I liked this page somuch that i am putting it as it is. It is a nice advise for beginner. 73 VU3INJ.
ORGANIZING A HOMEBREW PROJECT
by Dave Metz, WA0AUQ
Last week a friend ask, "just how do you get so much done?" He referred
to the steady stream of ham radio projects that I seem to be involved with.
To me, it seems like I am never getting anything done, yet all around me
are finished radio projects. This question and the ensuing conversation
led me to putting some thoughts on the subject down.
I'm going to use one of my latest projects, a 6 meter transverter as
an example. After being off of six meters for ten years, I decided to get
back on the band. I decided to do it the old fashioned way and build a
transverter that is a combination receiving and transmitting converter.
I started out only with the idea that this device would take a 28 Mhz signal
from my station HF rig and put it on six meters. Other than that, the course
was uncharted.
RULE 1. Be selective and
focus on something really important! The first step of doing
any project successfully is to be careful what you choose. You can't do
it all. No one has enough free time anymore so you have to be careful about
how much you take on. It is very tempting to try to do a little of everything
and dilute yourself to the point where nothing will ever get finished.
If it is important to you set some time aside. If you have a minute,
you can find ten. If you have ten, you can find an hour. An hour here,
an hour there and soon you'll get something done. The key is to be selective
in how you use your time. Shut off the TV and plug in your soldering iron.
RULE 2. Make a thorough
study of the subject before starting! I learned this from Thomas
Edison. Studying the life of Edison, the greatest inventor in history is
very beneficial and I strongly recommend it. One of Edison's secrets was
his technique of preparation prior to starting the physical work on a project.
At the time, Edison had the largest research library in the U.S.! He
subscribed to every technical and scientific journal published in the U.S.
and Europe. Before starting any research project, Edison made the most
complete possible study of all prior research in that area. Before he started
his work he knew of all that had been done before him. Most important,
he knew where the prior researchers had gone wrong!
In other words, he eliminated a great deal of work before he even started.
You can do the same. The best place to start any ham radio project is the
ARRL Handbook, aptly called the "bible of Amateur Radio." This is where
I started. Right off the bat, I found plans for six meter transmitting
converter. I now had a basic idea of a design in hand.
A copy of the Handbook should be the first purchase every ham makes.
A few hours with it can save you thousands of wasted dollars and hours
of time. The Handbook is dense and it does pack a huge amount of information
in it. It does take an effort to plow through it. Learn to use the index.
When you find that you don't understand something, backtrack to the section
on the basic theory.
Hamfests are great sources of books. I've found stacks of text books,
data books and manuals for pennies to a couple of dollars. For basic theory
you don't need the newest book. The fundamentals are not changing very
fast! The laws of physics are going to stay the same. I've often found
it very useful to sit down and reread the fundamentals every once and awhile.
An observer could also tell whenever I'm starting a new project. You'll
see me walking about the house with a book in my hand reading. I do a lot
of reading before starting anything new. The more I study, the less wandering
the wilderness of ignorance I'll have to do.
RULE 3. Study the new technology!
Read magazines, catalogs and data sheets. After looking through many back
issues of various radio magazines and thumbing through my stack of radio
parts catalogs a new idea came to my mind. The design I had found in the
Handbook had become obsolete. Newer parts (in this case MMIC amplifier
IC's) could greatly simplify the design! Amplifier stages with 15 parts
could be replaced with stages with six parts that cost less. Plus the complex
ten watt P.A. stage could be replaced with a single simple RF power amplifier
module (more on this saga later).
Make use of the Internet. Most of the parts suppliers have web sites.
Many of them have complete catalogs of the latest and greatest on line.
The best such as National Semi and Motorola have thousands of pages of
parts data on line. In the past to learn the specifications on say a new
IC you had to first locate in a catalog the proper data book that had the
specs in it.
In those days, if you are the typical ham, you paid $20.00 for the data
book, and then you sat back and waited two weeks for it to come in the
mail. Now you can get the same information for free in minutes. When you
do get the information, start a book on your project. Print off or copy
all of the pertinent information and keep it in a note book. This way you
have everything in one place where you need it. Your time is limited and
you can't waste it tearing the shack apart looking for scraps of paper
with notes on them.
