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NBSIR 78-880

UHF IMPULSE GENERATOR

James R. Andrews

Eugene E. Baldwin

Electromagnetic Technology Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

April 1978

NBSIR 78-880

UHF IMPULSE GENERATOR

James R. Andrews

Eugene E. Baldwin

Electromagnetic Technology Division

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303

April 1978

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

I. INTRODUCTION 1

II. SPECIFICATIONS 2

III. OPERATION 3

IV. CIRCUIT DESCRIPTION 6

V. CONSTRUCTION 12

VI. COMPONENT SELECTION 17

VII. ADJUSTMENTS 18

VIII. MODIFICATIONS 19

IX. PARTS LIST 20

REFERENCES 25
LIST OF FIGURES

Figure 1 NBS UHF Impulse Generator.

Figure 2 Typical waveform of an NBS UHF Impulse Generator. Vert: 10 v/div.;

Horiz.: 2 ns/div. (top) and 200 ps/div. (bottom).

Figure 3 Typical spectrum of an NBS UHF Impulse Generator. Vert.: 10 dB/div.,

log ref level = +30 dB/div., 3-MHz bandwidth; Horiz.: 100 MHz./div.

dc to 1500 MHz.

Figure 4 Avalanche transistor circuit.

Figure 5 Clock and delay circuit.

Figure 6 High voltage regulator circuit.

Figure 7 Power supply circuit.

Figure 8 Top view of the chassis.

Figure 9 Bottom view of the chassis.

Figure 10 Printed circuit board layout. 1:1 scale. (a) Top side. (b) Bottom

side. Double-sided, copper-clad, 1.6-mm thick, G-10 f igerglass-epoxy

board. Dark areas indicate regions where the copper cladding is

removed. Finished board size is 15.3 cm x 17.8 cm. Figure 11 Several views of the component layout of the Q2 Impulse forming circuit,

i V
UHF IMPULSE GENERATOR

James R. Andrews and Eugene E. Baldwin

This UHF Impulse Generator generates a narrow impulse with a flat

spectrum up to 1 GHz. The impulse amplitude is 55 volts and the duration

is 365 ps. The maximum repetition rate is 1 MHz. This report describes

the generator in detail and includes a complete parts list and printed

circuit artwork.

Key Words: Avalanche transistor; impulse; impulse generator;

pulse generator; spectrum; spectrum amplitude.

I . INTRODUCTION

The NBS UHF Impulse Generator (IG) , figure 1, generates a narrow impulse

with a flat spectrum up to 1 GHz. The complete specifications are listed in the

next section. The major features are a +55 V, 365 ps impulse and a 1 MHz repetition rate. It was originally designed by the Signal Waveform Metrology Group

for the NBS EM Sensing Metrology Group in its time domain testing program for

locating buried objects. Additional units have also been built for the EMIRadiation Hazards Group for use with its TEM cells and for the Signal Waveform

Metrology Group's time domain antenna range. This report describes the circuit

in detail and gives a complete parts list and a mechanical layout.

Figure 1. NBS UHF Impulse Generator.
II. SPECIFICATIONS

Table 1. Specifications

Amplitude

Polarity

Baseline

Duration (50%)

Source Impedance

Spectrum Amplitude, S(f)

Spectrum Ripple

Frequency Range for S(f) Spectrum

Impulse Output

55 V, ±10%, into 50 9. Positive

0 V

365 ps, ±10%

50 fi, nominal

90.5, ±2 dByV/MHz

±1.0 dB

100 MHz to 900 MHz

Repetition Rate, Trigger and Timing

Internal Repetition Rate

Repetition Rate Vernier

Ext. Sync. Input:

Frequency

Pulse Required

' Polarity ^ ^ i - ^jv

Input Loading j.; ^

. Trigger Output Pulse:

Amplitude

Polarity

Baseline

Transition Time (10%-90%)

Duration (50%)

Timing

Jitter

10 Hz to 1 MHz in 5 ranges

0.1 to 1 range

DC to 1 MHz, frequencies in excess of

1 MHz will be internally limited to

approximately 1 MHz maximum.

