How it works ( phasing interferometry )
A simplified explanation
Lets make a map of the radio-sky at 16:00 Mean Sederial Time (MST)
You need 2 identical antennas with
front end amplifier, 2 pieces of 100 m.
coaxial cable, 2 coherent receivers working at 31 MHz,
a digitiser which takes about 30 000 samples per second
over 2 channels
and a personal computer with some software.
Last but not least you need
a measuring field of about 64 * 64 meter.
You put marking stones in the measuring field at a regular grid.
The distance between the grid nodes is 4 meter.
Put the first antenna in the first point of the grid. (0,0)
This is in one corner of the field.
Now you put the second antenna at an other grid point. (0,1)
Wait until the time is 16:00 hour MST and do measuring during
During measuring, digitise the sound which is coming from the two receivers.
Receiver one gives channel A and receiver two gives channel B
Channel A will have about 1 000 000 digitised values.
Channel B will have the same number of samples.
Calcuate now the cross correlation of this two channels.
This uses a very simple formula and cost only 3 seconds of calculations.
remember this crosscorrelation value for gridnode (0,1)
Now put the second antenna an other gridnode (0,2)
Wait again until 16:00 hours MST and do an other measurement during
Do again the digitising and the calculation of the crosscorrelation.
Now you have a crosscorrelation for gridnode (0,2)
Do repeat this for all gridnodes to get 16 * 16 crosscorrelation values.
Now you can make a radio map of the sky with a 2D-FFT algoritme.
The map will have 16 by 16 pixels.
A very coarse map, but a real map of the radio sky at 16:00 MST.
My measuring field is only 35 by 70 meter, so i can not do
all measurements, but with less it also gives reasonable maps.
This is the principle of the work.