RadioBanter - View Single Post

March 14th 04, 01:32 AM

On 13 Mar 2004 19:00:20 GMT, (Avery Fineman) wrote:

In article , budgie
writes:

On Fri, 12 Mar 2004 15:32:23 +0000, Ian Bell wrote:

Paul Burridge wrote:

Hi all,

Is there some black magic required to get higher order harmonics out
of an oscillator?
I'm only trying to get 17.2Mhz out of a 3.44Mhz source and am thus far
failing spectacularly. I've tried everything I can think of so far to
no avail. All I can get apart from the fundamental is a strong third
harmonic on 10.32Mhz, regardless of what I tune for.

In RF circles, the 'normal' way to do this would be a simple Class C
amplifier with a collector load tuned to the fifth harmonic. In calls C,
conduction only occurs for a small fraction of a cycle which produces a
correspondingly higher proportion of higher harmonics than a square wave.

I've been waiting for someone to post this. I would only add "The drive
level,
and the bais point, will vary the amount of fifth (or whichever) you will
see."

It's as common as noses in RF, as Ian pointed out. Just look at the average
two-way radio prior to frequency synthesisers. Crystal freqs were multiplied
this way in transmitter chains and for receive injection, although use of
fifth
wasn't especially common because you normally had enough design control to
use the more efficient *2, *3 or *4.

Fifty years ago that was mostly true and multiplier stages rarely went
beyond the 4th harmonic. Two notable exceptions, though -

That IS what I said.

(snip exceptions)

However, all those multiplier types went the way of the dinosaur when
PLLs operating directly at the desired frequency came into being.

That IS what I said.

There isn't any advantage to using those old "exotic" technologies
other than in restoration for nostalgia's sake.

There IS advantage in being aware of analog techniques.