Message-ID: <001a01c243ec$f21fac20$26c828c3@erica>
From: "g3ldo" <g3ldo@ukonline.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <6a.23b88f69.2a798441@aol.com> <00a301c238e9$2266e7e0$389437d2@xtr743187> <000a01c242fb$2b68ace0$7211f4cc@jsm>
Subject: LF: Re: Oscillator Stabilty for QRSS?
Date: Thu, 15 Aug 2002 00:41:36 +0100
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Hi Steve


>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!).

In the early period of 73kHz experiments I first used an audio signal
generator as an exciter then  VFO. Neither of these were stable but was
useful to get going. When 136kHz became available I used an old RF signal
generator, which was better, fine for CW but QRSS signals were slightly
frequency modulated by the keying and produced distinctive wiggle on the
received display. I would imagine the synthesized signal generators would be
OK.

>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.

I used a two crystal arrangement with FETs and then was became aware of the
DJ1ZB design so I used his amplifier/driver and filter. I used differential
capacitor tuning with no inductors. By this I mean increasing the
capacitance across the one crystal while reducing it on the other. By this
time test transmissions were being made for transatlantic tests. In this
situation the requirement was to maintain the frequency within 1Hz over
several hours. This proved difficult with the crystal mixer arrangement.
Alan Melia, G3NYK, kindly supplied me with several crystal pairs, the lower
frequency crystals gave better stability but a reduced tuning range as you
might expect.
My first 136kHz transatlatic crossband QSO was done using a two crystal
exciter.


>Can I build two VFO's, somehwere around 1MHz and set them 136KHz apart,
that will  be stable enough to handle QRSS work?

No. Use crystals with no inductors or a synthesized signal generator; or go
for DDS.

Regards,
Peter, G3LDO

e-mail <g3ldo@ukonline.co.uk>

Web <http://web.ukonline.co.uk/g3ldo>