QEX_2006_11_12.pdf

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QEX 11/2006

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 239

About the Cover

Paul Wade, W1GHZ, shows us how to

design waveguide to coaxial cable

transition blocks. The cover photos

show a waveguide slotted line, which

Paul uses to measure the

complex impedance inside the

waveguide, along with some

resulting transitions.

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, KB1NSR

Technical Illustrator

Joe Shea

Production Assistant

Advertising Information Contact:

Janet L. Rocco, W1JLR

Business Services

860-594-0203 direct

860-594-0200 ARRL

860-594-0303 fax

Circulation Department

Cathy Stepina, QEX Circulation

Offices

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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,

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

ARRL member $31, nonmember $43;

Canada by Airmail: ARRL member $40,

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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 Measurement of Soil Electrical Parameters at HF

By Rudy Severns, N6LF

10 Rectangular Waveguide to Coax Transition Design

By Paul Wade, W1GHZ

18 IMD in Digital Receivers

By Leif Åsbrink, SM5BSZ

23 In Search of New Receiver-Performance Paradigms, Part 1

By Doug Smith, KF6DX

31 Seventh-Order Unequal-Ripple Low-Pass Filter Design

By Dave Gordon-Smith, G3UUR

35 A High-Efficiency Filament Regulator for Power Tubes

By Eric von Valtier, K8LV

40 Command and Control: Talk to Your Radio and

Your Radio May Talk Back

By Steve Gradijan, WB5KIA

Columns

49 Tech Notes

By Robert P. Haviland, W4MB

50 Next Issue in QEX

51 Antenna Options

By L. B. Cebik, W4RNL

59 Out of the Box

By Raymond Mack, W5IFS

60 Letters

63 2006 Index

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.

Nov/Dec 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 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 ).

American Radio Relay League: Cov II,

30, Cov III , Cov IV

ARA West: 48

Atomic Time: 39

Down East Microwave, Inc.: 64

Elkins Marine Training International: 48

International Crystal Manufacturing: 50

National RF: 59

Nemal Electronics International, Inc.: 64

Real Nerds: 17

RF Parts: 39

Teri Software: 64

Timewave Technology, Inc: 22

Tucson Amateur Packet Radio Corp.: 30

Nov/Dec 2006 1

THE AMERICAN RADIO

RELAY LEAGUE

Empirical Outlook

Doug Smith, KF6DX

kf6dx@arrl.org

The American Radio Relay League, Inc, is a

noncommercial association of radio amateurs,

organized for the promotion of interest in

Amateur Radio communication and experimenta-

tion, for the establishment of networks to provide

communications 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:

Twenty-Five Candles Burning Brightly

It wasn’t hard to select

an editorial topic this time.

It’s QEX ’s 25 th birthday!

You’ll find me near the

center of the celebration,

but it isn’t about me. It’s

about us.

Editors often write in

first-person plural, as if

writing for the entire staff.

For this occasion, that form

shall embrace not only staff

but also writers, readers,

artists, printer — the whole

lot of us. I’ll unabashedly

exercise my prerogatives, as

head cheerleader, in the

singular.

You’re reading the best

technical journal in its field. QEX rose to that

status through hard and intelligent work of the

same kind that sustains it now. Like many

other magazines, we began somewhat mod-

estly in an era when more emphasis was

placed on technical know-how than is placed

on it today. It’s irrefutable what a difference

25 years can make. I don’t equivocate because

judging by the results in the publishing world,

things have certainly changed.

Ham radio (1968-1990) had a 22-year

run. Billed as ham radio ’s logical succes-

sor, Communications Quarterly (1990-

1999) ran for nine. 73 (1960-2003)

survived for 43 years. QST (1915- ) is still

going strong, of course, and looks better

than ever in my opinion; but its formerly

heavy technical content has diminished by

choice. CQ (1945- ) is still percolating

along after more than 60 years but its tech-

nical material has also declined. Its sister

publication, CQ VHF , faltered in 1999 but

came back in 2002. QEX had its little

stumble, too, in 1997 when we missed six

issues. One of the given reasons was lack

of sufficient article submissions.

I’m happy to report that we’re in good

shape both financially and editorially now.

No, we don’t make a big monetary gain and

our circulation hasn’t grown significantly in

recent years, as we’d hoped; but we’re not

slipping either. We’re fortunate to get ar-

ticles and readers from all corners of the

globe. As opposed to some of those other

periodicals, our technical content has

steadily and dramatically improved. QEX

has garnered six of the last eight ARRL

Doug DeMaw, W1FB, Technical Excel-

lence Awards. We are justifiably proud of

all the great articles you’ve written! The last

few issues have been great and I think you’ll

find this Silver Anniver-

sary issue particularly out-

standing.

Sometimes it’s not

enough to produce a good

magazine, though. Folks

can’t be expected to read it

if they don’t know it ex-

ists. We need to promote

ourselves because just

about the only advertising

we get is in ARRL publi-

cations. Ask me for com-

plimentary issues and

anything else that may en-

tice new readers to sub-

scribe. I’ll fulfill all

reasonable requests.

