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Re: LF: Oscillator Stabilty for QRSS?

from [Rik Strobbe] [Permanent Link][Original]
To: [email protected]
Subject: Re: LF: Oscillator Stabilty for QRSS?
From: "Rik Strobbe" <[email protected]>
Date: Wed, 14 Aug 2002 10:15:01 +0200
In-reply-to: <000a01c242fb$2b68ace0$7211f4cc@jsm>
References: <[email protected]> <00a301c238e9$2266e7e0$389437d2@xtr743187>
Reply-to: [email protected]
Sender: <[email protected]>
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
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