Post on 16-Mar-2019
Observing the <100 MHz radio skyObserving the <100 MHz radio skyfrom the sub-Antarcticfrom the sub-Antarctic
H. Cynthia ChiangH. Cynthia ChiangMcGill UniversityMcGill University
Science at Low Frequencies VScience at Low Frequencies V4 December 20184 December 2018
Exploring lower frequencies
Image: Pritchard and Loeb, Nature, 2010
δTb ∝ xHI (1+z)1/2 (Ts – TCMB) / Ts
What lurks down here…?
The dream: lay groundwork for exploring dark ages
Ultimate dream: image the fluctuations
Most experiments operate here.
The state of the art at low frequencies
Experiment Frequency Resolution Year
Grote Reber 2.1 MHz ~5 deg 1968
RAE-B satellite 4.7 MHz ~10 (??) deg 1978
DRAO 22 MHz 1.1–1.7 deg 1999
LWA 36.5 MHz 15 arcmin 2017
How low can we go from Marion?
IRI model prediction: plasma frequency down to ~1.5 MHz during last solar minimum, next one is coming up...
How low can we go from Marion?
SANAP proposal has been renewed through 2020
Infrastructure: 9 huts around island perimeter, convenient ring-like layout for imaging
Deploy antennas at huts, write lowest 10–20 MHz baseband to disk, correlate afterward
8' FWHM synthesized beam @ 5 MHz
Kildalkey
Katedraal
Cape DavisRepetto's
PRIZMsite
Mixed Pickle
WatertunnelGrey-headedRook's
Swartkop
ALBATROS:
Array of Long Baseline Antennas for Taking Radio Observations from the Sub-antarctic
Newest team members
Jeff Peterson
José Miguel Jáuregui-Garcia
Cynthia Chiang
Jonathan Sievers
Rupert Spann
Jack Hickish Vhuli Manukha
Nivek Ghazi
Austin Gumba
Tankiso Moso
Liju Philip
Veruschka Simes
Low-frequency pathfinderExploratory Gizmo on the Ground: ALBATROS-EGG
PRIZM 70 MHzPRIZM 100 MHz
ALBATROS-EGG
ALBATROS-EGG
Command module110 meters110 meters
ALBATROS-EGG schematic
Bias tee>0.1 MHz
1.2 – 81 MHz High + low pass 20 dB
100mcoax
Back end Faraday cage
12 VDC batteries
Regulated voltage outputs
35 dB active balun
Dual pol LWA antenna
35 dB active balun
Dual pol LWA antenna 250
MSamp/s
SNAP board
Cross-correlation
SD card on RPi
4 auto6 xspec
Antennas: using LWA hardware
Two LWA antennas installed on Marion in 2018
Design frequency range: 5 – 90 MHz
Omnidirectional, dome-shaped beam pattern
LWA active balun
SNAP and back end electronics
RF tight enclosure with dividing shelf, single SNAP on one side and RF electronics on the other side
Spectrometer firmware on SNAP:0 – 125 MHz2048 channels (61 kHz)250 Msamp/s sampling
Full correlation of 4 inputs
Total system power draw ~45 WRun time ~1 weekBatteries: 3 x 150-Ah + 1 x 200-Ah
Enclosure can easily fit in a backpack
Whole assembly is placed ~50 m from the antenna to reduce self-generated RFI
Command module
Back-end electronics
Battery wiring harness
Chargers
Snacks
Mouse control
Comfortable space for the human
Prevailing wind direction
Raw ALBATROS-EGG autospectra
First fringes from ALBATROS-EGG
Tim
e (d
ays)
Frequency (MHz)
R&D in progress for autonomous stations
Data acquisition: need GPS disciplined clock, software/firmware development for writing baseband to disk, data storage plan (how much can we afford to write?)
Power: solar power for autonomous operation, need to ensure that charging circuitry is RF shielded
Mechanical considerations: package everything into a shipping container for rapid deployment
Calibration? Modify front ends to include switching between sky and cal sources?
Kildalkey hutKildalkey hut
Offshore tool box
McGill Arctic McGill Arctic Research StationResearch Station
79°26′N 90°46′W79°26′N 90°46′W
Summary and future prospects
Two pathfinder low frequency antennas installed on Marion in 2018
Clear sky signal down to ~10 MHz
Ionosphere plasma frequency may drop as low as 1.5 MHz, we'll see how low we can dig in our data
Ultimate plan: install and correlate array of autonomous stations