NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT 8520-12-85520 April 14, 1965

NBS REPORT 8796

DESIGN AND INSTALLATION OF THREE FORWARD SCATTER

TEST PATHS IN THE ARCTIC FOR MEASURING EFFECTS

OF LOW ENERGY SOLAR COSMIC RAYS

P. P. Viezbicke

Appendix

G. F. Montgomery IMPORTANT NOTICE

N A T I O N A L BUREAU O F STANDARDS REPORTS are usually preliminary or progress accounting documents intended for use within the Government. Before material in the reports is formally published it is subjected to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or op.en-literature l isting of this Report, either in whole or i n part, is not authorized unless permission is obtained in writ ing from the Office of the Director, National Bureau of Standards, Washington, D.C. 20234. Such permission is not needed, however, by the Government agency for which the Report has been specifically prepared if that agency wishes to reproduce additional wies tw it5 own use.

US. DEPARTMENT OF COMMERCE NATIONAL BUREAU O F STANDARDS

Contents

F or ewor d . . . . . . . . . . . . . . . . Abstract . . . . . . . . . . . . . . . . 1 . Introduction . . . . . . . . . . . . 2 . Site Survey . . . . . . . . . . . . . 3 . Systems Design . . . . . . . . . . .

3 . 1 Antenna System . . . . . . . . 3 . 2 Transmitting System . . . . . . 3 . 3 Receiving system . . . . . . . .

4 . Summary . . . . . . . . . . . . . . 5 . Acknowledgements . . . . . . . . . . 6 . References . . . . . . . . . . . . . 7 . Equipment Inventory . . . . . . . . .

Pages 15 and 16 h a w been d e l e t e d . Appendix . . . . . . . . . . . . . . . .

Page

. . . . . v

. . . . . vii

. . . . . 1

. . . . . 2

. . . . . 6

. . . . . 6

. . . . . 8

. . . . . 10

. . . . . 12

. . . . . 1 3

. . . . . 13

. . . . . 14

. . . . . 49

iii

FOREWORD

This work was car r ied out under project 85520, Arctic Forward Scatter,

The site surveys, design, equipment procurement, and installation at

terminal points of the three forward scatter tes t paths were car r ied

out with funds on P. 0. Number T-l5237(G), April 17, 1963,from

National Aeronautics and Space Administration, Manned Space craf t

Center, Houston, Texas. In compliance with purchase order request

this final repor t includes si te surveys and equipment inventory.

The R F section of the receiver described in the Appendix was modified.

The modification details will be supplied separately.

V

Abstract

This repor t describes transmitter and receiver

systems used in measuring effects of low energy solar

cosmic rays (mostly protons) over three HF forward

scat ter tes t paths in the arctic. Five-element Yagi

antennas, overlooking smooth te r ra in or water, a r e

employed a t terminal points of each path and are

mounted a t optimum heights above ground.

The main beam of radiation is directed to the

path midpoint, using a scattering volume height of

85 km. Transmissions over each path a r e recorded

on specially designed, calibrated, narrow bandwidth

equipment. The data, presented on s t r ip char t record-

ings, a r e interpreted and studied particularly for iono-

spheric absorption effects resulting from the mesospheric

ionization produced by solar cosmic rays.

vii

DESIGN AND INSTALLATION O F THREE FORWARD SCATTER TEST PATHS I N THE ARCTIC FOR MEASURING EFFECTS

O F LOW ENERGY SOLAR COSMIC RAYS

P. P. Viezbicke

1. Introduction

Forward scatter techniques [Bailey, Bateman, and Kirby, 19553

have been employed in Alaska and la ter in the Greenland-Iceland region

to observe the effects of proton f l u x [Bailey, 1962, 19641.

possible to study these effects only considerably after an event had

occurred, and useful observations were obtained only during a period

of high solar activity.

ness was growing of the need to observe solar-cosmic events in r e a l

time. Moreover, there was a need to investigate the infrequent and

much less intense solar cosmic-ray events that could be expected to

occur during the period of low solar activity defined by the IQSY program.

A suitable observing program in the arct ic would a l so complement in a

particularly valuable way a similar program of measurements to be

car r ied out in the antarctic a t the same time under NSF-IQSY sponsorship.

It was

With the advent of the Apollo program an aware-

T o meet the needs of such a program, three forward scatter tes t

Two paths a r e located in Alaska, the paths were installed in the a rc t ic ,

third in Canada, a s indicated on the map in figure 1.

were selected to represent a useful range in longitude, to provide

observations from a possible conjugate to one of the antarctic paths,

and to provide observations from a position slightly outside the polar

cap where the effects of a higher and changing magnetic cutoff could

be studied. T o make the observations more sensitive to small events,

the various tes t paths were operated at frequencies near 23 Mc/s ra ther

than in the 32-36 Mc/s range employed in an ear l ie r communication

system.

The three paths

This program was initiated on April 17, 1963 and completed

during the ear ly spring of 1964.

system design calculation (table l ) , site surveys conducted i n Alaska

and Canada, and the procurement and installation of t ransmit ter and

receiver systems together with the necessary antennas at the selected

sites .

The scope of the project involved

2. Site Survey

Selection of the antenna site and the determination of the cor rec t

height of the antenna above ground plays an important role in the success-

ful operation of the system.

obstacles, and extend in the direction of the opposite terminalf or a

sufficient distance to provide for the first F resne l zone. This zone

contributes to the gain of the system by allowing the plane-wave ground

reflection lobe to be properly formed.

The site should be nearly flat, f ree f rom

The extent of the zone over a plane ear th includes an a r e a bounded

by the geometrical figure presented in figure 2.

that the ground reflected energy undergoes a phase shift of 180 degrees

or less f rom the reference r a y and reinforces the direct r a y at an

angle of departure a.

It is within this zone

The problem of the effect of departure from te r ra in smoothness

is difficult to resolve.

surface a r e not greater than h/4, where h is the antenna height above

ground.

overlooking lower sloping te r ra in or water,

advantageously and shorter towers can be employed and still maintain

the effective design height over the geometric ground reflection point.

Three of the six s i tes in the Arctic exhibited terrain features that were

used to this advantage.

