QEX_2005_03_04.pdf

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Forum for Communications Experimenters

March/April 2005

Issue No. 229

WB8WGA’s Simple, inexpensive ($25) TNC

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QEX 3/2005

ARRL The national association for

About the Cover

INCLUDING:

A $3 PIC makes a simple TNC

that can be adapted for several

digital modes. The story begins

on page 16.

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 229

Doug Smith, KF6DX

Editor

Robert Schetgen, KU7G

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

Mike Daniels

Technical Illustrator

Joe Shea

Production Assistant

Advertising Information Contact:

Janet L. Rocco, Account Manager

860-594-0203 direct

860-594-0200 ARRL

860-594-0303 fax

Circulation Department

Kathy Capodicasa, Circulation Manager

Cathy Stepina, QEX Circulation

Offices

225 Main St, Newington, CT 06111-1494 USA

Telephone: 860-594-0200

Telex: 650215-5052 MCI

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 Designing Wideband Transformers for HF and VHF

Power Amplifiers

By Chris Trask, N7ZWY

16 An Inexpensive Terminal Node Controller for Packet

Radio

By Bob Ball, WB8WGA

26 28 kbps to 9 Mbps UHF Modems for Amateur Radio

Stations

By John Champa, K8OCL; and John Stephensen, KD6OZH

36 High-Efficiency Antennas for Hand-Held Radios

By Richard Kiefer, KØDK

46 A Study of Phased Vertical Arrays

By Al Christman, K3LC

57 Distortion and Noise in OFDM Systems

By Doug Smith, KF6DX

Columns

52 Antenna Options

By L. B. Cebik, W4RNL

62 Next issue in QEX

60 Letters to the Editor

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 2005 QEX Advertising Index

American Radio Relay League: Cov II,

59, Cov III, Cov IV

Atomic Time, Inc.: 63

Down East Microwave, Inc.: 63

Expanded Spectrum Systems: 45

National RF: 64

Nemal Electronics International, Inc.: 64

Noble Publishing Corp.: 64

RF Parts: 63

Teri Software: 63

Tucson Amateur Packet Radio Corp.: 51

Watts Unlimited: 64

League Inc. For permission to quote or reprint

material from QEX or any ARRL publication, send

a written request including the issue date (or book

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 )

Mar/Apr 2005 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 interests in Amateur

Radio communication and experimentation, for

the establishment of networks to provide

communications in the event of disasters or other

emergencies, for the advancement of 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 organiza-

tion 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 two 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 at 225 Main Street,

Newington, CT 06111 USA.

It Looked Good on Mountains of

Paper

Representative government is the

solution to society’s need to organize

and provide for itself. Our chief re-

sponsibility as citizens is to provide

information to our leaders about what

to do and how to do it. We judge lead-

ership by placing our leaders’ lists of

accomplishments against the yard-

stick of our expectations.

In the 1930s, Congress passed much

of its lawmaking authority to bureau-

cracies it created. One of those is the

Federal Communications Commission

(FCC), which falls under the supervi-

sion of those who manage the Com-

merce Department in the USA. The

Commission provides ample opportu-

nity for feedback regarding proposed

legal changes, then its members vote

on them. Elected officials in Congress

have prerogative powers to overturn

any decision. The executive branch of

our government is charged with en-

forcing adopted decisions. It sounds

like a good check-and-balance system,

doesn’t it? Can it be improved?

Michael K. Powell, son of erstwhile

Secretary of State Colin Powell, de-

parts as Chair of the FCC this month.

Get out your yardstick and let’s see

whether his self-proclaimed list of ac-

complishments stacks up. He points to

heavy fines levied against stations

airing lewd material, such as those

carrying the Super Bowl last year and

those carrying Howard Stern’s show.

Ask yourself whether such televised

material has decreased in general.

Powell extolled the virtues of broad-

band-over-power-line (BPL) technol-

ogy. Ask whether BPL has done more

good than harm, given that much of

its occupied bandwidth transports

the very content he promised to fight.

Powell embraced relaxed rules

against owning too many stations in

major markets. Ask if that has im-

proved our lot. Ask if Powell’s FCC

heeded the feedback we gave, espe-

cially on those decisions affecting

Amateur Radio. Consider whether his

actions reflected more concern for eco-

nomics than regulation. Finally, ask if

the mountains of paper generated and

promulgated by the FCC are worth

your hard-earned dollars.

Well, it’s no surprise that Mr.

