Punta Salinas radar blanking test

May 2006

Data taking setup:
Making the plots:
1382 Mhz total power versus rotation angle as we change the blanking:
System compression by the radar:


    The punta salinas radar currently blanks its radar beam when it points +/- 45 degrees from the observatory direction. The radar had undergone extensive maintenance during the first part of 2006. The people at punta salinas requested that we recheck the blanking. They wanted to know if it was working properly and if it was possible to narrow the blanking sector north of the observatory (the part that goes out to sea).

The blanking tests.

    On 09may06 we did a coordinated test with punta salinas. We took data at various blanking interval settings to see how the received signal varied at AO. The table below shows the test number, blanking intervals used, start time for test, and the rms of the measured power from the a/d converter.
Start Time
Min Beteewn
A/D sigma levels
1 (+45,-45) 13:29:16 0 6.5,5.6,1.4 Current blanking
(+30,-45) 13:40:17 11 6.4,5.5,1.2
3 (+30,-45) 13:45:18 5 1.1,5.6,1.1 Add 10db pad in front of square law detector.
4 (+20,-45) 14:06:44 22 12936.5,5.7,1.1 take out 10db pad.
5 (+10,-45) 14:19:09 12 6.2,5.5,1.2
6 (+10,-45) 14:22:57 4 1.1,5.5,1.2 Add 10db pad in front of square law detector
7 (+40,-45) 14:30:10 7 6.2,5.5,1.2
8 (+90,-90) 14:37:46 8 6.1,5.4,2.3 check for back lobes.

Data taking setup:

Making the plots:

    For each test the data was processed using:

The 1382 Mhz total power versus rotation angle as we change the blanking:

  • a peak hold over 100 samples (1 millisecond) was done for each test. This was to decrease the data so it could be plotted. The pulse lengths for the radar are 51.2 and 409 useconds.
  • The data was plotted as total power versus rotation phase (ao based). Each rotation was offset from the previous for display purposes. The vertical access is linear in power. In most cases the A/D converted saturated during part of the rotation phase.
  • Summary plot showing all 8 tests (.ps) (.pdf):
    Each line of the plot is a separate test. At each phase of the radar a peak hold was taken over the N rotations for this test. Some of the things you can see in this plot are:
    Test 1: +45/- 45 degree blanking (.ps) (.pdf): Test2: +30/-45 degree blanking (.ps)  (.pdf):
    The peaks at 45 and 125 degrees are the planes. On rotation 14 the signal from the plane at 45 degrees increased. The angle must have changed to give some spectral reflection.
    Test3: +30/-45 degree blanking with 10db pad (.ps)  (.pdf):
    This is the same blanking as test2. We added a 10 db pad before the square law detector. The peaks at 42 and 130 are airplanes. The 15th rotation shows a large increase in the power from the airplane at 130 degrees. It must have turned so that we were getting a spectral reflection between the radar and us.
    Test4: +20/-45 degree blanking (.ps) (.pdf) :
    Test5: +10/-45 degree blanking (.ps) (.pdf):
    The peak at 10 degree may be the first airplane (or it could be a sidelobe of the radar). The 2nd airplane is gone.
    Test6: +10/-45 degree blanking with 10db pad (.ps) (.pdf):
    The peak at 10 degrees is still there so it is probably from the beam and not from the airplane. This is the same setup as test 5 with an added 10db pad before the square law detector.
    Test7: +40/-45 degree blanking (.ps) (.pdf):
    This is 5 degrees less blanking than we normally use. There are no airplane reflections in this data set (other than the airport). The sidelobe at 40 degrees is being cut down pretty well except for rotation 10.
    Test8: +90/-90 degree blanking (.ps)  (.pdf):
    This has the radar completely blanked the half of its rotation period that points at the observatory. The only thing we see are the planes flying close to the san juan airport. The one spike on the second trace around -60 degrees is probably some other rfi.

    The system compression by the radar:

        The plots show the compression of the system (.ps) (.pdf):     We know that there is a strong azimuth dependence on the amount a signal from the horizon gets into the receivers at AO (see az dependence of faa radar using alfa). Az 270, za=18 is not the worst spot for the faa radar. That is probably why we did not see any compression. The same may hold true for the punta salinas radar.


    processing: x101/060509/puntsal_blank.pro