QEX №1 2014.pdf

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January/February 2014
About the Cover
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 281
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
Brian Washing
Technical Illustrator
Advertising Information Contact:
Janet L. Rocco, W1JLR
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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
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Members are asked to include their membership
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Copyright © 2013 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 office of the Publications Manager
(permission@arrl.org).
Martin Ewing, AA6E, is an ARRL Lab volunteer. He
became aware of the difficulty that Headquarters
Staffers had trying to operate the W1HQ Staff Club
Station while W1AW transmits bulletins on all bands
from across the parking lot. Determined to help find a
way to solve this problem, he built “A Software-Based
Remote Receiver Solution” for W1HQ. Now staffers
can operate the station while W1AW is on the air! You
can build a remote receiver system, too.
In This Issue
Features
3
7
15
24
31
34
43
44
A Software-Based Remote Receiver Solution
Martin Ewing, AA6E
Servicing and Upgrading Your Optoelectronics 2810
Frequency Counter
Tuck Choy, MØTCC
An Extremely Wideband QRP SWR Meter
Dr. Sam Green, WØPCE
A Polar Plotting Direction Finder
Bob Simmons, WB6EYV
More Octave for SWR
Maynard Wright, W6PAP
Actual Measured Performance of Short, Loaded
Antennas — Part 1
Barry A. Boothe, W9UCW
Letters
2013
QEX
Index
Index of Advertisers
ARRL: ..............................................................
Array Solutions: .................................. Cover III
Down East Microwave Inc:........................... 23
Kenwood Communications: ................. Cover II
Nemal Electronics International, Inc: ............ 30
Quicksilver Radio Products................ Cover IV
RF Parts:................................................ 41, 43
Tucson Amateur Packet Radio: ..........Cover III
QEX – January/February 2014
1
The American Radio
Relay League
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.
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:
ARRL
225 Main Street
Newington, CT 06111 USA
Telephone: 860-594-0200
FAX: 860-594-0259 (24-hour direct line)
Officers
President:
KAY C. CRAIGIE, N3KN
570 Brush Mountain Rd, Blacksburg, VA 24060
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 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 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.
Larry Wolfgang, WR1B
Empirical Outlook
Happy New Year! Welcome to the first issue of
QEX
in 2014. Starting a new year is always
exciting, and with the many Centennial activities planned by ARRL for this year, it seems even
more exciting than usual.
In September 2013 I ventured to Seattle, WA for another ARRL/TAPR Digital Communications
Conference. DCC is my favorite national Amateur Radio event, so I guess it is fitting that I write
a little about it.
As many of you know, DCC is a three day event that includes two full days of technical pre-
sentations as well as an in-depth seminar on Sunday morning. In addition to the high-level
technical presentations on Friday and Saturday, there are always some Introductory Sessions
on Saturday. The local hosts this year —especially Tina (KD7WSF) and Steve (N8GNJ) Stroh
— did an excellent job of promoting DCC in the local Seattle area. We had the highest atten-
dance of any DCC in memory, and nearly filled the excellent presentation auditorium to over-
flowing!
This year’s Intro Sessions focused on various aspects of digital voice transmission. There are
always many attendees who want to learn more about D-Star, and we had that opportunity this
year. A new “hot” topic in the digital voice realm was the FreeDV/Codec2 program. This system
is of special interest because Codec 2 is an open source Codec. FreeDV uses SSB transceivers
to transmit and receive digital voice signals. It is used primarily over HF, although nothing would
prevent its use on VHF or higher frequencies.
All of the technical presentations are quite interesting, but a few really stood out for me. Heikki
Hannikainen, OH7LZB, did an encore of his 2012 presentation by talking about the challenges
involved with running a secure “authenticated” Amateur Radio service application on the
Internet with his
APRS.fi
web server. Heikki described some of the steps he takes to ensure
that only licensed Amateur Radio operators can put a message out over his system, while not
being overly complicated for either the ham who wants to use the system or for the site admin-
istrator.
John Hansen, W2FS, stirred up quite a bit of excitement over his “Raspberry Pi Applications
in Digital Communications,” and especially with his mobile APRS station and a new version of
his popular TNC-X: TNC-Pi. For this and other reasons, I’ve decided I want a Raspberry Pi, to
learn about this little computer. I’ve put one on my Christmas Wish List.
Adam Farson, VA7OJ, described his “Noise Power Ratio (NPR) Testing of HF Receivers.”
Adam described the measurements that he has made on Amateur Radio transceivers with this
technique. At the time of the DCC, we were reviewing an article from Adam about this topic for
QEX. I was able to discuss some revisions to the article with Adam in person, and he is in the
process of revising it for us. I hope to bring you an article about NPR testing during 2014.
