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January/February 2011
About the Cover
This month’s
QEX
cover showcases the
HF digital transceiver designed by James
Ahlstrom, N2ADR. See his article “An All-Digital
Transceiver for HF.” The actual circuit board and
enclosure appear in the cover foreground. A
screenshot of the author’s Quisk control software
is displayed in the background.
QEX (ISSN: 0886-8093) is published bimonthly
in January, March, May, July, September, and
November by the American Radio Relay League,
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Periodicals postage paid at Hartford, CT and at
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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
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Publications Manager
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Production Supervisor
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Senior Technical Illustrator
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Members are asked to include their membership
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applying.
In This Issue
Features
3
An All-Digital Transceiver for HF
By James Ahlstrom N2ADR
9
A Two Diode Frequency Doubler
By John Pivnichny, N2DCH
12
A Driverless Ethernet Sound Card
By Sivan Toledo, 4X6IZ
18
Simulating Tapped Coupler Inductors
By Oleg Sergin, DL2IPU
29
Seventh-Order Unequal-Ripple SVC Low-Pass Filters with
Improved Second Harmonic Attenuation
By Dave Gordon-Smith, G3UUR
35
Loop Antennas—The Factor “N”
By Virgil Leenerts, WØINK
39
An All Purpose High Gain Antenna for 2400 MHz
By Roger Paskavan, WAØIUJ
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.
46
2010
QEX
Index
48
Upcoming Conferences
Copyright © 2010 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
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Index of Advertisers
American Radio Relay League: .........Cover III,
Cover IV
ATRIA Technologies, Inc: ............................. 38
Down East Microwave Inc:........................... 47
JWM Engineering Group, Inc:...................... 47
Kenwood Communications: .................Cover II
National RF, Inc: .......................................... 48
Nemal Electronics International, Inc: ............. 8
RF Parts ................................................ 45, 47
Tucson Amateur Packet Radio: ................... 11
QEX – July/August 2008
1
The American Radio
Relay League
Raymond Mack, W5IFS
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.
Larry is still recovering from an illness. He is ine, but unable to write for this issue, so it falls to
me again.
HSMM Losses
The HSMM activity lost a pioneer on November 12, 2010. John Champa, K8OCL, lost his
battle with cancer. Many people knew his work through the ARRL HSMM working group and
he was working on new topics until just recently. You can read more at
www.arrl.org/news/
john-champa-k8ocl-sk
. John was a visible part of the HSMM effort through his committee
work and articles in
CQ VHF Magazine
and
QEX
.
Only a fortnight later, we lost a tireless contributor to the work being done in Austin on the
HSMM Mesh project – Lloyd Crawford, N5GDB. Lloyd was a driving force behind the scenes
in our efforts to deploy wireless routers throughout the Austin area as well as other metropoli-
tan areas of Texas. Lloyd was responsible for the software installation and hardware modiica-
tions for a signiicant number of Mesh nodes throughout Texas. Lloyd’s passing is also a loss
for the VHF and microwave community in Texas. Lloyd was a founding member of the
Roadrunner Microwave Group and was an oficer in some capacity for its entire history. I will
miss our frequent lunches during the work week. Lloyd is survived by his wife, Ibbie, two broth-
ers, a son, two daughters, and many grandchildren.
Writing for
QEX
We haven’t mentioned writing for
QEX
in this space in a while. We are always interested in
articles about what you are working on that would be of interest to others. This is the
Experimenters Exchange, after all! It is not necessary that English is your irst language or that
you are an expert at writing even if English is your irst language. You will notice European and
Asian call signs on recent articles. While a well-written submission has a better chance for
acceptance, your work doesn’t have to be letter perfect. Get down your experiences as best
you can, and we’ll work with you. The main qualiication we require of authors is that they know
their topic. We need material at all skill levels. We actively support a wide variety of topics, from
simple construction projects to the advancement of theory. The rate is $50.00 per printed page
plus you get to see your name in print. You can ind the author guide at
arrl.org/qex-author-
guide.
It gives a more detailed description of the process of writing and submitting an article.
I look forward to seeing your article in
QEX
.
Looking Back/Looking Forward
I am writing this at the end of the year 2010 and it seems a good time to look back at the year
behind and ponder the year ahead. This was the 100 year anniversary of the Boy Scouts of
America. An every four year event called National Jamboree was moved to coincide with this
year and was held at Camp AP Hill, VA. The ARRL had a signiicant presence (including our
editor, Larry Wolfgang) to help Scouts learn about amateur radio and earn their license. The
Scouts also brought back four merit badges from 100 years ago that a Scout could only earn
during 2010. One of those was signaling merit badge. This required a Scout to learn the Morse
code as used for radio, light and wigwag lags. Hopefully, this exposure will encourage more
young people to join the amateur ranks.
