[hpsdr] Spectrum pics of 10 MHz clocks (longish)

[Bruce Beford]

Jeff Cook, G0AFQ wrote:

> Well done Bruce, that is indeed both interesting and informative.  I 
> realised some little while back that Excalibur was accurate enough to 
> make an external reference unnecessary, but nonetheless I use a 
> Thunderbolt and have done the Penelope modification.  There's something 
> satisfying about using HPSDR at its optimum, so is the next step to 
> disable the oscillator on board Excalibur leaving just the external 
> reference?  One might come to the conclusion that Excalibur was an 
> unnecessary purchase, however if I understand things correctly, even 
> without its oscillator running Excalibur still performs the necessary 
> function of conditioning the input from thunderbolt.


Hi Jeff. Thanks for your comments. I wouldn't say that with an external
reference that Excalibur is unnecessary. As you point out, It does condition
an external reference to make it suitable for use on the Atlas bus. I also
think it is useful to be able to use an on-board reference when there is no
external one available. In the true spirit of high-performance, however, I
would like to be able to automatically switch to the internal reference when
the external is not there. 

>From an experimenter's standpoint, it's no big deal to remove or add a
jumper, if your boards are sitting out on the bench. When inside an
enclosure like Pandora, with it's 83 screws (slight exaggeration), it's a
pain to open the case to change a jumper. This is why I hope to eventually
add some form of sensing circuit to Excalibur to automatically power down
the onboard TCXO when there is an external reference (presumably more
accurate) available. This same add-on could power up the onboard oscillator,
and switch it's output to the Atlas when there is no signal present on the
input jack on Excalibur.

Short term, I will probably add a jumper on Excalibur to remove power from
the TCXO. Long-term, I will give some thought to an add-on circuit that does
what I just described. The only problem with that is the usual- too many
projects, too little time.

Cheers,
Bruce N1RX



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