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

[John Andrews]

Andy,

What's that xtal frequency???

I just think that you have way too many variables with direct leverage 
on what's supposed to be a very accurate frequency. A Hz or two at 28 
MHz is better than most HF rigs can deliver, and you are mixing that 
with another crystal oscillator of similar frequency, and the errors are 
not divided -- they appear directly at LF. Definitely fine for SSB voice 
or PSK31, but not the critical stuff.

John, W1TAG

On 4/30/2010 1:37 PM, Andy - KU4XR wrote:
> - 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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