|A/D sigma levels
|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.|
|6||(+10,-45)||14:22:57||4||1.1,5.5,1.2||Add 10db pad in front of square law detector|
|8||(+90,-90)||14:37:46||8||6.1,5.4,2.3||check for back lobes.|
Summary plot showing all 8 tests (.ps) (.pdf):
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.
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):
- The AO blanking is easily seen. The start of the blanking remains constant since most tests started with blanking at -45 Degrees (south) of AO. The right edge of the blanking changes depending on the blanking interval of the test.
- There is a second blanking region centered at 210 degrees from AO zero. This blanking is at the airport. The larger signal about the airport blanking region is coming from radar reflections from planes above the airport getting back to AO.
- There are two large peaks that drift. One to positive phase and one to negative phase. The apparent motion of these peaks between tests varies because there was a different time interval between the start of each test. Both of these birdies saturated the digitizer. The birdies were:
- Starting at phase=105 degrees and moving to higher phase. It disappears in the fifth test. It was present until an azimuth of 180 degrees.
- Starting at phase=55 and moving toward lower phase. It disappears on the 7th test. It was last seen at a phase of 10 degrees.
- Online we thought that these large peaks were back lobes of the radar. After looking at the summary plot it is clear that these are reflections from airplanes. The birdie with increasing phase was moving west to east. It probably disappeared when it landed at either isla grande or the isla verde airport. The second birdie was a plane moving east to west. It disappeared due north of the observatory (0 degrees) when we went back to 40 degree blanking. The power in these peaks is much larger than the radar far out sidelobes. See test 3: +30 blanking with 10db pad. These two peaks stick well above any non blanked sidelobes.
- The phase less than 0 (south of AO) shows sidelobes at (-50, - 65, and -80). The negative blanking was never less than -45 degrees.
- The positive phase (north of AO) shows sidelobes at 40, 62, and 80 degrees. Some of the closer in sidelobes are swamped by the reflection from the plane.
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 airplane at small angle has moved inside the blanking region so we don't see it. Most of the close in sidelobes must be now coming from the beam rather than the airplane.
- The 2nd airplane is at 165 to 175 degrees. Its strength drops dramatically after the 15th rotation. It goes from very strong to barely noticeable in 12 seconds. The plane must have dropped low enough to not reflection much back in our direction. It looks like it was still flying on rotation 22 as it neared the isla verde airport.
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.