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NBSIR 73-332

DELAY LINE MEASUREMENTS

Keith C. Roe

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

August 3, 1973

Prepared for

Jet Propulsion Laboratory

Pasadena, California

NBSIR 73-332

DELAY LINE MEASUREMENTS

Keith C. Roe

Electromagnetics Division

Institute for Basic Standards

National Bureau of Standards

Boulder, Colorado 80302

August 3, 1973

Prepared for

Jet Propulsion Laboratory

Pasadena, California

w ^ %

U^. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

CONTENTS

Page

1. Background 1

2. Summary of Measurement Techniques 1

3. Bridge Technique 2

4. Frequency Variational Technique 3

5. Pulse Delay Technique 4

6. Results 6

7. Acknowledgments 9

References 10

LIST OF FIGURES

Figure 1. An X-Y Recording Used in a Pulse Delay

Measurement 5 LIST OF TABLES

Table 1. Time Delay Measurement Results for the

15 Nanosecond Line 7

Table 2. Time Delay Measurement Results for the

30 Nanosecond Line 7

Table 3. Time Delay Measurement Results for the

60 Nanosecond Line 8

i

DELAY LINE MEASUREMENTS

This report describes the techniques and results of time delay measurements made by NBS on

delay lines for JPL

.

Methods of measurement include frequency

variational, pulse delay, and RF impedance bridge

techniques.

Key words: Bandwidth; dispersion; group delay;

phase shift; pulse burst, time delay.

1 . Background

A problem in calibrating a ranging system for the Mariner

project generated several discussions between the staffs of JPL

and NBS. A project was formed wherein NBS was to measure the

group delay characteristics of three lengths of delay line

cable at 500 kHz, 2.113 GHz, 2.295 GHz, and 8.415 GHz. The

cables were supplied by JPL and had nominal delay times of 15,

30, and 60 nanoseconds. The proposed maximum measurement

uncertainties were ± 1.5 percent.

2. Summary of Measurement Techniques

The evaluation of time delay at 500 kHz was done by calculating the time delay characteristics from bridge measurements of open and short circuit impedances of the lines.

At each of the higher frequencies (2.113 GHz, 2.295 GHz,

and 8.415 GHz), two independent measurement techniques were

used. One was a "frequency variational" technique using
phase measurements; the other was a "pulse delay" technique,

' which was a time domain determination using particular waveforms and sampling oscillograph/.

A brief description of all three of these measurement

techniques and the associated errors follows

.

3. Bridge Technique

This measurement technique utilizes the relationship

of the complex propagation constant to the ratio of the short

and open circuit impedances of the line. This relationship

can be calculated from the Telegraphers Equations, and is given

by:

tanh y£ = /Z^ Y^, (1)

where: y is the complex propagation constant

Z is the line length

is the short circuit input impedance

is the open circuit input admittance.

The time delay was computed by dividing (where 3^ is the

imaginary part of y) by the angular frequency.

The uncertainty statement includes systematic error limits

derived from the impedance and admittance measurements and a random error component based on three times the estimated

standard deviation of the impedance and admittance determinations.

2
4. Frequency Variational Technique

The expression for group delay time, x IS :

T

1 d4)

gd 360 ar

and can be calculated, approximately, using finite differences

The frequency variational technique involves a phase shift

(A(j)) measurement with a simultaneous frequency shift (Af)

measurement

.

The group delay time for each delay line was determined

from the difference between a measurement with the delay line

in the system and a system reference measurement.

The uncertainties for this type of measurement are limited

almost entirely by the phase shift measurement error, as frequency measurement errors are several orders of magnitude

smaller than phase measurement errors. From eq . (2) the error

in time delay (Ej) can be expressed:

The error in a phase shift measurement, d(A(f)), is the arithmetic sum of the mismatch phase error and the phase meter error.

For each measurement the system insertion point VSWR was tuned

to _< 1 .005 at the measurement frequency and was found to be

from

:

"^gd 360 AT*

1 A(j) (2)

(3)

3
£ 1.00 7 over the range through which the frequency was varied.

In addition, the VSWR o£ the delay lines was ;< 1 . 050. The

limit of phase error resulting from mismatch [1]* is ± 0.035

degrees. The maximum error from the phase meter reading is

± 0.060 degrees and the resultant maximum phase error is

± 0.095 degrees. Substituting this value into eq . (3),

the maximum phase error for a 1 MHz frequency variation

(Af) is ± 0.26 nanoseconds and is ± 0.13 nanoseconds for a

2 MHz frequency variation. It would appear that a large varia

tion of the frequency, such as 100 MHz, would result in a very

accurate determination of group delay; however, only a perfectly nondispersive line could be measured in this manner [2]

'- ' 5. Pulse Delay Technique

The pulse delay technique requires recording the pulse

position of an rf pulse burst with respect to a sync trigger

with the delay line both in and out of the system.

The pulse is obtained using a diode switch to gate the

output from a microwave oscillator. The gating signal is

obtained from a countdown circuit using the microwave signal

so that the output pulse has an envelope coherent with its

microwave oscillations. In addition, the countdown circuit

^Figures in brackets refer to references.

4

produces the sync trigger to a sampling oscilloscope coupled

to an X-Y recorder so that the scope trace and recording are

also coherent with the microwave oscillations.

Figure 1 shows a reduction o£ one of the X-Y recordings

used for these measurements. The CW trace (diode switch on)

is recorded to obtain a time scale for the most precise measurement of time difference.