Standard TTL pulse

0 V < "0" < 0.8 V

2 V < "1" < 5 V

Trigger occurs on positive going transition

330 Q.

0.5 V into 50 9, Positive

0 V

2 ns nominal

80 ns Leading edge of trigger pulse is 80 ns

in advance of impulse output. ^ 20 ps nominal jitter in the delay

between the trigger output pulse and the

impulse output

General

Supply Voltage

Size

117 V, ±10%, 60 Hz

21 cm X 17 cm X 28 cm

2
III. OPERATION

The operation of the NBS UHF Impulse Generator (IG) is quite straightforward. There are only three controls, figure 1; namely, the power switch, the

repetition rate range switch, and the repetition rate vernier. Two signal

outputs, impulse and trigger, are provided along with an external sync, input.

A typical impulse waveform and spectrum for the NBS UHF Impulse Generator

are shown in figures 2 and 3. For time domain applications and for verifying

the impulse waveform, the auxiliary trigger pulse output is used. This is a positive going 0.5 V pulse that is 80 ns in advance of the impulse. This pulse

can be used for triggering a sampling oscilloscope or other instrumentation.

The NBS UHF IG's are calibrated by measuring the impulse voltage waveform

delivered to a 50 9. load connected to the impulse output connector on the front

panel. The spectrum amplitude, S(f), at the output is then computed from the

waveform using the Fourier transform [1,2]. S(f) can be determined by consulting the calibration report for the particular instrument. For frequencies not

included in the calibration report, it is normally acceptable to extrapolate

from the nearest calibration frequencies.

The IG can also be used for the calibration of a Field Intensity Meter

(FIM) . The IG's impulse output is simply connected to the FIM's antenna input.

For some FIM's it may be necessary to insert a wideband coaxial attenuator to

avoid overloading or destroying the FIM. For FIM's with a preselector-tuned

circuit before the first active element (transistor, diode, etc.), an attenuator

will probably not be necessary. However, some FIM's use a wideband preamplifier,

and some spectrum analyzers have no input preselection but apply the input

signal straight to the first mixer. In these cases it is usually necessary to

use an attenuator. A preselector filter between the generator and the FIM is

also sometimes useful for limiting the peak voltage applied to the FIM. When an external preselector filter is used, it should have padding attenuators on each

side. The amount of attenuation required is dependent upon the filter characteristics . When all connections are made, the power switch is then turned on, and the

repetition rate control is set to the desired repetiion rate. The maximum repetition rate is determined by the bandwidth, W, of the FIM being calibrated.

PRR(max) < BW/5.
lOOtiV 2t)S

Figure 2. Typical waveform of an NBS UHF Impulse Generator

Horiz.: 2 ns/div. (top) and 200 ps/div. (bottom)
1

Figure 3. Typical spectrum of an NBS UHF Impulse Generator. Vert.: 10 dB/div.,

log ref level = +30 dB/div., 3-MHz bandwidth; Horiz.: 100 MHz/div.,

dc to 1500 MHz.

5
IV. CIRCUIT DESCRIPTION

This generator forras an impulse using the classical technique of discharging a short transmission line [3]. An avalanche transistor is used as the fast

switching element to discharge the line [2,4]. The circuits for the UHF IG are shown in figures 4 through 7. Figure 4 shows the heart of the IG; namely, the

avalanche transistor circuitry in which the impulse is formed. Q2 is the output

transistor and is operated in the avalanche mode with the base to emitter shorted

via RFCl and with +140 V applied to the collector through 13 kfi. Delay line,

DLl , is charged to the B+ voltage (typically 140 V) through the string of resistors (DL2 and the 4.3 kfl). A large triggering pulse is applied to the baseemitter junction of Q2. This causes Q2 to go into avalanche breakdown and thus

rapidly discharge DLl into the 50 Q, output load and the internal 50 Q termination (R2 and R3 in parallel). The waveshape of the output impulse is determined

by the length and irapedence profile of DLl. The small inductors, Ll and L2,

also provide some peaking to increase the impulse amplitude. The B+ feedline,

DL2, critically affects the low level perturbations on the impulse baseline and,

as a result, the ripple on the impulse spectrum. DL2 is a lossy distributed

transmission line made up of six, 1/8 W resistors. It arches up and away from

Q2 and the circuit board, figure 11. It also contains RFC2, which is three

ferrite toroids slipped over the first resistor. A 150 Q, termination for DL2 is

supplied by R6.

