PAPER Antenna Polarimetry Project

Introduction

The goal of this project is to refurbish an old antenna from the Precision Array for Probing the Epoch of Reionization and repurpose it as a polarimeter. We will use it to collect data that can be used as machine learning training sets to assist in the creation of sky models which will be applied to the in-progress Cosmic Twilight Polarimeter instrument, soon to be deployed in Green Bank.

Project Timeline

This is a rough plan for how the project will progress over the 10-week period:

Week Goals Location
1 Get antenna in place, check quality of baluns, run cabling to antenna site GBO
1-2 Configure Raspberry Pi / temperature sensor setup Off site
3 Characterize balun's temperature performance and S Parameters GBO or CV?
3 Use spect. analyzer to assess RFI env. in order to determine best observing band GBO
4 Develop filters to prevent system noise from entering data (as much as possible) CV
5 Work out interface between Ettus box and laptop setup Off site
6-7 Configure pre and post processing steps Off site
8-10 Collect, calibrate, and package data from antenna GBO / off site
10 Finish end of term report and present results in GB and CV Off site, GBO, CV

Antenna Configuration / Setup

Summary of activities in Green Bank on May 30-June1:

  • 2 ground screens were moved to the 45-foot site by the GBO grounds crew on May 30.
  • The "coat hanger" antenna was taken down, also by the GBO grounds crew, on May 30.
  • We oriented the ground screen appropriately and checked that it was level on May 30.
  • 2 antennas were disassembled, cleaned thoroughly, and reassembled, completed on May 31.

Summary of activities in Green Bank on June 10:

  • Time Domain Reflectometer (TDR) measurements were performed to assess the state of the coax / power cables run from the 45-foot trailer to the old Yagi antenna (<50 ft from the previous site of the coathanger, where the PAPER antenna is located).
  • A feature was identified in the TDR plots from both coax cables, which could indicate a connector (or multiple connectors) at a point on the cable.
  • The ends of the two coax cables were then shorted, and after some troubleshooting we were able to see the appropriate trace on the TDR indicating that both cables were shorted as expected, showing that the cables were in fine condition and would not need to be replaced. We verified our results by calculating the length of the wire using the TDR display, and found that both were very nearly 500 feet, which was a good backup measurement.
  • Note: As a result of the fact that the end of the cabling was found to be located in an enclosure attached to the Yagi antenna -- instead of near the coathanger, as expected -- we will need to run a short length of cabling from the antenna to the Yagi.

Raspberry Pi

For this project, we will be configuring and using a Raspberry Pi to periodically record temperature, humidity, and voltage readings during observing. These readings will be used to apply post-processing corrections to the data that we record.

Here's a link to a Wiki page documenting our Raspberry Pi temperature and humidity sensor setup: RPiSensorSetup

The Raspberry Pi initial setup (as outlined above) was completed on June 6, 2019.

Temperature Chamber Measurements

Part of this project involved characterizing the S-Parameters of the balun and receiver as a function of temperature; the results of this characterization will be used in post-processing to properly calibrate the data.

Here is a page dedicated to summarizing the procedure and outcomes of the temperature chamber measurements: TemperatureMeasurements

Spectrum Analyzer Results

In order to characterize the RFI environment over the working bandwidth of our receiver, we are running a spectrum analyzer at the antenna site.

Here is a page summarizing the results of our spectrum analyzer experiment: SpectAnalyzerResults

RF Filters

Our original plan was to design and build two 8 MHz bandpass filters in the lab in Charlottesville. However, after some preliminary exploration of the Ettus SDR / the Soyuz computer's capabilities, it turns out that in fact the system can only accept up to 4 MHz of bandwidth, which is such a narrow range that it would have made filter fabrication difficult. So an alternative is being pursued -- using two pre-built tunable bandpass filters identified at the Central Development Lab.

Digital Signal Processing pipeline

Here is a page summarizing the DSP pipeline of the PAPER antenna, which consists of a stream of data from an Ettus research SDR and from the Raspberry Pi, which is processed and stored by two NRAO computers via a GNU Radio flowgraph: SignalProcessingPipeline

And here is a page summarizing work that was done to ensure proper calibration of the system: AntennaCalibration

Data collection

Here is a page containing observation data: DataCollectionPAPERPol

And here's a page with a detailed description of how to run and process observations: ObservationProcedures

-- EllieWhite - 2019-05-12
Topic revision: r12 - 2019-09-05, EllieWhite
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