I'm not terribly familiar with the MiniCircuits VCOs, but I have been
involved with getting the phase noise down to low values on some of
our designs. I can tell you that it's important to have power
supplies be very clean, as well as to have the control voltage very
clean (down into the microvolt region or below) as Harold says.

But from what you wrote, I gather there's a problem even with things
supposedly very clean. BTW, I don't 'zactly understand the "POS-900W
out of circuit
(ie. no PLL)" bit. What are you measuring if the oscillator is out of
the circuit? Or are you saying you're measuring the oscillator "bare"
and not in a feedback loop?

Do you have any other signal you can measure in the same frequency
range? Is your spectrum analyzer up to the task? I'd think your 1kHz
res bandwidth is pretty big to be seeing the noise level at 1kHz
offset...I'd want a res bandwidth at most 1/10th the offset. And it
might be interesting to look with much lower res bandwidth if you can,
to see if there is a particular structure to the sidebands, or if they
are indeed random noise.

Cheers,
Tom


"Alex Collins" wrote in message ...
"Harold E. Johnson" wrote in message
news:_fwlc.22193$kh4.1279179@attbi_s52...


What could I be doing wrong? (My other POS-900W's do the same).
Incidenatlly, I have a screenshot (23Kb) of the display which I can
e-mail.

Well, you don't specify the frequency coverage of your other VCO's, MCL's
have a very high MHz/volt tuning rate and unless the tuning voltage is
absolutely quiet, they'll look pretty bad. (BOTH the positive AND the
negative leads shielded to ground?)

W4ZCB




Thank you for the reply.

But surely if the Minicircuits datasheet says the trace will fall to less
than -75dBC at 1,000Hz away I should see that, or something close to it?
Irrespective of the frequency (800MHz)?

Even if the conections aren't ideal, I'd expect 10dB or so more noise, but
it doesn't change however good/bad it's shielded.

I'm probably doing something really stupid.

Al.
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