Alex Collins wrote:

Thanks for all the help.

Yes, you are right in the assumption that I've had it as 'clean' as is
realistically possible.

Yes, it's random noise.

To explain, when the output of my board showed a 'triangle' as an output on
the Spectrum Analyser, I first suspected by PLL, so I took the VCO module
off the board and 'benched it up'. I used separate batteries for Vtune and
Vcc supply, with very short (2cm) connections. I even put 1UF, 1N and 100N
caps across the Vcc ** and Vtune ** pins and took the RF out on RG316
directly to the Analyzer sheilded an grounded with extreme care. When I
still observed hideous phase noise, I even tried decoupling the batteries
with a resistors/caps in each supply line. I also tried all sorts of pads
using SMD resistors cleverly soldered to the output pin and case... So I'm
convinced I've given the VCO a better environment than anyone could possibly
achieve in reality (ie. even on the best PCB layout).

The phase noise results seem unachievable, but I hardly think Minicircuits
are lying, and that it should be pretty easy to achieve -75dBc at 1,000Hz
away. Even if it was -60dBc I'd be happy. But all I know is I'm getting the
same results on all POS-900Ws I have.

I'm using an Anritsu MS2661C, and basically just hoping to see the
traditional 'needle spike' at Fc. (which is what I see from other VCOs with
the Spectrum Analyzer on the same settings). But, instead, it's more like a
triangle than a needle, and nothing seems to change that.

Perhaps if one of you guys would mind me sending you a screenshot, direct
(23kB), that may shed some light on it?

Al.
----
mail[underscore]me[at]freenet[dot]co[dot]uk


Perhaps that's -75dBc at a bandwidth of 0.001Hz?

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com