EDGES MEMO #144
ARIZONA STATE UNIVERSITY
SCHOOL OF EARTH AND SPACE EXPLORATION
TEMPE, ARIZONA 85287
July 31, 2014
Telephone: 480-727-2553
E-mail: raul.monsalve@asu.edu
To:
EDGES Group
From: Raul Monsalve, Thomas Mozdzen
Subject: Characterization of RFI at the UNR Gund Ranch
1
Description
A characterization of radio-frequency interference (RFI) was performed in the region surrounding the Gund Ranch
between July 17 and July 19, 2014. This ranch is located in the Grass Valley, Nevada, and belongs to the University of Nevada at Reno. It is administered by Mr. Jon Wilker, who conducts several research and commercial
activities with livestock. The purpose of this RFI characterization is to determine if the area is competitive for the
observation of the redshifted 21-cm line emitted during cosmic dawn.
Two instruments were employed for the characterization:
• A calibrated EDGES system, corresponding to front-end, back-end, digitizing, and recording electronics
identical to those used by the instrument currently dedicated to EoR science in Western Australia. Two
fourpoint antennas were employed, in order to survey the ranges 50-120 MHz (low-band) and 100-200
MHz (high-band) separately and more efficiently. This instrument is referred to as Instrument 1.
• An instrument based on a spectrum analyzer, an LNA, and a biconical antenna. The purpose of this instrument is to perform quick measurements in order to compare the main features of different promising
sites without spending significant amounts of time assembling and disassembling the main system. This
instrument is referred to as Instrument 2.
Two practical spots were selected for measurements with Instrument 1. They are shown in red in figures 1 and
2. The criterion used to choose these spots was obtaining an adequate angle of the surrounding mountains - not
too high (which could affect science measurements) but not too low (so they provide some RFI attenuation). This
pushed us south of the ranch, toward the middle of the Grass Valley, since the homestead is blocked on the east
by tall mountains a few hundred meters away. Figures 1 also shows in blue the spots where measurements with
Instrument 2 were done. At all the locations the strength of the FM broadcast signal picked up by the car radio
was minimal.
The spots in figures 1 and 2 are labeled geographically, with numbers that increase clockwise starting with the
westernmost. However, that is not the chronological order in which they were visited and measured from. The
chronological order is as follows:
• July 17 (day 1) was devoted to measurements at site 2 with both instruments. With Instrument 1 we were
able to measure with the low- and high-band antennas orientated in the north-south and east-west directions,
spending 1 hour with each antenna and in each orientation.
• July 18 (day 2), due to rain and lightning most of the day, was devoted to measure with Instrument 2 only, at
the other spots shown in figure 1. These measurements were 10-minute long per orientation of the biconical
antenna, except for places were rain made us stop sooner.
1
• The first half of July 19 (day 3) was used for measuring with Instrument 1 at site 1, only with the lowband antenna. One hour of data in the north-south orientation was gathered, while only 40 minutes in the
east-west orientation due to incoming rain and lightning.
The coordinates of each site are presented in table 1.
Coordinates
Site
1
2
3
4
5
6
7
Landmark
Grass Valley Rd
South of Gund ranch
Homestead
Fye Canyon
Highway 278
Highway 50
Ackerman Canyon
Longitude
Latitude
116◦ 42’ 40” W
116◦ 37’ 31” W
116◦ 35’ 13” W
116◦ 32’ 42” W
116◦ 11’ 09” W
116◦ 19’ 43” W
116◦ 36’ 46” W
39◦ 44’ 52” N
39◦ 50’ 20” N
39◦ 54’ 02” N
40◦ 01’ 42” N
40◦ 00’ 18” N
39◦ 31’ 44” N
39◦ 31’ 19” N
Table 1: Site Coordinates
The pictures in figures 3 through 11 give an idea of the landscape at most of the spots visited.
2
Figure 1: Location of sites from which measurements were conducted. Top is north, and bottom is south. The
spots in red are the sites from which Instrument 1 was used, and the ones in blue correspond to Instrument 2. For
reference, site 3 correspond to the Gund ranch, and highway 50 is in the lower part of the map.
3
Figure 2: Zoom in on the Grass Valley, west and south of the Gund ranch. The ranch corresponds to the green
spot in the upper-right corner. Site 1 is ∼ 13 miles south of the ranch, by the road. Site 2 is ∼ 5 miles south of the
ranch, and a few minutes into the valley following a two-track road.
