Transcript Slide 1

Frequency Management
Aka why you can detect any astronomical signals at all
Dr. Karen O’Neil
Green Bank Site Director
Frequency Management
Does it really matter?
Frequency Management
Does it really matter?
GBT observations with
pocket digital camera
ON and OFF
U.S. Frequency Allocation chart
The United States has set aside some frequencies for astronomy…
U.S. Frequency Allocation chart
The United States has set aside some frequencies for astronomy…
But they are few and far between
U.S. Frequency Allocation chart
The United States has set aside some frequencies for astronomy…
Astronomy is not limited to pre-designated frequencies.
Redshift spreads even the allocated astronomy frequencies,
such as 1420 MHz, across more than 1000 MHz in band
Allocation process cannot allow for new discoveries,
exploration of frequency space
Many of the astronomy allocations are shared with other spectrum users
What do we do???
But they are few and far between
Frequency Management
There are three ways to handle interference:
– Spectrum allocation
– Regional protection
– Post-observation excision
Frequency Management
There are three ways to handle interference:
– Spectrum allocation
– Regional protection
– Post-observation excision
Algorithm development
Pattern recognition
The art of
Spectrum Management
Spectrum Allocation
Three Regions (International Telecommunications Union)
Spectrum Allocation
Three Regions (International Telecommunications Union)
All countries are sovereign inside their border
(Radio waves always know where to stop, eh?)
No country can operate a satellite transmitter without ITU-R permission
(Border issues are often important)
Most general set of rules (Radio Regulations) is an international
(every 4-5 years through the UN)
http://www.itu.int/ITU-R/12
Spectrum Allocation
IUCAF:
International Scientific Committee on Frequency Allocations for Radio
Astronomy and Space Science
Sponsored by:
– International Astronomical Union (IAU)
– The International Union of Radio Science (URSI)
– The Committee on Space Research (CoSPAR)
Represents astronomical interests at international spectrum meetings
U.S. astronomy is represented through the National Science Foundation
Spectrum Allocation
• Spectrum bands are allocated to ’services’:
– Service = purpose or application
– Most services are ‘active’ –they transmit
• Radio astronomy and Earth-sensing are ‘passive’ (only listen)
• Radar astronomy and EE-SS (active) also transmit but are distinct
• Concept of “use” elusive for passive services
• Examples of “services”:
– Radiolocation = radar
– Radionavigation/Radio Navigation Satellite Service = GPS
– Fixed service (terrestrial point to point)
– Fixed-satellite service (space-earth, earth-space)
– Mobile-satellite service (satellite phones)
– Broadcasting (TV)
Spectrum Allocation
• Spectrum allocation is extremely important to protect radio band
• It works very slowly, and new laws/protections can take many years
• In the U.S. the spectrum is typically sold by the FCC
– Radio astronomy is at a distinct disadvantage
– Sharing of even radio astronomy spectrum is likely coming soon
Regional Protection
• Regional protection comes in two ways:
– Natural or man made protection
– Legislation
Regional Protection
• Regional protection comes in two ways:
– Natural or man made protection
– Legislation
Green Bank:
Location
Location
Location
A high mountain valley
with natural terrain shielding
A great place for
a Radio Astronomy
Observatory!
National Forests around Green Bank
Green Bank
State and National Forests foster low population growth.
Regional Protection
• Regional protection comes in two ways:
– Natural or man made protection
– Legislation
Regional Protection
• Regional protection comes in two ways:
– Natural or man made protection
– Legislation
• Green Bank has two radio quiet zones:
– National Radio Quiet Zone
– West Virginia Radio Astronomy Zone
National Radio Quiet Zone
• Established by FCC and NTIA
on Nov 19, 1958.
• Established in law before radio
telescopes were built and before any
frequency allocations to Radio
Astronomy.
• +13,000 mi2 of WV, VA and MD
• As part of the normal coordination
process, the NRQZ office comments
on new or modified, permanent, fixed
radio transmitters.
• Work with applicants in finding a
mutually acceptable solution to their
coverage needs and our protection
criteria.
1. Only bounded area in the
US requiring coordination of
new or modified, permanent,
fixed transmitters.
2. The NRQZ is a unique and
valuable resource in an ideal
location.
3. Centered between Green
Bank and Sugar Grove.
WV Radio Astronomy Zoning Act
August 9, 1956: Protection from interference
by any electrical equipment within 10 miles
Regional Protection
Natural + legislative protection provide the best environment
– Legislation provide protection within designated region
– Natural barriers protect from transmissions inside and outside
the protected zones
Natural Obstacles
Power Transmitted in
the direction of the GBT
(depends on the antenna
and what direction it is
pointing as well as the
power into the antenna)
(mountains) in the path
(if the attenuation
manmade obstacles is
known, this too can be
considered)
Frequency and
Bandwidth over which
the power is distributed
(depends on the
technology being used)
Path Length
Regional Protection
• Regional protection comes in two ways:
– Natural or man made protection
– Legislation
• Green Bank has two radio quiet zones:
– National Radio Quiet Zone
– West Virginia Radio Astronomy Zone
– Combined protection of two quiet zones is very powerful
• Two new quiet zones now exist in the world:
– South Africa (protection for MeerKAT, Kat64, SKA)
– Australia (protection for SKA in Western Australia)
Community Agreement
Even with legal protection community agreement is vital
– Continuous challenge with outreach, education, and helpTeach the
community who you are and why you needs the protection
– Show the community the value of radio astronomy locally and
scientifically
– Help the community to mitigate the effects of the Quiet Zone(s) as
possible
This is the most difficult challenge, and one which must be
continuously considered
Spectrum Management is a challenging issue which must be
tackled for radio astronomy to flourish
Crowding of the spectrum will increase, and the space for radio
astronomy will shrink
You can help!
Report RFI whenever you see it in your data
Be conscious of your use of electronic devices near radio telescopes
Work with the IAU, URSI, other organizations to protect the radio spectrum