Radio Eyes Help
Fringe Calculator for Meridian Drift Scans
This calculator allows you to determine the expected fringe period of a transiting signal arriving at a two element interferometer that lies on an East - West baseline. Other configurations are not handled, however this simple arrangement is quite commonly used by amateur radio astronomers. Why is this useful? Knowing the expected fringe period for an object passing by your interferometer, provides you with a clue as to the declination of the object and thus is an aid in verification or identification of a radio source.
Usage
Required parameters are the baseline and the wavelength or frequency of the observation. To determine the declination of the source, leave the Declination box empty and input your measured fringe width in seconds or minutes. To calculate the expected fringe period, enter the declination and empty the Fringe Period box before pressing the calculate button. There are two Plot buttons. One draws a graph of period (Y) vs declination (X). You can see that the periods changes slowly as you near zero declination, and much quicker in the midrange declinations. As your beam nears one of the celectial poles the period becomes infinitely long - it disappears. The other plot button can display the theoretical pattern of relative signal intensity received during a meridian drift scan using a phase switching or adding type interferometer. You must specify an east-west Half Power Beamwidth (HPBW) of your antennas. The width of the plot is determined by the number of beam widths you want displayed. The default is four beam widths.
Adding Type Interferometer Plot
Phase Switching Type Interferometer Plot
