homebrewing from a schematic for the enthusiastic amateur
TRANSCRIPT
Homebrewing from a Schematic
For the enthusiastic amateur
Why not build another kit?
Kits are self contained: no extra parts to buy.
You know what you’re getting: the project has been tested and most of the kinks have probably been worked out.
Someone has thought out most of the details for you.
Why homebrew?
You have ample, by which I mean too much, free time.
You are afflicted with curiosity about how circuits work.
You get free vision and psychiatric care. You want to optimize. You want a truly custom piece of equipment. You want the satisfaction of knowing that you
are communicating around the world (or the block) with something you made yourself.
Obstacles to homebrew success
Start-itis. You don’t have exactly the right part on hand. You don’t know what you want to build. You have more fun collecting parts than building
circuits. You think that you have to have lots of test equipment
to make a circuit work. You think that circuits are too complicated. You think that you have to be smart to make a circuit
work. (That’s patently false: look at me!) You think that it has to be finished in one sitting. You think that it should work the first time you turn it
on.
What do I build?
Start with easy projects.Simple test equipment like crystal
oscillators, RF probes, etc. are great.A regenerative receiver is fun.Shack accessories: dummy load,
antenna tuner, keyer, etc. are always useful.
Radios!
Inspiration from the internet
The homepage of KD1JV: http://kd1jv.qrpradio.com
The homepage of Miguel, PY2OHH http://py2ohh.w2c.com.br
The homepage of Onno, PA2OHH http://www.qsl.net/pa2ohh
The homepage of PG1N http://home.hetnet.nl/~pg1n/hambrew/hb_hf.htm
Numerous others
Inspiration from books and magazines
DeMaw and Co. from the ARRL: QRP Notebook, EMRFD, QRP Power, More QRP Power, W1FB’s Design Notebook, etc.
The fine folks from RSGB and G-QRP club including the book Low Power Scrapbook.
The OU library has QST and Ham Radio magazines going back decades.
ARRL has most QST articles online for members.
What about parts?
Do not expect to find every part that you need for a project.
Expect to improvise.Order more than you will need (your
friends, if not your spouse, will love you for it.)
Consider shipping costs as part of parts cost.
Where can I get parts for a project?
Jameco, Digikey and Mouser carry most everything you could possibly want: except much in the way of RF components.
Electronics Goldmine: Dealer of choice for Parts Junkies. They also have the cheapest copper clad board stock around.
As a last resort: ebay. Keep in mind: leaded components are going
the way of steam passenger ships.
I need a variable capacitor for my project!
Ocean State ElectronicsNebraska SurplusPolyvaricons from Doug Hendricks at
QRPKits.comhttp://www.danssmallpartsandkits.net
Some toroid cores would be nice too.
Diz, W8DIZ runs http://www.partsandkits.com.
Palomar Engineers.Ocean State ElectronicsLast resort: ebay
Ugly Construction
Fast Ugly Easy to troubleshoot Can be easy to visualize
the circuit Is hidden when you put
the case on anyway Easy to modify Can write notes right on
the circuit board
Manhattan Construction
Neat Has all the advantages of
Ugly construction FAST Did I mention it is fast? Can blend leaded
components with surface mount components
Use to impress your non techie friends
See Jim Kortge’s stuff at http://www.k8iqy.com. He is the master.
More on Manhattan Construction
Circuits are built on bare copper substrate.
Interconnections are made on pieces of PC board glued onto the substrate.
You can build testable subassemblies and glue them onto the substrate when you know they are working correctly.
Can really simplify some tricky lead placement.
Manhattan/Ugly Subassemblies
Printed circuit boards
Used primarily by over achievers
A must if you are making more than one of any project
Free layout and schematic tools are widely available on the internet
Tools
Simple rule: one can never have too many.
Practical rule: you will end up using very few, so make sure the ones you actually use are of good quality.
What tools do I use?
Kenn’s most often used tools
Magnifiers, lots of ‘em, all shapes and sizes Soldering iron, 25W, with the smallest chisel tip I could find Soldering vacuum pump, because I make lots of mistakes Small pair of needle nose and wire cutters Forceps, curved and straight (for picking up small items and use
as soldering heat sinks) Clip-on flood light Exacto knife and saw Super glue and/or hot melt glue VOM Frequency Counter Crystal Oscillator (homebrew) 1 kHz square wave oscillator (555 timer, homebrew) Dummy load, 20W (homebrew) Huff Puff VFO (homebrew)
My magnifiers
Tools I have but hardly ever need to use
OscilloscopeRF Signal GeneratorAudio Signal GeneratorRLC Bridge (antique, but it looks cool!)
