Library, N.W. Bldg

OCT 2 2 1964

^ecknlcal v£ete 92©. 222

A MINIMUM TELEMETRY RECEIVING SYSTEM

FOR THE ALOUETTE TOPSIDE

SOUNDER SATELLITE

Earl E. Ferguson and Richard G. Green

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

tional Bureau of Standards is a principal focal point in the Federal Government for maximum application of the physical and engineering sciences to the advancement of technology in industry and commerce. Its responsibilities include development and maintenance of the national stand- ards of measurement, and the provisions of means for making measurements consistent with those standards; determination of physical constants and properties of materials: development of methods

for testing materials, mechanisms, and structures, and making such tests as may be necessary, particularly for government agencies; cooperation in the establishment of standard practices for incorporation in codes and specifications; advisory service to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; assistance

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listing of its four Institutes and their organizational units. Institute for Basic Standards. Electricity. Metrology. Heat. Radiation Physics. Mechanics. Applied Mathematics. Atomic Physics. Physical Chemistry. Laboratory Astrophysics.* Radio Standards Laboratory: Radio Standards Physics: Radio Standards Engineering.** Office of Standard Ref- erence Data. Institute for Materials Research. Analytical Chemistry. Polymers. Metallurgy. Inorganic Materials. Reactor Radiations. Cryogenics.** Office of Standard Reference Materials. Central Radio Propagation Laboratory.** Ionosphere Research and Propagation. Troposphere

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* NBS Group, Joint Institute for Laboratory Astrophysics at tl ** Located at Boulder, Colorado.
NATIONAL BUREAU OF STANDARDS

technical ^ote 222

Issued October 9, 1964

A MINIMUM TELEMETRY RECEIVING SYSTEM

FOR THE ALOUETTE TOPSIDE

SOUNDER SATELLITE

Earl E. Ferguson and Richard G. Green

Central Radio Propagation Laboratory

National Bureau of Standards

Boulder, Colorado

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

For sale by the Superintendent of Documents, U. S. Government Printing Office Washington, D.C. 20402

Price: 30 cents

Table of Contents

Page

1. Introduction 1

2. Description of Equipment 2

3. Operation 5

k. Description of Satellite Operation 6

5. Prediction of Telemetry Antenna Aiming Angles 7

6. Acknowledgments 11

in
Figure Captions

Page

1. Telemetry system 13

2. Crystal controlled converter lh

3. Connection to discriminator 15

k. Video format l6

5. FM and direct recorded ionograms 17

6. Operator tracking satellite 18

7. Location of satellite during turn-on for one week 19

8. Geometry for derivation of equation (l) 20

9. Base map with observers elevation, azimuth grid and

satellite track 21

10. Satellite track overlay 22

iv
A MINIMUM TELEMETRY RECEIVING SYSTEM FOR THE ALOUETTE

TOPSIDE SOUNDER SATELLITE

Earl E. Ferguson and Richard G. Green

A description is given of a minimum telemetry receiving system used

to receive topside ionospheric records from the Alouette (S-27) satellite,

Instructions are included for the determination of telemetry antenna aiming angles to the satellite from any location on the surface of the Earth.

1. Introduction

For many years, measurements of the electron density of the ionized

atmospheric layers located from 80 to 500 miles above the surface of the

Earth have been made from the ground by an RF pulse and echo ranging technique popularly known as ionospheric sounding. Until recently, incoherent

scatter radar and sounding rockets have been the primary sources of information from above the level of maximum ion density hereafter referred

to as the topside of the ionosphere. The first of a series of ionospheric

sounder satellites designed to obtain data from the topside was launched

on September 29, 1962. This satellite, named Alouette or S-27, has been

very successful. It was constructed by the Canadian Defence Research Telecommunications Establishment, Ottawa, Ontario, and launched from the Pacific Missile Range by the National Aeronautics and Space Administration.

The orbital period is 105.5 minutes, the inclination is 80.5 degrees, and

the eccentricity is .002 with a perigee of 620 miles (998 km) and an apogee of 6^0 miles (1030 km).

Soon after launch, the simple telemetry system described herein was

devised to obtain topside ionospheric data directly from the satellite when

it was sounding as it passed within range of Boulder, Colorado. This system was used until a permanent CRPL telemetry station could be completed

at a nearby field site.

Such a system including a suitable oscilloscope and a tape recorder —but not a camera—would cost less than $1000. Because this system has

proved satisfactory, this description has been written as a guide to other

experimenters. Additional equipment which is more effective and more
expensive is also described. The report first describes the equipment

used, then its operation, and finally, a relatively simple method of locating the satellite from any point on the Earth's surface.