One requirement is that bumps on the smooth

In some cases , the selected site may be located on high ground,

These features can be used

2

Specific si tes for the three tes t paths located in Alaska and

Canada a r e presented in a r e a topographic maps, drawings, and photo-

graphs. Figures 3 through 11 show specific details of the transmitter

and receiver si tes i n Alaska.

information for the Canadian sites.

Figures 12 through 17 provide s imilar

At Barrow, the t ransmit ter , towers , and antenna a r e located

a t the National Bureau of Standards field station as shown on the topo-

graphic map of figure 3. A photograph of the field station and antenna

system is presented in figures 4 and 5. Since the antenna is sited over

level smooth te r ra in , it was mounted at the design height of 33 meters .

At Anchorage, the receiver building and antenna a r e sited at Elmendorf

Air Fo rce Base overlooking the Knik Arm of Cook Inlet. In contrast to

the former , the te r ra in in front of the antenna slopes in the direction

of propagation and was used advantageously to employ shorter towers.

Although the antenna was mounted at a height of 16.8 me te r s above

ground, the effective design height of 33 meters was maintained over

the geometric ground reflection point.

showing the location of the receiver site a t Anchorage and a photograph

of the installation a r e shown in figures 6 and 7.

stationed at Barrow and Anchorage operate and main€ain the equipment

for this path.

An a r e a topographic map

NBS personnel

At Annette Island, the t ransmit ter t ra i ler and antennas a r e sited

on sloping te r ra in overlooking a bay in the direction of propagation.

topographic map of the island showing the location of the site and a

photograph of the installation a r e shown in figures 8 and 9.

site was 6 meters above mean s e a level.

was mounted at a height of 35 meters above ground instead of the 41

meter design height over level ground.

maintained by F A A personnel.

A

The selected

F o r this reason, the antenna

The facility was installed and

4

The receiver station, near Fairbanks, is sited in wooded te r ra in

near a NASA minitrack station.

features, the antenna was mounted at the design height of 41 meters

above ground.

of the Geophysical Institute, University of Alaska.

Because of relatively smooth te r ra in

The station is operated and maintained by staff members

In Canada, the transmitter installation at Frobisher Bay is sited

on an abandoned a i r s t r ip (designated as the West 40 si te) and is located

approximately 2 kilometers southwest of the community of Frobisher

Bay. A s shown in the topographic map of the a rea , figure 12, the a r e a

in front of the antenna, although limited in extent, is smooth level ground.

The extent of this level a r ea measured 0. 85 kilometers, approximately

0.6 of the distance to the far edge of the F resne l zone.

smooth reflecting a rea , the te r ra in slopes downward toward the bay.

This res t r ic t ion in the foreground a r e a is not considered to constitute

a significant detriment to the antenna performance.

a r ea i s approximately 170 meters.

installation a r e presented in figures 13 and 14.

Beyond the

The width of the

Photographs of the completed

The receiver site at Great Whale River is located approximately

2 kilometers north of the airstrip as shown on the map of figure 15.

towers and antennas a r e located on a plateau and overlook an extremely

flat a rea in the direction of propagation.

Frobisher Bay, extends to approximately 0.6 of the distance to the far

edge of the F r e s n e l zone and was followed by rolling terrain. It is 180

meters wide a t i ts narrowest point, or slightly greater than the design

width.

a r ea , the antenna was mounted 2 4 meters above the ground instead of

the 2 8 meter design height.

the antenna installation is presented in figures 16 and 17.

The

The smooth a rea , as a t

Since the selected site was 4 meters higher than the foreground

A photograph of the receiver building and

5

3 . Systems Design

In carrying out the investigation over an experimental path,

continuous signal intensity recordings a r e made of horizontally

polarized C W transmissions.

sited transmitter and receiver facilities which a r e separated by the

path length L, resulting in a propagation trajectory with an angle of

departure a in keeping with midpoint ionospheric scattering from a

height of 85 kilometers.

concerning the calculation of optimum antenna heights for practical

cases of interest in ionospheric scatter work [Merr i l l , 1958, 19591.

This study employs a model atmosphere and incorporates spherical

divergence, near horizon diffraction correction, parallax, and r e - fractive defocusing using a n ionospheric reflection height of 85 km.

Although the data presented by Merr i l l do not include antenna height

versus path length curves for frequencies below 30 Mc/s, lobe alinement

antenna heights were extrapolated from those presented for the different

path lengths at an operating frequency of 23 Mc/s.

together with path lengths, bearings, and Fresne l zone dimensions for

the different paths a r e presented in table 1.

The system consists of nearly ideally-

A detailed study has recently been made

These heights,

3. 1. Antenna System

Identical five-element Yagi antennas a r e used at the t ransmit ter

Each antenna is located at such an effective height and receiver sites.

above ground as to have i t s main lobe of radiation directed toward a

point 85 km above the path midpoint.

antennas a r e designed to withstand the adverse weather conditions en-

countered in polar regions where wind velocities of 120 mph can occur

and where the temperatures may range from plus 80 to minus 110

degrees Fahrenheit.

In physical construction, the

6

The antenna was designed to operate a t a frequency of 23 .3

f 0. 5 Mc/s. I t is 0. 8h long with elements equally spaced a t 0 . 2 wave-

lengths. Figure 18 presents dimensions and spacings of elements and

indicates materials used in fabrication, mounting, and interconnection

details.

P r e s t r e s s e d medium tempered 60-61T6, 3-inch diameter

aluminum pipe is used for the boom.

second and third directors and reinforced with a four-foot telescoping

plug secured with 1 /2 by 4-inch aluminum bolts and nuts.

A splice is placed between the

The elements consist of 1 - 5/8 inch 0. D. five-foot long tubes

located at 8 foot 5 - 1 / 2 inch intervals along the boom and a r e fitted

into holes, centered and heliarc welded into the boom. The outer par ts

of the elements, constructed of 1 - 1/2 inch 0. D. aluminum tubing, a r e

fabricated into two equal lengths.

aluminum plug and is designed to telescope into its matching counter-

part at the center of the boom.

facilitate centering the elements on the boom.

One length is force fitted with an

Markers, scribed on the elements,

The gain of the antenna is 9 . 2 db relative to a half-wave dipole

at the same height and i s characterized with E and H plane half-power

beamwidths of 45 and 60 degrees,respectively. Measured radiation

patterns of the antenna a r e presented in figures 19 and 20.