4
Figure 3: Overview of the homestead from the south. The uneven mountains in the north do not attenuate signals
sufficiently from that direction. Low-voltage lines provide power to the homestead and the actual house of the
manager, a few hundred meters south (not shown in the picture).
Figure 4: View from the homestead to the east. Tall mountains located a few hundred meters away become
a limitation for considering doing science measurements from this site. Thus, only Instrument 2 was used to
characterize this site.
5
Figure 5: Site 1, looking toward the mountains on the east, during measurements with Instrument 1 and the
low-band antenna.
Figure 6: Site 1, looking toward the mountains on the west, during measurements with Instrument 1 and the
low-band antenna.
6
Figure 7: Site 2, looking toward the mountains in the east, and the two-track road that leads to the main road
called Grass Valley Rd.
Figure 8: Site 2, looking toward the west, during measurements with Instrument 1 and the low-band antenna. The
setup is on top of the two-track road that continues into the valley.
7
Figure 9: Site 4, looking toward the east, during measurements with Instrument 2.
Figure 10: Site 5, looking toward the north, during measurements with Instrument 2.
8
Figure 11: Site 7, looking toward the east, during measurements with Instrument 2.
9
2
Measurements and Results
2.1
Instrument 1
The relevant aspects of measurements with Instrument 1 can be summarized as follows:
• Frequency resolution of ∼ 6.1 KHz.
• Temperature calibration assuming 300 and 400 K for the cold and hot loads in the LNA, respectively.
• Ground pickup is higher than with the science instrument since no metal ground plane was used, and sites
1 and 2 had mountains in the horizon of up to ∼ 10 degrees.
• Measurements were done with the antenna, the excited panels specifically, orientated along the north-south
and east-west axes.
• No correction applied due to ground pickup, imperfect impedance match between antenna and LNA, noise
waves, or scale and offset of LNA. Skipping these calibration steps has a small impact, since the focus of the
experience is to obtain representative behavior of the RFI with respect to the galactic-noise-limited baseline
in order to compare different sites.
• The instrument was run off car batteries, and therefore an inverter was required. The back-end electronics,
PC, and inverter were enclosed in a metal box that acted as a Faraday cage. This enclosure was essential for
capturing the RFI content of the environment alone, without the contribution of the electronics which was
significant, especially in the low-band.
• At site 1 only low-band measurements were taken, with both antenna orientations. The measurement with
the north-south orientation lasted 1 hour. With the east-west orientation it lasted 40 minutes due to approaching rain; however, only ∼ 50% of them are useful since the rest was affected by thunderstorms in the
vicinity.
• At site 2 it was possible to conduct low- and high-band measurements in both orientations, lasting 1 hour
each.
Figures 12 through 17 present waterfall plots of the observations, along with averages of the datasets.
Figures 18 through 23 present the average RFI content in the frequency domain after removing the baseline
from the data. In each figure, the upper plot has a vertical scale adequate for visualizing the strongest component
between both orientations. The lower plots zoom in to the vertical scale 0-100 K.
Figures 24 through 30 show timestreams of the frequency channels in the low-band that show significant RFI
for any of the two sites and orientations, except for the region of FM radio. The baselines in time, corresponding
primarily to drifting sky noise, have been removed from these streams. A label in each subplot identifies the
frequency channel as well as the service to which it has been assigned as reported by the FCC.
2.2
Instrument 2
Instrument 2 had the purpose of quickly characterizing interesting spots around the ranch in order to compare their
main features with those at the sites where Instrument 1 was employed. Its technical details can be summarized
as:
• The spectrum analyzer is operated with RBW of 1 KHz and a resolution of ∼ 273 KHz in the range 50-200
MHz.
• The short biconical antenna is operated horizontally with the cones orientated along the north-south and
east-west axes. It was mounted at a height of ∼ 1.6 meters.
10
• The LNA has a gain of ∼ 45 dB and an average noise temperature of ∼ 55 K in the range of interest. It was
connected to the antenna through a 12-inch cable.
• No calibration was conducted for this instrument, and therefore direct power readings cannot be translated
into temperature accurately. Moreover, the return loss of the antenna is very poor (to be expected from such
a short biconical antenna) which has the effect of making the system inefficient to sky noise (or RFI). This
also produces ripples in the spectra whose period depend on the length of the cable toward the spectrum
analyzer. Despite these limitations, this instrument was useful for allowing to compare the strong RFI
content at several sites.
