HP 11729c schematic

A

USER'S

GUIDE FOR AUTOMATIC

PHASE NOISE MEASUREMENTS

tflSES5S Product Note 11729C-3

For Complete

Application & Sales

Information

Call

Frank Engstrom

Sales Representative

HEWLETT PACKARD

NEELY

Sales Region

8080 POINTE PARKWAY WEST

PHOENIX. AZ 85044

[phone]

NOTICE

The information contained in this document is

subject to change without notice.

HEWLETT-PACKARD MAKES NO WARRANTY OF ANY KIND
WITH REGARD TO THIS MATERIAL, INCLUDING BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTIBILITY
AND FITNESS FOR A PARTICULAR PURPOSE. Hewlett-Packard shall
not be liable for errors contained herein or for incidental or consequential
damages in connection with the furnishing, performance or use of this
material.

Hewlett-Packard assumes no responsibility for the use or reliability of
ware on equipment that is not furnished by Hewlett-Packard.

This document contains proprietary information which is protected by copy­right. All rights are reserved. No part of this document may be photocopied,
reproduced or translated to another language without the prior written
consent of Hewlett-Packard Company.

Copyright © 1986 by Hewlett-Packard Company.

this

soft-

A User's Guide For Automatic
Phase Noise Measurements

Table of Contents Page

Chapter I: Introduction 5

What is EASY_j?f ? Software capabilities and limitations. Instruments

supported by the software. Measurement methods.

Chapter II: System Description 7

HP 11729B/C Carrier Noise Test Set 7
HP 8662/63A Synthesized Signal Generator 7
HP 3561A Dynamic Signal Analyzer 7
HP Technical Computers 8
Printer/Plotter 8

Chapter III: Set-Up Procedure 9

Configuring the System 9
Cabling the System 9
Driver Loading 10
Running the Main Program 11
Flowchart 11

Chapter IV: Measurement Methods Overview 13

Phase Detector Method 13

Typical System Sensitivity 13
Phase Locking Techniques 14
Loop Characterization 17

Using EASY_y; in the Phase Detector Mode 18

Loading the Main Program 18
Cabling the System 18
Specifying the Measurement Parameters for the System 19

Establishing Quadrature, Calibrating and Locking 22

Graphing the Phase Noise Data 23
The Process Data Menu 24
Frequency Discriminator Method 27

System Sensitivity and the Delay Line 28

Generating the 640 MHz Reference Signal 29

System Calibration 30

Maintaining Quadrature 30
Using EASY_J?? in the Discriminator Mode 31

Loading the Main Program 31

Specifying the Measurement Parameters 31

Generating the 640 MHz Low Noise Signal 33

Calibrating and Establishing Quadrature 33

Measure and Graph the Phase Noise Data 38

Chapter V: EASY_i? Softkey Listing 39
Chapter VI: Measurement Difficulties 42

Measured Data Appears in Error at Low Offset Frequencies 42

Beat Note Not Found 42

System Cannot Phase Lock to the Signal 42

Out of Lock Indicator Tripped 42

Incorrect Spurious Signal Level Observed 42

Noise Peaking 43

Discontinuities in the Graph 43

HP 11729 B/C Internal Misinterpretation of Quadrature Condition .. 43

3

Table of Contents (cont'd) Page

Appendix A: EASY_J?? Main Program Variables Definitions 44

Main Program Only 44

Subprogram Locations and Sizes 48
Appendix B: EASY_ J? Phase Noise Measurement Program 50
EASY_if Ordering Information 53

4

The increased focus on the spectral purity of microwave signal sources has created
a need for a measurement system that provides the high performance necessary for
R&D applications and that can be automated for production environments. The
HP 11729C Carrier Noise Test Set is the key element of a system that meets this
requirement. With appropriate companion instrumentation, phase noise measure­ments can be made on a broad range of
inexpensive, easy to use software solution that allows automatic operation of the
HP 11729B/C, along with the necessary spectrum analyzers and local oscillator, is
the subject of this product note.

sources,

from 10 MHz to 18 GHz. An

This internally modular, user-friendly software, called
make automatic phase noise measurements from 10 MHz to 18 GHz on both free­running and synthesized sources. The software implements both the Phase
Detector Method and the Delay Line Discriminator Method, and provides a plot
of the phase noise measurement in units of script-L („§?). Its drivers can also be

user-modified to control instruments other than those supported by the software.
However, it does not make 2-port or AM noise measurements, nor does it make
the necessary corrections to validate the data obtained inside the phase lock loop
bandwidth, offer a choice of units with which to display the phase noise data, or
display correct discrete signal levels. The software is not specified or warranted.
This product note is the only documentation available. It
so that enhancements can easily be user added to better match a particular
application.

