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Spectrum Management and RFI activity at AO
------------------------------------------

With the recent explosion in global communication systems, and the
ever-increasing usage of the radio spectrum in Puerto Rico, spectrum
management activities at Arecibo Observatory are becoming both complex
and multidimensional. The various tasks of the Spectrum Management And
RFI Group (SMARG) at the Observatory and their inter-relationship can
be categorized as shown in Fig 1. Given the present radio environment
in Puerto Rico, constant vigilance is needed over the entire frequency
range covered by the Arecibo Telescope (A in Fig 1). This has two
components; (a) spectrum monitoring of the radio environment due to
existing systems around the island (A1); and (b) keeping a watchful eye
on future on-coming installations, national and international trends in
spectrum usage, and regulatory actions by the various authorities
(A2). A mechanism for receiving user complaints and responding to
these is essential (C1). Both spectrum monitoring and user complaints
initiate in-house and off-site searches for Radio Frequency Interference
(B). The follow-up action resulting from these should to be documented
and easily accessible to users (C2). For the frequency-agile upgraded
Arecibo Telescope, there are bands where Radio Astronomy has either no
regulatory protection, only a "secondary" status or, at best, a
"shared-primary" status. In these bands, observations can only be
carried out either by utilizing RFI-excision techniques or in a
coordinated manner with other users (D). Finally, fostering a public
awareness of the effect of spectrum usage can only help towards
peaceful coexistence between active and passive users of the radio
spectrum (E).

~~~~~~~~~~~~~~~~~~~
Recent Activities
~~~~~~~~~~~~~~~~~~~

During the past year, significant progress has been made in a
number of the above areas. These are:

A1: On-Site Interference Monitoring

The Arecibo monitoring system continues its round-the-clock operation.
One-minute peak-hold values in 19 frequency bands, spanning 0 to 10
GHz, are recorded every 20 minutes. Plots showing the average daily
spectra, the time variation of the spectra over 24 hours, and
fluctuations (rms/mean) of signals per channel over a day are produced
and made available in the telescope control room. These data have
already been used to determine filter specifications for the various
Gregorian receivers. Recently, software has been written to generate
statistical information from this database. With this, statistics of
spectral occupancy can be calculated as a function of frequency and
time. Fig 2 shows an example of the output of this program, where the
variation of percentage occupancy is shown as a function of frequency
and time for the 11 lower-frequency bands. For this, all data taken
between Jan and Dec 1996 have been used. Such information will be of
considerable use when scheduling post-upgrade observations.

A2: New Spectrum Users

Little Leo, and DTV

********************
******* Paul, I am anticipating that in the contributions from Mike
Davis and Willem Baan, there will be sections talking about Little Leo
and DTV. These could be included here (Report on IRIDIUM coordination
comes later, under item D in this layout). In case, you would like
me write a few lines for these, please let me know. --- Tapasi *******
*********************

B/C: Users' Complaints and Response

With the recommencement of drift-scan pulsar searches in Oct 1996, the
430-MHz band was used after a gap of almost one year. The band was
found to be heavily occupied by interference. One source of this was
airborne radars operated by the Atlantic Fleet and Weapon's Training
Facility (AFWTF) at Roosevelt Roads. The on-going coordination between
the observatory and AFWTF was reviewed and considerably improved (see
section D). In addition, the fourth harmonic of a local radio station
was present, as well as a strong unknown signal which wandered in
frequency. Locating the latter required a mobile RFI-detection unit.
The group members put together a temporary mobile system, and with
persistent search, tracked the problem down to a malfunctioning pager
system located on a mountain top in the center of the island. In both
of these cases, the cooperation of the "offender" was obtained, and the
band "cleaned up".

Recently, the video camera system installed to monitor activities in
the Gregorian Dome for safety purposes was found to be causing
RFI at 430 MHz. Our newly acquired hand-held radio was instrumental
in tracing the problem. The cameras are now to be kept in shielded boxes.
This case clearly demonstrates the importance of internal RFI surveys
at the Observatory (B1).

D1: Hardware for Interference Excision

The lower frequency segment of the broad-band Gregorian L-band receiver
is plagued by the presence of 7 radars of various origins. Careful
measurement of the characteristics of all of these radars have been
made. This information is vital for building a radar blanker, which is
presently being designed. The RFI group has also worked closely with
the Astronomy and Electronics Departments to specify the filters
needed for different observations within this band.

D2: Software Interference Excision

An internal mini-workshop was held in May 1996, with the additional
participation of Riccardo Giovanelli from Cornell University. Both
on-line and off-line RFI-excision techniques were discussed in respect
of Aeronomy and Astronomy observations. These topics were further
discussed at the Workshop on "HI Spectroscopy with the Gregorian
Feed", held at Arecibo in October 1996. The need for fast data dumping
was established, and several excision procedures were considered.

D3: Coordination with Other Spectrum Users

(a) AFWTF: Members of SMARG visited the AFWTF at Roosevelt Roads in Dec
1996, and reviewed and extended the existing co-operation agreement
with the authorities there. A protocol has now been established for
contacting AFWTF whenever 430-MHz observations are hindered by the
presence of their airborne radars. The Arecibo observing schedule is
sent to AFWTF regularly, while they have agreed to notify us in advance
of any high level of activity expected (e.g. naval exercises).

(b) IRIDIUM:

*********** Contribution from Mike and/or Willem *******************



E: Public Awareness

A meeting of the Puerto Rican Spectrum Users Group was hosted by the
Observatory in Dec 1996. Twenty five delegates and observatory
staff gathered to discuss issues of spectrum usage on the island. There
were formal presentations, discussions and a tour of the Observatory.

In addition to making the participants aware of the vulnerability of
passive spectrum users such as Radio Astronomy, the meeting turned out
to have a special relevance to our then-overwhelming 430-MHz RFI
troubles. The Chief Engineer of the particular paging company that was
then generating spurious emission in the 430-MHz band attended the
meeting. Soon afterwards, the pager problem was rectified.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Work Plan for the Near Future
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This year, a major emphasis of the SMARG will be to make a survey for
on-site generated RFI. In addition, as part of telescope commissioning
post-upgrade, spectral surveys for RFI will be made with each of the
available Gregorian receivers. This will help identifying illegal
transmissions and aid scheduling the telescope minimizing data loss due
to RFI.

For the Mobile RFI-Detection Unit, a van has been acquired. This now
needs to be furnished, and equipment purchased and installed.

Work will continue towards making an electronic RFI-complaint logging
facility available to the users. The group will also design a
RFI-related display for the Arecibo Observatory Visitor and Education
Facility. In addition, an AO-SMARG World Wide Web home page is also
under construction.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Projected Long-term Activities
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

At present, the SMARG is working mostly on an emergency service basis
("putting out fires"). When post-upgrade observations in all frequency
bands take place, there will be constant need for rfi-related user
assistance. The Availability of additional human and material
resources seems to be vital for obtaining the "cleanest possible" data
from this unique Telescope.

_________________________________________________________________

Equipment Needs for Spectrum Management -'97-98
_______________________________________________

1. Mobile RFI unit

(a) Furnishing the Van
(b) Antenna mast & rotor
(c) Antennas
(d) Electronic components, filters, amplifiers
(e) Spectrum Analyzer
(f) Laptop computer
(g) GPS system
(h) Maps, Databases etc.

Total cost projection ---- $50,000


2. The existing hill-top monitoring system
(a) Screening the hut
(b) Filters to eliminate the strong 3.1 GHz Navy radar

Total cost projection ---- $10,000

Grand total cost (projection) ---- $60,000