RULE 4. Document what you
are doing! Draw out plans as you go. Having ISIS CADPAC schematic
capture software helped me greatly with this problem. I began by drawing
up some block diagrams of my proposed transverter. At this stage you don't
worry about details. You are just trying to get an idea of the organization
of the project. What the inputs and outputs will be, the flow and level
of signals. That sort of thing. By the way, this approach works well for
software projects as well. It is very hard to get somewhere if you don't
have a plan on the route!
Documentation is very important. You are not going to do this all at
one sitting. This means you are going to forget things, important things!
If you have drawings and notes, you are going to be able to trace back
years later your thought process and be able to repair what you built.
You think this won't happen? Last year I was contacted by a collector that
had just bought at a hamfest a "classic" tube type six meter converter
that I had built in 1965!
He found my call inside the chassis and contacted me by packet. I found
my original schematics from 32 years ago and sent copies to him. Someday
you will wish you had schematics of everything you do. Keep accurate ones!
The use of schematic capture software like ISIS encourages this. Draw
your schematic. Then keep updating all the changes you make in the design
while you make them. Programs like ISIS almost force you to be successful.
Since you have to fill in all the parts values, the program makes you think
about those values. Documentation encourages clear thinking. Drawing out
the schematic encourages you to consider the design carefully.
Software like ISIS also encourages you to make corrections as you go.
Since you don't have to start your drawing from scratch like a you would
with a hand drawn one, you'll find it easy to make corrections. If you
do this, when you get done you'll have a perfect "as built" schematic for
your records. And if your project really works well, you will be able to
provide your design to others so they can have the fun of duplicating it.
After doing the block diagram and some preliminary schematics I had
a pretty good idea of the basic structure of the design. Now I could look
harder at the "How" of the design. That is, what components would I use
and how would I arrange them.
RULE 5. Check out your
(and your friends) junk box! Read those surplus catalogs again.
Since this is a ham radio project, money is an important consideration.
If you have something, some physical resource, design your project around
it. In my case I had a bag of MRF966 GASFET transistors, lots of toroid
cores and several SBL-1 mixer modules. This meant that my converter would
use the 966 as the preamp stage, the tuned circuits would all be wound
on toroids and all the mixers would be SBL-1s. I could have used other
components, but those I would have had to pay for!
Remember that you don't need the newest and brightest parts for your
project. My new 220 Mhz transverter will have some 30 year old piston trimmer
capacitors in it. Some of the parts came from "under the table" at a hamfest.
They may not be the perfect parts, but they will work and that's what is
important.
Organization of your "junk box" is critical. Having the right parts
does you no good at all if you can't find them. I just counted, I have
750 little drawers of small parts in my shack. I could use another 120
drawers right now just to do the job right! Time wasted tearing the shack
apart looking for a part is time lost from your project. The frustration
drains your energy. What was fun becomes a drag. Organize before you start.
Keep every thing in its place and you will be amazed how much time it saves
you.
RULE 6. Eat the elephant
one bite at a time! Taken altogether my proposed transverter
would be complex. If I took it as a series of simple blocks of circuitry,
it became much simpler. Very simple in fact. Instead of trying to get an
entire transverter to work, instead I concentrated on getting small simple
blocks of circuitry to work properly.
RULE 7. Start with the
KEY portion of the project first. That is, the portion whose
success everything else depends on.
For my project the local oscillator was the key block of circuitry.
Without a clean local oscillator the rest of the transverter would be useless.
I broke the Local oscillator down into three smaller blocks of circuitry:
The crystal oscillator, the harmonic filter and the amplifier. Now the
whole thing had become manageable.
RULE 8. Prototype any circuit
whose operation you are not sure of. Build your project in small
modules.
For example I started by building a prototype of the crystal oscillator
on a scrap of PC board. No, it did not work as expected! My toroid cores
were made of a different ferrite than the ones the original designer had
used. A couple of coils later, I had a crystal oscillator and I knew how
much power it put out. More important, I knew how bad the harmonics it
put out were!
