James
In general, very wide tuning range and very good phase noise are sort of
antithetical. If you use the circuit I sent you, the phase noise will be
quite good for your simple spectrum analyzer application (unless you're
planning to have a very high resolution/very low bandwidth mode).

Don't get too hung up on your Spice modeling. It can keep you from trying
some things that are known to work. In general, if I can build it faster
than I can model it, I'll just go right for building it. I use modeling to
get another perspective, but not to get the whole picture.

Joe

"James Fenech" wrote in message
...
Thanks Joe,

I wouldn't have thought it would be too difficult. Minicircuits sells
parts
that have a 2:1 range (not the right range though), and I only want 1.7:1
or
so. Interesting idea about downmixing, but I really don't want another
mixer
and oscillator in this thing.

Acording to my pspice results I can get the range, but I'm a little
concerned about the high voltage swing on the varactors causing very poor
phase noise.

James.

"W3JDR" wrote in message
...
2:1 tuning range with varactor tuning is very doable in the frequency
range
he's considering. I've done 3:1 at lower frequencies. No steep hill at
all.

Joe
W3JDR


"Steve Nosko" wrote in message
...
You're climbing a steep hill here James. It is the % change in
frequency
that is the problem. Professional spec analysers use a 2 GHz LO with
a
2:1
range (to scan 0-2GHz), but I believe that is a magnetically tuned YIG
resonator. If you could get the frequency higher, so the sweep range
is
narrower, then mix to the desired freq with a balanced mixer...that
would
be
an easier VCO design.

Steve
K;9;d;c;i

The punctuation is my feeble attempt at spam-bot blocking.


"James Fenech" wrote in message
...
Hi Roy,

thanks for the suggestion. I am considering buying this book. Can I
ask
how
much theory, and how deep does it go? I am an engineer (digital
electornics
and software background) and actually like some theory to help me
understand
what I am doing.

I already have some "real" test equipment, 50MHz CRO, signal
generator,
multimeter, etc. So "simple" test equipment may not be too much of
an
improvement.

I've looked over the internet, and some books that I have, but found
no
real
example circuit on wideband VCOs. The only "sort of close enough"
circuit
I
found is at:




http://www.newwaveinstruments.com/resources/rf_microwave_resources/sections/oscillator_vco_theory_design_circuit.htm#Voltage%2 0Controled%20Oscillator%20(VCO)%20Circuits
The second one down - Colpitts. Are there any such examples in this
book?

Thanks,
James.


"Roy Lewallen" wrote in message
...
I highly recommend _Experimental Methods in RF Design_, by
Hayward,
Cambell, and Larkin. It's published by the ARRL and available from
them
and numerous other sources. Besides theory and a lot of real,
practical,
tested circuits and projects, it includes simple test equipment
you
can
build yourself.

Roy Lewallen, W7EL

James Fenech wrote:
. . .
I have the ARRL handbook (1997 or so) but this doesn't have much
in
the
way
of theory. Is there any other reference anyone can recommend?
. . .