NATIONAL RADIO ASTRONOMY OBSERVATORY
Green Bank, WV
September 14, 1999
TO: R. Fisher, J. Ford, F. Ghigo, R. Lacasse, C. Niday, T. Weadon
FROM: R. Lacasse
SUBJ.: Minutes of Interference Protection Group 09/14/99 Meeting
In attendance: Fisher, Ghigo, Lacasse, Niday, Weadon
Minutes of Previous Meeting
Call Outs for Interference
None. Ghigo plans to use the spectrum analyzer at the 140
ft. to monitor signals at the 20-meter telescope. He reports that
occasionally the correlator staff reports unusual fringes which may be
caused by interference.
Action Item Review
1. Automatic Paging
The OVLBI group has requested that an automatic paging system be used
to contact personnel in their group when errors occur in their system.
The paging system would use the site 43-MHz, 60-W transmitter. It
would be capable of penetrating buildings. In contrast, the new system
under development is much lower power (0.2 W) and does not have the capability
to penetrate all parts of all buildings on site. Members of the IPG
group voiced opposition to this proposal for several reasons: since it
is automatic, it is more difficult to disable the system when it would
interfere; it only provides coverage when people are on site, or very close
by; an automatic transmission for a nuisance problem could conceivably
mask an emergency transmission. The IPG concluded that coverage for
the OVLBI telescope was an Operations problem. Fisher will talk with
Bignell about this and invite him to a meeting if it seems worthwhile.
2. Turntable for the
Egan has located a unused turntable near the water tower. It
is fairly massive, but might be suitable for use in the chamber if it were
modified. Niday will inspect it and report back.
3. Allocation of Remaining
IPG Funds for 1999
Approximately 1K remains in the IPG coffers for 1999. After some
discussion, it was decided to allocate $300 for shielding and filtering
the amplifiers and associated supplies in anechoic chamber. The balance
of the funds were allocated to the monitoring station.
from the 140-ft. for the SOHO Mission
The possibility of using the 140-ft. telescope as a ground station
for the SOHO mission was brought up recently at a scientific staff meeting.
This would require that the 140-ft. have a transmitter which would make
it noncompliant with the Quiet Zone requirements. The transmit power
would be somewhere between 20 and a few hundred watts. Calculations
by Fisher and subsequent discussions between Fisher and Norrod recently
led to the conclusion that the radiated power would cause receivers on
the GBT, 560 meters away, to operate near saturation. It was noted
that it is possible but expensive to put filters in the receivers.
It raises the moral dilemma of NRAO requiring certain radiation limits
from outside groups while it violates those limits by large amounts internally.
The motivation for this use of the 140-ft. is to bring in some dollars
to supplement the existing tight site budget. The IPG concluded that
it should go on record as opposing this transmitter on the 140-ft.
It was pointed out that a transmit antenna could be located at some distance
from Green Bank, and that the 140-ft. could be used as a receive-only station.
This option is more palatable to members of the group. Fisher will
communicate this to Jewell.
5. Monitor Station
The rate of progress on this and other IPG projects has been frustratingly
slow. Engineering and technician time for IPG projects comes from
"what's left over" after other projects are serviced. With the GBT
nearing completion, the time available for IPG projects has dwindled remarkably.
Possibly more time will be available when the GBT is complete, but, by
then, some interference problems which should have been designed out will
be designed in, and be difficult to retrofit. If a conscious decision
is made by management to allocate some time for the IPG then progress should
be more noticeable. Fisher will discuss this with Ford.
6. Site radio system
Temporary FCC authorization has been received for the transmitter.
Niday hopes to begin installation on the water tower in the next few weeks.
Work on a permanent license is in progress.
7. Microwave oven in shielded
test box (John)
8. RFI Considerations
for the New Tour Center
Requests for bids are due in September 25 for exhibits for the tour
center. (Initially, these will be housed in the existing tour center.)
The bidders have been given no formal direction with regards to RFI emitted
from their proposed exhibits. After some discussion, the IPG concluded
that with such short notice, the only reasonable thing to do was to send
the bidders a letter stating that their exhibits must comply with FCC Part
15, class B. This is a fairly common requirement met by most home
appliances, including computers. Niday revisit data on FCC Part 15
Class B compliant equipment that has been measured by the IPG and report
No progress on
other items on action item list.
It was pointed out that the Continuum Detector System should
have been used for the recent of RFI from rectifiers and contactors.
Lacasse and Weadon will try this in the near future.
Next Meeting: October 12, 0800.