The input impedance to the antenna is approximately 200 ohms.

A one-half wavelength long, four to one impedance matching network

transforms the balanced 200 ohms impedance to 50 ohms unbalanced.

Foamflex coaxial cable connects the antenna to a double - stub tuner

located near the base of the tower. Additional lengths of foamflex

connect to receiving or transmitting equipment located in a nearby

t ra i ler or building.

presented in figure 18.

Interconnection details of the antenna system a r e

7

3.2 . Transmitting System

Identical antennas and equipment a r e used at the three arct ic :::

transmitting stations. The 1 kw transmitter, with its associated

control and recording equipment, is designed to operate on a fixed

frequency in the range of 23 to 24 Mc/s.

transmitter and one rack of associated control and monitoring equip-

ment occupies limited space.

located in a portable 8 by 8 foot insulated building that is completely

wired, fan vented, and heated.

is readily transportable.

gear, is used to house equipment a t Annette Island.

equipment is housed at the NBS field station.

receiver stations operate from a single-phase, 3-wire, 220-volt

60-cycle source.

to the NBS field station at Barrow, but emergency standby power is

available at the site.

part at Anchorage.

Island.

Alaska.

Power Company.

the receiving site.

Compact in design, the

At Frobisher Bay, the equipment is

The building is mounted on skids and

A magnesium t ra i le r , with detachable running

At Barrow, the

The t ransmit ter and

The Arctic Research Laboratory furnishes the power

The USAF furnishes power to its receiver counter-

The FAA serves the transmitter facility at Annette

The local power company serves the receiving site a t Fairbanks,

A t Frobisher Bay in Canada, power is delivered by the Canadian

At Great Whale River, the RCAF delivers power to

A block diagram of the transmitting system is shown in figure 21. 8

It consists essentially of a high stability, 1 part in 10

standard, multiplier, d r iver , and a 1 kw power amplifier which connects

to and is matched to the 50 ohm antenna system.

per day, frequency

A program clock

8 It should be noted that the transmitters employed in the antarctic for

the NSF-IQSY paths a r e not identical with those used in the arct ic ,

though the power output is the same.

8

operates a keying circuit used to break the signal typically for three

minutes at half-hour intervals to permit observation of the background

noise (or interference when present) at the receiving site. The t rans-

mit ters used in the tes ts a r e of NBS design and originally ra ted at 3 kw

power output. Since tes ts were to be car r ied out at reduced power, the

t ransmit ters were modified and use 4-400 tubes instead of the original

4-1 000 tubes. Circuit diagrams of the amplifier, multiplier, dr iver ,

power supplies, and control circuits a r e presented in figures 22 through

26.

is presented in figure 27.

A photograph of the transmitter and associated control equipment

The impedance and corresponding standing wave rat io of the

antenna system at t ransmit ter and receiver installations a r e checked

periodically. A diode bridge device, standardized to 50 ohms, is used

to measure the SWR of the antenna system.

accompany the instrument.

Instruction on its use

The transmitting forward and back power a r e measured and

recorded continuously on a dual channel s t r ip chart recorder . Ful l

scale deflection of the recording pens corresponds to 1 kw average

power.

the transmitter forward power is adjusted to and maintained at this

half scale level on the s t r ip char t recorder.

is zero and will not deviate therefrom unless the antenna system becomes

detuned or differs significantly from 50 ohms in impedance. The s t r ip

char t pen recorders not only monitor signal transmissions, but keep a

record of transmitting off time a t the half-hourly breaks and other

outages and fluctuations. These recordings a r e used to correct , i f

necessary, the receiver signal-intensity data.

made in the station log as well a s on the s t r ip char t record.

Since the experiment required a maximum power of 500 watts,

The back power indication

Every day entries a r e

Information

9

relative to station location, frequency, date, antenna system behavior,

and general notes a r e recorded.

3.3 Receiving system

Monitoring and recording of the CW transmissions a r e car r ied

out with narrow-band recording equipment. A block diagram and photo-

graph of the equipment a r e presented in figures 2 8 and 29 , respectively.

The receiving and recording equipment, normally mounted and housed

in portable buildings, function as complete self-contained receiver

facilities. As such, each includes laboratory constructed receivers , a

high stability c rys ta l oscil lator, d-c amplifier, s t r ip char t pen r eco rde r s ,

associated power supplies, and line voltage regulators.

temperature controlled by electr ic heaters and air conditioning equip-

ment.

and step attenuators is used to calibrate the equipment.

Each unit is

A laboratory-constructed signal generator complete with pads

Schematic

diagrams of the calibrating signal generator a r e presented in f igures

30 and 31. A description of the receiver detailing design, circuitry,

and operation is presented i n the Appendix.

The narrow-band recording receivers , designed to operate on

an assigned frequency near 2 3 Mc/s, were designed and constructed by

the Electronics Division, NBS, Washington, D. C.

stability frequency standard controls a multiplier circuit, the output of

which is used as a local oscillator in the receiver.

a r d is commercially available.

and included with the receiver manual.

The associated high-

The frequency stand-

The multiplier circuit is described in

The transmissions a r e recorded with a receiver which has a

characterist ic post-detection bandwidth of 2 5 cycles per second.

essentially a single-conversion rece iver , with a noise figure of approxi-

mately 4dB a t 2 3 Mc/s.

It is

I t has a 1000 c / s IF and by the use of

10

special electronic techniques has an image rejection of 26 dB. The

post-detection averaging time constant is 12 seconds and serves to

smooth the rapid signal fluctuations. The second detector output is

logarithmically proportional to the receiving input voltage.

d-c amplifier provides the necessary voltage to drive a pen recorder.

At present each receiving station is equipped with two identical receivers

and three chart recorders .

brated from t40 dB above one microvolt to receiver noise, R , on two

identical pen recorders .

to 70 dB (nominal) and is primarily used to record signal intensity when

sporadic-E propagation occurs.

