On Wed, 17 Mar 2004 08:58:18 -0600, John Fields
wrote:

It's an FFT of what's coming out of Larkin's suggested two-stage
bandpass filter.

The first vertical marker (f1) goes through the first peak, 17.19MHz,
which proves the fifth is in a 3.44MHz square wave. The second marker
goes through 34.38, so so's the tenth.

Curious that there should be a sizeable pass response at the tenth
harmonic, isn't it? It doesn't appear to be *that* much down on the
intended pass frequency although there appears to be no indexing for
the y axis.

Are you kidding? Count the high frequency cycles between the first
leading edge and the same point on the second leading edge of the square
wave and you'll find there are exactly five.

Well, I admit I'm a bit of a greenhorn on these things, but to my eyes
there appears to be some phase difference. I'll accept your word for
it there isn't.

What was the active device you used to generate them?

---
Tektronics FG502. Here's the layout:



[TEK FG502]-+-[BPF]-+-[TEK 2465A]---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]

Many thanks. I hope it didn't involve you in too much setting-up time
to investigate this and post your findings.

--

The BBC: Licensed at public expense to spread lies.