2. Description of Equipment

A block diagram of the complete system is shown in figure 1. The antenna, meter and headphones are used by an outside operator. The remainder

of the system is located "with another operator inside the laboratory building. The locations are selected near enough together to insure that the

136 Mc/s transmission line is no longer than 100 feet. This relatively

short distance and the use of RG-8U coaxial cable helps to minimize RF

losses between the antenna and converter.

The antenna is a low cost, two meter, five element, amateur beam modified by increasing the length of each element 6%, using tight-fitting split

tubing.

The 136-30 -Mc/s converter was constructed locally using a Nuvistor

front end and a crystal controlled oscillator to heterodyne the 136 Mc/s

telemetry carrier to 30 Mc/s. The converter circuit used is shown in figure 2. Several suitable commercial units are available at reasonable cost.

The converter used should have a noise figure of 3 db or better.

A popular brand commercial AM/EM receiver is used to tune to the 30

Mc/s output of the converter. The video signal is taken directly from the

discriminator output through the circuit shown in figure 3. It should be

noted that other converter-receiver combinations can be used. The most

economical would be a converter with an output frequency of approximately
100 Mc/s connected to a standard FM broadcast receiver covering the 96 to

108 Mc/s band. The video frequencies above 10 kc/s passed by a standard

FM receiver are not needed and tend to obscure the useful data. The addition of a low pass filter with a 10 kc/s cut-off will alleviate this problem.

The oscilloscope used is a popular 5" standard laboratory unit. Since

only •frequencies below 10 kc/s are important, any standard oscilloscope may

be used. The "A- scan" of the video format of the data received from the

satellite is shown in figure k. The oscilloscope is synchronized on the

negative going pulse at a sweep rate of approximately sixty-two per second.

Two methods of tape recording of the video data are used, viz., direct

recording and FM.

1. Direct recording of the video data from the receiver is done at

fifteen inches per second tape speed using a -5- inch width two-track tape.

The data are recorded on one track, and WW is recorded on the other. The

frequency response of many ordinary tape recorders at this speed will be

from 50 c/s to 15,000 c/s, which will be more than adequate for this purpose; however, a slight loss will be shown in the frequency markers and

plasma phenomena which lie below the 50 c/s range.

2. FM recording of the video data from the receiver is done on one

track at fifteen inches per second tape speed using a 27 kc/s subcarrier.

WWV as a time reference is directly recorded on the second track. The recorder used is a professional type with •§ inch tape and FM record and playback modules. The FM method of recording has a frequency response from

DC (zero c/s) to 5000 c/s at 15 inches per second. No appreciable loss
to any part of the record has "been found. This method is superior to "but

more expensive than the direct method.

While the recorded tape may be run as many times as desired, this will

yield only a temporary picture on the oscilloscope. To obtain permanent

records that can be studied at leisure, it is necessary to record the data

on film.

A convenient method is to use a B-scan mode by modulating the Z axis

of the oscilloscope with the video data. This B-scan is then photographed

with a moving-film camera to produce ionograms such as are shown in figures

5a and b. Normally the film rate may be between five and twenty inches per

minute. The record in figure 5a "was made with a film rate of twenty inches

per minute, and the data were taken from an FM recorded tape. Figure 5b

shows a record taken from a direct recorded tape at fifteen inches per second tape speed, and a film rate of twenty inches per minute. Either record

is useful. However, in the directly recorded data a loss of low frequency

response is revealed by the poor frequency marker and plasma resonance indications. The ionograms shown in figures 5a and b were not taken at the

same time, thus are not identical; also, the high frequency portions of the

ionograms have been masked for reproduction purposes . The 100 km range

markers seen on the ionograms, figures 5a and b, are generated by a local

oscillator/pulse generator synchronized to the transmitted pulse and external to the equipment shown in the block diagram. The frequency markers

are generated in the satellite.
3. Operation

This system can be operated by two persons, one to aim the antenna and

the other to check receiver and tape recorder operation. As seen in figure

6, the antenna is held by an operator who wears headphones carrying the

video signal from the receiver audio output. The operator also holds a

meter which indicates the AGC voltage from the receiver. At the predicted

time of start of pass and satellite turn on, the operator points the antenna at the predicted azimuth and elevation. While a satellite telemetry

station does not usually turn on a satellite at less than fifteen degrees

above the horizon, it has been proven in practice that it is possible to

follow S-27 from horizon to horizon with the system described in this report. Extreme accuracy is not necessary due to the relatively large beamwidth of the antenna and strong 136 Mc/s signal from the satellite. Plus

or minus fifteen degrees accuracy is adequate . The operator identifies

the signal from the characteristic sound of the sounder transmitter pulses

in the headphones and aims and rotates the antenna about its longitudinal

axis for maximum signal level indication on the meter. He follows the satellite with the antenna during the pass, constantly checking the rotation

of the antenna about its axis to compensate for polarization shifts in the

downcoming signal. There is usually at least a ninety degree rotation in

received polarization during any one pass.