A built-in

One measures signal intensity and is cali-

The second receiver extends this calibration

An oscilloscope built into the receiver is used to tune the receiver

The receiver output is connected to the transmitter operating frequency.

to one s e t of deflection plates; a secondary 1000 c / s tuning fork frequency

standard is connected to the second s e t of oscilloscope plates.

resulting Lissajous pattern is used to indicate the accuracy to which the

receiver is tuned.

The

It is monitored throughout the calibration process.

The receiver calibration is made with the c rys ta l controlled

generator in se r ies with two 50 ohm step attenuators connected as shown

in figure 28.

permits calibration of the receiver in terms of antenna open-circuit 2

voltage.

where E is the equivalent antenna open-circuit voltage and R is the

characterist ic 50 ohm impedance.

The 6 dB pad (mounted inside the generator - see figure 3 1 )

The available power a t the matched antenna is equal to E /4R

A calibration is made at least once during each 24-hour interval.

The signal generator output meter i s se t to a calibration mark on the

face of the generator output meter. This level corresponds to 60 dB

11

above 1 pV or 1000 microvolts. An additional 20 dB is inserted in the

calibrating step attenuator to reduce the signal generator output to 100

microvolts or 40 dB.

to receiver noise.

The sporadic-E receiver is calibrated to a higher level, nominally 70 dB

above 1 pV, to permit a n adequate display of high-intensity sporadic-E

signals.

The calibration is made in 5 dB steps f rom f 4 0 dE3

A sample calibration chart is presented in figure 32.

The pen recorders , with a chart speed drive of three inches per

hour, a r e used to t race s t r ip chart records of signal intensity and back-

ground noise levels.

a r e written on the chart by the operator.

transmission line impedance, date, time, observer ' s initials, and

other information such as antenna S W R , weather, interference, and

equipment o r antenna malfunctions.

During the course of recording, pertinent data

These include: path, frequency,

The s t r ip char ts a r e removed from the recorder daily. Each

chart represents a 24-hour record of data start ing and ending at 0000

hours UT.

transmitter as well as receiver stations a r e sent t o the sponsoring

agencies for further scaling and analysis. In Alaska, all data a r e sent

to NBS, Boulder, Colorado. In Canada, all data a r e sent to the Bartol

Research Foundation, Swarthmore, Pennsylvania.

zation is responsible fo r the operation and maintenance of the Canadian

path.

At the end of each week the s t r ip char t recordings from

The latter organi-

4. Summary

Fully equipped t ransmit ter and receiver facilities for three

forward scat ter tes t paths in the arct ic were installed in order to

permit studies of low energy (roughly 1 0 to 300 MeV) solar cosmic ray

events. The antenna systems a r e sited over nearly flat ground or water,

12

particularly including a n a r e a occupied by the f i r s t F r e s n e l zone. Yagi

antennas , exhibiting moderate gain and beamwidth character is t ics , a r e

used at the transmitting and receiving sites.

recordings are made of CW transmissions at the receiver locations.

The resulting data are analyzed and absorption effects in signal levels

a r e used to identify so la r cosmic r a y events and to determine the

variation with time of the intensity of the solar cosmic rays above

magnetic cutoff o r atmospheric cutoff (about 10 Mev), whichever is

higher.

Continuous signal intensity

5. Acknowledgements

Appreciation is extended to D. C. Whittaker and W. B. Harding

for their valuable ass is tance in regard to instrumentation of the t rans-

mitting and receiving equipment.

6. References

Bailey, D. K. (1962), The detection and study of solar cosmic rays

by radio techniques , J. Phys. S O C . Japan, - 17 , Supplement A - 1

(1 962 International Conference on Cosmic Rays and the Ear th

Storm ) . Bailey, D. K. (1964), Polar -cap absorption, Planetary Space Sei. 12, -

495-541.

Bailey, D. K . , R. Bateman, andR. C. Kirby (1955), Radio t rans-

missions at V H F by scattering and other processes in the

lower ionosphere, Proc . IRE 4 3 , No. 10, 1181-1230. - Merril l , R. G. (Sept. 10, 1958), Radiation patterns in the lower

ionosphere and F r e s n e l zones for elevated antennas over

spherical ear th , NBS Report 5599.

Merril l , R. G. (March 18, 1959), Optimum antenna height for

ionospheric scat ter propagation, NBS Report 6047.

13

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14

k rd a, 5 d

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k a, c1 c, rd u m a k

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tc

17

18

9 k fd Q)

Q) s! id %-I a rd k a, 3 0

0 a,

N

a, k!

NOTE TRUE NORTH AS SHOWN HERE IS BASED ON THE

- ..

BEARINGS OF U.S. SURVEY NUMBER 4615.

/

EC-I

P

\ma$,!, & - - G R b V E L AREA

xy -'&SHACK ON SKIDS

\

Figure 3 . Topographic map of the Barrow transmitter si te

19

F: 0

W 0

$I

PI cd k M 0 0 A PI

c,

2 0

Figure 5. Photograph of the antenna installation a t Barrow, Alaska

21

Figure 6. Topographic map of Anchorage a rea showing location of receiver ins tallation

22

2 2 (I]

Id

.b

a, M Id k 0

2 4 c, Id r c, .r( A .rl V Id +I

k a, 3 a, V a, k a,

.r(

5 w 0 A a Id k M 0 0 A @I

c,

F a,

2 M

.r(

cr

23

24

i

. .

Figure 9. Photograph of the transmitter installation at Annette Island, Alaska

2 5

I"

I .

d 4

a, k

26

i

Figure 11. Photograph of the receiver facility near Fairbarlks, Alaska

27

Figure 12. Topographic map of the West 40 site showing location of the transmitter facility at Frobisher Bay, Canada

-. a

. . m F: cd k c,

a, 5 w 0 SI a rd k M 0

d .rl

2 9

'I

.**

Figure 14. Photograph of the antenna installation a t Frobisher Bay, Canada

3 0

N

Figure 15. Map of the Grea t Whale River a r e a showing location of the receiver si te

31

cd a rd d Id u k a, ?