Parts to keep on hand ‘cause you never know…
Generic transistors: 2N3904, 2N3906, 2N3053, MPF102, 2N4401, 2N4403 etc. Capacitors: NP0/C0G ceramic for tuned circuits, high value polystyrene for tuned
circuits and critical audio circuits, electrolytics or tantalum for non-critical audio, power supply bypass, etc., silver mica for high power
Resistors 1/4W and 1/2W assortments, 1 or 2 watt 100 ohm, all in non-wirewound compositions
Toroids in various sizes of 2,6 and 43 mix Connectors of all kinds Copperclad Switches Diodes: 1N914, 1N4007, varactors, etc. IRF510/IRF511 for Power Amplifiers Generic IC’s like basic op-amps, comparators, audio amps. There are hundreds of
choices. Match your wallet to your noise tolerance. I use LM741, LM383, etc. because I can’t hear that well anyway.
Trimmer caps: 2-25pf, 3-60pf and 6-100pf are handy If you don’t have all or any of this stuff for a last minute project, call me, I probably
do.
Circuits that I avoid
Old designs that you’ll never find the right transformer, transistor or IC for.
Circuits that are needlessly complicated.Circuits that are so poorly drawn that you
can’t follow the biasing and signal flow. (You might redraw these if you are handy with a computer.)
Exception to the rule: 40673
Radio designs from the 1970’s used the RCA 40673 Dual Gate MOSFET EVERYWHERE.
They have been out of production since the early 1990’s.
The Philips BF991 is still in production and makes a good substitute, EXCEPT, it is a SMT part. $0.45 from Digikey.
It’s easy to make a small ½” X ½” PC board subassembly for the SMT part that makes it really easy to work with.
Oscillator/Mixer/Amplifier IC’s
NE602/SA612 integrated circuit has been hugely popular.
It’s getting hard to find. SMD versions are readily available and
can be made into subassemblies.The TA7358AP is a cheaper and easier
to work with part, but it’s hard to find now as well.
Topologies: common designs
Humor me, I like big words.Direct Conversion receiver/transceiverSingle Conversion transceiverSingle Conversion transceiver with
crystal ladder filterDouble Conversion transceiver (rare
these days)Transverters
Direct Conversion Receiver
NE602/SA612 74HC4066 40673/Dual Gate
MOSFET TA7358 Single Ended Diode Ring
Single Conversion with Crystal Ladder Filter
Single Conversion with Crystal Ladder Filter
Most popular topology you’ll seePopular because microprocessor
crystals are ubiquitous and cheapMost designs use NE602/SA612 or
TA7358AP. Exception: Check out Jim Kortge’s
2N2/40 which uses 2N2222 transistors with diode ring DBM’s.
3rd way: Phasing method
Check out PA2OHH’s website for his phasing method transceivers.
Software defined radios are using this method with great success
This is too much information! Where do I start?
Pick a simple project: a dummy load, a simple transmitter, a regenerative or direct conversion receiver, etc.
Lean on your buddies for parts and help. Use the manhattan or ugly construction
method. Try to understand the circuit and predict
voltages based on what you know. Measure those voltages when the circuit is
working. How close are you?
From Schematic to Circuit Board
Make a working copy of the schematic. Check off parts on the schematic as you work. Make notes directly on the board with a permanent ink
pen. Dry place your parts before you plugging in your
soldering iron. Beauty doesn’t count. Start from outputs and work toward inputs. Power your work as soon as you can to test each
section. Fuses and circuit breakers are our friends. Work slowly. Enjoy yourself. This is supposed to be
fun. Savor the moment.
Thanks so much for getting me into this, but my project doesn’t work.
Blame yourself first. Smoke is bad. Parts should only have smoke on the inside. Did you double check all junctions? Looking at the part from the bottom front, the pinout for the
2N3904 is EBC. Really. Remember electrolytics/tantalums are polarized. They are also
mildly explosive, given the right conditions. Diodes have a stripe. Did you know that? Take your time. This is supposed to be fun. A Volt/Ohm-meter is worth 10 oscilloscopes. Check voltages,
continuity and component values before worrying about waveforms.
Call for help. Hams LOVE to help people. Even if they have no clue how to help right at the moment. We can always figure it out together. Two heads are better than one, unless you only have one hat.
I built it, it works, now what?
Cases are expensive to buy, but cheap to make. Shielding is usually unnecessary when using
ugly/dead bug/manhattan construction thanks to the ground plane.
Knobs are obscenely expensive. Try making them out of hardware dowels.
Circuit components are cheap compared to interconnects and switches.
Use MS Word or Publisher to print out faces for cabinets. Laminate and stick or stick and spray.
Why spend $25 on a case and knobs for a project that cost $5 for components?
What I can do for you
Parts: if you need that one elusive part that will complete your project and your life, call me.
I have a small test bench and a little bit of troubleshooting knowledge if you’re really stuck.
I have most of the popular QRP project books if you want copies of a schematic or project.
If you need some internet links to get you started, give me a call or shoot me an email.
I can email this presentation to you as well.
