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 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).

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

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.

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.

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?

* Model your parasitics, including circuit-layout induced ones.
* Remember that _everything_ has parasitics if the frequency
is high enough.
* Transistor models are never perfect; you need ones intended for
use at your frequencies. RF transistors should have models that
include package effects.
* Tightly laying out your circuit board will reduce inductances
but increase capacitances.
* There are (very spendy) packages that will do parasitic
analysis of your PCB layouts that you can then run through
spice.

It is an art, and one that I haven't mastered myself, but you can put a
lot of science into it if you're careful.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html