The driving pulse for Q2 is generated by Ql, which is also an avalanche

transistor. Capacitor Cl is charged to +100 V through the 1 kfl resistor. The

negative 80 ns pulse from IC2a is differentiated by C2 . The positive spike from

the trailing edge of the 80 ns pulse is used to trigger Ql into avalanche breakdown. Cl then discharges the 51 Q, resistor and the pulse transformer through

Ql. The large 100 V) pulse from Cl is coupled through the transformer to Q2.

The secondary of the transformer is floating with respect to circuit ground.

Thus, terminals 1 and 3 produce, respectively, a positive and a negative going

pulse which is coupled to the base-emitter junction of Q2 through the 1 kfl resistors, R4 and R5. This differential drive pulse produces a large turn-on

base current for Q2, and yet is well balanced with respect to ground, producing

a negligible signal on the impulse output line. R4 and R5 are chosen to be

large, compared with R2 and R3, to produce negligible loading of the output

impulse.

6
The clock and delay circuits are shown in figure 5. ICl and IC2 are Schottky TTL, dual, monostable multivibrators. ICla and IClb are interconnected

to form an astable multivibrator that functions as the generator clock. Clock

frequency ranges from 10 Hz to 1 MHz are chosen by changing the timing capacitors with S2. A 10:1 vernier is supplied by Rl6a and Rl6b. The clock output

(IClb, pin 10) is connected to the delay monostable IC2a through S2c. The

positive going transition of the clock square-wave triggers IC2a, which then

generates an 80 ns pulse. The 80 ns Q pulse drives a 10 mA tunnel diode through

a 100 Q. resistor. The tunnel diode shapes it into the 500 mV, 2 ns transition

time trigger output pulse. The 80 ns Q pulse is used to drive Ql as described

earlier. It also triggers IC2b, which in turn generates a 0.9 ys pulse. This

0.9 ys pulse is applied to the input gate of IC2a, thus inhibiting the generation of any additional trigger pulses during the 0.9 ys hold-off period. This

is done to protect the avalanche transistors from damage due to overheating.

Avalanche transistors Ql and Q2 require stable, high B+ voltages. These

are supplied by the high voltage regulator shown in figure 6. From figure 7,

+220-V filtered dc is supplied to the regulator. The B+ voltage is sensed by

the voltage divider chain R10-R13 and applied to the (+) input of the 741 operational amplifier. This voltage is compared to the 6.8 V reference voltage

established by the zener diode. The error signal drives Q3 and Q4 . 04 is a high voltage transistor. The collector output of Q4 controls the series pass

transistor, Q6, to establish the regulated B+ voltage. R19 and Q7 are a current

limiter. The B+ voltage for Q2 is adjustable from +120 V to +150 V. Ql requires

+100 V. This is obtained from the 100 V zener diode and Q8.

The power supply, figure 7, uses conventional circuits and components. It

supplies +5 V for the TTL clock and delay circuit, +12 V for the 741 operational

amplifier, and +220 V for the B+ regulator.

7
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V. CONSTRUCTION

Figures 8 and 9 show the top and bottom internal parts layout of the

impulse generator. A 23 x 18 x 5 cm chassis is used to support the various

components. A large 14.5 x 12.5 cm hole is cut out for the pc board. The large

power supply components are located to the rear of the chassis. The majority of

the components are located on the pc board. Figure 10 shows the artwork for the

pc board. The board is 1.6 mm, double-sided, copper-clad, G-10 fiberglassepoxy. The parts layout and assembly are conventional with the exception of the

impulse-forming circuit.

The parts layout associated with avalanche transistor, Q2, is very critical. The impulse waveshape and amplitude are highly dependent upon the con- structor's duplicating the exact layout. Figure 11 shows several views of the

Q2 circuitry. The impulse output from Q2 is routed to the front panel by a short, 50 ft, 3 mm, semi-rigid, coaxial cable.