With this knowledge, I could safely design the rest of the Local Oscillator
(well pretty much so) and layout a printed circuit board. Naturally my
wonderful new oscillator on its new printed circuit board didn't work at
all. No problem! By this point you should be humble enough to know that
there will be mistakes in your layouts and designs.
RULE 9. Don't be afraid
of making mistakes! Accept that you will have to make corrections.
After I found the mistakes, I laid out a second board and tried it.
After all, small parts are cheap and most of the valuable stuff on the
board could be removed and reused. Using the Techniques PC-Blue laser printer
PC board fabrication system makes making new boards fast and easy. There
is no point in worrying about mistakes when you can make a new better board
so easily.
In the end I found that all of the boards in my transverter had to be
redesigned at least twice and in some cases three times. Although I found
this to be irritating at times, in the end it all worked out well. It is
very important to remember that when homebrewing a project, getting there
is most of the fun! If everything you do works the first time homebrewing
would get pretty boring pretty fast.
RULE 10. Keep your energy up!
Don't let your project weigh you down. This is a hard one. There always
comes that time when it seems that you are not making any progress and
you will never get your project done. At that point, don't quit, just set
it aside and walk away. That's right, just forget about it for awhile.
How long? It could be an hour, a day, a month or more. The point it don't
beat your head against the wall till you loose interest.
When the frustration builds too high, go do something else. I usually
keep two or three projects going at one time. When one gets to be a drag,
I work on another. I alternate between them (often on the same day!) This
keeps me fresh on all of them. There's nothing wrong with set a project
aside until the right parts, test gear, money, whatever come available.
RULE 11. When you get stuck,
ask questions! If I have noticed one change for the worse in
ham radio it is that hams are very hesitant now to discuss problems or
ask questions. OK, lets say you hit a rock. First hit the books again.
No answer there? All right use your other resources. Send a HELP message
on packet. If you have Internet access try posting on the newsgroups that
are relative. Call the ARRL and talk to the technical department. If you
know another ham in the area that is doing or has done similar work, ask
them.
The main thing is, don't sit still! DO SOMETHING! Don't fret if you
are unsure where to look for an answer to your problem. Learning where
and how to ask questions is an art too and one that you can only learn
by doing. Do not be afraid of being embarrassed or asking a "dumb" question.
The only dumb thing you can do is not ask at all. If someone does respond
in a negative manner, ignore them and move onward.
RULE 12. Finish what you start.
Nothing is more discouraging than a bench full of unfinished projects.
These mean you have both wasted your time and your money. Finishing a project
(and this means the documentation too!) is what it is all about. Anyone
can fail, that's easy. Always keep your path to completion and success
in mind as you work. If one module doesn't work, back track and try something
else.
I had to do this on my transverter. At first I tried to build my own
ten watt P.A. I soon discovered that RF power transistors that I had were
specified for 30 MHZ. They did not work well at 50 Mhz as I had been told.
This stopped me cold till I read an article on a six meter transverter
in QEX magazine from the ARRL technical department. They used a ten watt
P.A. module from RF Parts. I wisely did the same! Building the prototype
P.A. did not waste my time. Along the way, I learned a great deal about
transistor RF amplifiers and impedance matching.
In the end I had a fine transverter. It works very well and I'm happy
with it on the air. I have it completely documented too! Another bonus
is that since it is completely documented, I can use it as a starting point
for my next project, a 220 Mhz band transverter. This should go a lot faster
if I don't repeat the mistakes I made before.
Summary.Lets go over all of this one more
time:
-
Decide if its important to do
-
Study the prior work of others
-
Make a preliminary simple design, document everything you do!
-
Round up your parts
-
Build in modules! Make one module at a time work.
-
Don't get discourage, ask questions, finish what you start
When you are done, be proud of what you have accomplished! Use it on the
air and show it off to your friends an amaze them. Then clean the bench
and start dreaming about your next project.
David Metz, WA0AUQ
