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Up in smoke ... destructive interference
Harvey Liszt ALMA & NRAO, CHARLOTTESVILLE

Harvey Liszt

IUCAF SMSS Santiago April 2014


Destructive & Disruptive Interference
Harvey Liszt ALMA & NRAO, CHARLOTTESVILLE

Harvey Liszt

IUCAF SMSS Santiago April 2014


An emerging issue
· Radio systems for voice/data were not generally of concern, even when they have stronger emissions
· A cell phone emits more power than a car radar

· Radiolocation and radionavigation systems (radar) are of such concern
­ They typically use much higher power ­ Some w/ low power operate at high frequency, perhaps in proximity to the telescope

Harvey Liszt

IUCAF SMSS Santiago April 2014


An emerging issue
· Radio systems for voice/data were not generally of concern, even when they have stronger emissions
· A cell phone emits more power than a car radar

· Radiolocation and radionavigation systems (radar) are of such concern
­ They typically use much higher power ­ Some w/ low power operate at high frequency, perhaps in proximity to the telescope

Harvey Liszt

IUCAF SMSS Santiago April 2014


The basics
· As summarized in ITU-R Report RA.2188 it takes ~ 5-35 mW input power to burn out a modern RAS receiver
­ 1 V across 50 ohm, what could be simpler? ­ SiS junction or transistor amplifier ~ same

· There's much we don't know but it seems to happen quickly, depends only on wattage
­ Some tests done for defense in 1980's ­ The most sensitive devices had more problems at high signal levels, development was stopped
Harvey Liszt IUCAF SMSS Santiago April 2014


The basics
· As summarized in ITU-R Report RA.2188 it takes ~ 5-35 mW input power to burn out a modern RAS receiver
­ 1 V across 50 ohm, what could be simpler? ­ SiS junction or transistor amplifier ~ same

· There's much we don't know but it seems to happen quickly, depends only on wattage
­ Some tests done for defense in 1980's ­ The most sensitive devices had more problems at high signal levels, development was stopped
Harvey Liszt IUCAF SMSS Santiago April 2014


The basics RA. 2188
· Destructive mW for transistor amplifiers

Harvey Liszt

IUCAF SMSS Santiago April 2014


The basics RA. 2188
· Destructive mW for transistor amplifiers

Harvey Liszt

IUCAF SMSS Santiago April 2014


The basics RA. 2188
· Destructive mW for transistor amplifiers

Harvey Liszt

IUCAF SMSS Santiago April 2014


The basics RA. 2188
· Destructive mW for transistor amplifiers

Harvey Liszt

IUCAF SMSS Santiago April 2014


The basics RA. 2188
· Destructive mW for transistor amplifiers

Harvey Liszt

IUCAF SMSS Santiago April 2014


Something of a surprise
· The authors of RA. 2188 originally thought transistor amplifiers were more resistant

Harvey Liszt

IUCAF SMSS Santiago April 2014


Orbiting EESS(active) SAR
All SAR capable of damaging receivers on 25m ­ 100m telescopes

Harvey Liszt

IUCAF SMSS Santiago April 2014


https://www.sfcgonline.org !

Harvey Liszt

IUCAF SMSS Santiago April 2014


https://www.sfcgonline.org !

Harvey Liszt

IUCAF SMSS Santiago April 2014


https://www.sfcgonline.org !

Harvey Liszt

IUCAF SMSS Santiago April 2014


https://www.sfcgonline.org !

Harvey Liszt

IUCAF SMSS Santiago April 2014


https://www.sfcgonline.org !

Harvey Liszt

IUCAF SMSS Santiago April 2014


Coda
Lesser but permanent damage can be inflicted by substantially lower input power but quantifying this is impractical

Harvey Liszt

IUCAF SMSS Santiago April 2014


Why higher frequency is worse
for terrestrial interferers

Cell phones radiate more power than car radars by far (factor 10) but cell phone emission is isotropic and has low flux MM-wave portable devices emit less power but have narrow beams and higher eirp It is much easier to focus all the transmitted power onto the surface of an RAS dish or a stray sidelobe
Harvey Liszt IUCAF SMSS Santiago April 2014


How near can car radar be allowed?

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?
For 76 GHz radar HPBW = 6o = 0.1 radian So an antenna fills the radar beam at distance = 10 antenna diameters For 100m telescope, 1 km For 30m telescope, 300 m For ALMA, 120m

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?Detectors will not work properly in the presence of high signal levels This is what caused DARPA to stop developing the most sensitive amplifiers

II

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?Detectors will not work properly in the presence of high signal levels This is what caused DARPA to stop developing the most sensitive amplifiers SiS junctions suffer 1% gain compression at input power of 0.2 nW (ALMA memo 401) and subtle intermodulation products at 0.1 nW according to NRAO
Harvey Liszt IUCAF SMSS Santiago April 2014

II


How near can car radar be allowed?A car radar with eirp = 55 (33) dBm, received with 0 dBi gain will produce an input power of 0.1 nW at a distance of 560 (45) m SiS junctions suffer 1% gain compression at input power of 0.2 nW (ALMA memo 401) and subtle intermodulation products at 0.1 nW according to NRAO
Harvey Liszt IUCAF SMSS Santiago April 2014

II


How near can any radar be allowed?
How does 0.1nW = 10-10 W compare with the receiver noise power? kTB = 1.6x10-23 * 15 * 16x109 = 4x10-12 W

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
How does 0.1nW = 10-10 W compare with the receiver noise power? kTB = 1.6x10-23 * 15 * 16x109 = 4x10-12 W

Only factor 25 difference

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can car radar be allowed?Conclusion: car radars begin to disrupt radio astronomy receivers at the same distances where they could destroy them

II

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
Corollary: The cross-section for disruption by an orbiting SAR is much larger than suggested by the size of the RAS primary beam

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
Corollary: The cross-section for disruption by an orbiting SAR is much larger than suggested by the size of the RAS primary beam Orbiting radars can put 1 W across a dish

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
Corollary: The cross-section for disruption by an orbiting SAR is much larger than suggested by the size of the RAS primary beam Orbiting radars can put 1 W across a dish The ratio between 1 W and 0.1 nW is much greater than any antenna gain in the problem

Harvey Liszt

IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
Corollary: The cross-section for disruption by an orbiting SAR is much larger than suggested by the size of the RAS primary beam Orbiting radars can put 1 W across a dish The ratio between 1 W and 0.1 nW is much greater than any antenna gain Our receivers are functioning in a disruptive environment with continuous jamming
Harvey Liszt IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
Corollary: The cross-section for disruption by an orbiting SAR is much larger than suggested by the size of the RAS primary beam Orbiting radars can put 1 W across a dish The ratio between 1 W and 0.1 nW is much greater than any antenna gain Our receivers are functioning in a battle-field environment with continual disruption
Harvey Liszt IUCAF SMSS Santiago April 2014


How near can any radar be allowed?
Corollary: The cross-section for disruption by an orbiting SAR is much larger than suggested by the size of the RAS primary beam Orbiting radars can put 1 W across a dish The ratio between 1 W and 0.1 nW is much greater than any antenna gain Created by "friendly fire" from other science services
Harvey Liszt IUCAF SMSS Santiago April 2014