12

Figure 10. Printed circuit board layout. 1:1 scale. (a) Top side, (b) Bottom

side. Double-sided, copper-clad, 1 . 6-inm thick, G-10 fiberglassepoxy board. Dark areas indicate regions where the copper cladding

is removed. Finished board size is 15.3 cm x 17.8 cm.

14
Figure 10. (b) Bottom side.

15
gure 11. Several views of the component layout of the Q2 impulse forming

16
VI. COMPONENT SELECTION

The majority of the components in this instrument are standard tolerance,

off-the-shelf items. The only exceptions are IC2, Ql, and Q2, which must be

hand selected for the proper characteristics.

IC2 is either a 96S02 or a 9602 dual, monostable, integrated circuit. The

instrument will function with any off-the-shelf 9602 or 96S02. However, it may

not meet the 20 ps or less timing jitter specification. It is necessary to

select IC2 on the basis of minimum timing jitter between the trigger pulse

output and the impulse output.

Ql and Q2 are ordinary, inexpensive ($.50 and $2 respectively) switching

transistors. They are used in this generator as avalanche transistors although

they are not specified by the manufacturer as avalanche transistors. The important selection parameter for this application is the collector-emitter breakdown

voltage (base-emitter shorted), BV . For Ql, BV__„ should be 110 V or greater.

LtiO CEb

For Q2, BV^gg should be 130 V or greater. In addition, neither Ql nor 02 should

evidence any sign of instability in the BV curve tracer test or in the actual

impulse generator circuit.

17
VII. ADJUSTMENTS

There are only two internal adjustments (DELAY and HV Adj.) within the

impulse generator. The adjustment procedure is as follows:

1. Disconnect RFC4 (figure 4) from the 4.3 kfi resistor and the B+ line.

2. Set the repetition rate switch to 100 kHz.

3. Turn the power on.

4. Connect the trigger output to a 50 input impedance oscilloscope.

5. Set the oscilloscope time base to 20 ns/cm.

6. Adjust the oscilloscope to trigger on the positive edge of the trigger

signal.

7. Adjust the DELAY pot, R7, to set the trigger pulse 50% duration to 80 ns. The adjustment range is from 50 ns to 150 ns approximately.

8. Disconnect the trigger output from the oscilloscope.

9. Connect a DVM to the B+ line.

10. Adjust the HV Adj. pot, R13, through its full range and note the upper and

lower limits (+120 V to +150 V typical).

11. Set the B+ to the lower limit.

12. Turn the power off.

13. Reconnect RFC4 to the 4.3 kfl resistor.

14. Connect the trigger output to the trigger input of the oscilloscope.

15. Connect the impulse output to the signal input of the oscilloscope.

16. Turn the power on.

17. Adjust the oscilloscope for a stable display.

18. Slowly increase the B+ (turn HV Adj. CW) and note an increase in the

inpulse amplitude.

19. Continue increasing the B+ until instability in the impulse is observed.

Note the B+ voltage at which this first occurs.

20. Reduce the B+ voltage 2 V below the level at which instability is noted.

21. The adjustments are now completed.

18
VIII. MODIFICATIONS

For some special measurement applications, it may be desirable to modify

the IG to have a different trigger delay and/or impulse duration. The IG is

normally adjusted for 80 ns trigger delay; however, the delay may be changed

from 50 ns to 150 ns by simply adjusting the internal DELAY pot, R7

If a different impulse waveshape is desired, this is accomplished by changing the charge line, DLl. A narrower impulse can be obtained by shortening DLl

However, the price paid will be a reduction in the impulse amplitude. Longer

duration impulses can be obtained by lengthening DLl. To facilitate this, an additional SMA jack, J4, is already installed on the circuit board 5 mm from the

end of DLl. To use this jack, a short strip of 3 . 2 mm V7ide copper tape should

be soldered between DLl and the jack. A longer charge line can then be attached

to this SMA jack. A 50 Z, RG-174/u coaxial cable with an SMA male connector

is recommended. The opposite end of the coax is left open-circuited. If this

modification is made, the maximum repetition rate limit must be decreased from 1 MHz

by increasing the hold-off period set by IC2b . The hold-off period should be

increased in proportion to the increased impulse duration. For example, if the

impulse duration is increased from 0.36 ns to 3.6 ns, then the hold-off period

should be increased from 0.9 -^s to 9 us. R22 and/or C15 should be changed to

determine the hold-off period. The impulse duration should not be increased

beyond 50 ns.

