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Forum for Communications Experimenters

January / February 2005

Issue No. 228

Subassemblies of AK4AA’s

Effective CW/SSB Receiver

for 40m and 80m

ARRL

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Newington, CT USA 06111-1494

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QEX 1/2005

ARRL The national association for

About the Cover

INCLUDING:

Dave Lyndon’s (AK4AA)

homebrew receiver 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.

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 228

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:

Joe Bottiglieri, AA1GW, Account Manager

860-594-0329 direct

860-594-0200 ARRL

860-594-4285 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 An Effective 80 and 40 Meter SSB/CW Receiver

By Dave Lyndon, AK4AA

16 Anatomy of a Homebrew Messaging APRS Tracker

By Dennis Nendza, W7KMV

29 RF Power Amplifier Output Impedance Revisited

By Robert L. Craiglow

38 Why Antennas Radiate

By Stuart G. Downs, WY6EE

43 Low-Noise Frequency-Synthesizer Design

By Randy Evans, KJ6PO

Columns

52 RF By Zack Lau, W1VT

57 2004 Index

59 Letters to the Editor

62 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 2005 QEX Advertising Index

American Radio Relay League: Cov II,

42, Cov III, Cov IV

ARA West: 62

Atomic Time, Inc.: 63

Down East Microwave, Inc.: 63

jwm Engineering: 37

National RF: 64

Nemal Electronics International, Inc.: 64

Noble Publishing Corp.: 64

RF Parts: 63

TechNote Time Watch Co.: 42

Teri Software: 63

Tucson Amateur Packet Radio Corp.: 62

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 )

Jan/Feb 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.

Lies, Damned Lies and Statistics

With apologies to Benjamin

Disraeli, our heading refers to preci-

sion and accuracy in measurement

and estimation. After such a charged

political cycle in the US, the foibles of

pollsters provide a convenient start

for discussion; but at the outset, let

us agree to disagree. The question is:

By how much?

Precision relates to the repeatabil-

ity and consistency of measurements.

We define accuracy as the degree to

which measurements agree with

some value of known precision. Those

two terms apply to both political poll-

ing and electrical measurements,

with some differences.

Imagine that we took a nationwide

pre-election poll of registered voters

to see how many votes each of two

candidates was likely to get. Since we

couldn’t poll the entire electorate, we

selected a sample of, say, 1200 at ran-

dom. From that sample, we guessed

how all national voters were going to

vote. Because the sample was but

0.001% of the electorate, we declared

a margin of uncertainty based on that

sample size. We also guessed how

many of those polled would change

their minds between poll and election

or simply not vote at all.

Through grungy statistical pro-

cesses, we determined that our un-

certainty was about ±3%. The two-

man race seemed close but after the

poll, however remote the chance, can-

didate A could have suddenly em-

braced some mortifying political

position, and all 1200 in our sample

would vote for candidate B, but the

likelihood of that was virtually nil,

especially if candidate A stuck to his

advisors’ (read puppeteers’ ) lines.

Then on Election Day, we take an

exit poll. This time, we’re sampling

with higher inherent accuracy and

precision, because we deem it quite

unlikely that voters would lie to us

about the choices they just made.

Still, the size of the sample sets the

margin of uncertainty when predict-

ing the entire nation’s vote.

At least one wag points out that if we

combined the results of our polls with

those of other pollsters, we’d get a

larger sample size and less uncer-

tainty. That’s likely for truly random

samples. In every case, though, we

should really title our results, “Regis-

tered voters who respond to polls.”

Only a post-election tally reveals the

accuracy of the polling and only then is

the term margin of error appropriate.

In electronics, we rarely encounter

precisely known quantities. Accord-

ingly, a margin of uncertainty must

accompany our measurements. Nu-

merical results should appear with

only as many significant figures as the

margin of uncertainty supports.

For example, were we to state a

receiver’s noise figure as 7.1 dB, we’d

imply that our uncertainty was

±0.1 dB; or if we announced a trans-

mitter’s power output to be 101 W,

we’d tacitly claim an uncertainty of

±1 W or ±0.04 dB. That is, unless we

explicitly stated a different margin!

Adherence to statistical rules is im-

portant politically and electronically,

lest the results fall into the wrong

category of this column’s heading. It’s

just one of those many small improve-

ments that might better our lot.

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

Dave Lyndon, AK4AA, details his

homebrew 80- and 40-m receiver.

Dave takes a bit of the old and a bit of

the new in his design.

Dennis Nendza, W7KMV, reports on

building a messaging APRS tracker.

He takes us through hardware, soft-

ware, packaging and operation.

Bob Craiglow addresses some is-

sues surrounding amplifier output

impedance using nonlinear theory.

On the theoretical side of things,

Stu Downs, WY6EE, contributes his

look at why antennas radiate. Like

the famous “Why is the sky blue?”

question, getting a true understand-

ing requires some study.

Randy Evans, KJ6PO, delivers

ways to optimize phase-locked loop

performance in frequency synthesis.

His spreadsheets for type-1 and

type-2 loops allow simulation beyond

“cookbook” predictions of perfor-

mance

Zack Lau, W1VT, presents a 10-GHz

waveguide preamplifier in RF —

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 Jan/Feb 2005

40 Meter SSB/CW Receiver

An Effective 80 and

Something old and something new in a

homebrew dual-band receiver.

By Dave Lyndon, AK4AA

of possible architectures for

amateur-band receivers. This is

yet another entry, an 80- and 40-meter

SSB/CW receiver that uses modern

technology (something new) to imple-

ment a high-performance design in a

small package with its roots in the

1950s and 60s (something old). In ad-

dition, there’s something borrowed,

too. Although relying heavily on ARRL

Handbooks and personal experience,

much of the circuitry was borrowed

from others without embarrassment.

(I only steal from the very best! See

the references at the end of this ar-

ticle for acknowledgements.) It has

noise-figure, dynamic-range, and

intermodulation performance as good

as most high-quality commercial re-

ceivers, and it’s better than many.

The receiver is kept as simple as

possible without sacrificing perfor-

mance by foregoing optional bells and

whistles. However, it is not a weekend

project, nor a task for the faint-

hearted. It will take some time and

patience to duplicate, but the result

will be rewarding—and relatively in-

expensive, too. New parts are readily

available from various sources on the

Internet and can be purchased for less

than $200. A well-endowed junk box

will reduce that considerably. You will

also need some test equipment to

make various adjustments. My test

bench is quite modest: an inexpensive

digital multimeter, a 20 k

nal generator, an even-more-ancient

Heathkit RF signal generator, a “bot-

tom-of-the-line” frequency counter, a

vintage 20 MHz dual-channel oscillo-

scope and a homebrew inductance

meter described in Reference 8. You

can get through this project with less

equipment, but I found the scope and

counter invaluable. It’s amazing what

can be accomplished with reasonably

simple tools.

Fig 1 is a photograph of the com-

pleted receiver, and Fig 2 is the block

diagram. The antenna is connected to

the first mixer through passive filters

that select either the 80- or 40-meter

band. The local oscillator is a VFO,

tunable from 5.2 to 5.7 MHz.

Signals either from 3.5 to 4.0 MHz

or 6.9 to 7.4 MHz (7.0 to 7.3 MHz is

the 40-meter amateur band) are down-

converted to a common intermediate

85 Woody Farm Rd

Hot Spring, NC 28743

dlyndon@director.com

/V analog

multimeter, an old Heathkit audio sig-

Jan/Feb 2005 3

T here is no limit to the number

Ω

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