Powell looks good in our rear-view

mirror. The question at the time of

this writing is: Who comes next?

Somewhat unlike Supreme Court jus-

tices, FCC candidates may be scruti-

nized at confirmation hearings about

their proposed courses of action.

After all, the FCC belongs to the same

branch of government as the con-

firming body. Take firmly your gov-

ernmental reigns and write your

Congresspersons. Now is the best time

to apply your leverage to the situation.

If you haven’t already done so, get

Edward Tenner’s Why Things Bite

Back: Technology and the Revenge of

Unintended Consequences (Knopf

1996, ISBN 0679747567). Read it and

include in your letter some of his bril-

liant examples as quotations. Get with

your friends and add their signatures

to your letter. Send a copy to Presi-

dent Bush. Pray.

Our answer is yes, we can improve

things. If you feel we are wrong,

forget about Tenner and pick up

William J. Lederer’s A Nation of

Sheep (W.W. Norton, 1961, ISBN

0393052885).

Telephone: 860-594-0200

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

Officers

President: JIM D. HAYNIE, W5JBP

3226 Newcastle Dr, Dallas, TX 75220-1640

Executive Vice President: DAVID SUMNER,

K1ZZ

In This Issue

Chris Trask, N7ZWY, looks at de-

signing broadband transformers, es-

pecially for power amplifiers. Chris

covers parasitic effects, magnetic

materials and various topographies.

Bob Ball, WB8WGA presents an in-

expensive TNC that you can build for

$25. Now what packet projects could

you build with that?

John Champa, K8OCL, and John

Stephensen, KD6OZF, describe high-

speed UHF modems. Richard Kiefer,

KØDK, studies end-fed verticals for

hand-held transceivers. Read about

the theory behind them, construction

methods and results.

Al Christman, K3LC, begins a two-

part study of phased vertical arrays

and their ground systems. Al concen-

trates on four-square and certain

other configurations in a thorough

analysis. In “Antenna Options,” LB

Cebik concludes his tale of Yagis with

practical construction techniques. I

close the issue with a paper about dis-

tortion and noise in OFDM systems.—

Doug Smith, KF6DX; kf6dx@arrl.

org.

The purpose of QEX is to:

1) provide a medium for the exchange of ideas

and information among Amateur Radio

experimenters,

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

on IBM or Mac format 3.5-inch diskette 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.

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 2005

Transformers for HF and

VHF Power Amplifiers

The author describes the alternatives available in the design

of transformers for solid state RF amplifiers. The key

parameters of different construction techniques

are discussed with results shown for each.

By Chris Trask, N7ZWY

Introduction

In the design of RF power amplifiers,

wide-band transformers play an

important role in the quality of the

amplifier as they are fundamental in

determining the input and output

impedances, gain flatness, linearity,

power efficiency and other performance

characteristics. The three forms of

transformers that are encountered,

unbalanced-to-unbalanced (unun),

balanced-to-balanced (balbal), and

balanced-to-unbalanced (balun), are

used in various combinations to

accomplish the desired goals.

Careful consideration needs to be

given when making choices of the

magnetic materials (if any is to be used),

the conductors, and the method of

construction, as the choices made weigh

significantly in the overall performance

of the transformer. The type and length

of the conductors and the permeability

of the magnetic material are the

primary factors that determine the

coupling, which in turn determines the

transmission loss and the low frequency

cutoff. The type and length of conductor

used and the loss characteristics of the

magnetic material also affects the

coupling, and further influences the

parasitic reactances that affect the high

frequency performance.

and the manner in which they are con-

structed. The transmission losses and

the low frequency cutoff are primarily

dependent upon the method of con-

struction, the choices of magnetic ma-

terial and the number of turns on the

windings or length of the conductors.

These choices further determine the

parasitic reactances that affect the

high frequency performance, which

include, but are not limited to, resis-

tive losses, leakage inductance,

interwinding capacitance and winding

self capacitance. A complete equiva-

lent model of a wide-band transformer

is shown in Fig. 1. 1 Here, the series

resistances R 1 and R 2 represent the

losses associated with the conductors

in the primary and secondary wind-

ings, respectively. These resistances

are nonlinear, increasing with

1 Notes appear on page 15.

Sonoran Radio Research

PO Box 25240

Tempe, AZ 85285-5240

christrask@earthlink.net

Parasitics and Models

Transformers are not ideal compo-

nents, and their performance is highly

dependent upon the materials used

Mar/Apr 2005 3

Designing Wide-band

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