EASY-i? works with:

• HP 11729 B/C: Carrier Noise Test Set

• HP 8662/8663 A: Synthesized Signal Generator

• HP 8566/8568 A/B: Spectrum Analyzer

• HP 3561A: Dynamic Signal Analyzer

All instruments are linked together via HP-IB and their functions are controlled by
a HP Series 300 or 200 technical computer. The software coordinates the
instruments during the measurement, and makes the necessary calibrations to
improve the accuracy of the results.

"EASY_Jzf,"

is

written in HP BASIC

is designed to

The user is allowed to choose between two methods for making automatic phase

noise measurements on sources: the Phase Detector Method, and Frequency

Discriminator Method.

Phase Detector Method

This method requires the HP 8662A or HP 8663A, acting as a reference source,
to be phase-locked to the device under test (DUT). Two configurations are used
for phase-locking in this method. The first technique, called Electronic Frequency

Control (or EFC), uses the phase-lock circuitry of the Carrier Noise Test Set to
directly change the frequency of the HP 8662A/63A Signal Generator's 10 MHz
crystal reference oscillator. EFC is used to make accurate measurements on low
drift sources such as synthesized sources.

The second technique, called DC-FM, uses the phase-lock circuitry of the Carrier

Noise Test Set to control the FM circuitry of the HP 8662A/63A Signal Genera-

tor. DC-FM is used for measurements on sources with a greater drift rate. (For

more information on the Phase Detector Method refer to Product Note 11729B-1,

"Phase Noise Characterization of Microwave Oscillators, Phase Detector

Method", HP Literature No. 5952-8286).

5

Frequency Discriminator Method

This method does not require a reference source to make the measurement.
However, a discriminator such as a delay line or a resonator, and a phase shifter
are needed. This technique is useful for characterizing sources with large, low rate
phase instabilities such as free-running sources. Two configurations for down­converting the test frequency are implemented in the software. The first configura­tion, uses the HP 8662A/63A for down-conversion, and provides a lower noise
floor close to the carrier. The second configuration uses the HP 11729C in stand­alone (self-oscillator) mode to generate the down-conversion frequency. This
configuration does not require an HP 8662A/63A Signal Generator for down
conversion and provides a lower broadband noise floor. (For more information on
the Frequency Discriminator Method, refer to Product Note 11729C-2, "Phase
Noise Characterization of Microwave Oscillators, Frequency Discriminator
Method", HP Literature No. 5953-6497).

This product note discusses the use of the "EASY_Jz?" program for making auto­matic phase noise measurements. Chapter II describes the instruments controlled
by the software. The set-up procedure is shown in Chapter III. Chapter IV shows
two techniques for measuring the phase noise of

technique should be applied and what the software limitations are for each tech­nique. The different software menus and softkeys are covered in Chapter V.
Finally, Chapter VI outlines some of the measurement difficulties that the user

may encounter. To order your copy of

Information section at the end of this Product Note.

"EASY_Jzf",

sources;

it explains when each

refer to the Ordering

NOTE: This product note assumes the user has had some previous experience in

making phase noise measurements and has read Product Notes HP 11729B-1 and

HP 11729C-2. Copies of these product notes may be obtained at no cost from

your local Hewlett-Packard Sales and Service Office.

6

CHAPTER

11 System Description

INSTRUMENTS SUPPORTED
BY EASY_^

HP 11729B/C Carrier Noise
Test Set

HP 8662A/63A Synthesized
Signal Generator

This section describes

1

for a

block diagram representation

This instrument provides
tion

and

phase-locking
HP 8662A/63A
of two modes
mode, a selected harmonic
HP 8662A/63A
DUT

to an

baseband.

