EMRFD Message Archive 28
Message Date From Subject 28 2006-07-21 15:43:05 Wes Hayward The Homebrew Challenge
League's technical editor who presented a Homebrew Challenge.
Joel echoed a suggestion by N4AUP that ask readers to try to come up
with a complete radio that hams could build themselves with an
outlay of $50 or less. I urge you to all read this item in QST
and see what you can can generate.
I received an email yesterday from a friend and colleague in this
homebrewing game that we play. He ask "Is this possible, or is
Hallas dreaming?" I thought about it a lot last night. I
didn't start making any parts lists, but merely thought about what I
might do to generate a cheap rig. It's difficult for me to
evaluate, for I have a deep junk box. I will often purchase parts
to replenish the junk box rather than to build a single rig. But
after thinking about it for a while, I concluded that the answer
is "Yes" to both parts of the question. Joel is indeed dreaming,
but I think it is a possible and noble dream. Similar
competitions have appeared in SPRAT, the journal of the G-QRP Club,
often the brainchild of George Dobbs, G3RJV.
Some ground rules are listed in QST, but they are not complete.
They really do require clarification.
One of the rules states that the only test equipment allowed for
construction is a multimeter. If something else is required, it
must be part of the $50 budget. I assume that more test equipment
is allowed, and is probably expected for the development of the
design.
The rule that lists the $50 budget says that the power supply, key,
microphone, and headphones or speaker are all extra, which is in
some ways reasonable, but in other ways obtuse. It is reasonable
to exclude these items if we are asking you, the
experimenter/builder, to generate a cheap project for assembly by
the greater QRP gang. Virtually all of these folks are going to
have a 13.6 volt power supply, earphones, key, and even a
microphone, although the microphone may be kept well hidden by
some. Conversely, Joel compared the proposed building process with
the efforts that many of us experienced in the 1950s when we bought
WW-II surplus gear for a very few dollars, allowing us to get on the
air with a first station, or to upgrade an existing marginal
station. If the goal is to generate a rig suitable for a
beginner who has nothing, some of the accessories need to be
included in the budget. These necessary items, especially a power
supply, were part of the package that we used in our beginning
station. (Earphones were used in earlier receivers. A key was
purchased when learning the code.)
A rule picks the 40 meter band as the core for the project. This
is a good choice, although other bands might also be just as
good. We would hope that the reader/builder could adapt a 20
meter design to 40. A project description should address the band
choice problem.
The more interesting "zinger" is the rule stating that the rig
should operate in both the phone and CW portions of the 40 meter
band. Operation must mean that it is a phone transmitter and not
just a CW rig that can operate in the phone band. This is a
major, and most worthwhile departure from the projects often pursued
by the QRP clan. SSB rigs are really great fun to design and
build. QRP SSB can get out and be effective, especially in the
quiet band conditions found during daylight hours on 40 meters.
The current licensing structure is one that allows and even
encourages phone operation by folks without a CW history. We need
to set personal history and preferences aside and try to embrace
these folks by generating equipment designs that they can build and
effectively use to get on the air. The rig should be good enough
that it could be the main station and not just a weekend project
that produces one contact before being thrown into the box of "last
month's kits" under the workbench.
I recently hit the 50 year anniversary of my first QSO. I have a
photo of my high school station on my web site. I found it
interesting to review what I paid for the four items in that
photo. The Viking Adventure transmitter was a kit that cost me $55
in 1955. The NC-46 receiver was a 1953 SWL second hand purchase
for $50. The homebrew receiver, including the surplus BC453
component and the receiver power supply, was around $40. Finally,
the homebrew VFO was around $30, my first project after the
transition from novice to general class license. (Antennas were
low dipoles and wire verticals.) The total is $175, most of it
having come from newspaper route earnings. This was not a
deluxe station, even for a novice. Rather, it was very similar to
most of the other stations I worked. Inflation (10X) would value
my "junker" station at $1750 in today's money. I would submit
that $50 is a low and synthetic budget for the Challenge project.
It is a project cost that is low enough that it would allow nearly
anyone to build it with discretionary funds as a "let's try building
a rig for a new and different activity." The resulting station
will probably be a low commitment thing, a quick sojourn into the
homebrew world before the user goes back to his or her commercial
or kit rig. A budget of $100 or even more might be more in line
with a rig that could be "the one and only station. " Comments
about goals from N4AUP and W1ZR would be interesting.
How might one accumulate and account for the costs of a rig like
this? We might begin the project with a plan and perhaps an order
to Digi Key, Mouser, and/or Bytemark. We then plug in a
soldering iron and hand drill, and start building. Most of the
parts that we use in a first prototype will be from the junk box.