Since I mentioned adver-

tising, let me ask whether any of you intrepid

entrepreneurs could use a four-color, full-page

cover ad. It’s a lot less expensive than you

might think and you’ll be reaching a reader-

ship that includes leaders in communications

from academia, industry and Amateur Radio.

Check out our rate sheet at www.arrl.org/

ads/#QEX .

Aside from being head cheerleader, a

magazine editor must play other roles from

time to time, such as referee, business man-

ager, grammar cop, jury and chief cook and

bottle washer. From this point in the middle

of my ninth year, I have to write that it’s

been a blast! A highlight for me personally

is getting acquainted with so many of you

astute technical types whose thoughts and

projects light the way for the rest of us. Only

one thing is missing: I can’t recall having

received even a single article submission or

letter from a female writer. Where are you

gals hiding?

Casting a gaze to the future, we must ask

ourselves what else we need in QEX . Our

stated policy has been one of many small

improvements but big improvements don’t

hurt. How about more microwave? More

simple construction articles? We’ve decided

to press again for more practical information

about new components and software of in-

terest to communications experimenters.

Please send us your announcements.

I extend hearty thanks to you who’ve

supported this forum through the years. We

continue to gobble up the material that helps

us meet our stated purpose (in column 1 at

the left). If your last submission wasn’t ac-

cepted, please refer to our Author’s Guide

at www.arrl.org/qex/#aguide and try

again. Drop me a line anytime. My door is

always open.

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

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 Nov/Dec 2006

QEX, Number 1,

December 1981.

Measurement of Soil

Electrical Parameters at HF

The author describes the technique he uses to measure soil

conductivity and relative dielectric constant over a range of

frequencies on the HF bands.

Rudy Severns, N6LF

Introduction

Modeling of antennas over real ground

requires at least a reasonable guess of the

values for the soil conductivity (

) and

There are common situations where the

values for the soil constants (which are

anything but constant!) are really not very

important for modeling purposes. For

example, for horizontal polarization with

antenna heights above 1 / 4 -

antennas are certainly practical but they’re

not easy, being large and relatively

expensive. The option is to go to a vertical

array, which may be easier. Accurately

predicting the performance of a possible

vertical array in comparison to a competing

horizontal array requires at least a reasonable

guess for the ground characteristics on that

band. The decision as to which way to go

may depend, at least in part, on having a

reasonable estimate of the ground

characteristics.

Another problem with present ground

modeling practice is the assumption that soil

parameters, whatever they may be in a given

location, are constant over frequency. For ex-

ample, for a given soil, the assumption is that

ground constant values at 160 m are the same

as the values at 20 m. That’s not the case. As

pointed out by Bob Haviland, W4MB, and in

many professional papers, ground parameters

at HF vary substantially with frequency. 1, 2

There is a need for a practical method to

estimate soil parameters at HF for amateurs.

By practical, I mean a mechanically simple

test apparatus and measurement equipment

r ), also referred to as

“relative dielectric constant.” Unfortunately

these numbers are usually not readily

available. From broadcast (BC) work we

have charts of ground conductivity covering

large areas, but these numbers give only

, the numbers are

not very critical for determining feed-point

impedances, near-field losses or the formation

of the far-field radiation pattern. Another case

would be for vertical antennas where one has

the space, money and patience to lay down a

large number of long radials. With this brute

force approach, the near-field ground loss can

be made arbitrarily small regardless of the

soil, and you really don’t care what the ground

constants are, at least from a local loss point

of view. The far-field pattern, however, is still

just a guess without real data.

If your space and/or financial resources

are more limited, then a modestly accurate

estimate of your ground characteristics will

allow you to design a ground system that

minimizes the loss within the constraints of

the space and resources you do have. There

is also the situation that arises fairly often

on 80 m. On that band a 1 / 2 -

r data is

because, for sites where you would want to

build a BC station, the soil characteristics

are usually dominated by

r . In part, the absence of

r has only

a second-order effect. This is often true at

BC frequencies but is usually not the case

in all but the most conductive soils at HF. In

addition, the values for

, and

will be different

between BC frequencies and HF. Another

problem is that the BC ground conductivity

charts cover much too large an area to take

into account the details of local ground

variation, which can deviate greatly from

local averages.

It would appear that the best approach is to

simply measure your local soil characteristics

at the frequencies of interest. Unfortunately,

this is much easier said than done. None of

the known methods is anywhere near perfect,

and many are difficult to implement. In fact

there is a school of thought that the problem is

impossible and we should not waste our time

worrying about it. I don’t share that view as a

general proposition, but it is not without some

justification, given the difficulties involved.

is about

130 feet, which is not an exceptionally tall

tower for amateur use. Horizontal gain

1 Notes appear on page 8.

PO Box 589

Cottage Grove, OR 97424-0025

rudys@ordata.com

www.antennasbyn6lf.com

Figure 1 — This diagram shows the Wenner array, the traditional method used by

amateurs to measure ground parameters.

Nov/Dec 2006 3

relative permittivity (

not

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