The

HP
640 MHz SAW filter
SAW oscillator capable
this mode,

When making phase noise measurements with
8662A/63A serves
provides
down-conversion process. When using
mode, the HP 8662A/63A may be used as the calibration source
discriminator.

to

IF. A second mixer

11729C

the 640

the

fixed 640 MHz

the

instruments controlled

of

the system components.

the

down-conversion

of

the resultant

as

well as baseband signal processing.

generate

is

can

the

required IF. When using

of

the fixed 640 MHz signal from

used

as a

reference signal

also

be

used

in the HP

of

generating

MHz reference signal from

as the

voltage controlled oscillator

LO

IF

in the HP

in a

SAW "oscillator" mode.

11729C

the

signal required

of

product with

to

11729C then down-converts this

is

configured into a low-noise internal

necessary reference signal. When used

the HP

the

the HP

by the

software. Refer

the DUT signal, the phase detec-

the RF
It can be

the HP

down-convert

8662A/63A

Phase Detector Method

in the

by the HP

11729C

11729C

the

the

phase-lock-loop

11729B/C

in the SAW

to

output signal

configured

in

normal

rear panel

frequency

In

this mode,

is not

required.

for the

oscillator

for

the frequency

Figure

of

the

in one

of

the

of

the

IF to

the

in

the HP

and

HP 3561A Dynamic Signal
Analyzer and HP 8566/68
Spectrum Analyzer

Figure

1.

Instruments controlled

the software.

A/B

by

Two baseband spectrum analyzers
from

the

Carrier Noise Test Set.

HP 3561A Dynamic Signal Analyzer

rapidly produce results
the necessary frequency domain data.

For higher offset frequencies,
Analyzer
frequency
COUNT UW SIG softkeys
spectrum analyzers
range
range,
software will allow
ranging from 100 Hz
software

of 1 Hz

DUT

is

selected. This Spectrum Analyzer

of

the DUT

to 10

or any

portion

an HP

(HP

the

8566

}

by

taking time domain data

and the IF

8566/68

MHz.

The

of

it.

HP 8566/68

to

10 MHz.

or an HP

HP11729B/C

CARRIER NOISE

are

For

the

broad range

frequency when

are

pressed. The combined capabilities

A/B and HP

user

can

If

an

HP

In

8568

TEST

SET

m

HP 8662/63A

SIGNAL GENERATOR

used

to

measure the noise spectrum output

offset frequencies from 1

is

used.

For low

and

of

the

HP

is

also used

the

3561A) give

select a measurement covering

3561A

is not

available
A/B to be
order

is

required

used

for

to

make a measurement with

to be

DYNAMIC SIGNAL

HP 8566/68

SPECTRUM ANALYZER

Hz to 100

offsets,

the HP

performing

8566/68

to

measure

COUNT

the

to the

offsets from

present

in the

HP3561A

ANALYZER

kHz

3561A

an FFT to get

A/B

Spectrum

the

IF SIG or the

of

the

two

system

an

the

entire

user,

the

the

carrier

the

system.

<^

A/B

the

can

offset

HP-IB

TE

IE

HP MODEL 236A,

310A, 0R320A

TECHNICAL COMPUTER

7

216A,

IF

HP Technical Computers

The software runs on an HP 9816A (requiring the large keyboard model number
98203B) or an HP 9836A series 200 computer. It will also run on the HP 9000

Series 300 computers Model 310 and 320. The Series 300 computers must be
configured with an HP 98546A display compatibility interface. The software, on
two

5'/4-inch
memory and needs the system to be configured with BASIC 2.1, 3.0, or 4.0 with
extensions. The BASIC software with extensions, occupies 500K bytes of memory,
so a total of 1M bytes of memory is needed to run the program. The BASIC 3.0
or 4.0 binaries needed to run the program are listed below.

discs or on two single sided

3^-inch

discs, requires 450K bytes of

Printer/Plotter

NAME
GRAPH

IO
MAT
KBD

CLOCK
TRANS

ERR

HPIB

CRTA

Depending on which mass storage device you are using, select the appropriate

version of the following BASIC 3.0 binaries:

SRM

DISC
CS80

A hardcopy output of the phase noise measurement can be obtained using any
printer (with "raster dump" capability) and/or plotter supported by the HP Series
200 (models 216A and 236A) or Series 300 (models 310A and 320A) Technical
Computers.

