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ADS#01611
March/April 2011
About the Cover
Much of the test equipment made during the last
couple of decades requires 10 MHz external frequency
references. But what if all you have is an older 5 MHz
frequency standard, a common device back in the day?
Rather than purchase a new standard John Roos,
K6IQL, created a solution in the form of a quadrature
driven mixer frequency doubler and output ampliier.
John’s design converts a 5 MHz standard to 10 MHz
and does so with exceptionally low spurious levels.
Read about it in this issue!
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 ofices.
POSTMASTER: Send address changes to:
QEX, 225 Main St, Newington, CT 06111-1494
Issue No 264
Harold Kramer, WJ1B
Publisher
Larry Wolfgang, WR1B
Editor
Lori Weinberg, KB1EIB
Assistant Editor
Zack Lau, W1VT
Ray Mack, W5IFS
Contributing Editors
Production Department
Steve Ford, WB8IMY
Publications Manager
Michelle Bloom, WB1ENT
Production Supervisor
Sue Fagan, KB1OKW
Graphic Design Supervisor
David Pingree, N1NAS
Senior Technical Illustrator
Advertising Information Contact:
Janet L. Rocco, W1JLR
Business Services
860-594-0203 – Direct
800-243-7768 – ARRL
860-594-4285 – Fax
Circulation Department
Cathy Stepina,
QEX Circulation
Ofices
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;
International and Canada by Airmail: ARRL member
$31, nonmember $43;
Members are asked to include their membership
control number or a label from their QST when
applying.
In This Issue
Features
3
On Determining Loop Gain through Circuit Simulation
By John E. Post, KA5GSQ
9
Network Control of the W8ZR StationPro II
By Paul Christensen, W9AC
15
The Effects of Ground Conductivity on Antenna Radials
By Arch Doty, W7ACD
19
Converting a Vintage 5 MHz Frequency Standard to
10 MHz with a Low Spurious Frequency Doubler
By John C. Roos, K6IQL
36
SDR2GO: A DSP Odyssey
By Charles Hill, W5BAA
44
Octave for L-Networks
By Maynard Wright, W6PAP
In order to ensure prompt delivery, we ask that
you periodically check the address information on
your mailing label. If you ind any inaccura-
cies, please contact the Circulation Department
immediately. Thank you for your assistance.
47
An All Purpose High Gain Antenna for 2400 MHz
(last page from Jan/Feb 2011)
By Roger Paskavan, WAØIUJ
Copyright © 2011 by the American
Radio Relay 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 ofice of the Publications Manager
(
permission@arrl.org
).
Index of Advertisers
American Radio Relay League: .........Cover III,
Cover IV
Array Solutions ............................................ 48
ATRIA Technologies, Inc: ............................. 14
Down East Microwave Inc:............................. 8
Kenwood Communications: .................Cover II
National RF, Inc: ............................................ 8
Nemal Electronics International, Inc: ........... 46
RF Parts ................................................ 41, 43
Tucson Amateur Packet Radio: ................... 48
QEX – March/April 2011
1
The American Radio
Relay League
Larry Wolfgang, WR1B
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 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.
Becoming a
QEX
Reader
Many of you noticed that in the January/February 2011 issue of
QEX
, the end of the article
by Roger Paskvan, WAØIUJ, “An All Purpose High Gain Antenna for 2400 MHz” was missing.
A last-second error in preparing the ile to send to our printer resulted in that problem, and we
sincerely apologize for the confusion and inconvenience it caused you. Shortly after discovering
that the last page of the article was missing, I posted the complete article to the “This Month in
QEX
” section of the ARRL website:
www.arrl.org/this-month-in-qex
. For those who did not
ind the article posted there we have printed the missing page in this issue. See page 47. In
addition, I have posted a new photo for Figure 1 and new graphs for Figures 2, 3 and 4 to the
QEX
iles web page:
www.arrl.org/qexiles
. The new photo and graphs have higher resolution
than those printed in
QEX
, but otherwise do not present any different information.
