Re: LF: Oscillator Stabilty for QRSS?

["Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>]

Hi Steve,

If you want to go for a VFO design I wouldn't use 2 VFO's and mix down
but a single VFO and divide down.
In my early days on 136kHz I used a 8.7MHz VFO and divided it by 64.
Using a simple 'no nonsense' VFO I achieved a stability of a few Hz, more
than good enough for normal CW. Later, as QRSS became,  popular I
phase-locked the VFO improving stability to better than 0.1Hz.
There are a lot of nice (and excellent)  DDS designs, but the advantage
of a good old PLL design is that you can do it with a handfull of cheap
and easy-available CMOS IC's.

73, Rik  ON7YD

At 11:56 13/08/2002 -0700, you wrote:
> Perhaps
> someone who has already 'been there' can offer their advice. 
> I would like to start building the exciter
> stages for what will be my 136KHz tx (hopefully we will have access to
> the band within the year!). The DJ1ZB exciter (modified by DF3LP) is the
> circuit that I am questioning. It mixes two xtal controlled 4MHz
> oscillators, 136 KHz apart, to extract the 136KHz signal. Can I build two
> VFO's, somehwere around 1MHz and set them 136KHz apart, that will 
> be stable enough to handle QRSS work? I am worried about drift but also
> thinking that they may be stable enough if kept in the 1 - 2MHz region.
> As well, they should (if identical) drift by the same amount and thus be
> self-correcting? Is this a reasonable avenue to pursue or should I just
> break down and buy a couple of xtals??
>  
> Steve / VE7SL  Mayne Island,
> BC