2

M c

k a, ? a, u a, k

.d

3 2

rl b

Figure 17. View of the antenna installation a t Great Whale River, Canada

3 3

Figure 18. The 23 Mc/s five-element Yagi antenna design showing dimensions, mounting, and connection details

Figure 19. Radiation pattern in the E-plane of the five-element 0. 8 wavelength long Yagi afitenna (Deflection proportional to voltage)

35

Figure 20. Radiation pattern in the H-plane of the five-element 0. 8 wavelength long Yagi antenna (Deflection proportional to voltage)

36

J

\ Antenna Impedance Matched to !jO ohm

Dir . Coupler A

Figure 21. Block diagram of the transmitting system

Therm Them

37

Overload Reset Clock Keyer

RF Amplifier

i -- 4

. r

b - Meter

Driver

w J

DU,d Str ip Chart Recorder r

I .r

I . M u l t

P

4 3 d

3 8

1 a

"t

3 9

+ P P 3

4

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cd

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41

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a,

w 0

cd k M rd a u rd

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9 c\l

a, k

23 .rl

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42

Figure 27. View of the power amplifier and associated control equipment

43

p t Recorder

I i

Calibrating 0-12 db 0-120 db signal 6db - ldb Step ,- lOdb Step

Generator Pad Attenuator Attenuator

coaxlal cable with double stub tuner

c.c To HybrJ.d Input

Attenuator

.- I Sporadic-E Strip Scatt el:

Receiver Recorder Receiver 1000 cycle -

Tuning Fork -

. DC Amp1 Scope d i DC ~ m p l scope

msqumw b

Multiplier i

Frequency Standard

1 Indicator I

F igure 28. Block diagram of the receiving system

44

Figure 29. Photograph of the receiving equipment 4 5

E Id k M

k 0

m a Q

0 d d

0 m

46

nn 73-0 0

x 0 m

W + 3 a

a 0 s 1

m W

G 0 0

[r)

k cd a d

+

c,

a,

a 0 0 w 0

E

.rl c, rd 0 0

M 4

-$ 0 A cn k 0 cd k a,

M

rd d M

c,

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al .d

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e-l rc)

a, k 5 M

G-l .d

47

m a, a c rl

N cc)

48

Appendix

Nar r ow-B and Heterodyne Recording Receiver Instructions

G. Franklin Montgomery

1. Summary

The receiver , represented in figures A-1 through A-8, is

designed to record the amplitude of a continuous wave 24 Mc/s radio

signal,"' The 50 ohm antenna feeds a 12AU7 cascode amplifier a t

24 Mc/s.

plate coil is L4.

rejecting a local transmission.

backed all the way out (counterclockwise).

The input coil is L2, the cathode coil is L3, and the cascode

Coil L1 is a shunt antenna trap, to be used only for

When not used, its slug should be

The 12AU7 cascode stage feeds a 6BJ6 pentode a t 24 Mc/s. I ts

plate coil is L5, which is a lso loosely coupled to L6.

a pair of diode balanced mixers.

for these mixers is generated by the frequency multiplier on a separate

1 3/4-inch panel.

L5 and L6 feed

The 12 Mc/s local-oscillator voltage

The R F circuits L2 through L5 should be peaked on a high-side

24 Mc/s signal.

simultaneously (two hands) adjusted to null a low-side 24 Mc/s signal.

L6 and the IMAGE NULL potentiometer a r e then

The diode mixers feed audio phase-shift circuits and transistor

amplifiers that combine the mixer outputs and deliver the combination

to a BNC output connector a t 1 kc. This output then passes a narrow-

band filter and is fed to the 1 kc IF amplifier.

The IF amplifier begins with three triode-connected 6BJ6 stages.

The first stage i s shock mounted.

(headphones, loudspeaker, and monitor oscilloscope input).

:::The receiver tunes to a fixed frequency in the 23 to 24 Mc/s range.

A 12AU7 section is used for audio

The other

49

triode section drives a balanced diode detector, yielding both negative

and positive d-c outputs.

positive output operates the 12AU7 recording meter amplifier.

The negative output is used for AVC. The

In the linear position (up) of the front-panel LINEAR/AVC

switch, there is no AVC, and the receiver gain is controlled entirely

with the IF GAIN control, which follows the first 6BJ6 I F stage.

Maximum full-scale Esterline-Angus (E-A) meter sensitivity is

approximately 0. 2 microvolt (open-circuit 50 ohms), although this

voltage depends considerably on antenna input circuit adjustment, etc.

Several AVC character is t ics a r e available. In the AVC position

(down) of the LINEAR/AVC switch, the three 6BJ6 triodes receive

negative signal bias.

with the AVC LEVEL control, permitting expansion of the meter scale.

If more compression is wanted, or i f strong signals a r e to be recorded,

bias can be applied additionally to the 6BJ6 R F stage through the AVC

toggle switch on the R F chassis.

front-panel LINEAR/AVC switch is in the linear (up) position.

The relative amount of this bias is adjustable

Al l AVC bias is removed when the

The zero adjustment for the 12AU7 meter amplifier is on the

front panel (METER ZERO).

overcome static friction of the E-A pen.

the IF chassis terminal s t r ip a r e a t t100 volts and should be avoided

with the power on.

A small dither at 60 c / s is introduced to

The E-A meter terminals on

2. Operating Data

Power supply:

30 milliamperes d-c at t 100 volts, regulated.

2.1 amperes a-c a t 6.3 volts, 60 c / s .

10 watts a t 117 volts, 60 c / s .

Antenna impedance: 50 ohms, unbalanced.

5 0

Recorder: 1 mil l iampere, 1400 ohms, Esterline -Angus, Model AW.

Terminals:

F r ont pane 1

Antenna (ANT), type BNC coaxial connector.

Headphones (PHONES), standard phone jack.

R F chassis

Antenna (ANT), type BNC coaxial connector.

Local-oscillator input (12 Mc/s IN) , type BNC.

Intermediate-frequency output (1 kc OUT), type BNC,

connected to input of band-pass fi l ter .

Band-pas s filter

Intermediate-frequency input (1 kc IN) , type BNC.

Intermediate-frequency output (OUT), type BNC, connected

to 1 kc input of IF chassis.

IF chassis

1 kc input, unmarked, type BNC.

AVC line external connection (RF AVC), sc rew terminal.

1 kc signal fo r monitor oscilloscope (SCOPE), connected to

terminal (V) on oscilloscope amplifier, sc rew terminal.

Direct - current signal for E s terline -Angus recorder (METER),

sc rew terminals. CAUTION: These terminals a r e at

+ l o 0 volts to ground.