I have spent the past 6 months on a medical leave from my responsibilities at ARRL
Headquarters. In my absence, Publications Manager Steve Ford, WB8IMY, and
QEX
columnist
and technical proofreader, Ray Mack, W5IFS, have been illing in for me. You have probably
noticed that Ray’s “SDR: Simpliied” column last appeared in the Sep/Oct 2010 issue. Ray had
that column just about completed before I went to Virginia for the Boy Scout National Jamboree
last July. Since then, he has been too busy editing articles for publication, and was unable to
ind time to write another column. I hope that will change shortly.
While at the Jamboree, I became ill, and was hospitalized with a cellulitis infection of my leg.
I have now nearly recovered from that infection, as well as surgery and a skin graft that resulted
from it. During my absence, Steve and Ray have completed one and edited four more issues
of
QEX
, along with also carrying out their normal full time responsibilities. My “Thank you”
seems totally inadequate!
Now I have a confession to make to you. Prior to my illness, I had not been a
QEX
reader.
That is, not in the same sense that you enjoy
QEX
in the comfort of your home.
You are probably wondering how I could have missed the pleasure of really
reading
this great
magazine as you read it, as it is meant to be read, for so long. From the time
QEX
was irst
published, I would pick up a copy at ARRL HQ, and occasionally read an article or two.
Frequently an article would look interesting, and I would skim through it, but I did not read any
issue cover to cover! After becoming a
QEX
assistant editor, and later Managing Editor and
then Editor, I still picked up a copy and paged through, but almost never read anything in the
inished, bound magazine. (Of course by the time the magazine is printed, I have read every
manuscript several times as I edited them, and read several versions of page layouts as we
prepared the magazine to go to the printer.)
While on medical leave, I really started to look forward to each issue arriving in the mail.
Perhaps this gives me a better perspective for how you feel as you await the arrival of each issue
in your mailbox. I would quickly grab my copy and examine the cover, and then open it to the
table of contents to see the list of articles inside. Each article seemed to demand to be read irst!
Although I had read all of the manuscripts as we reviewed submitted articles, that is not at all
the same as reading the inished product printed in the magazine.
I had helped select the articles for the Sep/Oct issue, but did not edit any of the articles. I
always enjoy Phil Anderson’s articles and “Synthesizing an Audio AGC Circuit” was no excep-
tion. I wondered how the “WB2EZG Five-Band Trap Dipole” turned out, and was anxious to read
that article. Andrew Daretti’s “Simple and Effective Power Reference” article sure was interest-
ing.
Horst Steder’s “High-Frequency Ladder Filters with Third Overtone Crystals” was a fascinat-
ing read, as was Dave Bowker’s “RF Phase Meter.” Ron Skelton presented some very interest-
ing information about “HF Balun Performance.” I may need to consider adding a vector network
analyzer to my stock of test equipment.
James Ahlstrom’s “All Digital Transceiver for HF” is a tremendous project. Few of us are likely
to duplicate his efforts, but there is so much to learn in that article! I will probably never absorb
everything, but it is deinitely worth reading several times. Sivan Toledo’s “Driverless Ethernet
Sound Card” presents me with another learning opportunity. While I am not active on 2400 MHz,
any project that involves hardware and plumbing construction techniques holds my interest. I
imagine I am more likely to be able to complete such a project than one involving magniiers,
tweezers and a needle-point soldering iron. In spite of that missing page, Roger Paskvan’s
article looks like something I could build.
This issue includes another solid line-up of articles that I am anxious to read. In fact, I’ve
already started reading this issue, because I received the page layout PDF iles to review before
the issue went to press. Happy reading.
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
oficers are elected or appointed by the Directors.