NOTE: The instruments described above are the HP instruments controlled by the
software. The only HP instruments required to run the program are the HP

11729C Carrier Noise Test Set and an HP 8566/68 A/B Spectrum Analyzer. (If
you are using EASY_J/f in the Phase Detector Method, the HP 8662A/63A is
required to be connected to the system.) A user supplied RF spectrum analyzer,

FFT spectrum analyzer, or signal generator can be integrated into the system

provided that the necessary programming changes are made by the user in the

appropriate instrument driver. The following line identifiers are used to locate the

appropriate instrument driver (via | EDIT | line Identifier):

DESCRIPTION
Graphics

I/O

Matrix Statements
Keyboard Extensions
Clock
Transfer Statement
Error Messages
HP-IB Interface Driver
ALPHA CRT Driver

Shared Resource Mgm
Small Disc Driver
CS80 Disc Driver

IDENTIFIER
Lo_Begin

Sa_Begin
Sa856XX_Begin
Sa3561a_Begin

8

INSTRUMENT
Signal Generator

SA Interface
Spectrum Analyzer
FFT Spectrum Analyzer

FILE NAME
EL866XA

ELsaSTUBa
EL856XX
EL3561A

CHAPTER

III

Set Up Procedure

Configuring the System

Before running the program, the user must configure the HP-IB instruments con­nected to the system and controlled by the software.

After loading BASIC
Drive 0 and Disc 2 in Drive 1. Then type LOAD "ELautost" and press

EXECUTE | to load the greeting file. The start-up message gives detailed address
setting instructions for each instrument. The following is a list of the instruments
controlled by the software and the addresses they should be set to in order to run
the program:

INSTRUMENT ADDRESS
Hi-Frequency Spectrum Analyzer (HP 8566/68 A/B) 718

Low Frequency Spectrum Analyzer (HP 3561 A) 711
Local Oscillator (HP 8662/63A) 719
Carrier Noise Test Set (HP 11729C) 706*
External Plotter (HP 7470A, etc.) 705
External Printer (to dump graphics) 701

NOTE:

digit (7) is a select code used to specify the internal HP-IB interface.

*Since computer peripherals usually occupy bus addresses 0 through 7, the software will recognize the

HP 11729C Carrier Noise Test Set when this instrument is set to either address 706 (original address
with which the instrument is shipped) or an alternate address of
716 refer to the HP 11729C Operating and Service Manual.

The last two digits are used to specify the instrument address. The first

2.1,

3.0, or 4.0 and all necessary binaries, insert Disc 1 in

716.

To set your instrument address to

Cabling the System

In some cases, depending on the user's needs, some of the above instruments may
be omitted. The printer/plotter provide for the hardcopy output and are not neces­sary for the operation of the system. The LO may be omitted if another source is
used to provide for the calibration sideband in the Frequency Discriminator
Method. For users interested only in offset frequencies greater than 100 Hz and up
to 10 MHz, the HP 3561A may be omitted and the only spectrum analyzer used
will be the HP 8566/68 A/B. For users interested in the entire range of offset
frequencies, from 1 Hz to 10 MHz, both spectrum analyzers need to be provided.
The software cannot do a Microwave Signal Count if the HP 8566 is not con-

nected to the system. The Carrier Noise Test Set is required to be present in the
system at all times, regardless of the offset frequency, method chosen, or cali­bration procedure used.

Once the user decides which instruments are needed for his specific measurement,
the address setting instructions in the start-up message provide the guidance for
configuring the correct adresses.

The start-up message gives the user instructions to set up the system for the Phase
Detector Method. The program assumes this configuration exists when it guides
the user through the cabling for the discriminator method. If the Frequency Discrim-

inator Method is chosen at the Main Menu, the user is then instructed to change
the connections from the phase detector to the discriminator configuration.

Figure 2 shows the connections that should be made to set up your system for the
Phase Detector Method:

9

Figure 2. System set up for the Phase

Detector

Method;

instruments supported

by the software and connections needed.

HP 8566/68

SPECTRUM

ANALYZER

A/B

HP 3561A

DYNAMIC SIG

ANALYZER

Cabling the System

I

HP11729C

CARRIER NOISE TEST SET

DUT

1.

Connect the DUT to the HP 11729C Microwave Test Signal Input.

2.

Connect the RF Output of the HP 8662/63 A to the HP 11729C's 5

640 MHz IN

HO

MHz OUT

±10tl

HP

8662/62A

SYNTHESIZED SIG GEN

EFC

I

±llf

FMIN

5

TO

1280 MHz

RF OUTPUT

to

1280 MHz Input.

3.

