09mar11: 327 Mhz birdies and their Azimuth
Links to plots/tables:
and peak hold spectra for the az swings (.ps) (.pdf):
power versus azimith for the 60 strongest birdies (.ps) (.pdf):
Table summarizing the birdies.
Processing the data
Dynamic spectra of the azimuth swings
Average/PeakHold spectra for each az
The azimuth dependence of the birdies
birdies with common az
On 09mar11 2 azimuth swings were done with the 327
receiver to see if there was an azimuth dependence for the birdies that
were seen in the band. The dome was at 15 degrees.
The setup was:
- The azimuth was moved between -90 and 270 degrees at .35
This was done 2 times (clockwise CW and then counterclockwise CCW). A
took 1100 seconds.
- The 327Mhz rcvr (cooled) with the 302 to 352 Mhz filter was used.
- The mock spectrometer sampled a 57 Mhz band centered at 327 Mhz
with 8192 channels. The spectra were integrated for a second.
- The alfa motor controller and the dome cameras were turned off.
- This is a repeat of the data taken 28oct05 (which used the interim
correlator and the 30 Mhz filter)
- For each azimuth swing a bandpass was constructed from the 1029
A fit to a bandpass was needed rather than an average since some rfi
constant and would remain in the bandpass average. The bandpass was
- Compute a median bandpass from the 1029 spectra.
- Fit a 20th order harmonic and a linear polynomial to this
using robfit_polyfft(). This iterates the fit throwing out outliers.
- Divide each of the 1029 spectra by this fitted bandpass. This
most of the IF bandpass.
- For each spectra compute the median total power and subtract
remove the source contribution.
- PolA and polB were averaged.
Dynamic spectra were made for each of the
swings showing spectra density plotted against azimuth and frequency.
plots were aligned so that azimuth always increased bottom to top (so
swings from 270 to -90 were flipped). At the bottom of each image
is a peak hold spectra (maximum in each frequency channel) for the
Dynamic spectra of the
- Clockwise swing:
- Counter clockwise swing:
- There are a number of frequencies that are time variable and
together. They all have modulation on them. The strongest of these are:
- 308.7, 309.9, 311.07, 313.1. 314.3, 317.5, 318.9.
- Some other signals that are modulated and tend to be there all
are: 312.31, 320 , 321.9 Mhz being the most prominent.
- The radio was tuned into the IF signal and the following radio
were heard (in the IF):
- 312.31 is the 3rd harmonic of 104.1 (FM).
- 321.9 is the 3rd harmonic of 107.3 (FM). This is the
- 317.5 was heard to be 107.3 (FM). This may mean that the
(308.7,309.9.. ) are also intermods of 107.3 since they turn on and off
with 317.5 .
- The large narrow spikes (327 Mhz 30*Tsys and 317.4 20*Tsys)
for a few seconds. The spikes that are broader (and show the modulation
) were there more often.
- You can see a number of weak combs in the image. They will
when the channel width is narrowed (since they tend to be narrow).
For each azimuth swing an average
(over the 1029 spectra) was computed as well as a peak hold spectrum
largest value in each frequency bin was kept). Colors were used to
between azimuth swings. The plots show
for each az swing: (top)
average and peak hold spectra for the az swings (.ps) (.pdf):
- Top avg.: The average spectra for each swing. The
birdie is at 306.98 (22*tsys)
- 307.00 (22*Tsys)
- 313.51 (2.*Tsys)
- 338.30 (3.0 Tsys)
- 2nd avg.: This blows up the vertical scale on the top
- 3rd Pk hold: This has a peak hold for each az swing
value in each freq channel from the 1029 spectra). The largest values
- 307.00 (600*Tsys)
- 309.90 (19*Tsys)
- 338.30 (65*Tsys)
- 4th Pk hold blowup: The vertical scale on the 3rd
The frequencies of the 60 strongest birdies were
and then a mask (in frequency) was placed around each one. The largest
value in each mask was taken as the value of the birdie at each time
(this was needed since some birdies drifted in frequency). Birdie power
plotted for each of the 60 birdies (5 birdies per frame). The black
trace is the CW azswing while the red trace is the CCW trace. The
vertical scale is in Tsys
of the birdies: (top)
The plots show the
power versus azimith for the 60 strongest birdies (.ps) (.pdf):
- many of the birdies are changing together with azimuth.
- Some birdies with little az dependence may be in the dome:
- 16: 313.51,
- ind 58 (350.00 Mhz) is coming from the interim correlator in the
- ind53:346.53 has similar az dependence as 350.00.. it may be
coming from the same spot.
Looking at the dynamic spectra, there are a
large number of birdies that occur at the same azimuth for the CW and
CCW azswings. These are coming from the same az location (and probably
the same set of intermods).
The the birdies that have a
common azimuth dependence.: (top)
The dynamic spectra were blown up to show (300 to 327Mhz, 130 to240 az)
how the signals change together:
- Blowup: Clockwise
- Blowup: Counter
clockwise swing (.gif)
- The 3rd harmonics of the 4 strongest radio stations are flagged
with a solid vertical line:
- 107.3*3=321.9 Mhz
- many of the birdies show azimuth (time) variation that matches
the 308.7 (the 3rd harmonic of 102.9).
- dashed vertical lines centered on 308.7 (102.9*) and spaced
by 1.2 Mhz fall on many of the signals.
- 1.2 Mhz is:
- 1.2= 3*.4 (the FM station spacing.
- 1.2= 104.1 - 102.9 (radio Rendor - HQ fm stations)
- These 2 station transmitters are located in utuado
within a few hundred feet of one another.
- The birdies at 314.5 and 314.5+1.2 do not line up in frequency
with the comb
from 308.7 although they show the same azimuth (time) dependence.
The plots show the azimuth dependence:
birdies that show a FM station dependence (.ps) (.pdf).
- Page 1 Clockwise spin:
- top: Each color is a separate rfi vs azimuth.
- Bottom: Different rfi's vs azimuth has been plotted
with offsets for dispay
- Page 2: same plots for the CCW azswing.
- Page 3-5: plot each of these frequencies separately.
- Group then so that rfi with similar azimuth dependence is
- The black trace is the CW swing, the red trace is the
- The table
summarizes the values.
- The third harmonics of some FM stations are seen in the band (see
- Back in 2005 a filter was put in front of the receiver and the
3rd harmonics were still seen. This implies that the harmonics are
being created outside of the receiver.
- A large number of intermods (11 to 15) are also related to the fm
stations (see table below).
- There are some narrow constant birdies that may be coming from
the az,el encoders. Need to test turning encoders on and off while
monitoring the band.
- The table below summarizes the info on various birdies.
Table of frequencies
|3rd harmonic of HQ . located next to 104.1 radio
redentro in utuado
|3rd harmonic of radio redentor
transmitter in utuado
|3rd harmonic of delta107.3
- These all show time/azimuth variation that match that of
- Many of these are spaced by 1.2 Mhz (104.1-102.9)
- * these are spaced by 1.2 Mhz but are offset from the other
set. They may be related to 107.3 (see below)
- back in 2005 This was heard (with the radio in the
control room ) to be 107.3.
- Looking at the dynamic spectra, the other frequencies look
like they may line up in az,time with 317.5 which would also make them
related to 107.3
- 321.9-317.5 =4.4 Mhz. This is the difference
|350.00 comes from the interim
correlator in the control building.
346.53 has similar az dependence so it may also come from the same place
|Little az dependence ..may be in