• Measurements were conducted for 10 minutes in each orientation. This allowed for the recording of ∼
75 traces per orientation, given the sweep speed of the spectrum analyzer. The exceptions to this are the
measurements at site 6 (only 2 minutes of measurements in the NS orientation) and site 7 (only 1 trace in
each orientation). These measurements were stopped early due to the risk of imminent rain and lightning.
• Just like for Instrument 1, the baseline of the measurements in the frequency domain was removed by
subtracting a low-degree polynomial. Due to bad impedance match, sinusoidal residuals remain in the data,
which are of order ±0.5 dB.
The results of the measurements with Instrument 2 are presented in figure 31, as averages of all the available
data in each orientation, where the amplitude corresponds to power relative to the baseline. Site 2 can be used as
a reference when judging sites 3 through 7, since at site 2 we also have measurements with Instrument 1.
11
Figure 12: Site 1, low-band, NS orientation.
Figure 13: Site 1, low-band, EW orientation. The top panel shows the average after removing from the dataset the
spectra affected by thunderstorms in the vicinity.
12
Figure 14: Site 2, low-band, NS orientation.
Figure 15: Site 2, low-band, EW orientation.
13
Figure 16: Site 2, high-band, NS orientation.
Figure 17: Site 2, high-band, EW orientation.
14
4
∆ antenna temperature [K]
7
x 10
6
5
4
3
2
1
0
50
60
70
80
90
100
110
120
60
70
80
90
frequency [MHz]
100
110
120
∆ antenna temperature [K]
100
80
60
40
20
0
50
Figure 18: Site 1, low-band, NS orientation.
4
∆ antenna temperature [K]
7
x 10
6
5
4
3
2
1
0
50
60
70
80
90
100
110
120
60
70
80
90
frequency [MHz]
100
110
120
∆ antenna temperature [K]
100
80
60
40
20
0
50
Figure 19: Site 1, low-band, EW orientation. This result is noisier due to the less amount of data available.
15
4
∆ antenna temperature [K]
7
x 10
6
5
4
3
2
1
0
50
60
70
80
90
100
110
120
60
70
80
90
frequency [MHz]
100
110
120
∆ antenna temperature [K]
100
80
60
40
20
0
50
Figure 20: Site 2, low-band, NS orientation.
4
∆ antenna temperature [K]
7
x 10
6
5
4
3
2
1
0
50
60
70
80
90
100
110
120
60
70
80
90
frequency [MHz]
100
110
120
∆ antenna temperature [K]
100
80
60
40
20
0
50
Figure 21: Site 2, low-band, EW orientation.
16
6
∆ antenna temperature [K]
6
x 10
5
4
3
2
1
0
100
110
120
130
140
150
160
170
180
190
200
110
120
130
140
150
160
frequency [MHz]
170
180
190
200
∆ antenna temperature [K]
100
80
60
40
20
0
100
Figure 22: Site 2, high-band, NS orientation.
6
∆ antenna temperature [K]
6
x 10
5
4
3
2
1
0
100
110
120
130
140
150
160
170
180
190
200
110
120
130
140
150
160
frequency [MHz]
170
180
190
200
∆ antenna temperature [K]
100
80
60
40
20
0
100
Figure 23: Site 2, high-band, EW orientation.
17
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 50.098 MHz, Amateur
200
100
0
0
10
20
30
40
50
60
30
40
50
60
40
50
60
40
50
60
40
50
60
300
f = 50.189 MHz, Amateur
200
100
∆ antenna temperature [K]
0
0
10
20
300
f = 54.102 MHz, TV−channel 2
200
100
0
0
10
20
30
300
f = 54.309 MHz, TV−channel 2
200
100
0
0
10
20
30
300
f = 55.249 MHz, TV−channel 2
200
100
0
0
10
20
30
time [minutes]
Figure 24: Timestreams of channels with RFI in the low-band (except region of FM radio).