Connect the HP 11729C <1 MHz Output to the HP 3561A Input (if

available).

4.

Connect the HP 11729C <10 MHz Output to the HP 8566/68 A/B RF

Input.

5.

Connect the HP 8662/63A front panel FM Input to the HP 11729C rear

panel DC-FM Output (±1V).

6. Connect the HP 8662/63A rear panel 640 MHz OUT to the HP 11729C
rear panel 640 MHz IN.

Driver Loading

7.

Connect the HP 8662/63A rear panel EFC IN to the HP 11729C rear

panel EFC Output (±10V).

All instruments (except the DUT) must be connected to the technical computer

via HP-IB cables. Remember not to exceed the IEEE-488 specifications on total

cable length: 2 meters/device up to 20 meters. Avoid long cable lengths.

Once the start-up message has been loaded press the LOAD MAIN PGM
softkey. After pressing the LOAD MAIN PGM softkey and the program

is
loaded, the software identifies the instruments that are turned on and connected to
the technical computer at the addresses previously specified. The user is then
prompted to load the subprogram drivers for those instruments into memory.
Press the LOAD SUBS softkey (K5) to automatically load the instrument's
drivers. Press the ABORT LOADING softkey (K4)

if

you only want to use the

PROCESS DATA menu.

If at a later time the user wants the program to stop using one of the instruments,
the procedure to follow

is:

turn off the instrument, press |STOP| on the technical
computer and then press |RUN|. The computer search will not find the instrument
(respond NONE OF THESE when the controller asks you what instrument is
connected at the unused instrument address) and will only use those instruments
that remained ON when |RUN| was pressed.

10

Running the Main Program

The MAIN MENU is used to set up all parameters prior to performing the test or
calibrations.

Once the program has been run and all drivers for the connected instruments have

been automatically loaded, the user is prompted to set up the specific

measurement parameters. To set up the measurement parameters, use the knob on

the HP 9836A or HP 9816A Technical Computer keyboard to move the double

arrow to the parameter that you wish to modify (you may use the t and i arrow

keys if you are using a Series 300 Technical Computer). Then press the

CHANGE PARAMS softkey-and follow the directions to enter the appropriate
information. (Refer to Figure 3 for a software flowchart.)

Figure 3. Software Flowchart

ENTEfl

DUTFREQUENCY

PRESS

COUNT

APPHOX,

I.F. SIG

START

UPDATE

RESET

S/A BW

8566/68

TO

TO

A/B)

DEFAULT VALUES

DEFAULT VALUES

CALIBRATE

(HP

!»-*-

PRESS

COUNT MW SIG

FflOlfi
NEXT
PAGE

FREQUENCY
DISCRIMINATOR
METHOD

OBTAIN APPROPRIATE

LENGTH

OF

DELAY LINE

SELECT

IF

OR

^WCAL

MEASUREMENT

PHASE
DETECTOR
DC-FM

SELECT LBWF

SELECT

FM

DEVIATION

SELECT

METHOD

~r

PHASE
DETECTOR
EFC

SELECT LBWF

-4-

11

MANUAL
LOCK

Figure 3. Software Howchart
Continued

SELECT OFFSET

START AND STOP

FREQUENCIES

SELECT PLOT RANGE

Oil AUTORANGE

SELECT APPROPRIATE
SMOOTHING FACTORS:

-NUMBER OF AVERAGES

-

WHERE TO AVERAGE

-

SMOOTHING RATIO

(FOR ANALOG S/A]

SELECT

DATA LABEL

PRESS

MEASURE NOISE*

RE-MEASURE

PROCESS DATA

CHANGE ANY OF:

■ DATE/TIME

-

DATA LABEL

-

PLOT RANGE

-

NUMBER OF AVERAGES

-

SMOOTHING

-

DIFFERENT DUT WITH

SAME PROPERTIES

1 \

PREVIOUS
PAGE

"Both calibration and measurement take place here

•>

V

12

i.n.m J ticv

IV Measurement Methods Overview

There are basically two methods of making phase noise measurements, each with
its own set of advantages and disadvantages. This software allows the user to use
either the Phase Detector Method or the Frequency Discriminator Method. The
final decision to use one or the other of the two methods depends on the charac­teristics of the device under test (DUT), the offset frequencies the user is interested
in, the availability of the necessary equipment, and the capabilities and limitations
of the software and the instruments.

