[Lowfer] Can a DDS replace the crystal in an oscillator ??

[Andy - KU4XR]

- On Fri, 4/30/10, John Andrews <w1tag at charter.net> wrote:

> Andy,
> 
> Be more specific about what you think is causing the drift.

A 23 year old radio with a crystal that goes haywire if you touch
it. Hold it between your fingers for a few seconds, and the warming 
from your fingers causes the frequency to go wild. As the temp. in 
the radio rises with use, the frequency goes up, and once the rig 
reaches operational temperature; the frequency doddles around from
+2 to -2 Hz from the desired frequency setting. Soldering a wire to
the crystal case to ground helped, as well as encasing the crystal
inside styrofoam. But it is still un-usable for long transmissions
as I found out quickly last night trying JASON in slow mode.



Andy - KU4XR - EM75xr - Friendsville, TN. USA
LOWfer Beacon " XR " @ 185.29875 KHz ( QRSS-60 )
Coordinates:  N:  35º 43' 54" - W:  84º 3' 16"
http://www.myspace.com/beaconxr
http://webpages.charter.net/ku4xr/


--- On Fri, 4/30/10, John Andrews <w1tag at charter.net> wrote:

> From: John Andrews <w1tag at charter.net>
> Subject: Re: [Lowfer] Can a DDS replace the crystal in an oscillator ??
> To: "Discussion of the Lowfer (US, European, & UK) and MedFer bands" <lowfer at mailman.qth.net>
> Date: Friday, April 30, 2010, 1:21 PM
> Andy,
> 
> Be more specific about what you think is causing the drift.
> If it's an 
> oscillator in the 10 meter rig, that's one discussion, as
> there are a 
> number of oscillators involved. If it's the crystal in the
> 
> downconverter, that's another.
> 
> A DDS performs no magic as far as stability goes -- it will
> only be as 
> good as its clock oscillator. Depending on what you are
> doing with the 
> DDS, you <<may>> get the advantage of division
> to a lower frequency. 
> I've got a bunch of AD9851 DDS chips running in various
> rigs, but the 
> magic comes from clocking them with proportional
> oven-controlled or 
> GPS-locked signal sources.
> 
> John, W1TAG
> 
> On 4/30/2010 12:59 PM, Andy - KU4XR wrote:
> > I don't know, so I ask. The HTX-100 10 meter rig
> drifts unacceptably
> > to use it for slow mode work. Can I replace the aging
> crystal in the
> > oscillator circuit with a DDS unit to obtain better
> frequency stability ??
> > An un-noticable drift at 28 MHz, when converted down
> to LF becomes
> > excessively noticable, and makes many modes
> un-usable.
> > Using the 10 meter rig to drive the homebrew HF to LF
> Transverter.
> > It works well, but the radio drift hurts. So a $50.00
> DDS unit will be
> > a lot cheaper than buying another late model radio to
> use with the
> > Transverter.
> >
> > Thank you, and 73 :::
> >
> >
> >
> > Andy - KU4XR - EM75xr - Friendsville, TN. USA
> > LOWfer Beacon " XR " @ 185.29875 KHz ( QRSS-60 )
> > Coordinates:  N:  35º 43' 54" - W: 
> 84º 3' 16"
> > http://www.myspace.com/beaconxr
> > http://webpages.charter.net/ku4xr/
> >
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