QEX_2003_01.pdf

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Forum for Communications Experimenters

January / February 2003

XQ2FOD’s elegant autotuning mobile

antenna — inside!

ARRL

225 Main Street

Newington, CT USA 06111-1494

The national association for

AMATEUR RADIO

INCLUDING:

About the Cover

An alternative approach to

screwdriver antennas, the

story starts on p 3.

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.

Yearly subscription rate to ARRL members is $24;

nonmembers $36. Other rates are listed below.

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 216

Mark J. Wilson, K1RO

Publisher

Doug Smith, KF6DX

Editor

Robert Schetgen, KU7G

Managing Editor

Lori Weinberg, KB1EIB

Assistant Editor

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

David Pingree, N1NAS

Technical Illustrator

Joe Shea

Production Assistant

Advertising Information Contact:

Joe Bottiglieri, AA1GW, Account Manager

860-594-0329 direct

860-594-0200 ARRL

860-594-4285 fax

Circulation Department

Debra Jahnke, Circulation Manager

Kathy Capodicasa, Senior Fulfillment Supervisor

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 An Automatically Tuned 7-30 MHz Mobile Antenna

By Manfred Mornhinweg, XQ2FOD

21 Theory of Intermodulation and Reciprocal Mixing:

Practice, Definitions and Measurements in Devices

and Systems, Part 2

By Ulrich L. Rohde, KA2WEU/DJ2LR/HB9AWE

32 Understanding Switching Power Supplies, Part 2

By Ray Mack, WD5IFS

41 Linrad: New Possibilities for the Communications

Experimenter, Part 2

By Leif Åsbrink, SM5BSZ

49 International Digital Audio Broadcasting Standards:

Voice Coding and Amateur Radio Applications

By Cédric Demeure and Pierre-André Laurent

Columns

57 RF By Zack Lau, W1VT

59 Letters to the Editor

61 Next Issue in QEX

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.

Jan/Feb 2003 QEX Advertising Index

American Radio Relay League: 61, 63,

64, Cov III, Cov IV

Array Solutions: Cov II

Atomic Time, Inc.: 40

Buylegacy.com: 62

Down East Microwave Inc.: 58

Expanded Spectrum Systems: 63

Roy Lewallen, W7EL: 58

National RF: 58

Nemal Electronics International, Inc.: 40

Noble Publishing Corp: 63

Teri Software: 31

Tucson Amateur Packet Radio Corp: 62

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 )

Jan/Feb 2003 3

THE AMERICAN RADIO

RELAY LEAGUE

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.

Empirical Outlook

QEX Forums On Line

A friend of QEX , Chris Karpinski,

AA1VL, has created a new Web site at

www.neoamateur.org. It is devoted

to experimentation and technical is-

sues related to Amateur Radio. He set

up at least two on-line forums there

for you, our readers. While not offi-

cially sanctioned by ARRL, the fo-

rums have our support for the

following reasons.

Sixty days can be a long time to

wait for corrections to published ma-

terial and from time to time, we may

put them there so that readers might

get them quickly. Further, we feel

that an on-line forum logically sup-

ports a mission of QEX : to facilitate

the exchange of ideas and information

among Amateur Radio experiment-

ers. Finally, it provides a place for

feedback, opinions and other items

for those who prefer the speed and

informality of on-line publication.

We understand that you sometimes

have questions about authors’ asser-

tions or about sources of parts and in-

formation. Our policy is to correct all

errors and allow authors a chance to

defend their claims. We encourage

criticism of published material where

productive, but we view negative per-

sonal remarks with disdain. Please

consider that when you post things to

the forums. Chris welcomes sugges-

tions for new groups under the QEX

heading that pertain to particular

projects or topics.

Regrettably, Peter Bertini, K1ZJH,

is unable to continue as Contributing

Editor. We plan to keep Tech Notes,

though, and we welcome your submis-

sions for it. The column is a neat ve-

hicle for articles of 3000 words or less,

summarizing new techniques, ideas or

materials. Keep those projects going!

On November 22, 2002, Didier

Chulot, F5MJN, operating F8KGG in

Paris, France, and yours truly in east-

ern Tennessee made a two-way contact

using the digital voice system de-

scribed in this issue. Believed to be the

first transatlantic contact of its kind,

the feat took place on 21,218 kHz us-

ing about 400 W EIRP at each end.

Signals were of readability 5 and

strength S-5 to S-7. QPSK and 16-

QAM modes were used, achieving a

peak symbol rate of 2400 bauds. I re-

corded a mean opinion score of 3.5 us-

ing the 1200 bit/sec QPSK mode.

