On May 22, 5:49 am, Alan Peake wrote:
amdx wrote:
Here's an interesting simple circuit to generate odd harmonics.
"New Topology Multiplier Generates Odd Harmonics"
http://www.wenzel.com/pdffiles1/pdfs/RFDesign2.pdf
Mike

Yeah, saw that. Trouble is that I need EVEN harmonics
Anyway, there was some interesting info on snap diodes etc. Makes me
think that the diode used in the gear I have, aren't SRDs as these seem
to be mainly for microwave use. The other info I gleaned was that it's
easier to get low phase noise with straight multiplication than it is
with PLLs. Not that I have an urgent need for low phase noise - but it's
interesting nonetheless.
Alan

Huh? I thought you wanted to multiply by 18. 18 = 3 * 3 * 2.

If you were specific about what you want to do with the output, I
missed it. If it's just low-level stuff (e.g., a signal to feed into
the receiver input), you don't need much power and the multiplier can
be very inefficient and still do what you want. As you note, phase
noise will be better (possibly much better) than other ways of doing
it, and it could be that the signal level will be a lot closer to what
you want. You'll have to shield things pretty carefully to get down
to microvolt levels from a PLL or other full-blown oscillator on
1.2GHz. There might already be enough 18th harmonic in the oscillator
output to do what you need. I have some little very fast CMOS single
gate chips that have square enough edges (under half a nanosecond rise
time, unloaded) to generate quite a bit of harmonic content up that
high. Though a PLL would work fine, you then need a way to set up the
PLL chip, assuming you use one of the readily available programmable
ones. I know for me, I could hack a decent analog multiplier with
filters a lot quicker than I could a decent synthesizer. I had to do
a x9 not long ago, and used a multiplication scheme. Also, I've seen
small crystal oscillator modules from two different vendors that used
a PLL to lock a 100MHz crystal to a lower frequency reference, and
then used analog multiplication up to several times 100MHz--they are
doing it for low phase noise.

Cheers,
Tom