Text below is largely a copy with some small augmentations from alancordwell.co.uk site on Radio Navigation Systems

"Trisponder was a short-range position fixing system manufactured by Del Norte Technology Inc of USA. It operated at X-band microwave frequencies around 9.5 GHz. By the use of relatively high peak power pulsed transmitters (1000 watts) along with very narrow pulses it gave a range of up to 80 km and could achieve a range accuracy of 3 metres or better under good conditions. The system comprised a of fixed/stationary transponder units and a maximum of 4 vessel-mounted transponder (beacons) with a control-interrogator unit (Display Measuring Unit –DMU) which interfaced to one or more display units. All units operated from 24 V DC and despite the high peak RF output power, the transmitter-receiver units only consumed an average 17 watts of power. Each mobile could operate on two fixed beacons.

In the early ‘80s an updated control unit was released called the DMU540. A more versatile item it could range to up to 4 different beacons and the results were shown on an orange C.R.T.. It would work with both the older and the slightly updated type of beacons. Another major advance was that the DMU540 had an internal microprocessor and could perform the computations to convert the measured ranges to a geodetic position PROVIDING that correct co-ordinates for the remote stations and geodetic constants had been inserted."

The last version, the 1009, was in 2006 still reported in use [Dredge Magazine with the British, Spanish, Indian and Indonesian Navy.

Shown are a 202, a 202A, a R04A, a 520 and a 540 DMU, a 220 data printer, two transmitters and a box of spares. All were once part of Nederlandse Survey Apparaten (NeSA) from Rotterdam which later became Racal and then Thales Survey before the instrument division became Reson and then Teledyne Reson. When no longer usefull with the NeSA they arrived in the collection of Rob Berlijn (together with a number of other instruments also in my collection). When Rob passed away to early his widow donated the objects to CT-Systems who in turn, after many years of custody donated them to my collection with the exception of a few land survey instruments which are now in the collection of Nicolas de Hilster as they are more fitting in that collection. I am very happy to be able to show these as I was afraid that they had become lost to history. Thank you Rob for your foresight!

More Information / other collections:

Alan Cordwell

National Maritime Museum

Laval University