Type DM Raydist
4-4-285
A Raydist distance measuring system using circular co-ordinates, capable of producing a position fix to greater precision than that obtained with the hyperbolic system.
Two transmitters are used, one on the ship and one on the shore.
One frequency is nearly twice the other, so that the shore station can receive the signal from the vessel without interference.
This station doubles the lower frequency and compares it with the higher.
The resultant beat note is transmitted to the ship via a radio link. A second shore station likewise treats the two frequencies and transmits the resultant beat note via a radio link.
The vessel then compares these two beat notes with that similarly generated locally, enabling the distance to each shore station to be obtained.
Saturation is alleviated by having other vessels using different offset frequencies.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