The second operator stationed at the receiver adjusts the receiver

tuning so that the video signal "A-scan" on the oscilloscope (figure k)

shows approximately equal negative-going sync pulses and positive-going

sounding-transmitter pulses (base line centered) . Once adjusted at the
start of a pass, the receiver should not have to he retuned.

k. Description of Satellite Operation

Following a turn-on command hy a ground telemetry station the ionospheric sounder in the satellite will operate for a little less than ten

minutes. During this time the ionospheric echoes are placed on a 136.077

Mc/s FM link by direct FM modulation of the carrier. This information is

received hy the ground station and recorded on magnetic tape. When these

data are transferred to 35nmi film, approximately thirty-two ionograms result from each ten minute run. Each ionogram requires eighteen seconds

for completion and during this eighteen seconds the sounder in the satellite sweeps from 0.5 Mc/s to 11.5 Mc/s and returns to 0.5 Mc/s.

During the first year, S-27 produced approximately 1+23,000 ionograms.

As noted above, the satellite does not sound continuously throughout every

orbit. It operates only during the ten minute turn-on periods. Satellite

power restrictions as well as the location of the telemetry command stations are both limiting factors. Since the launch of S-27 on September 29,

1962, the number of ten-minute turn-ons has averaged thirty-five daily. Of

this number, two to five turn-ons have been for the purpose of VLF experiments which are not usable for ionospheric sounding data. To give some

idea of the frequency pattern of the turn-ons, we have indicated in figure

7 the actual ionosonde data portions of satellite tracks for a one week

period. This gives some indication of the probability of finding the satellite turned on for any particular pass. The satellite is turned on during most passes over North America.
5. Prediction of Telemetry Antenna Aiming Angles

A simple, semi-graphical method for determining the local elevation

and azimuth of Alouette is used. Essentially the method consists in first

constructing an elevation-azimuth grid for the observing location on a

base map of the world having a scale of 1/70,000,000 or better. Then an

overlay of the satellite track is placed on this map to determine the satellite track relative to the observer. Equatorial crossings data provide

a means for locating the satellite at any instant. Here it is assumed that

the satellite has a very low eccentricity and that the geocentric angular

velocity is nearly constant. Such an assumption of a circular orbit will

produce a maximum error in time of less than 0.3 min, an error of less

than 1 in elevation, and a very small error in azimuth.

To construct the elevation grid one must compute the elevation angle

E corresponding to various positions of the satellite. Assume that the

Earth is a perfect sphere of radius 6378 km and that the height of Alouette

is 1028 km. Then the relation

R = 90 - (arcsin

1Q2|

3

J\37Q

cosE + E) (l)

gives the angular distance R between the observing station and the satellite (see figure 8). Values of R for elevations between and 75 degrees

are given in the table below. The quantity R(km) is the surface distance

from the station to the subsatellite point.
E

0° 15° 30° kf 6o° if

R 30.67° 18.71° 11.77° l.hf h.kf 2..V?

R(km) 3^10 2080 1310 830 500 2kO

The speediest procedure for plotting the elevation angle grid is to describe on a globe circles of the prescribed radius about the station, after which the geographic coordinates can be read in order to transfer the

circles to the "working base map.

If preferred, the coordinates .may be calculated directly from the cosine

formula for spherical triangles

cosAX = (cos R - sincp

s sincp) seccps seccp (2)

where L\ = the difference in longitude between the observer and a point on

the circle of elevation grid,

cp g = the observer's latitude,

cp = the assumed latitude of any circle of elevation grid point, and

R = the radius of a circle of elevation in degrees.

An azimuth grid may be made "while carefully holding a circular protractor on the globe, tangent at the station. Azimuth lines every 30° or

so can thus be transferred to the base map. To compute these lines, however, take the following as derived from the cosine formula for spherical

triangles

8
tancp = (sinAX cot A + cosAX sincps ) seccp

s (3)

where AX = the difference of longitude between the observer and a point on

an azimuth line,

cp = the latitude of the point,

cp s = the observer's latitude as before, and

A = the azimuth.

