1385 MHz birdie feb09
Project a2010 (alfalfa: alfa with 100 MHz
centered at 1385, wapps, and 1 second dumps) reported birdies at 1384
and 1385 MHz during their observations on 21feb09 and 22feb09.
Project a2130 (galfacts: alfa with 300 MHz, pdev
Spectrometer, and 1 millisecond dumps) ran on 23feb09 in the evening.
They had birdies at 1385 and 1386 MHz.
- The first image shows dynamic
spectra for 600 secs (file:20090221.a2010.00006.fits) (.gif):
- The 1385 interference occurs every 12 seconds. The data comes
from alfa beam 1.
- A weaker interference can be seen at 1384. It also has a period
of 12 seconds and is offset from the 1385 interference by 6 seconds of
- The strong interference at 1380.5 is gps L3.
- 1350 is the faa radar. It has a weak intermod at 1380.
- The second plot shows the total
power vs time around the interfering frqeuencies (.ps) (.pdf). Data is sampled once a second.
- The bottom traces are total power vs time for .6 MHz around
1384. Black is polA, Red is polB.
- The middle traces are total power vs time for .6 MHz around
1385. Green is polA, blue is polB.
- The top trace is total power vs time for .2 MHz around 1350
(faa radar). It is the sum of polA and polB.
- the 1385 radar is offset from the faa radar by 1 second so it
is not coming from the faa radar.
- the 1384 radar is offset 6 seconds (1/2 a period) from the 1385
- The first image shows a blowup of
the 1385,1386 birdies and the 1300 MHz band (.gif):
- The data was averaged to .1 second.
- The left image has 4 MHz about 1386.
- The right image shows 1210 to 1390
- the 1345,1358 birdies are images of 1242,1257
- The second set of plots has the avg
bandpass, rms/mean by chan, and freq of the rfi (.ps) (.pdf):
- Page 1 has the average bandpass (over 65 seconds):
- Top: 1300 MHz band. 1242,1257 is the aerostat. 1330 is the
- Center: 1450 MHz band. You can barely see the 1386 MHz birdie.
- Bottom: Blowup in frequency of the 1386 MHz birdie
- Page 2: rms/mean by channel.
- Top: 1300 MHz band, Center: 1450 MHz band, bottom: blowup of
- Total power vs time for the various birdies:
- Top: 1385 MHz birdie. the dashed blue line is aligned with
the 1386 MHz birdie every 12 seconds. There is a dip in the 1385
birdies before the dashed blue line. This lines up with the narrow
blanking of the aerostat (2nd plot).
- 2nd: The 1257 MHz aerostat radar.
- There are two dips in the power every 12 seconds. A wider
dip (at 20 secs) and a narrower dip (at 22 secs). The wide dip is the
aerostat blanking toward the observatory. I think the narrower dip is
when the aerostat blanks pointing at the san juan airport. The 1386
(blue line) occurs right after the aerostat blanking toward the airport.
- 3rd. The 1386 (green line) birdie. It is also spaced every 12
- 4th. The 1330 Faa Radar. It does a pretty good job of lining
up with the faa radar. It is also about 6 seconds from the blue line
- The 3rd set of plots shows the
periodicity of the 1385 and 1386 rfi (.ps) (.pdf):
- The pwr vs time for the 1385, 1386, 1330 , and 1257 MHz birdies
was computed at the 1 millisecond rate and then the power spectrum this
total power was computed to get the periodicities of each birdie in
- The top plot shows the frequencies for the 1330 faa radar
(black), 1290 remy radar (red), and the 1257 aerostat radar (green).
They all have different frequency signatures because their prf's vary.
- The bottom plot shows the time frequencies for the 1385 and
1386 birdies. They are the same as the aerostat radar.
- a2010 data:
- The 1384,1385 birdies have 12 second periods
- The 1384 birdie is offset 6 seconds from the 1385 birdie
- The 1385 birdie is offset 1 sec in time from the faa 1330 radar.
- The 1385,1386 birdies from a2130:
- Both birdies have a period of 12 seconds and are offset from
each other by 6 seconds.
- The 1385 birdie shows the same blanking as the aerostat radar.
It occurs near the aerostat blanking toward the airport.
- This may be the echo from a plane. During the punta salinas
blanking test we saw echoes from planes that were stronger than
the direct path signal.
- The periodicities from the 1384, 1385 birdies matched that of
the aerostat so they are coming from the aerostat (probably from
intermods in our system).
- Why are we seeing these birdies now??
- The hilltop monitoring shows
that the aerostat ran continuously from 17:00 20feb09 thru 03:00
24feb09. Normally they do not run 24 hours a day.
- Why is the a2010 and a2130 frequencies a bit off? Is it
the different mixing??
- I'm not quite sure how we get these frequencies from the
1242,1257 rf frequencies and our mixing, IF frequencies.
processing: x101/090223/a2010.pro,a2139pro, rdrfreq.pro,