Excellent...!! Professional engineers also spend a lot of the time in
the lab waving their arms in hopes that they can dissipate the smoke
before someone runs in to see where the bang came from!

I dont mean to be too highbrow...its just Ive spent so much of my
working life ensuring that if you build something on a production line
100,000 times 5% failure is pretty bad. And people obviously build
small transistor FM/AM/shortwave radios in china with the worst cheap
components...and most of them seem to work of sorts. Though i have
designed high end audio amplifiers and each time a new batch of
capacitors came in there was lots of "listen tests" as amazingly you
really could here 100nF placed on a supply line (dont ask me how...I
still dont understand it).

If the pro rf engineers do too much of the "try it and see" approach
they deserve their sky high salaries for the loss of hair and frayed
nerves waiting for the customer returns from their first 10,000 units!

I did wonder whether selling the car and buying some impressive test
equipment would make me feel better


On 30 Apr, 20:47, Straydog wrote:
On Mon, 30 Apr 2007, bigorangebus wrote:
I'm a professional electronics engineer (not rf enginneer though), and
what I really find frustrating about radio projects is the
uncertainty!

I am a real _amateur_ ham operator. I _love_ to make homebrew stuff but
with tubes (not solid state), and will offer MY version of your story.

I spend hours designing and analysing filters. Designing oscillators
and minimising harmonics, noise etc. Then I cheerfully commit it to a
PCB (I tightly laid out surface mount PCB to minimise layout
inductances etc).

I do tinkering (not _engineering_), and do pretty sloppy, ugly, breadboard
construction of:

1. the real thing
2. only a small part of the whole project at a time
3. turn on "the juice" for the smoke test: results: 1-smoke and no
action (then scratch head), 2-no smoke but action (cigars for all), or
3-no smoke & no action (also scratch head). There are variations on
this. Beyond the scope of this post.

Nothing ever works as simulated. Transistors never have the rf gain
as SPICE seems to suggest.

Decades ago I built, in a physics research lab on a university campus,
several dual-delay line pulse amplifiers (5-6 tubes, fancy delay lines).
All identical parts, identical schematic, identical tubes. One of these
amplifiers put out a trailing spike that was not supposed to be there. I
tried everything to figure out where it came from. I spent weeks on this.
Finally, I put in a bypass cap that was not supposed to be there and that
fixed it. Told the boss about all this. He shrugged his shoulders.

And local oscillators...well carefully chosen components just get
thrown out the window to be replaced by more and more random changes
in component values.

I have found commercially made components that were crap. eg. Precision
resistors 20% off value. Parts dead out of the box.

If it does finally work, I'm left feeling nothing like an exacting
engineer, and more like an artist that has piles on layers and layers
of oil paint till the right effect was achieved.

The object of the game is to get stuff that works and forget the castles
in the sky. Oh, yes, I worked at a place where another guy--making very
very very fancy-schmantzy stuff--built a circuit according to "plan" and
it didn't work either. Much cussing, grunting, cussing,
yelling-and-shouting-and-huffing-and-puffing and in the end, I recall that
they pulled a kludge fix, too.

I now find any mention of the 612 mixer and its (non)osclillator gives
me panic attacks. (well i'm currently trying to get it to work at
130Mhz with voltage tuning).

So I wonder, what would be your top tips for someone moving into the
radio design arena? Are there hidden secrets that nobody tells and
the books omit? I'm not thinking about PCB layout here, more things
like, are simulation programs of any use (if so which ones) and what
kind of design procedures can result in predicatable results?

I don't know about _you_, but for me, I do better when I build small parts
of the whole thing, then test them individually, and I have minimum test
equipment (oscilloscope, meters, signal generators) and you can put
inputs, measure outputs, measure voltage & currents, and tinker and adjust
as you go.

You sometime have to test the part separately from the circuit to actually
prove to yourself that it really does work. Its a big pain, but it makes
you check everything.

You might ask yourself if you are assembling things with good techniques
(yes--I kid you not--I have actually run into people who did not know
that you had to strip the insulation, whether enamel or plastic, off of
wires before putting them into sockets or clips) including soldering
technique.

Oh, yes, since I work with tubes that run hundreds of volts on the
plates-screens, yes, I've gotten a few electrical shocks (they hurt, and
at higher current, burn flesh) but also be careful about not having a
finger from each hand in contact with "hot" metal conductors. High power
RF also burns flesh and feels like heat rather than pain and you might
smell burnt flesh (its terrible) before you feel anything.