1 kc signal for 4 ohm loudspeaker ( S P K ) , sc rew terminals.

Cathode -f ollower direct - cur rent signal output (AUX ), sc rew

terminals.

to ground.

recorder other than the Esterline-Angus.

This output is offset approximately t4 volts

It is provided a s an auxiliary signal f o r a

51

Oscilloscope amplifier chassis

Vertical deflection (V) and horizontal deflection (H) inputs,

s crew terminals . Controls:

Front Panel

AUDIO GAIN controls the 1 kc signal amplitude delivered to

the monitor oscilloscope, headphones, or loudspeaker.

It has no effect on other receiver adjustments.

AVC LEVEL controls the amplitude of direct voltage used as

AVC grid bias for the variable-gain stages.

amplitude of this bias is maximum with the AVC

LEVEL control full counterclockwise.

The

AVC FILTER switches the capacitance in the smoothing o r

averaging circui t that follows the detector.

constant of this c i rcui t is 30 seconds with the switch

The time #C

on (up) and 0. 30 seconds with the switch off (down).

METER ZERO adjusts the zero-signal or r e s t position of the

recorder pen.

LINEAR/AVC switches the receiver from linear recording to

LINEAR i s up. approximately logarithmic recording.

IF GAIN controls the gain of the IF chassis beyond the first

stage. Ful l gain is full clockwise.

RF chassis

AVC switches the gr id bias of the 6BJ6 amplifier ( V 2 ) f rom

fixed to AVC bias.

is on (up).

Bias is applied when the switch

IMAGE NULL is an alinement adjustment made in conjunction

with L6. See R F chassis circuit description.

::The time constant of this c i rcui t was changed to 15 seconds.

52

Tube and transistor complement:

4 e a . 6BJ6

5 ea. 12AU7

3 ea.

3 ea. 2N1396

1 ea. l E P l (cathode-ray tube)

2N414 (Satisfactory substitutes: 2N404, 2N1305)

3 . General Description

The receiver described here is designed to record the amplitude

The receiver band- of a fading, continuous wave, 24 Mc/s radio signal.

width is approximately 25 c / s .

to the receiver is amplified, converted to intermediate frequency (IF),

fi l tered, rectified, time-averaged, and used finally to deflect the pen

of a s t r ip char t recorder .

ally to be either (a) linearly proportional to an average of signal

amplitude or (b) approximately proportional to the logarithm of an

average of signal amplitude.

A radio-frequency (RF) signal supplied

The pen deflection can be chosen option-

An essentially s imilar receiver was developed previously a t

the National Bureau of Standards fo r use a t 50 Mc/s and 36 Mc/s. In

designing the present receiver , the objective was to improve both the

electrical design and the mechanical construction of the original set.

The prior receiver (not including its local oscil lator) required a local-

oscillator voltage of exceptional spectral purity, used thirteen vacuum

tubes of three types, and was annoyingly microphonic. In comparison,

the present se t requires no special purity of its local-oscillator voltage,

uses three t ransis tors and seven vacuum tubes of two types, and is

much less microphonic,

tube receiver and is mechanically sturdier.

I t occupies less volume than the all-vacuum-

A separate frequency

53

multiplier is included to provide the local-oscillator voltage from a

stable source at approximately 1 Mc/s. It uses three t rans is tors and

obtains its power from the receiver chassis.

4. Theory of Operation

The antenna signal is first amplified at radio frequency (see

block diagram).

whose output voltages differ by 90 degrees.

separately converted to intermediate frequency ( 1 kc) in a balanced

mixer, with both mixers using the same local-oscillator voltage.

two 1-kc signals a r e modified by a pair of resistance-capacitance

phasing networks and a r e then added in a common amplifier.

It is then modified in phase by a pair of tuned circuits

Each of these outputs is

The

The purpose of the twin frequency conversions, i n combination

with the R F and IF phase shifts, is to eliminate the receiver image

response that lies 2 kc from the signal frequency in the direction of the

24 Mc/s harmonic of the local-oscillator frequency.

net phase difference produced by the R F and IF networks determines

whether the signal will be accepted above or below the local-oscillator

harmonic frequency.

by either pair of networks r eve r ses this relationship.

The sense of the

Reversing the sense of the phase change produced

The combined IF signal is fi l tered by a band-pass filter whose

response is centered a t 1 kc.

the receiver ' s selectivity and bandwidth.

It is this f i l ter that chiefly determines

Following the fi l ter i s a relatively unselective resis tance-

coupled amplifier.

tubes.

signal amplitude when automatic -volume-control (AVC) gr id bias is

used.

Its f i r s t three stages use remote-cutoff vacuum

Their output is approximately proportional to the logarithm of

The output voltage of the amplifier is rectified and filtered. It

54

is then used as AVC bias and as the input to a direct-coupled amplifier

that de fle c t s the r e cor ding mill iammeter . A separate monitor amplifier, using the 1-kc signal a s i t s

input, provides inputs for a monitor oscilloscope and for headphones.

5. Circuit Description

Radio-frequency chassis

The two sections of a 12AU7 a r e connected a s a cascode ampli-

f ier (VI).

relatively long gr id base or bias range.

a gr id bias of approximately 2. 5 volts, and this relatively large bias

should be helpful in preserving immunity to overload or desensitization

from strong adjacent-frequency signals.

A 12AU7 has only moderate transconductance, but it has a

Both sections a r e operated at

The required source (antenna) impedance is 50 ohms, one

terminal grounded.

coupling capacitor a r e tuned for minimum noise figure, an adjustment

that is made most conveniently using a thermionic diode noise source.

Inductor L1 and its 7-45 pF ser ies capacitor comprise a shunt

The input inductor L 2 and the adjustable 7-45 pF

t rap for rejecting interference at one frequency.

capacitor and the inductor a r e adjustable, it is possible to set the

rejection frequency within a wide range above and below 24 Mc/s. If

the rejection frequency is close to 24 Mc/s, then the t rap setting and

the settings of L2 and its coupling capacitor will interact.

adjustments a r e required in this circumstance so that the signal

sensitivity will not be degraded.

capacitor should be s e t near minimum capacitance and L1 should be

se t near minimum inductance (screwdriver adjustment full counter - clockwise). Inductors L3 and L4 a r e both tuned to signal frequency.

