harvey liszt - itu · harvey liszt chair, iucaf () & nrao spectrum manager () astronomers do...

Radio Astronomy and Satellite Interference:a brief & selective history

Harvey LisztChair, IUCAF (www.iucaf.org)

&

NRAO Spectrum Manager (www.nrao.edu)

Astronomers do Spectrum

• 1st Generation 1956 ‐ 1982– 21 cm H I line 1420.4 MHz

• Detected 1951, protected 1960 & 1971

– OH 1612, 1665, 1667, 1720 MHz • Detected 1963‐64, • Protected 1963, ’71, unprotected ’79, re‐affirmed ‘92

• 2nd Generation 1982 –• cm‐wave guys (yes, guys, but not me) stirred by RNSS• Mm‐wave astronomers, even, from mid‐90’s

Services & Satellites

• RNSS (L‐band)– GPS 1978 – 1993 – GLONASS 1982 – 2007

• MSS (L‐band)– Iridium 1990’s – now

• EESS (active) (9.6 & 94 GHz)– Terra‐SAR X at WRC‐15– CloudSat 2004 ‐ now

Interference at the GBT – Day 1(all days are from one week Jan. 2015)


RR 5.340 (passive)

Primary, shared w/MSS (earth‐space)

US246 (passive)


RR 5.340 (passive)


US246 (passive)MSS (s‐e)

RNSS


RR 5.340 (passive)



RNSS

50,000 x the protection threshold


RR 5.340 (passive)



RNSS

A real H I 21cm line signal

Interference at the GBT – Day 1


RFI gone now


Both clean now

RNSS‐GPS

• GPS Block I produced RFI at 1612 & 1665 MHz– Fitful start to GPS between 1979 and 1989– Sweden, Canada, IUCAF protested ca. 1990– GPS uses different modulation of same carrier

• More easily filtered than somebody else we know …

– Block II satellites had ~40 dB lower noise by 1993

GPS Block I vs Block II(Ponsonby 1991, J. Nav)

RNSS‐GPS

• GPS Post 1993– TG 1/9 studies showed GPS compliant at WRC‐07

• Subject to Res. 739 (WRC‐07)– RA. 769 + RA. 1513 epfd 2% data loss criterion

– Military testing (lightly coordinated with RAS) generates harmful interference into the passive band at 1420‐1427 MHz

null spikes

> 100 MHz blocked for radio astronomy

RNSS‐GLONASS

Navigation signal

• Unlike GPS, each GLONASS satellite uses a different frequency channel

RNSS‐GLONASS Timeline

As summarized by R. J. Cohen for IUCAF in Y2K

GLONASS ‐ IUCAF

• New GLONASS Frequency plan– Moved channels down below the RAS band

• Fewer chans, re‐used on opposed sides of orbit

– Filters to be installed on GLONASS‐M satellites

• IUCAF believed that the agreement would provide RFI‐free observing for RAS in 2006

GLONASS ‐ IUCAF

• Prior to WRC‐07, GLONASS unexpectedly informed TG1/9 that it had satisfied the IUCAF agreement– IUCAF did not agree– No administrations supported IUCAF at the WRC

• At WRC‐07 GLONASS was exempted

GLONASS – Res. 739

GLONASS ‐ IUCAF

• At WRC‐07 GLONASS was exempted– At first insisted that ALL RNSS be exempted– Finally “settled” for being exempted individually– Generally considered a dead letter now for RAS

MSS‐Iridium• Interference noticed during testing at NRAO immediately after launch of first satellites

RA 769

Iridium 1998 at VLA w/voice

Iridium 1998 NRAO GB, broadcast only

• NRAO subject to NDA & MOU, did not protest publicly and quietly buried the test results

• Arecibo signed a second MOU under NDA• European radio astronomers were incensed, the sense of community had been broken

• EU exacted a commitment for clean observing by 2006

• Still occuring ~ 20 years later

MSS‐Iridium

RR. 5.372

• EESS (active) SAR (radars) and scatterometers– Lay down ~ 1 Watt across the area of 100 m dish– Would fry an RAS rcvr in (main beam)2 encounter

• ~ 0.01W will destroy a superconducting junction

– RAS rcvr saturates whenever a site is illuminated

• SFCG maintains a database for RAS users• Formed basis of ITU‐R Rec. RS. 2066

– Incorporated by reference in RR at WRC‐15

EESS (active) 9.6 & 94 GHz


Allocated for horizontal polarization? Vertical?

• In 2004, JPL informed NRAO of impending CloudSat 94 GHz cloud‐profiling radar– 16 day repeating orbit overflying many RAS sites– And CloudSat was NOT designed to avoid RAS

• RAS, having wholly ignored the subject between 1997 and 2004 was shocked, shocked, I tell you

• NRAO/IUCAF/JPL collaborated to disseminate info to the RAS community

• JPL built an informational website for RAS with info on the latest orbit etc.


• RAS operating systems incorporated Cloudsat– Control room alarms– Cessation of data‐taking

• Operations were modified– Antennas no longer stowed at zenith if possible– Transportable antennas needing zenith access were outfitted with mechanical baffles


• Cloudsat later suffered a “battery incident” – Was removed from its normal orbit– Its radar was no longer fixed along the nadir

• The zenith cone of avoidance was much larger, ~12o

• When it returned to operations it could no longer operate without illumination of its solar panels

• When it passes overhead in darkness now it cannot transmit :)


• In response WP 7C and 7D jointly created


• Will RA. 1750 translate into real cooperation?– Stay tuned for IUCAF‐SFCG collaboration


What’s next? Back to the ’90s

• FSS provider planning 2018 launch of ~1000 (round numbers) broadband wireless satellites downlinking at 10.7 – 12.75 GHz– 10.6 – 10.7 GHz allocated to RAS– 10.68 – 10.7 GHz subject to RR. 5.340– My inference: they planned to operate down to the lower band edge in a few, broad channels

• With the RR. 5.340 band taking their spillover

Round‐up

• Every case different– But the dog’s philosophy of life often prevails– “What are these passive bands, anyway, really?”

• Some good, some rather poor outcomes– Good outcomes depend on exceptional good will on the other side, sometimes long after the fact

• End results somewhat haphazard– Rules and regulations do not always carry the day

My personal view

• Most radio astronomy better done in space– But cost way more expensive than at present– $100,000,000 on ground > $1bln in space– Space astronomy subject to binge/bust cycles– Space agencies way more adept at procuring projects than ground‐based science foundations

• You realize this when a telecom consultant asks how a 1988 list of telescopes can possibly still be complete

My personal view

• Passive bands must survive– Even after astronomy abandons the earth– Even for bands not now observed heavily

harvey liszt - itu · harvey liszt chair, iucaf () & nrao spectrum manager () astronomers do...

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