual it was left to the operators ability to sense the signal null. However in Automatic Mode this was done automatically and a scale pointer on its front panel simply rotated to and pointed to the bearing on a scale 0-360 degrees relative to the ships "head" or central fore-aft axis. This was way ahead of its time for merchant ships. It used the Bellini-Tosi principle of crossed loops erected on the front of the "Monkey Island" just above the bridge. Overall this unit was excellent. It had an excellent receiver with good selectivity and sensitivity and good band spread and stability".

Lodestar  3:   The cover for some of the controls is in the closed position.  (Photo courtesy Ships Nostalgia web page)

In this view, the cover for some of the front panel controls is in the open position. Download  image to enlarge. (Image courtesy Marconi Mariner magazine)

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Contributors and Credits:

1) http://www.shipsnostalgia.com/gallery/showphoto.php/photo/103831/title/marconi-marine-automatic-direction-finder/cat/530
2) http://www.elderdempster.me.uk/shippage%206.html
3) http://www.seefunknetz.de/lstar.htm
4) Ross Bradshaw [ross.bradshaw@mypostoffice.co.uk]

Mar 30/202