The errors in pulse delay result from time scale resolution, pulse distortion, and countdown circuit jitter. The

estimated limits are:

time scale resolution = ± 0.001 t , gd

pulse distortion = ± 0.001 t , gd

countdown circuit = ± 0.020 nanoseconds

Total = ± [0.020+0.002 t ^] nano-

* .- ^ seconds . ^

6 . Results

The results from each of the measurements previously

described are shown in tables 1, 2, and 3. Because of dispersion, the group delay times are affected by the frequency

components contained in the delayed signals; therefore, the

approximate bandwidths for each measurement are included with

the results.

6
TABLE 1. Time Delay Measurement Results for the 15 Nanosecond

Line

.

Frequency

iMt? do U. 1 C illdl L Technique Bandwidth

Dp 1 ?5 V T 1 mp

Nanoseconds

Uncertainty

Nanose conds

500 kHz r> X -L U-gt; n IS 6 S + (0 .05 + 0 .01)

2.113 GHz n \F QY**! qI"! r\T\ FIt?v_[ VdiXclL-LUli + 0 .26

2.113 GHz rXt?L[ Vd-I-Ld-UXUll 7 MH7 + 0 .13

2 . 113 GHz IT Li ± O C JJt/ X d y 40 0 MH 7 14 9 5 + 0 .05

2 .295 GHz L Iwvj VdJ.J.dL'XWIi _i_ 1 MH7 I'll X 14 9 7 + 0.26

2.295 GHz 1 iC^-^ VdlXdLX*Jll 7 MH7 15 09 + 0 .13

2.295 GHz Pulse Delay 400 MHz 15.04 + 0 .05

8.415 GHz Freq Variation ^ Q 17 i D . i / + 0 .26

8.415 GHz Freq Variation 2 MHz 15 . 10 + 0 .13

8.415 GHz Pulse Delay 1 . 3 GHz 15.03 + 0.05

TABLE 2. Time Delay Measurement Results for the 30 Nanosecond

Line .

Frequency

Measurement

Technique

Approximate

Bandwidth

Delay Time

Nanoseconds

Uncertainty

Nanoseconds

500 kHz Bridge 0 31.03 + (0 .08 + 0 .02)

2 .113 GHz Freq Variation 1 MHz 29 .99 + 0 .26

2 .113 GHz Freq Variation 2 MHz 30 .03 + 0 .13

2 . 113 GHz Pulse Delay 400 MHz 30.18 + 0.08

2 .295 GHz Freq Variation 1 MHz 29 .91 + 0.26

2 .295 GHz Freq Variation 2 MHz 30 .02 + 0 .13

2.295 GHz Pulse Delay 400 MHz 30 .21 + 0 .08

8.415 GHz Freq Variation 1 MHz 30 .19 + 0 .26

8.415 GHz Freq Variation 2 MHz 30 .06 + 0 .13

8.415 GHz Pulse Delay 1.3 GHz 29 .90 + 0 .13

7
TABLE 3. Time Delay Measurement Results for the 60 Nanosecond

Line .

Frequency

Measurement

Technique

Approximate

Bandwidth

Delay Time

Nanoseconds

Uncertainty

Nanoseconds

500 kHz O I J- u.gt? nu fi 1 i\ (0 .15 + 0 .0 2}

2.113 GHz rXt;L[ VcH-LdLXUll o y . o u 0.26

2.113 GHz riCt{ VdlJ-clLJ-UIl L Inn L 0.13

2 .113 GHz D 1 1 T CO T^£i 1 OAT" Ann MH -7 u u Inn L D U . U / 0.14

2 .295 GHz ^lt;^ Vd-XXclLXUll 1^ Q Q 7 + 0 .26

2 .295 GHz F 1 t;C[ Vd-lXd-LXUii ^ Fin L J i7 . J O

+ 0.13

2.295 GHz Pulse Delay 400 MHz 59 .82 + 0 .14

8.415 GHz Freq Variation i MnZ CO OA + 0 .26

8.415 GHz Freq Variation 2 MHz 60 .03 + 0.13

8.415 GHz Pulse Delay 1.3 GHz 59 .91 + 0.27

8
7. Acknowledgments

The major portion of this measurements project was accomplished through the efforts of the individuals named below.

Raymond Jones -- bridge techniques

Philip Simpson -- pulse techniques.

In addition, background information was provided by Mr. Doyle

Ellerbruch and Dr. Robert Beatty.

9
I

References '

E [1] G.E. Schafer, Mismatch Errors in Microwave Phase Shift

Measurements, IRE Transactions on Microwave Theory and

Techniques, November 1960, 617-622. i

[2] R.W. Beatty, D.A. Ellerbruch, D.H. Russell, G.E. Schafer,

j R.S. Turgill, J. P. Wakefield, and T.L. Zapf, Lecture

Notes for the Phase Shift Measurements Seminar, unpublished NBS Report, 10-1 to 10-11, June 1967.

10
FORM NBS-114A (1-71) U.S. DEPT. OF COMM. 1 . PU B LIC AT ION OR R E PORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA ^gglR 73-332

3. Recipient's Accession No.

|

! 4. TITLE AND SUBTITLE

Delay Line Measurements

5. Publication Date August 1973

6. Performing Organization Code

7. AUTHOR(S)

Keith C. Roe

8. Performing Organization

1 9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS, Boulder Labs.

DEPARTMENT OF COMMERCE

Boulder, Colorado 80302

10. Project/Task/ Work Unit No. 2724630

11. Contract/Grant No.

12. Sponsoring Organization Name and Address

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 significant information. If document includes a significant

bibliography or literature survey, mention it here.) This report describes the techniques and results of time delay measurements made

by NBS on delay lines for JPL.

Methods of measurement include frequency variational, pulse delay, and RF

impedance bridge techniques.

17. KEY WORDS (Alphabetical order, separated by semicolons) rs ^ : j i ' ^ ' Bandwidth; dispersion; group delay;

phase shift; pulse burst; time delay.

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