The Make movement definitely has some parallels with Amateur Radio, and it is great to see
the enthusiasm that so many of these “do it yourself” experimenters can bring to our hobby. In
addition to a video update from Chris Testa, KD2BMH, about his “HT of the Future,” which he
first described at the 2012 DCC, this year we heard from Michael Ossmann, who described his
“Hack RF: A Low Cost Software Radio Platform.” Michael is working on marketing his project,
which is a 30 MHz to 6 GHz radio, to the Information Security community. He uses an IF of
2.5 GHz to obtain 15 to 20 MHz bandwidth with 20 kbit sampling. You can find more about
Michael’s project at
greatscottgadgets.com/hackrf/.
Gary Pearce, KN4AQ, was again in attendance at the DCC, recording the presentations for
his HamRadioNow TV website:
http://arvideonews.com/hrn/.
As he has done in the past,
Gary will put the video on his website for your viewing pleasure, although it does not seem to be
available yet as of this writing. This is a great way to learn about the technical presentations at
DCC, but the conference is so much more than those presentations. It is an opportunity to talk
with the presenters, share ideas with other attendees, and generally have a great time.
No discussion about DCC is complete without some mention of “The Play Room.” Whether
or not you are presenting a talk at DCC, you are encouraged to bring projects to display in the
Demo room. There were tables with several of the projects presented in talks on display. John
Hansen had his TNC-Pi APRS tracking system on display. Michael Ossmann had information
about his HackRF project. Mel Whitten had a demonstration of the FreeDV digital voice system.
David Bern, W2LNX, has been experimenting with a Raspberry Pi to control a pair of inex-
pensive TV rotators to create an Az-El rotator system for satellite antennas. David was present-
ing this project at the AMSAT Symposium in November, so the DCC was an opportunity to
shake out a few bugs. I have talked with David about writing about this project for
QEX,
so that
is another one I hope to bring you in the pages of
QEX
in the not too distant future.
Next year’s DCC is already in the planning stages, with preliminary efforts focused on holding
it in the Austin, TX area on the weekend of Sep 5-7. Watch for announcements and start making
your plans to attend now!
2
QEX – January/February 2014
Martin Ewing, AA6E
28 Wood Rd, Branford, CT 06520;
aa6e@arrl.net
A Software-Based Remote
Receiver Solution
Need to get your receiver off site to avoid interference?
Here is how one amateur connected a remote radio to a club station
using a mixture of
Linux, Windows,
and
Python.
The local interference environment is an
increasing problem for ham radio operation,
making weak signal operation impossible
at some times and frequencies. The ARRL
Staff Club Station, W1HQ, has this problem
in spades when W1AW, just across the
parking lot, is transmitting bulletins and
code practice on seven bands with high
power. Operating W1HQ on HF in the prime
evening hours is not possible. There is no
problem transmitting in this environment
— it’s a receiver problem. We could solve
the problem by setting up a full remote base
station, but for W1HQ, this is not necessary.
A remote receiver is all that we need. That is
the origin of this project.
There was only a small budget for a
remote operation, but we did have a number
of usable receivers, and we had an offer of
software support from an eager volunteer.
(That would be me.) So we were off and
running to develop a low-cost remote
receiving capability.
The club wanted a receiver capable
of operating at least CW and SSB on all
HF bands, controllable from the W1HQ
operating desk. It needed to be located far
enough from W1AW so that interference
was negligible, but close enough so that
propagation would be nearly the same at
both locations. The system that evolved
was a small remote computer that could
be deployed at a ham’s home (the “host
QTH”) and that would require little if any
local support. The remote would require
an all-band antenna of some kind, while
it would attach to the host’s home Internet
connection. At the base station (W1HQ), the
station computer would run control software
to manage the remote operation.
This article focuses mostly on the
software — how we developed a mixed
C
and
Python
(and mixed
Linux
and
Windows)
project with audio and Internet aspects.
Interested readers will probably want to
consult the code listings. These are provided
at
www.aa6e.net/wiki/rrx_code
and are
also available for download from the ARRL
QEX
files website.
1
Additional project
1
details are available at
www.aa6e.net/wiki/
W1HQ_remote.
Hardware construction is
straightforward for anyone with moderate
experience.
System Overview
Figure 1 shows the overall system design.
The BeagleBoard XM or “BBXM” is an
inexpensive (~$150) single board computer
with a 1 GHz ARM processor, Ethernet
and USB connections, and on-board audio
capability.
2
It has 512 MB of RAM and
Notes appear on page 6.
Figure 1 — This block diagram shows an overview of the remote receiver system.
QEX – January/February 2014
3

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