The League is noncommercial, and no one who
could gain inancially 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 ide
interest in Amateur Radio is the only
essential qualiication 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
Telephone: 860-594-0200
FAX: 860-594-0259 (24-hour direct line)
Oficers
President:
KAY C. CRAIGIE, N3KN
570 Brush Mountain Rd, Blacksburg, VA 24060
Chief Executive Oficer:
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 ield, 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
igures 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
QEX – March/April 2011
John E. Post, KA5GSQ
Embry-Riddle Aeronautical University, 3700 Willow Creek Rd, Prescott, AZ, 86301; john.post@erau.edu
On Determining Loop Gain
through Circuit Simulation
Loop gain is a fundamental parameter for electronic circuits
that employ either positive or negative feedback. This article
discusses how to determine loop gain through circuit simulation.
Ampliiers employing positive or nega-
tive feedback are fundamental building
blocks in electronic circuits. Negative feed-
back is employed to linearize amplifiers
in order to reduce distortion of the input
signal and improve amplifier bandwidth.
Conversely, applying sufficient positive
feedback to an ampliier results in an oscilla-
tor because an output signal occurs when no
input signal is present.
1
Figure 1 depicts a block diagram for a
simple ampliier with positive feedback. The
gain of the ampliier is
A
while the gain (or
loss) of the feedback network is
K
. The input
and output voltages of the overall circuit are
v
i
and
v
o
respectively, while the voltage at the
output of the feedback network is
v
f
. Again
referring to Figure 1, the output voltage is
obtained from the ampliied sum of the input
and feedback voltages, or
(
Figure 1 — Block diagram of positive
feedback ampliier depicting input voltage
v
i
, output voltage v
o
, and feedback voltage
v
f
.
Figure 3 — Alternative model of a
positive feedback ampliier consisting of
a dependent current source with current
g
m
v
x
in parallel with a feedback impedance
Z
f
. Each “X” indicates locations where it is
possible to break open the loop in order
to determine loop gain.
electronic circuit will actually function as
an oscillator.
In order to develop a method to deter-
mine the loop gain, consider Figure 2, which
is redrawn to emphasize the feedback por-
tion of the loop from Figure 1. If the loop is
opened at either “X” and a test voltage
v
test
is applied to the side of the loop that leads
to the ampliier input, what voltage
v
measure
is
measured at the other side of the loop open-
ing? Obviously
v
measure
=
AKv
test
so that the
loop voltage gain is
v
measure
/
v
test
=
AK
=
T
.
Figure 3 shows a circuit model of the pos-
itive feedback ampliier, Figure 2. As shown
in the igure the circuit consists of a depen-
dent source, in this case a voltage controlled
current source that represents an ideal trans-
conductance ampliier and an impedance
Z
f
that represents the load of the feedback net-
Eq. 1
)
v
=
A v
+
v
o
i
f
Figure 2 — Positive feedback ampliier
redrawn to emphasize the feedback loop.
Each “X” indicates locations where it is
possible to break open the loop in order
to determine loop gain.
while the voltage at the output of the feed-
back network is found from
v
f
=
Kv
o
Eq. 2
Combining Equations 1 and 2 in order to
eliminate the feedback voltage term allows
the voltage at the output of the ampliier to
be expressed in terms of the input voltage as
A
ier to sustain oscillations the Barkhausen
criteria requires that the magnitude of
T
is equal to unity at a frequency where the
phase of
T
is equal to 0 degrees or radi-
ans (or some integer multiple of 360
o
or 2π radians). In order for oscillations to
start
the loop gain must be greater than unity
at a frequency where the phase is 0 degrees
or radians (or some integer multiple of 360
o
or 2π radians).
2
Thus, the loop gain provides
critical information concerning whether an
1
1
v
=
v
=
v
o
i
i
1
1 A K
−
K
Eq. 3
−
1
A K
In Equation 3 the term
AK
is referred to
as the loop gain
T
.
In order for the positive feedback ampli-
1
Notes appear on page 7.
QEX – March/April 2011
3
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