QEX_2006_03_04.pdf

ARRL

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AMATEUR RADIO

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■ Language of modeling

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QEX 3/ 2006

AMATEUR RADIO

QEX (ISSN: 0886-8093) is published bimonthly

in January, March, May, July, September, and

November by the American Radio Relay League,

225 Main Street, Newington, CT 06111-1494.

Periodicals postage paid at Hartford, CT and at

additional mailing offices.

POSTMASTER: Send address changes to:

QEX, 225 Main St, Newington, CT 06111-1494

Issue No 235

About the Cover

Gary Steinbaugh, AF8L, describes his

Pizzicato Pulse Generator and teaches us

how to observe the characteristics of a

transmission line by watching the reflected

pulses on an oscilloscope. This is

one piece of test gear that could

be music to your eyes!

Harold Kramer, WJ1B

Publisher

Doug Smith, KF6DX

Editor

Larry Wolfgang, WR1B

Managing Editor

Lori Weinberg, KB1EIB

Assistant Editor

L. B. Cebik, W4RNL

Zack Lau, W1VT

Ray Mack, WD5IFS

Contributing Editors

Production Department

Steve Ford, WB8IMY

Publications Manager

Michelle Bloom, WB1ENT

Production Supervisor

Sue Fagan

Graphic Design Supervisor

Devon Neal

Technical Illustrator

Joe Shea

Production Assistant

Advertising Information Contact:

Janet L. Rocco, W1JLR

Business Services Manager

860-594-0203 direct

860-594-0200 ARRL

860-594-0303 fax

Circulation Department

Cathy Stepina, QEX Circulation

Offices

225 Main St, Newington, CT 06111-1494 USA

Telephone: 860-594-0200

Fax: 860-594-0259 (24 hour direct line)

e-mail: qex@arrl.org

Subscription rate for 6 issues:

In the US: ARRL Member $24,

nonmember $36;

US by First Class Mail:

ARRL member $37, nonmember $49;

Elsewhere by Surface Mail (4-8 week delivery):

ARRL member $31, nonmember $43;

Canada by Airmail: ARRL member $40,

nonmember $52;

Elsewhere by Airmail: ARRL member $59,

nonmember $71.

Members are asked to include their membership

control number or a label from their QST when

applying.

Features

3 Pizzicato Pulse Generator

By Gary Steinbaugh, PE, AF8L

9 A 100-W Class-D Power Amplifier for LF and MF

By Frederick H. Raab, W1FR; Mike Gladu, N1FBZ, and Dan Rupp

14 An Expanded Reflection-Coefficient Equation for

Transmission-Line Junctions

By Roger Sparks, W7WKB

20 Perfecting a QSK System

By Markus Hansen, VE7CA

25 An L-Q Meter

By Jim A. Koehler, VA7DIJ

35 Blocking Dynamic Range in Receivers

By Leif Åsbrink, SM5BSZ

40 An Analysis of Stress in Guy-Wire Systems

By William Rynone, PhD, PE

46 An Accidental Discovery Put to Work

By Vidi la Grange, ZS1EL

Columns

8 Book Review

61 Next Issue in QEX

51 Antenna Options

By L. B. Cebik W4RNL

59 Letters

61 Upcoming Conferences

In order to ensure prompt delivery, we ask that

you periodically check the address information

on your mailing label. If you find any inaccura-

cies, please contact the Circulation Department

immediately. Thank you for your assistance.

Mar/Apr 2006 QEX Advertising Index

League Inc. For permission to quote or reprint

material from QEX or any ARRL publication, send

a written request including the issue date (or b ook

title), article, page numbers and a description of

where you intend to use the reprinted material.

Send the request to the office of the Publications

Manager ( permission@arrl.org )

American Radio Relay League: Cov II,

45, 58, 62 , 64, Cov III

ARA West: 63

Atomic Time: 19

Down East Microwave, Inc.: 39

Elkins Marine Training International: 63

Expanded Spectrum Systems: 63

jwm Engineering: 34

Kenwood Communications: Cov IV

National RF: 64

Nemal Electronics International, Inc.: 64

RF Parts: 63

Teri Software: 50

Tucson Amateur Packet Radio Corp.: 62

Mar/Apr 2006 1

THE AMERICAN RADIO

RELAY LEAGUE

Empirical Outlook

The American Radio Relay League, Inc, is a

noncommercial association of radio amateurs,

organized for the promotion of interest in Amateur

Radio communication and experimentation, for the

establishment of networks to provide communica-

tions in the event of disasters or other

emergencies, for the advancement of the radio art

and of the public welfare, for the representation of

the radio amateur in legislative matters, and for

the maintenance of fraternalism and a high

standard of conduct.

