Sunday, May 27, 2007

The Homebrewer's Lab

We are fascinated by the pictures of famous homebrewer's labs. How did they assemble it all? How does one create a junk box? I will try answering those questions in my first post.

The first question usually is about What do I require in my lab? The answer an unhelpful 'depends'.

A Soldering iron and a nail clipper - The impossibly minimal homebrewer
Minimum requirement is a soldering iron. You also require a way to strip and cut wires (forget about using your teeth). I (and my cousin) have used nail clippers to do that. A few 9 volt batteries can power quite a few projects unless you are planning on building power amplifiers.

The Minimal homebrew lab is really really minimal. Unfortunately, to use it you have to be an expert. So it is not really an option for the beginners. Lets see what are the requirements for a decent homebrewer's lab.

A better budget - $200
Setting up a small lab will take some money. You cannot build everything yourself. Also, investing in some good tools is always worthwhile. So here is my list of things:
  • Soldering iron: Buy a decent 25 watt iron that has an earth pin too. The chinese irons lining up at your local DIY store are good enough. Check that it has an earth pin too.
  • Analog VOM: As a kid, I tried getting by without a VOM for a long time! Don't do that. Buy an analog VOM. It will work without batteries too. The digital VOMs are not a good idea (though cheaper). The analog meter allows you to monitor fluctuations easily. It also works without using the battery (except to measure resistances).
  • A small wire cutter. Buy a nice one. Check that the jaws close without leaving a gap and they are made of hardened steel.
  • A small plier. Same as above. Make sure that both have insulating sleeves on them!
  • A screw driver set. The one with interchangeable tips is fine to start with. Don't buy the precision set. Most of them are too small to be used for homebrewers. Buy the sort that has bigger tips that you can use to open PC cabinets etc.
  • A good roll of solder. Bad irons and bad solder have dissuaded too many builders.
  • A small hacksaw. You will require this for everything from sawing stalks off volume controls to cutting copper clad boards. Buy a few spare blades while you are the shop. Don't buy the big standard hacksaw - it is too unwieldy for most radio work. If you have to buy just one, buy the small hacksaw or buy both.
  • Drill. Even a hand powered drill is good enough. Buy a set of drill bits with it too. Electric drill is an overkill. It is too big for the QRP projects. Unless you aspire to be the governer of California, stick to a small drill.
  • A flat file and a round file. Buy a small round file that is about 0.2 inch thick and with a fine score. You will need this to enlarge holes in boards. Buy a flat file with a similar score that is about half inch wide. You will need this to straighten the edges of your boards.
  • Car battery charger (12V). Ask your mechanic to suggest a cheap one. If you add a 78H12 or 7812 to it, you have a ready and robust power source available.
  • A Small Vice. Buy a vice that you can clamp onto your work table to hold a board while you file or saw it. You can usually get by with keeping the board at the edge of a wooden chair or bench and clamping it down with your foot. One hand holds the board and the second hand can work the saw/file.

A second hand Oscilloscope - the big buy

I am not being ridiculous. After living without a scope for years, I finally realized that without an oscilloscope, you might as well try homebrewing blindfolded. As they say, a picture is worth a thousand words. So, to be really successful at homebrewing, you should have a decent scope. This is a the big ticket investment. Make it. I don't think that any serious homebrewing is possible without an oscilloscope. This is a dramatic statement and I am sticking to it.

Get onto eBay and look for a good buy. What should you look for? here are my 5 considerations (I am not an expert, I have bought just one oscilloscope in my life):
  1. At least 20MHz bandwidth. More is fine. But 20 Mhz scope will easily work to 30 Mhz. If you can afford better, buy it.
  2. Buy an aligned scope. Scopes go out of alignment routinely. Buy it from someone who deals in scopes and can offer you an aligned scope.
  3. Get the manual including alignment procedure. It is a fairly elaborate drill to align an oscilloscope. Most oscilloscope dealer will align it for you before selling it. This is an important consideration.
  4. At least two 10x probes. The 10x probes will attentuate the signal a factor of 10. But they will load the circuit very lightly. Check that the probes are also aligned for you.
  5. Don't buy the cheapest. An oscilloscope is a prized possession of a builder. It should last your lifetime. Buy a Tektronix if possible.
I have an Tektronix 265-B. It bought it for $200 with probes about 3 years ago. It is a very fine thing that is rated for 100MHz but allows me to see upto 200Mhz. That way I can observe any VHF parasitics and also occasionally indulge in VHF experiments.

The Frequency Counter
A frequency counter is really a must. You can't survive without it. You can use it to do a lot of things apart from measuring frequency. You can measure capacitors, inductors, transformers, even align crystal filters.