(An elevation and azimuth grid map prepared for Boulder, Colorado, is shown

in figure 90

Next a tracing paper overlay of the satellite track (such as figure

10) is prepared for use with the base map. This is made from the geographic

position of the satellite every minute through one revolution as is given

below in table 1. Note that we have used a fictitious reference longitude

of 0° at the zero time instant of S-N equator crossing, and that the longitudes increase as the satellite moves towards the east.

9
T able

Lat.

1. Geogi

Long.

-aphic Position of Satellite Th rough On.e Revollit ion

Time

(Min)

Time

(Min) Lat. Long.

Time

(Min) Lat. Long.

Time

(Min) Lat. Long.

0.0 0.0 27 80.3 95.3 5U - 3.9 167.1 81 -78.8 282.1+ 1 3.3 0.3 28 79-1 112.8 55 - 7.2 1&7.

82 -76.6 291+.7 2 6.7 0.6 29 77.1 125.9 56 -10.6 167.7 83 -71+.1 303.3

3 10.1 1.0 30 7U.6 135.1 57 -ll+.O 168.1 81+ -71.2 309.1+

1+ 13.5 1.3 31 71.8 11+1.6 58 -17. 1* 166.1+ 85 -68.3 313.8

5 16.9 1.7 32 68.9 11+6.3 59 -20.7 168.8 86 -65.2 317.2

6 20.3 2.0 33 65.6 11+9.9 60 -2U.1 169.2 87 -62.0 319.8

7 23.7 2.1+ 3U 62.7 152.6 61 -27.5 169.7 88 -56.8 321.8

8 27.0 2.9 35 59.5 151+.7 62 -30.8 170.2 89 -55.6 323.5

9 30.1+ 3.1+ 36 56.3 156.5 63 -3I+.2 170.7 90 -52.3 321+.9 10 33.7 3.9 37 53.0 157.9 6); -37.5 171-3 91 -1+9.0 326.0

11 37.1 k.3 38 U9.7 159.1 65 -U0.8 172.0 92 -1+5.7 327.0

12 l+O.U 5.2 39 1+6.1+ 160.1 66 JA.2 172.8 93 -1+2.1+ 327.9

13 1+3.8 5.9 Uo 1+3.2 160.9 -1+7.5 173.7 91+ -39.0 328.6

11+ 1+7.1 6.8 1+1 39-8 161.7 68 -50.8 17U.8 95 -35.7 329.2

15 50.1+i 7.9 1+2 36.5 162.U 69 -5);. 1 176.0 96 -32.3 329.8

16 53.6 9.1 1+3 33.2 162.9 70 -57.1+ 177.5 97 -28.9 330.3

17 56.9 10.6 kh 29.8 163.5 71 -60.6 179-1+ 98 -25.6 330.8

18 60.1 12.1+ 1+5 26.5 163.9 72 -6^.8 181.7 99 -22.2 331.2

19 63.3 H+.6 1+6 23.I 16U.1+ 73 -66.9 1&U.7 100 -18.8 331.6

20 66.1+ 17.5 1+7 19.8 161+.8 7'* -69.9 188.7 101 -15.1+ 332.0

21 69.5 21.2 1+8 16. k 165.1 75 -72.8 19^.0 102 -12.0 332.3

22 72.1+ 26.2 1+9 13.0 165.5 76 -75.6 201.1+ 103 - 8.6 332.7

23 75.1 33.2 50 9.6 165.8 77 -77.9 211.9 10l+ - 5.2 333.0

2U 77.5 1+3.0 51 6.2 166.1 76 -79.6 226.7 105 - 1.8 333.3

25 79.

57.0 52 2.9 166.5 79 -80.5 2145.7 105.!+ 0.0 333-5

26 80.1+ 75.2 53 - 0.5 166.8 80 -80.1 265.7

The final step in local azimuth and elevation determination is to refer to a current NASA G-oddard Space Flight Center four-part bulletin for

62 Beta-Alpha 1 (Alouette) (available to investigators by -writing that

agency at Greenbelt, Maryland 20771) that provides the Universal Time

and West Longitude of each S-N equator crossing. A portion of such a bulletin is reproduced here in table 3- As an example, we have selected Revolution 86^-5 as seen from Boulder on 23 June I96U. The table gives the time

and longitude of equator crossing as 17^8.37 UT and 275. 7°W. We now find

that if the "zero" end of the satellite track overlay is placed at 275. 7°W

we may write down the following information on this pass as shown in

table 2.