ARRL is an incorporated association without

capital stock chartered under the laws of the state

of Connecticut, and is an exempt organization

under Section 501(c)(3) of the Internal Revenue

Code of 1986. Its affairs are governed by a Board

of Directors, whose voting members are elected

every three years by the general membership. The

officers are elected or appointed by the Directors.

The League is noncommercial, and no one who

could gain financially from the shaping of its

affairs is eligible for membership on its Board.

“Of, by, and for the radio amateur,” ARRL

numbers within its ranks the vast majority of active

amateurs in the nation and has a proud history of

achievement as the standard-bearer in amateur

affairs.

A bona fide interest in Amateur Radio is the only

essential qualification of membership; an Amateur

Radio license is not a prerequisite, although full

voting membership is granted only

to licensed amateurs in the US.

Membership inquiries and general corres-

pondence should be addressed to the

administrative headquarters:

ARRL, 225 Main Street, Newington, CT 06111 USA.

Familiar Faces in New Jobs

Please join us in welcoming Larry

Wolfgang, WR1B, as Managing Editor of

QEX . Larry comes aboard with consider-

able experience as a technical editor. His

ARRL duties also include being Senior

Assistant Technical Editor of QST. Pre-

viously, he was a member the “Book

Team” editorial staff. He was the han-

dling editor for Now You’re Talking,

ARRL’s Tech Q&A, The ARRL General

Class License Manual, ARRL’s General

Q & A, Your Introduction to Morse Code

— on cassettes and CDs — and The

ARRL Extra Class License Manual .

Larry was responsible for the video li-

censing courses, as well. He wrote Un-

derstanding Basic Electronics , a popular

book among young hams and hams-to-

be. Larry has also edited several chap-

ters of The ARRL Handbook .

Larry formats articles and shepherds

them through our production process,

among other things. His attention to

detail is a tremendous asset to our edito-

rial team. You’ll find him to be a techni-

cally savvy fellow with a positive attitude

and some very good ideas about how to

ensure that QEX remains the top peri-

odical in its field. Give him the support

you gave his predecessor and QEX will

continue to improve.

On January 20, 2006, Joel Harrison,

W5ZN, of Judsonia, Arkansas, was

elected League President for the next

two years. He succeeds Jim Haynie,

W5JBP, who chose not to run for a

fourth term in the uncompensated, vol-

unteer post. Gathering in Windsor, Con-

necticut, for its annual meeting, the

Board voted 10 to 5 to choose Harrison

over ARRL Central Division Director

Dick Isely, W9GIG, the only other nomi-

nee.

First licensed in 1972 as WN5IGF,

Harrison says he’s interested in virtu-

ally all aspects of Amateur Radio, from

HF DXing and contesting to VHF/UHF/

microwave and moonbounce. He’s an

ARRL Life Member. His wife, daughter

and son all are Amateur Radio licensees.

He’s the League’s 14th President since

its founding in 1914.

Harrison also says he’ll promote the

League’s Petition for Rule Making

(RM-11306) to regulate Amateur Radio

allocations by necessary (occupied)

bandwidth. “Right now we do that by

mode, and we’re one of the few countries

in the world that does that,” he pointed

out. “We need to change that and move

forward with this initiative of regulation

by bandwidth instead of mode.” Related

to that issue, the Board is in the process

of developing effective band plans to

support the rule changes it’s requesting

in RM-11306.

We feel RM-11306 is a much-needed

change. The existing rules are arcane

when it comes to allowing for the devel-

opment of new modes and the efficient

use of our spectrum, especially on HF.

We hope you’ve sent your comments to

the FCC.

The ARRL Board also elected Vice

President Kay Craigie, N3KN, as First

Vice President, succeeding Harrison,

and Delta Division Director Rick

Roderick, K5UR, to Vice President, suc-

ceeding Craigie. Both were unopposed.

As always, certain minor changes are

afoot here, as well. Note that we’ve

dropped Communications Quarterly

from our banner. The effects of our

merger with that erstwhile publication

have long since reached equilibrium.

Award-winning artist Sue Fagan has re-

styled our cover. We’re eliminating the

“In This Issue” portion of this editorial

because it regularly delays finalization of

the column, which in turn places undue

last-minute deadline pressure on the

staff. We’ll occasionally comment on cer-

tain content as conditions warrant.

You’ve helped us fill these pages with

some very interesting and informative

pieces and we’re not starving — good job!

