[hpsdr] Call for comments - EXCALIBUR

[Graham / KE9H]

Hi Rob:

I think the answer is all about frequency stability and accuracy.

I'll reference everything to 10 MHz, but it actually scales with the
operating frequency, that is, the error will be three times as great
at 30 MHz than at 10 MHz, or five times as great on 6 Meters.

The basic oscillators on either Penelope or Mercury can be calibrated
to +/- 10 to 30 Hz using the calibrate function in PowerSDR, and will
probably walk around over room temperature variation +/- another
50 or 100 Hz.  That is good enough for casual operating,
and a tremendous improvement over the VFO radios I grew up with.

Using the optional TCXO I have selected for Excalibur, the
oscillator is "instant-on" (unlike an oven based oscillator,) and
can be calibrated to a fraction of a Hz, and will typically hold
within one Hertz over room temperature variation, and age at
the rate of one Hertz every several months. (But you will need
an external standard to set it to these levels.)

I think this kind of accuracy is well matched to the basic PowerSDR
since it currently tunes in one Hz steps.

For persons wanting more accuracy, you can use an external
standard and lock the radio to what ever the accuracy of the
standard is.  This would be important for frequency measurement
tests, or perhaps microwave radios, where the errors could
be multiplied by hundreds or thousands.

This card offers a convenient way for people with external standards
to frequency lock their HPSDR.

For those that asked about Gibraltar, this card is a step below
Gibraltar, which is a (self contained) GPS-disciplined oscillator on
an Atlas card.  I view this as a separate project, although
portions of this circuit could be reused in Gibraltar.

For my own purposes, I believe that the GPS-DO should be
a separate piece of equipment from HPSDR, so that the GPS-DO
can be be left powered-on, and is available to the rest of the
shack, independent of the HPSDR and any experiments that
might be going on.  And, if you populate the TCXO on this board,
you have a TCXO to fall back on, if the GPS-DO is off line.

--- Graham / KE9H

==


Rob Frohne wrote:
> Hi Graham,
>
> Interesting project.  What are the things you can do with a TCXO 
> reference that are not feasible with the regular oscillator?  How much 
> more difficult is it to get a GPS stabilized oscillator going and what 
> are the things you can do with it that are not feasible with this 
> one?   Answers to these questions might help us answer yours.  :-)  
> Thanks!
>
> 73,
>
> Rob, KL7NA
>
> Graham / KE9H wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> All:
>>
>> If you might be interested in a card to hold a "medium performance"
>> 10 MHz TCXO, or to inject a signal from an external 10 MHz reference 
>> standard
>> onto your HPSDR Atlas bus, please download and read and comment
>> on the attached proposed "Excalibur" project card.
>>
>> I am assuming this would be available as a bare card or parts
>> kit.
>>
>> Download proposal:
>> *http://www.hamsdr.com/dnld.aspx?id=956*
>>
>> Is this something worth setting up as an HPSDR offering?
>> Would you be interested in purchasing/building one?
>> Anything missing?
>> Other comments?
>>
>> Thanks,
>> --- Graham / KE9H
>>
>> ==


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