Radio Frequency Interference at the VLBA
Radio Frequency Interference (RFI), both internally and externally generated,
is an increasingly significant problem at VLBA sites, particularly at wavelengths
of 18cm and longer. This page points you to information on known RFI at
each VLBA antenna, current developments, and plans for handling the problem
in the future.
For each band surveyed, current and past postscript and giff interference
plots show signal power vs. frequency. Overlay plots identify the known
emitters in each band.
This page is currently under developement.
If an error is displayed next to a link,
that plot is currently unavailable.
VLBA RFI Survey (all sites)
- RFI Listings
- A text file list of known RFI sources and frequencies at the VLA and VLBA.
- RFI Bulletins
- Current announcements and Bulletins on RFI at the VLBA.
- RFI Memoranda
- Recent VLBA memoranda related to RFI.
- Satellite
Survey
- A Survey of Satellite Constellations that could effect RFI at the
VLBA antennas.
- World Radio Astronomy Frequency
Allocations
- List of frequencies allocated and footnote-protected by the International
Telecommunications Union--Search on "astronomy" in your .pdf viewer.
-
- VLBA RFI Survey
- The plots included here were created from RFI surveying with all 10 VLBA
antennae. Frequencies surveyed are P through U bands, and the data was
reduced on the date shown on the plot. If a VLBA station was not available
during the survey period then that particular site does not appear on the plot.
Each plot is a series of spectral line observations stepped accross the entire
band, thus a composite of a number of 16 MHz baseband autocorrelation spectra,
overlapped by 0.5 MHz at each BBC end. The uneven noise level of the plots
results from the VLBA baseband converter filter roll-off. The frequency
resolution of the data is ~ 60 KHz. Since the survey ranges beyond the normal
frequency limits of each band, those bands which have band-limiting filters
will show reduced power levels at band extremities.
The amplitude scale is in normalized units of Tsys for each 16MHz baseband
auto correlation spectra; i.e. in the absence of RFI, each 16MHz BBC output
has a baseline floor equal to Tsys. With strong RFI present the surrounding
baseline is supressed such that the integral of the 16MHz BBC chunk is
normalized; for example, a spike standing twice as high as the bandpass has a
magnitude equal to about 2 * Tsys.
-
HOW TO READ THE PLOTS
-
On the right side of each plot is a numerical list of VLBA stations, usually
in order 1-10 running from the top of the plot to the bottom; the spectra corresponding to each VLBA station is also in descending order from the top of the plot to the bottom. Thus the uppermost spectra corresponds to the first VLBA station listed.
- If you have access to the network at the AOC, the xmgr files from which
these plots are created are available at
/home/vlbiobs/VLBA_rfi/YYYYMMDD/band.xvgr, where YYYYMMDD is the date of the
observation, and /band is the frequency band of interest. Using the xmgr
files, one may zoom in to focus on particular frequencies, deactivate stations,
change the amplitude scale, etc. If you do not have access to the NRAO AOC
network, then you may FTP download gzip versions of the xmgr data files for
these plots; to do so FTP to ftp.aoc.nrao.edu, login as "anonymous," use your
full email address for your password; once connected go to the subdirectory
/pub/staff/rarmenda, then download and gunzip the files. Click here for help on
xmgr.
-Socorro IPG
- U-band (11.5-16.06GHz)
- Latest interference
plot for 11.5-12.7GHz (18Oct07)
- Latest interference
plot for 12.7-13.9GHz (18Oct07)
- Latest interference
plot for 13.9-15.1GHz (19Sep07)
- Latest interference
plot for 15.1-16.06GHz (19Sep07)
- All interference plots of RFI from 11.5-16.06GHz
X-band (7.5-9.18GHz)
- Latest interference
plot for 7.5-8.34GHz (18Oct07)
- Latest interference
plot for 8.34-9.18GHz (18Oct07)
- All interference plots of RFI from 7.5-9.18GHz
C-band (4.25-5.35GHz)
- Latest interference
plot for 4.25-5.35GHz (18Oct07)
- All interference plots of RFI from 4.25-5.35GHz
S-band (1.8-2.88GHz)
- Latest interference
plot for 1.8-2.88GHz (20Sep07)
- Latest interference
plot for 2.15-2.45GHz (09Mar05)
- All interference plots of RFI from 1.8-2.88GHz
L-band (1.2-1.9GHz)
- Latest interference
plot for 1.2-1.9GHz (18Oct07)
- Latest interference
plot for 1.32-1.45GHz (09Mar05)
- Latest interference
plot for 1.6-1.75GHz (09Mar05)
- Latest interference
plot for 1.6-1.62GHz (09Mar05)
- Latest interference
plot for 1.65-1.675GHz (09Mar05)
- Latest interference
plot for 1.7-1.74GHz (09Mar05)
- All interference plots of RFI from 1.2-1.9GHz
At Saint Coix an IF filter limits the L-band intermediate frequency from
665 MHz to 1000 MHz. Thus a VLBA sched file choice of the lower IF corresponds
to a sky frequency pass of 1259-1435MHz. Choosing the higher IF correseponds
to a sky frequency pass of 1400-1735MHz. For these RFI surveys, the lower IF
was used for frequency 1191-1544 MHz, and the higher IF for 1559-1900 MHz.
Phi-band (.545-.665GHz)
- Latest interference
plot for .545-.665GHz (18Oct07)
- Latest interference
plot for .595-.630GHz (09Mar05)
- Latest interference
plot for .607-.615GHz (09Mar05)
- All interference plots of RFI from .545-.665GHz.
Plow-band (.265-.385GHz)
- Latest interference
plot for .265-.385GHz (19Sep07)
- Latest interference
plot for .31-.345GHz (09Mar05)
- All interference plots of RFI from .265-.385GHz.