19
IX. PARTS LIST*

Resistors

(All resistors are 5% carbon composition unless noted)

Rl 100 9. 1/8 w

R2 1 Kn 1/4 w

R3 51 Q, 1/8 w

R4 1 Kfi 1/8 w

R5 1 Kfi 1/8 w

R6 100 u 1/8 w

R7 100 1/8 w

R8 4.3 Kfi 1/4 w

R9 150 n 1/8 w

RIO 4.7 m 1/8 w

Rll 2.2 KQ 1/8 w

R12 1 Kfl 1/8 w

R13 . 470 1/8 w

R14 220 1/8 w

RI5 100 1/8 w

^l^g } 100 Kn Dual Variable Pot., Linear Taper

R17 4.7 Ki^ 1/4 W

R18 4.7 Kfl 1/4 W

R19 300 a 1/4 W

R20 10 KQ, Miniature 1 Turn Pot.

R21 1.5 Kn 1/4 W

R22 12 KQ 1/4 W

R23 100 ft 1/4 W

R24 47 Kft 1/2 W

R25 3.9 KQ 1/4 W

The inclusion of manufacturers' names in this parts list is not intended as an endorsement. Other manufacturers' products might perform equally as well

or better.

20
R26 100 m 1/8 W Metalized 1%

R27 1 KQ 1/8 W Metalized 1%

R28 510 1/4 W

R29 10 Kfi, Trim Pot., 15 Turn

R30 4.7 K^^ 1/4W

R31 1.8 Kfl 1/4 W

R32 100 Kfl 1/4 W Metalized 1%

R33 15 n 1/4 W

R34 39 K.Q 1/4 W

R35 ' 100 m 1/4 W

R36 510 1/2 W

R37 1 K.Q. 2 W Wire-wound

R38 100 2 W Wire-wound

Capacitors

CI 150 pF Silver Mica

C2 33 pF Silver Mica

C3 3 pF Silver Mica

C4 100 pF Silver Mica

C5 100 pF Silver Mica

C6 1,000 pF Silver Mica

C7 1,000 pF Silver Mica

C8 0.01 yF Plastic

C9 0.01 yF Plastic

CIO 0.1 yF Plastic

Gil 0.1 yF Plastic

C12 1.0 yF Plastic

C13 1.0 yF Plastic

014 10 pF Silver Mica

C15 100 pF Silver Mica

C16 0.1 yF 250 V (Low Leakage Current)

C17 0.1 yF 250 V

C18 680 yF 25 D.C.W.V. Electroloytic , Tubular

C19 4.7 yF 25 V Tant

C20 4.7 yF 25 V Tant.

C21 0.01 yF 50 V Disc Ceramic

21
C22 20 m¥ 450 V Electrolytic, Tubular

C23 20 yF 450 V Electrolytic, Tubular

R. F. Chokes

RFC 1 2 Turns #28 insulated wire through 3 mm ferrite bead

RFC 2 3 ferrite toroid cores (CF-101-Q3 or equal.)

slipped over 100 Q., 1/8 W res^.stor, R15 and held

in place with RTV

RFC 3 3 mm ferrite bead over lead of RFC 4

RFC 4 10 yH, Miniature

RFC 5 Ferrite bead over lead of Rl

RFC 6 Ferrite bead over lead of R2

Ll and L2 4 Turns of 100 Q, resistor lead wound 1 mm, dia.,

4 mm long, starting at body of resistor.

Diodes

J. .J

(

'

•

CRl i Diode, hot carrier, H.P. 2800 or equal.