Our article acceptance criteria are not

changing; but an increasingly important

criterion is whether submitted manu-

scripts are in the standard form. We

must be able to place your exhibits —

tables, figures and the like — where

they best fit within our published for-

mat. We therefore ask that you place

tables and figure captions at the end of

your manuscript, and place graphics in

separate files.

We use Microsoft Word for most of our

editing work but not for final page lay-

outs. We’d rather devote our editing

time to your text than to deleting embed-

ded exhibits, reformatting what’s left

and begging for graphics files. Many

magazines automatically return material

not in standard form because of the ex-

tra work required. Give your articles

their best chance of acceptance by re-

viewing “Preparing a Manuscript — The

Standard Form” on our Web page at

www.arrl.org/qex . To those of you

who’ve been heeding that advice:

Thank you! — 73, Doug Smith, KF6DX,

kf6dx@arrl.org

Telephone: 860-594-0200

FAX: 860-594-0259 (24-hour direct line)

Officers

President: JOEL HARRISON, W5ZN

528 Miller Rd, Judsonia, AR 72081

Chief Executive Officer: DAVID SUMNER, K1ZZ

The purpose of QEX is to:

1) provide a medium for the exchange of ideas

and information among Amateur Radio experiment-

ers,

2) document advanced technical work in the

Amateur Radio field, and

3) support efforts to advance the state of the

Amateur Radio art.

All correspondence concerning QEX should be

addressed to the American Radio Relay League,

225 Main Street, Newington, CT 06111 USA.

Envelopes containing manuscripts and letters for

publication in QEX should be marked Editor, QEX.

Both theoretical and practical technical articles

are welcomed. Manuscripts should be submitted in

word-processor format, if possible. We can redraw

any figures as long as their content is clear.

Photos should be glossy, color or black-and-white

prints of at least the size they are to appear in

QEX or high-resolution digital images (300 dots per

inch or higher at the printed size). Further

information for authors can be found on the Web at

www.arrl.org/qex/ or by e-mail to qex@arrl.org .

Any opinions expressed in QEX are those of

the authors, not necessarily those of the Editor or

the League. While we strive to ensure all material

is technically correct, authors are expected to

defend their own assertions. Products mentioned

are included for your information only; no

endorsement is implied. Readers are cautioned to

verify the availability of products before sending

money to vendors.

2 Mar/Apr 2006

Pizzicato Pulse Generator

Your oscilloscope and the Pizzicato create a time domain

reflectometer, a handy piece of test equipment for

checking your transmission line’s characteristics.

By Gary Steinbaugh, PE, AF8L

A n Amateur Radio station has

∂

said, “From a long view of the his-

tory of mankind — seen from, say,

10,000 years from now — there can

be little doubt that the most signifi-

cant event of the 19th century will

be judged as Maxwell’s discovery of

the laws of electrodynamics.” 1

You can think of a transmission line

or a violin string as a row of little

masses connected by springs (a lumped-

parameter model). Any given mass is

affected only by the two adjacent

masses connected to it by springs. Look

at the left column of Figure 1, which

shows a wave being “launched” by giv-

ing the left end a tug upward, then an

equal tug downward. You can see how

the masses and springs yank each other

up and down to form a wave that trav-

els toward the right end (note that the

1 Notes appear on page 8.

much in common with a violin:

the transmitter is like a bow, the

transmission line is like the strings and

the antenna is like the wooden body.

Now, a violinist will recognize the mu-

sical term pizzicato as a direction to

pluck the strings instead of using a bow.

The pulse generator described in this

article electrically “plucks” a transmis-

sion line; by observing the line’s reac-

tion on an oscilloscope, you can check

the line’s length, terminations, and pos-

sible defects.

The radio/violin similarity is actu-

ally mathematical, as both obey the

wave equation,

∇

∂

The Scottish scientist James Clerk

Maxwell (1831-1879) collected, com-

pleted and combined the electromag-

netic equations of Gauss, Ampère and

Faraday, obtaining a wave equation for

the electric field, and a corresponding

wave equation for the magnetic field.

Maxwell showed that the wave

equation’s constant 1 / c 2 (the prod-

uct of the permeability and permit-

tivity of free space) is equal to the

reciprocal of the square of the speed

of light in a vacuum (c = 299,792,458

m/s). He correctly theorized that light

is electromagnetic, and paved the

way for the likes of Hertz, Marconi,

and Einstein. The Nobel Prize-win-

ning physicist Richard Feynman

9534 Appomattox Ct

Loveland, OH 45140-7140

gsteinbaugh@yahoo.com

Mar/Apr 2006 3

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