This would include all resistors and capacitors and most of the
semiconductors, at least for me. After the smoke clears, the
measurements have been done, and the first contacts have been made
(This is a VITAL part of the process and should be one of the
rules!), we assemble a bill of materials and start to add up the
costs. Which cost do we use? Do we use $0.25 for a transistor
that we would pay if we bought one or a few, or do we use the $.07
that we actually paid when we bought 100? Do we use the $10 that
we might pay for a role of #28 wire, or do we use the actual $0.30
that is the cost for the wire that ends up on the toroids?
Exercises of this sort quickly show how some QRP clubs can put out
100 kits for only a few bucks while still delivering a good
value. How do we count the beans this project?
There are several interesting technical questions that may be
influenced by the cost. Is a PC board a requirement, or is a
less costly breadboard scheme allowed? Should one use phasing or
a superhet architecture, or just a raw direct conversion
transceiver? Is a transceiver required, or is there value to a
separate receiver and transmitter? A DSB transmitter with a DC
receiver is a system that is compatible with SSB stations already on
the 40 meter band. However, two such stations may not be able to
work each other on phone. I have always been a strong proponent of
DSB, especially for portable QRP phone gear or for VHF rigs. But
recent arguments have encouraged me to dismiss this as a viable
approach because of the excess spectrum used and, of greater import,
the expanded potential for intermodulation. Should we even
consider DSB transmitters? Many existing designs for phasing
receivers and transmitters tend to make extensive use of moderate
sized audio inductors. These parts are becoming harder to find
and more expensive. Should we instead consider active filters as
an alternative for low cost with available components? Can one tune
the entire band without junk box variable capacitors with junk box
reduction drives while staying within the budget?
I'm not going to make any suggestions about solutions to these
questions. That is some of the fun that will be available to
those of you who chose to participate in this most interesting
competition. But we all need to seriously think about the
challenge. It is a worthwhile general problem and is deserving of
careful thought, both for those of you who will build and those who
will just ponder the issues. In a sense, this is at the very
core of amateur radio as we know it. If we can't do projects of
this sort, we may as well take our antennas down and send emails to
each other about the good ole days, interspersed with an occasional
chat on an FM-HT.
A really useful web reference is
http://www.phonestack.com/farhan/bitx.html This is a link to the
description of a transceiver that has also generated a fairly active
Yahoo Group, BITX20.29 2006-07-21 18:15:22 kc8sbv Re: The Homebrew Challenge
Wee Willy wins out as starting point, and moved to the band of choice.
Note the homebrew enclosure that can save some dollars.
http://www.qrp.pops.net/willy.htm
Can't help but be drawn by it's simplicity
Ed KC8SBV30 2006-07-22 07:28:18 Don Kelly Re: The Homebrew Challenge
Homebrew Challenge in context to the book.
One theme throughout EMRFD is to test your work. It is not a
suggestion but a "best pratices" requirement and chapters are
provided to build the test equipment. Another is that you can build a
circuit but it might not always operate as inteneded and testing
indicates the problem and leads one to a solution. Honestly, in two
frank replies to e-mails with Wes in the past it was suggested I test
more. I took the criticism to heart and now I am somewhat to the
exteme in measurement.
I believe the dollar value limit was perhaps too arbitrary second
only to the lack of any ability to use even basic testing gear and
procedures to evaluate the quality of the rig operation. To me that
is not a good practice to encourage.
It is my observation that the challenge was to stimulate interest in
a homebrewing challenge, not merely for the expert but for the
moderately experienced builder too. The rules should have included
some measure of "good" practice in rig construction.
For me it would be a step backward to comply with the stated
requirements or should I say limitations. Being a moderately
experienced builder I would certainly be hesitant to present an entry
without being confident in the rigs operation.
Off topic and a compliment on the book and its accompanying articles.
I finished a DSB transceiver using a mix of KK7B/W7ZOI/W7EL DC
receiver designs and info from chapter 8. I added a LM386 and used
the 4MHz low pass filter from the KK7B article. My DSB TX is also a
composite of ideas from EMRFD and uses the 6W IRF510 linear PA from
the book. The receiver in spite of the LM386 is fantastic and is used
in a current SSB receiver as the PD and audio section with the LM386
replaced by a 14 pin LM380N. I worked my 18th state one week ago. I
also built two osillators..a VXO for camping and a Hartley VFO for
home use.
Please excuse my "bragging" and accept it as a thank your for EMRFD
but it was kind of exciting to work my 1st sideband contacts. The DSB
project was also a good way to get my feet wet with sideband
construction. I am working on the TX portion of my SSB rig.