CR2 • IN 4007

CR3 ^ Zener diode, 6.8 V, IN 5235A

CR4 = Zener diode, 100 V, IN 5271A

CR5 Tunnel diode, 10 ma., IN 3719

CR6 IN 4004

CR7 IN 4004

CR8 IN 4007

CR9 IN 4007

CRIO IN 4007

CRll IN 4007

L. E.D.I Light emitting diode, 10 ma

' Transformers

Tl Transformer, 36 V, multi-tap T.E.C. 080100 or equiv.

T2 Transformer, 6V, 1.2A, Stancor P-6134 or equiv.

T3 Transformer, Min. , Pulse, 1:1, 50 MCL Tl-1

22
Transistors

Ql 2N3904, Motorola, selected

Q2 2N4014, Motorola, selected

Q3 2N3904

Q4 MJE-340

Q5 Deleted

Q6 MJE-340

Q7 2N3904

Q8 ^ MJE-340

Integrated Circuits

ICl 9602

1C2 9602 or 96S02 selected for min. jitter

1C3 741

1C4 7812

1C5 7805

Miscellaneous

51 Switch, toggle, D.P.S.T.

52 Switch, Rotary 3 pole, 6 position

Fl Fuse, 1/4A. SLO-BLO

Fuse holder

FLl Line filter, Corcom 3EF1 or equal.

Line cord to fit above

Jl Connector, BNC Bulkhead UG-492 A/U

J2 Connector, BNC Bulkhead UG-492 A/U

J3 Connector, GSM P.C. board, E.F. Johnson 142-0298-001

or equal.

J4 Connector, GSM P.C. board, E.F. Johnson 142-00298-001

or equal

23
J5 Connector, OSM P.C. board E.F. Johnson 142-00298-001

or equal

J6 ' Connector, Bulkhead, SMA female/N female

Cabinet, BUD BB 1801 RB or equiv.

Chassis, 23x18x5 cm. Aluminum

Large knob, 3.8 cm, 6.35 mm Shaft

Small knob, 1.9 cm, 6.35 mm Shaft

Cables as follows:

12 cm RG-174/U with BNC male on one end and pigtail on other end

. 6 cm RG-174/U with SMA male on one end and BNC male on other end

12 cm of 3 mm, 50 9., semi-rigid coax with one SMA male on each end, bending

gently to shape

24
REFERENCES

Andrews, J. R. , Impulse generator spectrum amplitude measurement techniques,

IEEE Trans, on Instr. and Meas . , IM-25 , No. 4, 380-384 (Dec. 1976).

Andrews, J. R. , and Arthur, M. G. , Spectrum amplitude—definition, generation

and measurement, Nat. Bur. Stand. (U.S.) Tech. Note 699, 100 pages (Oct. 1977).

Millman, J., and Taub , H., Pulse, Digital and Switching Waveforms, Chaps. 3 and 13 (McGraw-Hill Book Co., Inc., New York, N.Y., 1965).

Andrews, J. R. , A frequency calibrator for UHF using an avalanche transistor,

QST, LVI, No. 5, 16-18 (May 1972).

25
NBS-l 14A (REV. 7-731

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. FUBI.K A l lON OR RKPORT NO.

NBSIR 78-880

2. Gov't Acccs.sion No.

4. T!Tl,I-; AND SL'BTITIJ-: UHF IMPULSE GENERATOR

3. Recipient's Accession No.

5. Publication Date April 1978

6. Performing Organization Code

276.04

7. AUTHOR(S)

James R. Andrews and Eugene E. Baldwin

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

. DEPARTMENT OF COMMERCE

Washington, D.C. 20234

10. Project/Task/Work Unit No. 2764153

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as Item 9

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.)

This UHF Impulse Generator generates a narrow impulse with a flat spectrum

up to 1 GHz. The impulse amplitude is 55 volts and the duration is 365 ps.

The maximum repetition rate is 1 MHz. This report describes the generator

In detail and includes a complete parts list and printed circuit artwork.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Avalanche transistor; impulse; impulse generator; pulse generator;

spectrum; spectrum amplitude

18. AVAILABILITY (xj Unlimited

I I For Official Distribution. Do Not Release to NTIS

I I Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. C13

I X I Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

26

22, Price

$4.50

USCOMM-DC 29042-P74