10
Table 2. Predicted Telemetry Antenna Aiming Angles

Time (UT) Az. El.

l8h 20m 3U3 0°

22 3^0 6

2h 335 15

26 32U 28

28 29I+ ^1+

30 2^0 J+5

32 210 28

3h 198 15

36 192 6

38 189

Note that the weekly soundings are cyclic in nature. As may be verified by reference to the table of equatorial crossings, the satellite will

appear at the same longitude of equatorial crossing (to within 0.1°) at intervals of 6 23 0^.8m, or 95 revolutions. This means that each Alouette

pass observed at any one station will be repeated one week later less 55.2

minutes .

6. Acknowledgments

The authors are indebted to Mr. James M. Watts for the initiation of

this system and to Mr. Leray LaBaume for his assistance in the development

and operation of the final system.

11
Table 3. Alouette S-N Equator Crossings

REV TIME Z LONG W REV TIME Z LONG W REV TIME Z LONG W

18 JUN

8576 I 8579 2

19 JUN

8581

8584

8587 1 8590 1 8593 2

20 JUN

8594

8597

8600 1 8603 1 8606 2

21 JUN

8608

8611

8614 1 8617 1 8620 2

22 JUN

8622

8625

8628 1 8631 1 8634 2

23 JUN

8635

8638

8641 1 8644 1 8647 2

24 JUN

8649

8652

8655 1 8658 1 8661 2

25 JUN

8663

8666

8669 1 8672 1 8675 2

26 JUN

8676

8679

8682 1 8685

8688

64

627.18

143.77

64

114.82

631.39

147.96

704.53

221.11

64

6.63

523.20

039.78

556.35

112.92

64

43.97

600.55

117.12

633.69

150.26

64

121.31

637.89

154.46

711.03

227.60

64

13.13

529.70

046.27

602.85

119.42

64

50.47

607.04

123.62

640.19

156.76

64

127.81

644.38

200.96

717.53

234.10

64

19.63

536.20

052.77

609.34

125.92

245.45

325.03

18.08

97.65

177.23

256.80

336.38

2.91

82.48

162.06

241.63

321.21

14.26

93.84

173.41

252.99

332.56

25.61

105.19

184.77

264.34

343.92

10.44

90.02

169.60

249.17

328.75

21.80

101.37

180.95

260.53

340.10

33.15

112.73

192.30

271.88

351.46

17.98

97.56

177.13

256.71

336.29

8577 1812.72 271.98

8580 2329.29 351.55

8582 300.34 44.60

8585 816.91 124.18

8588 1333.49 203.75

8591 1850.06 283.33

8595 152.16 29.43

8598 708.73 109.01

8601 1225.30 188.58

8604 1741.88 268.16

8607 2258.45 347.73

8609 229.50 40.79

8612 746.07 120.36

8615 1302.64 199.94

8618 1819.22 279.51

8621 2335.79 359.09

8623 306.84 52.14

8626 823.41 131.72

8629 1339.98 211.29

8632 1856.56 290.87

8636 158.65 36.97

8639 715.23 116.54

8642 1231.80 196.12

8645 1748.37 275.70

8648 2304.95 355.27

8650 235.99 48.32

8653 752.57 127.90

8656 1309.14 207.48

8659 1825.71 287.05

8662 2342.29 6.63

8664 313.33 59.68

8667 829.91 139.25

8670 1346.48 218.83

8673 1903.05 298.41

8677 205.15 44.51

8680 721.72 124.08

8683 1238.30 203.66

8686 1754.87 283.23

8689 2311.44 2.81

8578 1958.24 298.50

8583 445.86 71.13

8586 1002.44 150.70

8589 1519.01 230.28

8592 2035.58 309.86

8596 337.68 55.96

8599 854.25 135.53

8602 1410.83 215.11

8605 1927.40 294.68

8610 415.02 67.31

8613 931.59 146.89

8616 1448.17 226.46

8619 2004.74 306.04

8624 452.36 78.67

8627 1008.93 158.24

8630 1525.51 237.82

8633 2042.08 317.39

8637 344.18 63.49

8640 900.75 143.07

8643 1417.32 222.65

8646 1933.90 302.22

8651 421.52 74.85

8654 938.09 154.42

8657 1454.66 234.00

8660 2011.24 313.58

8665 458.86 86.20

8668 1015.43 165.78

8671 1532.00 245.35

8674 2048.58 324.93

8678 350.67 71.03

8681 907.25 150.61

8684 1423.82 230.18

8687 1940.39 309.76

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