Further tests are ongoing at the time

of this writing.

In This Issue

Software radio, digital audio and

other advanced digital techniques con-

tinue to shine. That does not mean

QEX is going entirely digital; it is just

that digital techniques constitute an

especially fruitful area for experimen-

tation these days. We still have a lot to

print about analog electronics.

Interestingly, Manfred Mornhinweg,

XQ2FOD, wrote about his 13.8-V, 40-A

switching power supply for The ARRL

Handbook . Here, he takes us inside the

design and construction of his multi-

band mobile HF antenna. Learn how

he overcame the battle against low ef-

ficiency, while operating his automati-

cally tuned unit over more than two

octaves. The article features many in-

teresting mechanical ideas and plenty

of illustrations.

Ulrich Rohde, KA2WEU, focuses on

pragmatic issues of receiver IMD mea-

surement in the concluding segment of

his series. He discusses why IMD does

not always behave as predicted and

presents information about an inter-

laced dual AGC system.

We have been declaiming that

switch-mode power supplies deserve

more coverage. Contributing Editor

Ray Mack, WD5IFS, is addressing

that as he brings us Part 2 of his se-

ries on switchers. This segment con-

tains something we have been

wanting: a discussion of magnetic de-

how to select materials and how to

build inductors and transformers

that work. Follow the rules and get a

healthy, nonsmoking circuit that

lasts a long time!

Leif Åsbrink, SM5BSZ, returns with

a second installment on Linrad . We’ve

had the introduction; now we get to

the nitty gritty. Software unites with

some relatively simple front-end hard-

ware in this segment.

Cédric Demeure and Pierre-André

Laurent describe the new digital audio-

broadcasting standard called DRM, for

Digital Radio Mondiale. Their Ama-

teur Radio system is a subset of the

standard, operating in a 3-kHz band-

width. It is capable of simultaneous

digital voice and data at over 3000 bits/

second on HF. The authors discuss

practical advantages along with some

of the technical details.

In RF, Contributing Editor Zack

Lau, W1VT, describes a 6-meter Yagi

antenna.—Happy New Year!— Doug

Smith, KF6DX ; kf6dx@arrl.org .

Telephone: 860-594-0200

Telex: 650215-5052 MCI

MCIMAIL (electronic mail system) ID: 215-5052

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

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.

4 Jan/Feb 2003

An Automatically Tuned

7-30 MHz

Mobile Antenna

Here’s a beautiful, weatherproof alternative to

screwdriver antennas for the mechanically adept.

By Manfred Mornhinweg, XQ2FOD

and who often travels by car, a

mobile installation soon becomes

a necessity. This is especially true when

traveling on roads like the one depicted

in Fig 1! While in inhabited areas there

is usually some VHF repeater cover-

age, in many other places VHF radios

are useless. HF can provide reliable

contacts, and lots of fun, from any-

where. That led me into setting up a

combined VHF-HF mobile station as

soon as I got my first car.

The VHF antenna is easy enough:

An NMO mount on the center of the

roof takes either a

rience in both building and using HF

mobile antennas, and it has me com-

pletely happy!

Any ham who has ever operated HF

mobile knows that mobile antennas,

especially those for the lower bands,

tend to be notoriously narrow-banded.

In addition, most mobile antennas re-

quire replacing resonators, or at least

plugging jumpers, to change bands. I

used to solve the problem of insufficient

bandwidth by using an automatic an-

tenna tuner, but this did not solve the

band-changing problem. Much too of-

ten, it happened that someone invited

me over to a different band or the propa-

gation closed down on the current band.

Not wanting to pull over, stop, get out

into the rain and change a jumper, I

simply switched off the radio.

That happens no more. The an-

tenna presented here covers all ham

ele-

ment for better performance when out

on the highways. The HF portion in-

volves a lot more difficulties. Many

commercial mobile HF antennas are

less than practical because of their

size, weight and stiffness; others have

low performance. So, I preferred to

homebrew antennas from the start.

Over the years—and when chang-

ing cars—I have gone through four it-

erations in my aim for a “perfect” an-

tenna. While of course nothing can be

really perfect, the antenna presented

here is the result of 10 years of expe-

Buenaventura Osorio 720 Dpto. 1

La Serena, Chile

mmornhin@gmx.net

Fig 1—The antenna has survived well during trips through rugged country.

Jan/Feb 2003 3

F or any ham who likes to travel,

/4 whip for mod-

est operation in cities, or a 5 / 8 -

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