The tuning of L3 will appear to be relatively broad.

Since both the ser ies

Careful

When the t rap i s not used, i ts se r ies

55

The gimmick capacitor is intended to neutralize the internal

capacitance f rom plate 6 to grid 2.

fed through the partition astr ide the 12AU7 socket) is not especially

critical.

sharp tuning of L2 and L4. In this case, the stage will be found to

oscillate with the feedthrough wire s e t either close to or far from the

winding of L2.

located by trial, and the wire should then be se t halfway between them.

Its adjustment (by bending the wire

Maladjustment is indicated by R F oscillation or by very

These positional extremes of oscillation should be

The second section of the 12AU7 is a lso used as a source of

direct current for the receiver ' s t ransis tor stages (at t 12 volts) and

for the transistor stages in the frequency multiplier (at t 6 volts) for

the local -oscillator voltage. Grid 7 is returned to a voltage divider

at approximately t12 volts, and the d-c drop in the cathode network is

used as the transistor supply.

is approximately 5 milliamperes.

The plate current for each 12AU7 section

A 6BJ6 pentode amplifier (V2) follows the cascode. This stage

is neutralized by returning i t s sc reen grid to a low-potential point of

the tuned plate circuit L5.

the 1. 5 - n F bypass capacitor and is out of phase with the voltage at the

plate.

acting upon the grid-plate capacitance is neutralized by an opposite

current due to screen voltage acting upon the grid-screen capacitance.

The choice of screen bypass capacitance is not critical, and this stage

is quite stable. The control-grid d-c re turn connects to a toggle switch

so that AVC bias can be applied to this stage when wanted. With the gr id

re turn grounded, the cathode cur ren t is approximately 7 milliamperes.

The voltage at this point is determined by

Consequently, the grid-circuit current due to plate voltage

56

Tuned circuit L6 is loosely coupled to L5, and each circuit

drives a balanced mixer formed of a pair of point-contact germanium

rectifiers.

90 degrees) the signal voltage developed at L5.

driven by a 12 Mc/s local-oscillator input supplied from L7.

optimal amplitude of this 12 Mc/s voltage, the d-c drop across each

rec t i f ie r ' s 4.7K load res i s tor is approximately 0. 5 volt.

drop is not cri t ical , and it is more important that all four drops be

equal than i t is that they be exactly 0. 5 volt.

When L6 is tuned properly, i ts signal voltage leads (by

Both mixers a r e a lso

F o r an

This voltage

The outputs of the mixers a r e at audio frequency (1 kc) and a r e

balanced to ground.

phase shifter, the phase-shifter constants being chosen to produce a

differential shift of 90 degrees between the two network outputs at 1 kc.

Transis tor emitter-follower amplifiers Ql and Q2 combine the two

outputs proportionally in the potentiometer labeled IMAGE NULL, and

the combination is amplified by the transistor common-emitter stage Q3.

Each output is fed to a resistance-capacitance

The transistor stages a r e direct-coupled, and the collector

direct current of the output transistor Q 3 remains at approximately 1

milliampere regardless of moderate changes in t ransis tor parameters.

Note the 100-ohm degenerative emitter res is tor in the output stage.

This res i s tor i s located at the output end of the mixer c i rcui t board

and is a convenient means for adjusting the overall amplification of

this section of the receiver.

To aline the R F section, adjust circuits L2 through L5 for

maximum receiver output using a 24 Mc/s input signal whose frequency

is 1 kc above the 24 Mc/s harmonic of the local oscillator source. Ad-

just c i rcui t L7 for maximum receiver output, although this maximum

will be very broad if the frequency multiplier has been properly tuned.

57

Retune the signal source to a frequency 1 kc below the local-oscillator

harmonic.

ously for minimum output.

Inter mediate -fr equency fi l ter

Adjust L6 and the IMAGE NULL potentiometer simultane-

The band-pass fi l ter couples the 1-kc output of the RF chassis

The filter produces a resonant voltage to the input of the IF chassis.

amplification; at 1 kc, the rat io of IF chassis input voltage to RF

chassis open-circuit output voltage is approximately 4.

The fi l ter contains two tuned circuits using toroidal inductors.

Careful init ial tuning of the filter yields a half-power bandwidth of

25 c / s .

Intermediate -frequency chassis

The IF amplifier consists of three resistance-coupled stages

using 6BJ6 tubes connected a s triodes (V3, V4, V5) and a fourth stage

using one section of a 12AU7 (V6A). The f i r s t 6BJ6 is shock-mounted

to reduce its microphonic response to vibration.

resistance-capacitance networks provide a broad band-pass character - ist ic centered approximately a t 1 kc.

balanced detector yielding equal positive and negative output voltages.

Each voltage is fi l tered in a low-pass RC section whose t ime constant

can be s e t a t ei ther 0 .30 second or 30 seconds. The negative voltage

can be used either in full or partly attenuated a s AVC bias for the 6BJ6

stages, including the R F stage V2 i f wanted.

The interstage

The fourth stage V6A drives a

*

The positive voltage drives gr id 2 of a 12AU7 balanced amplifier

(V7) for the recording meter.

to critically damp an Esterline-Angus 1 -milliampere recorder move-

ment.

signal to overcome the static friction of the recorder pen.

'%The time constant was changed to 15 seconds.

Amplifier resistances have been chosen

Approximately 1 volt a t 60 c / s i s applied to gr id 7 a s a dither

58

The 1-kc output of V5 is separately amplified by a 12AU7 section

(V6B) and is available for driving the monitor oscilloscope , headphones,

loudspeaker, or for other uses.

Frequency multiplier

If the receiver is to operate successfully with a bandwidth of

25 c / s , the local-oscillator voltage required by the balanced mixers

must be stable in frequency. It is assumed that the receiver will be

used with a stable oscillator at approximately 1 Mc/s as the ultimate

source of the local-oscillator voltage.

generates the twelfth harmonic of this 1 Mc/s voltage for use as the

local-oscillator input.

harmonic of the 12 Mc/s input must be 1 kc less than the signal

frequency. The oscillator frequency F for a given signal frequency

F is therefore

The frequency multiplier

With the mixer circuit shown, the second

0

S

F = (1/24) (F - l ) , 0 S

where both frequencies a r e in kilocycles per second.

