NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2015 Jul 18, 10:19 -0700
Robert you wrote: Assuming this is the correct I don't know what change to look for between the 2 nulls which would indicate which is the correct direction.
This is how I understand sense aerials from about 50 years ago, so don’t jump on me from a great height if I’m slightly or even a lot wrong. The polar diagram of a DF aerial looks like a figure eight. Depending upon the type of aerial, there are two nulls, either perpendicular to or in line with the line to the beacon. For a loop aerial the nulls occur when the loop is perpendicular to the line from the aircraft/ship to the beacon. The sense aerial has a circular polar diagram. Adding the two together gives a gentle heart shaped polar diagram known as a ‘limacon’ (funny how words stick). The good thing is there is only one null at 90 degrees to the loop aerial nulls (don’t ask me if it’s clockwise or anticlockwise!). However it’s not a very precise null, so it’s no good for taking a bearing on. It’s just for sensing. Depending upon the age of the set, sensing has to be done manually by the operator, or it’s all done by magic inside the kit. Frank Atkins is the chap to explain this properly. DaveP
