SKA Site Spectrum Monitoring Sites: X1 - X4 and Y1 - Y4 · at each of the two candidate SKA hosting...

Date of issue: Sept. 28, 2011 Project: SKA Spectrum Monit., RM

Revision nr.: 1.0 Authors: A.J. Boonstra and R.P. MillenaarStatus: Final Kind of issue: Limited

SKA Site Spectrum Monitoring

Sites: X1 - X4 and Y1 - Y4

Measurement Mode: Rural Mode (RM)

Annex to the report

”SKA site spectrum monitoring, measurement program and data processing”

Verified:

Name Signature Date Rev.nr.

... 1.0

Accepted:

R.P. Millenaar R.T. Schilizzi

.................. .................. ..................

date: date: date:

c©ASTRON 2011

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Distribution list:

Group: For Information:

Expert Panel on RFI and EMI R.T. Schilizzi

Document revision:

Revision Date Section Page(s) Modification

1.0 Sept. 28, 2011 all all creation

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Contents

1 Introduction 4

2 Measurement results 5

2.1 Spectral power flux density results, overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.2 Spectral power flux density results, expanded scales . . . . . . . . . . . . . . . . . . . . . 11

2.2.1 Spectral power flux density, sites X1 and Y1 . . . . . . . . . . . . . . . . . . . . . 12




2.3 Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Appendix A. Calibration results 58

A1. Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

A2. Receiver and system temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

A3. Calibrated spectra, all sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

A4. Calibrated spectra, percentiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

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1 Introduction

As part of the SKA site selection process the Radio Frequency Interference environment has been mea-

sured at the candidate sites X and Y. This was done under the “Agreement on radio frequency interference

monitoring 2008”. This Agreement entails the development of instrumentation, control and data pro-

cessing software, infrastructure and carrying out of measurements at the two candidate core sites, plus

at a selection of remote sites in the hosts proposed array configuration. This spectrum monitoring report

is one of a series and is annex to the report “SKA site spectrum monitoring, measurement program and

data processing”. The results of complete Rural Mode (RM) runs are presented for four remote sites

at each of the two candidate SKA hosting countries, respectively X1, X2, X3, X4, Y1, Y2, Y3, and Y4.

This measurement annex report presents the following:

• calibrated and baseline corrected overview spectra for the frequency range 70-2000 MHz in section

2.1.,

• 200 MHz wide zoomed-in spectra in section 2.2.,

• sensitivity spectra in section 2.3..

In order to help judging the validity of the data, calibration results are included in appendix A:

• calibrated gain curves in appendix A1,

• calibrated Trec and Tsys curves in appendix A2,

• calibrated site-overview spectra without “baseline correction” in appendix A3,

• calibrated percentile spectra without “baseline correction” in appendix A4.

The Rural Mode measurement uses the following settings:

• integration time: 60 s (per spectrum)

• number of repetitions: 10

• net integration time per pointing/polarisation/band: 600 seconds (10 minutes)

• calibration: equal time on noise source on/off/antenna (60s/60s/60s), each repetition.

A complete scan (1 pointing, 1 polarisation, 9 bands), including calibration and overhead, takes a total

of about 5.8 hours. For a complete survey, all pointings and polarisations, a total of about 2 days was

required.

This report does not contain detailed descriptions of the presented results as these are included in the

main report mentioned above. The basic information is present in the figure captions, for more details

please see the main report.

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2 Measurement results

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The figures that follow result from observations at locations X1-4 and Y1-4; these figures for sites X and

Y are combined when displayed on each page. This may suggest that site X1 is to be compared with site

Y1 and so on. This however is not the case: in fact the sites identified by the numbers 1 to 4 are selected

without having a particular order in mind. The selection of the four sites at each of the two countries

was done to include expected noisy and relatively quiet locations from the set of 25 remote station sites.

Concerning the quality of the data please note that the gain settings of the equipment was adapted by

adding an additional attenuator. This was done to improve the dynamic range of the monitoring systems

at all 2 × 4 sites, some of which may be near to strong transmitters. This additional attenuaton led to

a lower noise source calibration signal power. Together with (relatively) strong interference this has led

to distorted calibration of part of the data. This effect can be seen in the calibration curves, but also in

some cases as distorted (baseline) curves for median Ψ and Ψc data.

For the data at hand, no detection was done on self-generated RFI. When inspecting the data, care nust

be taken not to confuse self-gerated RFI from “real” external RFI. Known issues are mid-band narrow

RFI spikes (visible in the receiver noise temperature calibration curves) which may occur at 243.770,

719.985, 975.020, 1218.765, 1452.488, 1679.985, and 1912.513 MHz.

Another artefact is apparent RFI in baseline-calibrated data Ψc stemming from false detection of RFI at

frequency band transitions. This kind of self-generated RFI may occur at the band edges at 190, 440, 540,

855, 1080, 1340, 1595, and / or 1780 MHz. At these frequencies the calibrated non-baseline subtracted

data Ψ in some cases show jumps in the calibrated spectra. Comparing the Ψc and Ψ (Matlab fig-file)

data will show whether a spike in Ψc data at a band edge is an artefact or not.

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2.1 Spectral power flux density results, overview

Figure 1: Calibrated and baseline-corrected power flux density Ψc in dB(Wm−2Hz−1). Plotted are the 50 (median),

75, an 95 percentile curves, which were computed from datasets obtained in four azimuth directions (North, South,

East and West) and for two polarizations (horizontal and vertical). The 1 σ level is shown in black; the actual

detection level for the baseline subtraction procedure is 6 σ.

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2.2 Spectral power flux density results, expanded scales

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2.2.1 Spectral power flux density, sites X1 and Y1

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Figure 5: Calibrated and baseline-corrected power flux density Ψc in dB(Wm−2Hz−1) using expanded frequency

scaling. Plotted are the 50 (median), 75, an 95 percentile curves, which were computed from datasets obtained in

four azimuth directions (North, South, East and West) and for two polarizations (horizontal and vertical). The 1

σ level is shown in black; the actual detection level for the baseline subtraction procedure is 6 σ.

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2.3 Sensitivity

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Figure 45: Sensitivity ∆Ψ in dB(Wm−2Hz−1) estimates based on calibrated Trec curves. Plotted are the median

curves computed using data obtained in four azimuth directions (North, South, East, West) and two polarizations

(horizontal and vertical). The depicted estimations are 6σ values, but as these curves are based on Trec (and not

on Tsys) the underestimation factor is at least 3 dB. Please note the mid-band spikes, which are instrumental

artefacts.

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Appendix A. Calibration results

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A1. Gain

Figure 46: Calibrated gain curves G in dB: shown are the median values for each of the sites, computed using data

obtained in four azimuth directions (North, South, East, West) and two polarizations (horizontal and vertical).

Only the in-band sections are depicted; the “jumps” are band transitions.

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A2. Receiver and system temperature

Figure 47: Receiver temperature Trec in K: shown are the median values for each of the sites, computed using data


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Figure 48: System temperature Tsys in K: shown are the median values for each of the sites, computed using data


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A3. Calibrated spectra, all sites

Figure 49: Calibrated but not baseline-corrected power flux density Ψ in dB(Wm−2Hz−1). Depicted are the 75

percentile curves, which were computed from datasets obtained in four azimuth directions (North, South, East and

West) and for two polarizations (horizontal and vertical).

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A4. Calibrated spectra, percentiles


(median), 75, and 95 percentile curves, which were computed from datasets obtained in four azimuth directions

(North, South, East and West) and for two polarizations (horizontal and vertical).

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