These days it is so easy to build a counter. Just google around for a PIC frequency counter or if you want something really simple, try Han's amazingly simple counter.
Many hams that have told me that they are put off by having to program the PIC. Programming is a PIC is really simple. You don't have to know anything about programming it! All you need to do is solder a simple circuit, connect it to your PC, plug in the PIC, then just run the software to all it to do its magic ... abracadabra! you have a frequency counter. Make this your first homebrew project. If you are a chicken, then you can buy one from any of the ham radio kit suppliers. Anything that goes up to 40Mhz is fine.

Some counters are noisier that others. My own counter uses LEDs instead of LCDs and I find that the noise in a circuit goes up when I connect it. I am OK with that. I never use the counter on radios in service. I would guess that the LED counters are inherently noisier that LCD counters.

Which ever counter is used, have as many digits as you can (mine has 10Hz resolution). House it in an all metal enclosure and make it have it's own power supply. (Rip out electronics from a wall wart 9 volts battery charger and add a 7805 regulator to it).

Ready to build
You will realise that except for the oscilloscope and the frequency counter, the rest of the tools required are no more that those required to build a simple kit. While our instrumentation is minimal, you will realise that you are now able to build the rest of the instruments using these are tools. For instance, even building a spectrum analyzer is possible with just these tools. More on that later. Now to populate your junk box ....

Resistors, Capacitors, Inductors, Transistors and ICs
These should be available as assorted packs from several places. I am told that RadioShack stores as well as has several assorted packs. If you are assembling a new junk box, here is my recommendations. Buy all the resistors and capacitors in packs of hundred. They are very cheap that way (at least in India).
  • Resistors (all quarter Watts): 220K, 100K, 22K, 10K, 2.2K, 1K, 220 ohms, 100 ohms, 22 ohms
  • Capacitors: 0.1uF, 0.001uF, 1uF, 10uF, 50uF, 560pf, 220pf, 100pf, 47pf, 22pf, 2.2pf.
  • Transistors: npn garden variety, low power transistors like 2N2222/BC148/BC149 that can be used for audio as well as RF work with Ft above 200MHz. Buy 100.
  • FETs: low power versions like MPF102 or BFW10s (buy a dozen) and a couple of high power HexFets IRF510 or IRF511.
  • ICs: not too many, a couple of LM386s and some good quality Op-Amp ICs like the LM3352.
  • Odds and Ends: 22pf standard trimmers, 365pF broadcast radio variable capacitors, 10K Log volume control with on/off switch, 100K linear pots, DPDT toggle switches, RCA audio jacks and sockets, 'Banana' jacks and sockets, shielded audio grade cable, 10Mhz, 4MHz and 14.318 MHz crystals.
I buy the plastic lunch boxes available at supermarkets with small partitions inside them to store the components. Two such boxes store most of my components.


Nawab said...

Hi! Farhan

This is exactly the way we began. Nail cutters exactly what I use even now when my Multitech stops cutting. Scope hmmmm was lucky to get a Tek 2465B 4Ch 400meg. Supply a 30V variable is handy but even a free older non ATX PC supply gives generaly used 5&12V at least for experimentaion. Lately if RF work is involved I would suggest an AD8307 based meter probably W7ZOI after all the chip is shipped as free sample.

Now if you get thru to this point just order another sample ofAD9851 DDS chip and go in for a sig gen.

Things can be had for peanuts these days just an example:

Something for a die hard RF engineer.


Rahul VU3WJM

kc7fys said...

Excellent material. I hope you continue this blog, and that some dialog ensues. My grandfather, W0XO was and is still a great homebrewer of tube-based breadboard kind of equipment. He was also an engineer at Collins Radio, so he has cred. I hope to live up to some of that, but I am a sad appliance operator who builds kits from time to time.
Anyway, I'm reading your blog, and will supscribe.

Daniel Perez said...

Farhan... Farhan... are you the author of the BITX, in India???. Glad to read you!. Here in Argentina we talk much about you, "the inventor of the plastic core toroids"!.
Thanks for your contributions to the homebrewing community!.
Daniel Perez

julius said...

analog VOM with high impedance/volt will help as a sensitive measurement tool, also use it with a good probe. of course it will cost more, but worth the money.

Highland Ham said...

Hi Farhan , an excellent initiative .
I have bookmarked your blog site , with the aim to have a look at least once a week .
Good to see references to other AR homebrew sites .
I could send you a simple circuit diagramme for a charger for a battery operated soldering iron powered by 2 Nicad or NiMH 1.2V cells ,if there is any interest.Although I don't know whether this info could be absorbed by a blog site.
Frank GM0CSZ / KN6WH

William R said...

FB Farhan! The new blog is great. You have caused me to reevaluate my test bench. I dug out my old analog meter and got it working and I now have the urge to get a better 'scope. 73 Bill N2CQR M0HBR

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