THE PHASE DETECTOR
METHOD

Figure 4. Basic Phase Detector Method
implementation, using a double-balance
mixer as the phase detector.

The Phase Detector Method is sometimes called the two-source technique. In this
method, the DUT and a low noise reference source are connected to a phase de­tector at the same frequency and 90 degrees out of phase (phase quadrature) as
shown in Figure 4. The output of the phase detector is then proportional to the

combined

band spectrum analyzer.

Since the output of the phase detector is proportional to the combined noise of the
two input sources, it is necessary to use a reference source that has lower noise than
the source under test. The combination of the HP 11729C and the HP 8662A/
63A represent the lowest noise 5 MHz to 18 GHz reference source available from

HP.
works optimally with fairly stable test sources. See HP Product Note 11729B-1
"Phase Noise Characterization of Microwave Oscillators, Phase Detector Method"
for a complete discussion of this measurement technique.

phase noise of the two input sources, and can be measured on a base-

Because the two input signals must be phase locked, the phase detector method

LOW PASS

DUT £ jA

OUT /^

PHASE

PHASP A.

DETECTOR

REF V

FILTER

LNA

4>

v

BASEBAND

ANALYZER

<s>

PHASE LOCK LOOP

AND QUADRATURE

MONITOR

Typical System Sensitivity The overall sensitivity of the Phase Detector Method is shown in Figure 5. The

Phase Detector Method provides good sensitivity over the entire offset frequency
range; it can be used to measure high quality standards (good close-in noise) or
state-of-the-art free-running oscillators (good far-out noise).

13

Figure

5.

Typical HP 11729C/8662A

system noise (Phase Detector Method,

locking via EFC).

The most critical component of the Phase Detector Method is the reference source.
Since the spectrum analyzer measures the rms sum of the noise of both oscillators,
the most important criterion for choosing a reference source is that its phase noise
be less than that of the source being measured. At any given frequency offset from
the carrier, one of the source's noise will dominate.

Generally, the choice of a reference source depends on the frequency of the DUT,
the required noise performance, and whether or not the reference source must
operate as the loop VCO. The HP 11729C/8662A/63A provides the lowest noise
floor for test signals ranging from 5 MHz to 18 GHz (see Figure

6).

It also provides

the loop VCO needed for the Phase Detector Method.

Figure 6. Typical HP 11729C/8662A
system sensitivity.

Phase Locking Techniques

40

20

o

m

0

•o

-20

I-

<

E

-40

tc

m

CO

FREE-RUNNING <

VCO AT 10 GHz O

SYNTHESIZER
_AT_1J)_GHz_ £

DRO AT i

1_GHf_

10 MHz i

XTAL a.

O

K

-100

en

(/>

tn

-120

-140

-160

-180

m

-SO

-80

\

\

\

\

\

\

0.1

*

»,

CN.,,

<

^

*N.

%

*

- .>.

^ „ *-

^T^

NS.

*

HP

117;

AT 10

'3'Att

IV

-640 Ml

!9C/S66

IHz-

LOW NOISE "•
340 MHz

"s

10 100 1k 10k 100k

OFFSET FROM CARRIER (Hz)

1M

Hz

2A

***

10M

Depending on the source under test and how wide a phase-lock-loop bandwidth
will be needed to maintain the phase detector in its linear range, there are two
techniques supported by the HP 11729C and the software to phase lock. First, for
very stable sources, phase lock can be established through the electronic frequency
control (EFC) of the HP 8662A/63A internal 10 MHz reference oscillator, using
the HP 11729C +10V phase lock loop control voltage output (Figure 7). This
yields a loop holding range of 1 kHz at 10 GHz and a maximum loop bandwidth
of about 1 kHz also. The advantage of locking using EFC is lower noise, but with
narrow tuning range

(1

part in 107).

14

Figure 7. Phase locking with the HP
8662A/63A Reference Oscillator.

DUT

HP11729C

1

XN

T

PHASE
DETECTOR

•

PLL

640 MHz IN

HP S662A OPT 0C3

XG4

5T0 1280 MHz A

640 MHz OUT

*-»•

m/n

INPUT

FRONT

PANEL

RFOUT

x

FREQ CONTROL
TO XTAL ± 10V

For synthesized sources, this loop holding range would probably be sufficient.
However, for free-running sources and some stabilized sources, the drift character­istics or the rate of large phase instabilities in the source under test may be such
that larger loop holding range and loop bandwidth are required.

