Decca Roller Map Display

[djrm]

I bought this at the local radio rally this morning, quite a find to add to my aviation instrument collection. I'm not quite sure what it is designed to be used for but most likely from an aircraft. I Can't find much about it by searching the internet and the Decca systems don't have a lot of technical information on line. I'll probably try and make a paper map for it and see if I can get the motors turning. I cant even be sure of the age yet, post war at any rate.

   

   

I'd love to be able to find out more... David.

[Radio Fixer]

http://www.jproc.ca/hyperbolic/decca_people.html

and maybe you found this?

http://www.jproc.ca/hyperbolic/decca.html

Gary

[djrm]

Thanks Gary.

[Mike Watterson]

Loran might be better known today, but the DNS was started during WWII (only commercial after WWII). Only just simple enough for valves and no CRT, but eventually used transistors and then microprocessors. Very ingenious though accuracy dropped a lot at night.
https://en.wikipedia.org/wiki/Decca_Navigator_System

The SatNav systems (US, EU, Russian, Chinese and a local Japanese) are vulnerable to a strong solar flare. They will all fail at once, eventually.

DNS and Loran were in use till about 2000 when US GPS became public.

[Mike Watterson]

Loran-C ran till about 2015 and may be restarted as a backup

The National Timing Resilience and Security Act of 2017, proposed resurrecting Loran as a backup for the United States in case of a GPS outage caused by space weather or attack.

my emphasis.

https://en.wikipedia.org/wiki/Loran-C#Future

It's not entirely dead.

It's unlikely the DNS will return as backup as USA always opposed it for political reasons.

[djrm]

So far I have identified the lamp power inputs and that it has five sets of three wire devices and another two terminal input. No much to go on really. I expect it to contain some synchros and perhaps an AC motor. Getting inside to see doesn't look too easy but I'll probably have to do it. Here it is with a piece of paper instead of a map lit up from the lamps behind.

   

[Mike Watterson]

What is your goal?

Basically the box was originally a an X - Y display device driven by the DNS receivers. The signals are gone and the receivers are complex. The roll map for one axis suggests it was for a fixed route longer than wide that would fit on the rectangle of the map. So there are at least 3 possible goals: An item on display, part of a DNS simulator or driving the map and pointer for a new application from a mpu / computer.

Obviously it will have a motor system to move the map and one for the pointer, with feedback of current position on both. An X-Y plotter often uses dead reckoning (typically stepper motor drive with X & Y end stop sensors). This application can't be rewinding the map, so that axis certainly needs a continuous sensor.

[Radio Fixer]

The map, as I undertsand it, was for fixed areas with the pointer that could include a pen to draw a trace of the route travelled. Very popular wuth fishng trawlers who could lift the lid and and add an X where they had found good fishing on previous occasions.

There must have been loads of maps and it would be good to find one for it.

Gary

[djrm]

What is your goal?

Hi Mike, I would like to exercise the unit by driving the motors and reading any feedback from the controls, I have means to generate variable phase/amplitude AC waveforms with microprocessors but I'm not familiar with what this unit is going to require. 

I found a picture including the insides of a similar unit online here: https://www.worthpoint.com/worthopedia/r...1110950028

A few more photos of my unit here: https://github.com/DavidJRichards/Aviati...ain/photos I printed a single sheet of a map to make a better photo. I'm looking into a way to make a roll map.

Best regards, David.

[djrm]

The map, as I understand it, was for fixed areas with the pointer that could include a pen to draw a trace of the route travelled.  Very popular wuth fishng trawlers who could lift the lid and and add an X where they had found good fishing on previous occasions.

There must have been loads of maps and it would be good to find one for it.

Gary

I had assumed this was an aviation device, I se the Decca system was used for both ships and aircraft too. Getting an actual map would be great, or even seeing what one looked like. D