K5UOS31 2006-07-22 08:00:37 Don AE5K Re: The Homebrew Challenge
> I believe the dollar value limit was perhaps too arbitrary secondMaybe some clarification is in order here -- it should really come from
> only to the lack of any ability to use even basic testing gear and
> procedures to evaluate the quality of the rig operation. To me that
> is not a good practice to encourage.
>
> It is my observation that the challenge was to stimulate interest in
> a homebrewing challenge, not merely for the expert but for the
> moderately experienced builder too. The rules should have included
> some measure of "good" practice in rig construction.
the author of the challenge, but I would like to point out some key
words from page 20 of the August QST:
"...that can be successfully reproduced for under $50."
To me, this does NOT at all restrict the cost of *developing* a design
-- in fact there is nothing that would keep someone from using $50,000
worth of test equipment to assure *the design* would meet all spectual
and good practice requirements. The cost of $50 is for the end builder,
and a well developed design that is reproducible should not need a lot
of test equipment for the end builder.
I believe the challenge is in the same vein as the recent news of
producing under $100 or under $50 (I forget the exact amount) computer
for third world countries.
And I really don't believe the challenge was meant for a newbie.
73,
Don AE5K32 2006-07-22 09:18:06 Don Kelly Re: The Homebrew Challenge
I think you are correct Don. This is not a novice challenge. The
intention to have a reproducable project is however one of the
toughest requirements considering the testing limitations. I trully
subscribe to the philosophy presented in Wes's publications.
Let me clarify my thoughts with an example. I mentioned a 40M SSB
receiver I just finished. The front end is a triple tuned BP filter
and a TUF-3 mixer.
My first iteration of the BP filter was to wind the inductors per the
standard typical values for the toroids. I did not initially measure
the inductors with my LC meter. My design software was a spreadsheet
compiled from formulas in EMRFD.
I tested the BP filter with my spectrum analyzer which has a tracking
generator. The filter was radically different from the expected pass
band with the very best practice I knew to wind them coupled with
careful termination and adjustment of the filter. The filter would
have seriously deteriorated the performance of the receiver.
I then removed the cores and measured them with my LC meter (Bill
Carver design) and adjusted them accordingly. I did the same with the
fixed capacitance. I reassembled the filter and measured it again.
After adjustment, the filter was exactly what I had designed and was
expecting.
I hope I did not sound defeatist in my comments. But reproducing even
a BP filter from assembly instructions provided with a kit would
require some measurement assuming toroid cores are not all alike. Not
everyone has a SA. Other more tedious methods could be used such as a
signal generator and an RF detector by plotting the results but even
in this instance more than a DVM would be used.
Well anyways, I hope my comments were viewed as more philosophical
i.e. thinking out loud and not discouraging. I guess after Wes posted
some of the same thoughts I had and have seen on other sites I wanted
to see what others were contemplating.
With all this said I certainly see your interpretation of the
development stage of the project.
73
K5UOS33 2006-07-22 19:23:22 michael taylor Re: The Homebrew Challenge
> I think you are correct Don. This is not a novice challenge. TheThe DMM limitation is a bootstrapping limitation, this does not mean
> intention to have a reproducable project is however one of the
> toughest requirements considering the testing limitations. I trully
> subscribe to the philosophy presented in Wes's publications.
that additional tools cannot be created as part of the design. I think
the best known example of this approach in transceiver building is the
built-in diagnostics in the Elecraft K2 which includes voltage,
current drain, RF probe, and frequency meter, but requires the builder
only has a DMM.
An example of how trivial and cheap it can be to include a frequency
counter can be easily seen at
<http://www.qsl.net/dl4yhf/freq_counter/freq_counter.html> using a low
cost PIC microcontroller. One could also add a L-C meter based upon
the approach used in NJQRP's Elsie Meter
<http://www.amqrp.org/kits/elsie/> using a LM311 voltage comparator
and an microcontroller such as the Atmel AVR used in Elsie. If the
transceiver design already includes a frequency display method (LCD,
Morse code output) for the VFO, these test features are simple and
cheap to add and enhances the reproducibility of the design.
-Michael, VE3TIX35 2006-07-23 20:56:21 Steven S. Coles Re: The Homebrew Challenge
Assuming I have my years right and this is 2006, there's plenty of
time to ask for rules clarification.
I'd love to see the ARRL Homebrew Challenge become an annual event.
Perhaps it could circulate through 80, 40, 15, 10, 6, 2, and 1.25
meter bands or some such.
Best regards,
Steven, KD7YTE