The multiplier consists of three stages. In each stage, a

harmonic of the input to that stage is first generated by a rectifier

network, is then fi l tered, and finally is amplified by a tuned class-B

transistor amplifier.

when there is no input. F o r full output, the 1 Mc/s input required is

approximately 1 volt ac ross 50 ohms, or 20 milliwatts.

The t ransis tors Q4, Q5, Q6 draw no current

T o aline the frequency multiplier , begin at the 1 Mc / s input

end and connect a d-c vacuum-tube voltmeter to the neares t tes t

point. Adjust L1 for maximum voltmeter reading. Connect the volt-

meter to the second tes t point and adjust L2 and L3 for maximum

readings. Connect to the third tes t point and adjust L4 and L5 for

59

maximum.

maximum. Voltmeter readings a t all tes t points normally range from

3 to 6 volts.

Oscilloscope amplifier

Connect to the last tes t point and adjust L6 and L7 for

A Millen No. 90911 oscilloscope is included for use as a tuning

aid. A 1-kc source, with which the band-pass filter has been previously

alined, supplies the horizontal deflection signal. The vertical deflection

signal is supplied by the r ece ive r ' s IF amplifier.

indicated by an elliptical oscilloscope trace.

should not be used, as the small cathode-ray tube screen burns easily.

Correct tuning is

A very bright dot or t race

Both deflection signals must be amplified to produce usable

deflections.

input to balanced-output amplifiers.

a phase inverter (V8, V9).

approximately 20.

The amplifier chassis contains two separate unbalanced-

Each uses a 12AU7 connected as

The overall voltage amplification is

6. Electr ical Measurements

The following measurements are typical. F rom one receiver to

another, differences in voltages and currents of as much as twenty per-

cent can be expected because of component variations.

ment deviations a r e suspect and may be due to component aging or

failure.

voltage reference.

voltmeter whose input resistance is 10 megohms.

IF chassis

Larger measure-

All voltage measurements are made with ground as the zero-

D-c measurements a r e made with a vacuum-tube

The d-c detector voltage E is the voltage measured a t the

junction of one diode rectifier terminal and its 150K load res i s tor .

One diode produces a positive E d;

d

the other diode produces an equal

6 0

but negative E E is the r m s voltage of the 1-kc input measured at d' i n

the IF chassis input connector with the band-pass filter disconnected.

With the LINEAR/AVC switch i n the LINEAR position (up), IF

GAIN control full clockwise, t h e detector voltage for full-scale (1 -mA)

deflection of the Esterline-Angus (E-A) recorder is:

E d = 6 volts

E. = 1. 2 millivolts in

At the point where the amplifier begins to overload:

Ed = 18 volts

E = 3 . 6 millivolts. in

With the LINEAR/AVC switch in the AVC position (down) IF

GAIN full clockwise, AVC LEVEL maximum (full counterclockwise),

and full-scale E-A recorder deflection:

E = 60 millivolts. in

F o r one -tenth - scale r e c or der deflection:

E = 100 microvolts in

With the LINEAR/AVC switch in the A V C position, IF GAIN

full clockwise, AVC LEVEL minimum (full clockwise), and full-scale

E-A recorder deflection:

E = 7 millivolts. in

F o r one-tenth-scale recorder deflection:

E = 9 0 microvolts. in

61

F o r calculation purposes, the voltage amplification of the 1 -kc

band-pass filter is 4.

circuit voltage of a 2000-ohm, 1-kc source required to produce the out-

puts in these examples is E

R F chassis

Therefore , with the filter in the circuit , the open-

divided by 4. in

The gain of the R F chassis is fixed, in that no controls a r e

provided for adjusting it routinely, with one exception.

is the optional use of AVC at the second R F amplifier V2.

however, to adjust the overal l amplification by a factor of 3 to 4 with a

simple modification.

emitter of the output t ransis tor Q3.

reduce the amplification; reducing the resistance will increase the

amplification. Typically, short-circuiting the res i s tor increases the

amplification by a factor of 3 .

with the 100-ohm res i s tor short-circuited.

The exception

It is possible,

A 100-ohm res i s tor is shown in se r i e s with the

Increasing this resistance will

The following measurements were made

The gain of the R F chassis also depends on other adjustments,

especially upon the settings of the antenna input circuit and rejection

trap.

the band-pass filter in place.

minimum noise figure, which was 4 decibels.

circuit voltage of the 50-ohm source.

In these measurements , the receiver was operated as a unit with

The antenna circuit was adjusted for

Elf is the r m s open-

With the LINEAR/AVC switch s e t to LINEAR (up), IF GAIN

full clockwise, the full-scale E-A recorder deflection:

= 0 .2 microvolts.

With the IF GAIN reduced to accommodate greater inputs, the first IF

stage V3 begins to saturate with:

E = 100 microvolts. r f

6 2

With the LINEAR/AVC switch se t to AVC (down), R F AVC off

(down), IF GAIN full clockwise, AVC LEVEL full counterclockwise, and

full- scale recorder deflection:

= 10 microvolts. r f

E

With the IF GAIN reduced to accommodate greater inputs, the t ransis tor

amplifier Q 3 begins to saturate with:

= 1 millivolt. r f

E

With the LINEAR/AVC switch se t to AVC (down), R F AVC on

(up), IF GAIN full clockwise, AVC LEVEL full counterclockwise, and

full- scale recorder deflection:

= 150 microvolts. Erf

With the IF GAIN reduced to permit greater inputs, the R F amplifier

begins to saturate with:

= 5 millivolts. rf

E

An important resu l t is i l lustrated by this s e r i e s of measurements.

F o r any setting of the receiver controls and for any choice of circuit

adjustments (such as the value of emitter res i s tor for Q3), there is a

certain antenna input that will produce receiver overload.

record is to be valid, the receiver must be operated well below over-

load.

the observed signal i s strong or weak, whether it fluctuates over a

large dynamic range or a smal l one, and to adjust the receiver to

accommodate this range below i ts overload input voltage.

If the signal

Consequently, i t is most necessary to take into account whether

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