Re: How to measure LC oscillator phase noise.

From: Ian Buckner (Ian_Buckner_at_agilent.com)
Date: 06/15/04 

Date: Tue, 15 Jun 2004 11:12:04 +0100

"Andrew VK3BFA" <ablight@alphalink.com.au> wrote in message
news:1fc7b362.0406150030.1c78e42@posting.google.com...
> I am in the process of building a 20m SSB transceiver using a LC
VFO -
> how can you measure phase noise of the device without a roomfull of
> complex expensive test equipment - is this possible with simple
> techniques even if only in a relative good/bad way? - I have a
decent
> CRO and a tempermental HP141 which works if thumped in the right
> place. I am not an engineer, and the only references I have here are
> in the ARRL hanbook for 2002 - they talk about pahes noise with
> respect to DDS synthesisers but give no practical help. Or am I
asking
> an impossible question - can it be done by "good" oscillator design
> and it flows from this - the groups comments appreciated.
> 73 de VK3BFA Andrew

Do a google search on "phase noise measurement", there's lots of
good stuff there on how to do this. However, you will need a low
frequency spectrum analyser. I'm not sure of the HP141 low frequency
limit.

Basically, you use a PLL to demodulate the phase noise using
a second oscillator, either identical to the one you are testing, or
much
quieter. For SSB work you are likely to be interested in offset
frequencies down to a few hundred Hertz, hence the need for a LF
spectrum analyser.

Regards
    Ian