observing the

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