July 1 found the end to arguably the worst BPL installation with respect to interference to ama-
teur bands. The end of the Manassas, VA system came due to a lawed inancial model rather
than due to compliance with interference regulations, but at least it is gone. Hopefully, it stands
as an example of the signiicant laws in both the inancial and technical aspects of BPL. On
another front, ReconRobotics seems to be stalled in deploying systems that are likely to inter-
fere with operations on 70 cm. This delay is due in large part to ARRL spectrum defense efforts
to convince the FCC to follow proper procedures.
Looking forward, the 900 MHz band appears to be moving toward use only as a strong local
signal band. Kent Brittain, WA5VJB, of the North Texas Microwave Society reports measure-
ments of RFID devices near retailers like WalMart along with other ISM uses of the band have
raised the noise loor to the point that weak signal amateur work will be pushed to the band
edges near 902.00 MHz to 902.05 MHz. In Texas, those uses also include RFID tags used by
the State’s toll road automatic billing systems.
My crystal ball is a little fuzzy on what is likely to appear in electronic devices for us to use in
experiments. It seems reasonable to expect that data converters for SDR use will continue to
drop in price and increase in frequency. Today, you can buy data converters below $200 each
that operate above the 70 cm band. That is still a pretty steep price. Perhaps this could be the
year for a VHF and UHF transceiver with only level shifting ampliiers between the antenna and
data converters. The power ampliier companies are hard at work on new materials. Gallium
Nitride (GaN) has reached the mainstream in commercial use. Now, they are working on Indium
Arsenide materials that could produce even more powerful high frequency power transistors.
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
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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 – January/February 2011
James Ahlstrom, N2ADR
221 Pleasant Plains Rd, Stirling, NJ 07980; jahlstr@gmail.com
An All-Digital Transceiver for HF
Build your own HF transceiver using an FPGA and software.
In a previous article, I described a digi-
tal SSB exciter that used a personal com-
puter (PC), a ield programmable gate array
(FPGA), and software.
1
That design used an
Ethernet controller connected to a micro-
controller (MCU) and then connected to the
FPGA. The microcontroller ran the Ethernet
and IP code, leaving the FPGA free to do
the digital signal processing. The microcon-
troller was a bottleneck that slowed down
the data speed to barely acceptable levels. I
wanted to work at higher sample rates and
clock speeds, so I started this new project.
At irst, I tried to connect the Ethernet
controller chip to both the MCU and the
FPGA, but this proved awkward. In the end,
I decided to eliminate the MCU and con-
nect the Ethernet controller directly to the
FPGA. This resulted in a high data rate but
meant that I had to write new Ethernet and
IP code for the FPGA and throw my MCU
code away. This was worrisome, as I had
never written a large FPGA program before.
I purchased some new Verilog books that
proved to be highly useful, thought about it
for a while, and then dove in.
2,3
With the MCU gone, I could change to
a faster 10/100 megabit per second Ethernet
controller. The FPGA would now be at the
center of the design with the digital to analog
converter (DAC) transmitter chip connected
to it. Then I realized I could just add an ana-
log to digital converter (ADC) for receive,
and I would have a complete transceiver.
122.88 MHz, and the numbers it measures
range from –8192 to +8191. These numbers
will be crunched by software to ultimately
result in received audio. To transmit, you
need a DAC: a digital to analog converter.
You take microphone audio, convert it to
numbers with a (different) ADC, crunch
those numbers and send them to the DAC for
direct conversion to RF. Then, amplify and
ilter the RF and send it to your antenna. The
numbers we are talking about are actually
pairs of numbers, an in-phase and a quadra-
ture number, or an I/Q pair. These are most
easily thought of as a complex number in the
form x + jy. Or you could think of them as
representing both the amplitude and phase
in one number.
The software mostly consists of ilters
and mixers just like in an analog radio.
A digital mixer is the multiplication by
cos(2πft) + j sin (2πft). You need to gen-
erate this I/Q number somehow, and the
CORDIC algorithm is a good choice.
6
To
tune numbers with a digital mixer you feed
the I/Q pairs of numbers into a CORDIC
module, and get new I/Q pairs out the other
end. The new numbers represent the original
signals shifted in frequency by a constant
frequency; that is, they have been “mixed”.
The advantage that I/Q number pairs have
over plain numbers is best seen in a digital
mixer. Analog mixers always have images;
they produce sum and difference frequen-
cies. These digital mixers have no images.
They produce either a sum or a difference
frequency but not both.
The digital ilters we are most interested
in are low-pass FIR and CIC ilters. The
FIR (finite impulse response) filters can
have very nice pass-band and stop-band
responses, but they require hardware mul-
tipliers. The FPGA does have hardware
The Basics
For background, you might want to read
my original article. For digital signal pro-
cessing basics, be sure to see the book by
Lyons
4
and the ARRL digital radio Web site
5
.
But if that is not handy, here is a crash course
in digital radio.
An ADC is an analog to digital con-
verter; it converts your antenna voltage to a
number. I am using a 14-bit ADC running at
1
Notes appear on page 8.
QEX – January/February 2011
3
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