18
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 59.747 MHz, TV−channel 2
200
100
0
0
10
20
30
40
50
60
40
50
60
40
50
60
40
50
60
40
50
60
300
f = 60.309 MHz, TV−channel 3
200
100
∆ antenna temperature [K]
0
0
10
20
30
300
f = 61.249 MHz, TV−channel 3
200
100
0
0
10
20
30
300
f = 65.741 MHz, TV−channel 3
200
100
0
0
10
20
30
300
f = 66.309 MHz, TV−channel 4
200
100
0
0
10
20
30
time [minutes]
Figure 25: Timestreams of channels with RFI in the low-band (except region of FM radio).
19
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 67.261 MHz, TV−channel 4
200
100
0
0
10
20
30
40
50
60
40
50
60
40
50
60
40
50
60
40
50
60
300
f = 71.759 MHz, TV−channel 4
200
100
∆ antenna temperature [K]
0
0
10
20
30
300
f = 71.997 MHz, TV−channel 4
200
100
0
0
10
20
30
300
f = 73.047 MHz, Radio astronomy
200
100
0
0
10
20
30
300
f = 76.312 MHz, TV−channel 5
200
100
0
0
10
20
30
time [minutes]
Figure 26: Timestreams of channels with RFI in the low-band (except region of FM radio).
20
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 77.252 MHz, TV−channel 5
200
100
0
0
10
20
30
40
50
60
40
50
60
40
50
60
40
50
60
40
50
60
300
f = 81.000 MHz, TV−channel 5
200
100
∆ antenna temperature [K]
0
0
10
20
30
300
f = 81.750 MHz, TV−channel 5
200
100
0
0
10
20
30
300
f = 82.312 MHz, TV−channel 6
200
100
0
0
10
20
30
300
f = 83.246 MHz, TV−channel 6
200
100
0
0
10
20
30
time [minutes]
Figure 27: Timestreams of channels with RFI in the low-band (except region of FM radio).
21
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 108.197 MHz, Aviation
200
100
0
0
10
20
30
40
50
60
30
40
50
60
30
40
50
60
30
40
50
60
30
time [minutes]
40
50
60
300
f = 108.398 MHz, Aviation
200
100
∆ antenna temperature [K]
0
0
10
20
300
f = 110.602 MHz, Aviation
200
100
0
0
10
20
300
f = 112.201 MHz, Aviation
200
100
0
0
10
20
300
f = 113.000 MHz, Aviation
200
100
0
0
10
20
Figure 28: Timestreams of channels with RFI in the low-band (except region of FM radio).
22
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 114.099 MHz, Aviation
200
100
0
0
10
20
30
40
50
60
30
40
50
60
30
40
50
60
30
40
50
60
30
time [minutes]
40
50
60
300
f = 114.502 MHz, Aviation
200
100
∆ antenna temperature [K]
0
0
10
20
300
f = 115.198 MHz, Aviation
200
100
0
0
10
20
300
f = 115.503 MHz, Aviation
200
100
0
0
10
20
300
f = 116.498 MHz, Aviation
200
100
0
0
10
20
Figure 29: Timestreams of channels with RFI in the low-band (except region of FM radio).
23
300
NS site 1
NS site 2
EW site 1
EW site 2
f = 116.992 MHz, Aviation
200
100
0
0
10
20
30
40
50
60
30
40
50
60
30
40
50
60
30
40
50
60
30
time [minutes]
40
50
60
300
f = 117.200 MHz, Aviation
200
100
∆ antenna temperature [K]
0
0
10
20
300
f = 118.048 MHz, Aviation
200
100
0
0
10
20
300
f = 119.202 MHz, Aviation
200
100
0
0
10
20
300
f = 119.751 MHz, Aviation
200
100
0
0
10
20
Figure 30: Timestreams of channels with RFI in the low-band (except region of FM radio).
24
∆ power [dBm]
40
10
0
∆ power [dBm]
40
∆ power [dBm]
70
80
90
100
110
120
130
140
150
160
170
180
190
200
80
90
100
110
120
130
140
150
160
170
180
190
200
80
90
100
110
120
130
140
150
160
170
180
190
200
80
90
100
110
120
130
140
150
160
170
180
190
200
80
90
100
110
120
130
140
150
160
170
180
190
200
80
90
100
110 120 130 140
frequency [MHz]
150
160
170
180
190
200
SITE 3
20
10
0
40
60
70
SITE 4
30
20
10
0
50
∆ power [dBm]
60
30
50
40
60
70
SITE 5
30
20
10
0
50
∆ power [dBm]
NS orientation
EW orientation
20
50
40
60
70
SITE 6
30
20
10
0
50
∆ power [dBm]
SITE 2
30
40
60
70
SITE 7
30
20
10
0
50
60
70
Figure 31: Summary of measurements with Instrument 2, after removing the baselines. Most of them represent
10-minute averages, except sites 6 and 7 for which there are less data available. The EW traces have been shifted
