MM-wave issues -- Myth and reality - atnf.csiro.au · Radar_book_chapter?.pdf . Myth: MM band...

Harvey Liszt IUCAF SMSS Santiago April 2014

MM-wave issues -- Myth and reality Harvey Liszt

ALMA & NRAO, CHARLOTTESVILLE

mm-waves •  The ITU-R radio spectrum is 0-3000 GHz

–  3000 GHz = λ100µ called FIR by astronomers – FIR astronomers would be very surprised to

learn they are doing radio astronomy L




learn they are doing radio astronomy J •  The mm-wave domain is ~60-300 GHz

– Beyond is sub-mm (300-1000 GHz) – After sub-mm is the THz region (1000+ GHz)




learn they are doing radio astronomy •  The mm-wave domain is ~60-300 GHz


•  The spectrum is allocated up to 275 GHz




learn they are doing radio astronomy •  The mm-wave domain is ~60-300 GHz


•  The spectrum is allocated up to 275 GHz •  ALMA works up to 950 GHz, soon beyond Harvey Liszt IUCAF SMSS Santiago April 2014

Myth: Air absorbs stray mm radiation

MM-wave transmission at median ALMA weather


Plots have linear vertical scale for transmission


MM-wave transmission at median ALMA weather


There are narrow bands where the myth is true but no interfering applications were put there


A broader view in the 1st octile of ALMA weather


ALMA is currently taking band 10 test data (787-950 GHz) and band 11 (1000-1600 GHz) is under development




Things get pretty choppy above 350 GHz




Things get pretty choppy above 350 GHz but look how much things improved at 183 GHz




Things get pretty choppy above 350 GHz

There is abundant spectrum for use by short-range high frequency applications in non-interfering spectral regions

Some numbers

ITU-R 79 GHz radar studies use 6 dB/km in “wet” air when doing studies against most services


ITU-R 79 GHz studies use ~0.15 dB/km vs RAS

ITU-R 230 GHz studies would use 0.34 dB/km vs RAS (based on median 230/79 GHz conditions at ALMA)

Myth: MM-wave radio astronomy does not need to engage in spectrum issues



The vast majority of all spectrum allocated to radio astronomy is mm-wave spectrum





Until a few years ago there seemed to be few strong reasons to engage





The traps were laid





The traps were laid The pigeons are now coming home to roost





The traps were laid The pigeons are now coming home to roost CloudSat 94.05 GHz radar





The traps were laid The pigeons are now coming home to roost EarthCare 94.05 GHz radar





The traps were laid The pigeons are now coming home to roost EarthCare 94.05 GHz radar

35.5-36, 133.5-134 GHz


Myth: MM band structure protects RAS


Case study Level Probing Radar Myth: MM band structure protects RAS



If one of these things interfered with your telescope it could be there forever



If one of these things interfered with your telescope it could be there forever

regulators acting badly


Case study Level Probing Radar

Ohmart/VEGA has a nice radar primer!





Ohmart/VEGA has a nice radar primer!

http://www.vega.be/downloads/Radar_book_chapter?.pdf

Myth: MM-wave radio astronomy …




Divide 231 GHz/3 = 77 GHz

Myth: ALMA is the only major radio astronomy observatory without a spectrum management

program


Myth: “Sandy” is a real person


Sandy is a real person


Myth: It is possible to convert from Jy to µV/m


MM-wave issues -- Myth and reality - atnf.csiro.au · Radar_book_chapter?.pdf . Myth: MM band...

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