- the drifting birdie was coming from the sbn postamp
chassis. it was brought down to the lab 20mar14 15:00 to be
- The problem is the same problem that we had back in jun
2004 with drifting birdies in lband (more
- the cal control board in the postamp chassis used some
hi speed chips.
- Some of the gates in the chips were unused and were left
open. They then oscillated (many volts).
- We supposedly fixed all of these cards back in
2005 by putting terminations on the unused gates.
- The problem may be that when some cards went bad, they
were replaced with new cards that did not have the
terminations in place.
- We need to make sure that there are no other postamp
chassis's that have these cards with no terminators in
- We also to need ensure that this doesn't happen a third
- We spent 1 month of telescope down time using the 327
receiver for pulsar search.. with this birdie drifting
all over the place.
- p1693 took 327 MHz pulsar search data during the
M8-4 cable repair.
- A birdie was seen to slowly drift from 319 -> 325
MHz over 24 hours. (see
dynamic spectra of drifting birdie).
- The 24
hours of data from 23Feb14 shows a complete cycle in 24
- the drifting is continuous. The image was made using
the first two minutes of each 1 hour scan. There are 129
rows in the image (2 minutes) and then a jump in time
of 1 hour).
- The birdie started near 325 MHz at 7:30 am on 23Feb14.
- it went down to 319 around 17:00
- it then drifted back to 325 MHz near 6am on 24Feb14.
- The birdie strength would get up to 20 times Tsys in
the 57KHz channels of p1693.
- An examination of the p1693 data on 20Feb14 looked
like the rfi was compressing the total power every 1.5
- high frequency resolution data taken on 27Feb14 showed
that the band was not compressing.
On 27Feb14 voltage sampled data was taken using the mock
spectrometer. The setup was:
Dynamic spectra from 8
seconds of the 1.6 MHz band (.gif)
- 327 receiver.
- mock spectrometer with 2 bands both centered at 325.73440
- band1 : 1.6 MHz bandwidth
- band2 : .160 MHz bandwidth
- The frequency resolution is 195Hz, about 300 KHz is
- The birdie is about 30 kHz wide
- You can see the birdie jumping every 1.2 to 1.5 seconds.
- It jumps by about 20 KHz.
- The total power of the rfi was computed between the dashed
The plots show the birdie
strength and time variation (.ps)
- page 1:average spectra
- top - 1.6 MHz average spectra
- bottom: .16 MHz average spectra
- Page 2:
- top: time variation of the birdie.
- This integrates the spectral channels between the
dashed lines of the dynamic spectra (see above)
- The dips occur when the rfi jumps in frequency
- middle: the total power in the birdies was fft'd and the
squared to show how the birdie changes with time
- each spectra lasted for 5 milliseconds, so the max
frequency was about 100 Hz.
- bottom: blowup in frequency
- the largest spike was around 1.22 Hz. this is close to
the crosshead frequency.
- It may be that the jumps are not evenly spaced in
time, so the cross head frequency power may no be
- There is a strong drifting birdie seen in the 327 receiver
during the p1693 pulsar search observations.
- It was seen 28jan14. I don't have date before this
- over 24 hours the birdie drifts from 325 MHz down to 319
MHz and then back to 325 MHz.
- The birdie is about 30 kHz wide. It jumps by 20kHz
- The jumps are spaced by 1.4 and 1.6 seconds.