0.5 MHz to the left for better comparison with the NS cases.
25
3
Conclusions
• In the high-band, Instrument 1 picks up strong but intermittent aeronautical communications (below 137
MHz) and miscellaneous communications (above 138 MHz). In addition, the signature of digital TV channels 7 through 11, including their ATSC pilots, is clearly identifiable above 174 MHz in the EW orientation.
• In the low-band, the only significant contributors to RFI other than FM radio are signals corresponding
to channels 2 through 5 (ATSC pilots or analog transmissions), although the wideband signatures of digital channels cannot be distinguished using the data gathered. Other transmissions below FM radio are
intermittent and weaker in comparison.
• When comparing site 5 with site 2 using data taken with Instrument 2 it can be argued that site 5 is potentially better in the low-band. This site is off highway 278, in an area with a local dip in the terrain. The exact
spot corresponds to the entrance to a private property with houses visible in the distance. Unfortunately we
could not do measurements here with Instrument 1.
A
Appendix: RFI Characterization at Deep Springs/OVRO
As a reference, this appendix includes results of the RFI characterization conducted at Deep Springs/OVRO by
Gregg Hallinan.
26
Frequency (MHz) Frequency (MHz) Frequency (MHz) Frequency (MHz) Frequency (MHz)
100
98
96
94
92
90
88
86
84
82
82
80
78
76
74
72
70
68
66
64
64
62
60
58
56
54
52
50
48
46
46
44
42
40
38
36
34
32
30
28
28
26
24
22
20
18
16
14
12
10
10000
20000
30000
40000
50000
10000
20000
30000
40000
50000
10000
20000
30000
40000
50000
10000
20000
30000
40000
50000
10000
20000
30000
Time [s] since 2013-08-16 01:13:20 UTC
40000
50000
Figure 32: Deep Springs.
Frequency (MHz) Frequency (MHz) Frequency (MHz) Frequency (MHz) Frequency (MHz)
100
98
96
94
92
90
88
86
84
82
82
80
78
76
74
72
70
68
66
64
64
62
60
58
56
54
52
50
48
46
46
44
42
40
38
36
34
32
30
28
28
26
24
22
20
18
16
14
12
10
5000
10000
15000
20000
25000
30000
35000
40000
5000
10000
15000
20000
25000
30000
35000
40000
5000
10000
15000
20000
25000
30000
35000
40000
5000
10000
15000
20000
25000
30000
35000
40000
5000
10000
15000
20000
25000
Time [s] since 2013-08-15 00:48:57 UTC
30000
35000
40000
Figure 33: OVRO.
27
Power (dBm)
Power (dBm) Power (dBm) Power (dBm)
Power (dBm)
55
60
65
70
75
80
85
9082
86.0
86.5
87.0
87.5
88.0
88.564
82.5
83.0
83.5
84.0
84.5
85.0
85.5
86.0
86.546
80.5
81.0
81.5
82.0
82.5
83.0
83.5
84.028
65
70
75
80
85
90
9510
Deep Springs Valley Site
84
86
88
90
92
94
96
98
100
66
68
70
72
74
76
78
80
82
48
50
52
54
56
58
60
62
64
30
32
34
36
38
40
42
44
46
12
14
16
18
20
Frequency (MHz)
22
24
26
28
Figure 34: Average Deep Springs.
Power (dBm)
Power (dBm) Power (dBm)
Power (dBm) Power (dBm)
20
30
40
50
60
70
80
9082
82
83
84
85
86
87
8864
81.5
82.0
82.5
83.0
83.5
84.0
84.5
85.0
85.546
79.5
80.0
80.5
81.0
81.5
82.0
82.5
83.028
50
55
60
65
70
75
80
85
90
9510
84
86
88
90
92
94
96
98
100
66
68
70
72
74
76
78
80
82
48
50
52
54
56
58
60
62
64
30
32
34
36
38
40
42
44
46
12
14
16
18
20
Frequency (MHz)
22
24
26
28
Figure 35: Average OVRO.
28