The second phase-lock method for maintaining quadrature at the phase detector
permits greater loop holding range and loop bandwidth. By applying the HP

11729C ±

1V

Frequency Control DC FM signal to the HP 8662A/63A DC­coupled FM input, the HP 8662/63A front panel signal acts as the loop VCO (see
Figure 8). The HP 8662A/63A has ±200 kHz maximum DC-FM deviation, and

a maximum loop bandwidth of about 50 kHz. Since the maximum obtainable HP
8662A/63A DC FM deviation is a function of output frequency and can drop as

low as 25 kHz, the obtainable Loop Holding Range (LHR) and Loop Bandwidth

(LBW) is dependent on the frequency of the source under test and the resultant IF
frequency. If in a situation where the allowable deviation is only 25 kHz and lock
cannot be established, first change the test source frequency if possible to yield a
new IF. If this cannot be done, use the Frequency Discriminator Method.

15

Figure

$.

Phase locking with the

8662A/63A DC FM input.

UP

Figure 9. Typical system noise floor at 10
GHz using the Phase Detector Method.

In general, choosing a loop VCO with more tuning range increases the system
noise. However, since it is usually noisier sources that require more loop band­width, the increased system noise typically does not limit the measurement. Figure
9 shows the effect on system noise floor of choosing either of the two phase lock
techniques described above.

20

HP 11729C/8663A

/IN EFC

HP 11729C/8662A

AN DCFM

IOC

Ik 10k 100k

OFFSET FROM CARRIER (H2)

1M

Choosing between the two locking techniques described above requires the user to
have some previous knowledge about the applicabilities and advantages of each
technique. As a "rule-of-thumb", EFC is a good choice for measuring noise on
very stable sources like frequency synthesizers. However, DC-FM provides the
larger LBW needed for maintaining lock on sources with greater drift, like
low-drift, free-running sources.

16

If the user is interested in offset frequencies very close to the carrier and the source
under test can be locked by either technique, EFC would probably be the right
choice. With the EFC technique the noise floor of the HP 8662A/63A at these
close in frequencies is lower than that obtained when locking via DC-FM. This is
exactly what is required if the phase noise of the source under test is very low at
small offsets from the carrier.

Loop Characterization

Figure 10. Typical system output of a
phase noise measurement using the
Phase Detector Method.

In the Phase Detector Method a PLL (phase lock loop) forces the VCO to track
the source under test in phase for offsets less than the bandwidth of the PLL. This
tracking results in suppression of phase noise within the loop bandwidth at the
output of the phase detector. Since no software correction is made for this effect,
the measurement data obtained is not valid for those offset frequencies less than
the loop bandwidth. A vertical line at the offset frequency corresponding to the
phase locked-loop bandwidth is added to the data plot of measurements using the
Phase Detector Method. See Figure 10.

BW NORMALIZED) * NOMINAL LOOP BW-8 kHz

0

£ -40
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OO
TJ

—*t

I

-160
tOO 1k 10k 100k 1M 10M

(GRID LINES IN SEQUENCE OF 1, 2, 4, 6, 8)

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i

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OFFSET FREQUENCY Hz

*?

The lack of correction inside the loop bandwidth is a very important fact to take
into consideration when making phase noise measurements using this software. In

general, a wider loop bandwidth is needed when locking via DC-FM since less

stable sources need more frequency tracking. The two equations below show how
to calculate the nominal loop bandwidth when using either technique. The pro­gram computes this value and displays it both on the Main Menu and on the data
plot.

nominal EFC LBW (Hz)

11729CLBF*f

10

10

DUT

(Hz)

nominal DC-FM LBW (Hz) =

(8662 A/63 A FM Peak Deviation [Hz])*11729C LBF

1

"lb

Thus,

the loop bandwidth can be changed by varying the Lock Bandwidth Factor
(LBF) when using EFC or by varying the Lock Bandwidth Factor and varying the
peak FM deviation when locking with DC-FM. Note that changing the Lock
Bandwidth Factor changes the loop bandwidth in decade steps, while changing the
FM deviation can change the loop bandwidth in finer increments.

17